The goal I set for myself was to create, modify, or discover a high-quality TRF (Tuned Radio Frequency) radio circuit that could perform at least as well as the MK484 - TA7642 AM radio chip, while using as few parts as possible. My aim was to learn about the constraints of early tube designs from the twenties (1920s). Back then, designing a TRF radio presented numerous challenges. The tubes of that era had limited gain, necessitating the use of multiple stages, which, in turn, led to additional issues requiring filters and workarounds. Moreover, these designs lacked sensitivity, paving the way for Regenerative Radios and the Superhets. Tube gains hovered around 10, whereas modern transistors, like the 2n3904, range from 200 to 800. However, even with this improvement, the gain remained insufficient without regeneration (superheterodyne). I tried all sorts of designs, using FET's, Darlingtons, etc. They were all pretty awful. This led me to think of the existence of a transistor with a gain of 5000 to 10000, a concept nonexistent in the 20s. Eventually, I stumbled upon a straightforward design employing multiple MPSA13 transistors (Darlington). I streamlined it to the detector stage, it worked really well! Adding a preamp stage on the output and connecting it to my headphone amp yielded good sound quality. By adjusting the voltage to the collector, you can enhance the gain, and it even performs OK up to about 17 MHz (Needs an antenna of a few feet at least). The preamp section using the 2N3904 is a great audio preamp design you can use anywhere. Utilizing a ferrite core antenna wound with litz wire, I achieved satisfactory results on the AM broadcast band without an antenna, but you can use anything at hand.  I am able to pick up AM Broadcast stations 600 miles away. It will even work great with an aircore winding on a 1 inch diameter core of plastic or cradboard, but you will need an antenna of some sort, even a 2 foot length of wire. Earth ground is not required if using a ferrite antenna core I'm planning to explore the MPSA14 Darlington, which boasts twice the gain of the MPSA13, to further enhance sensitivity. Despite its success, there are a few drawbacks: 1. Driving it too hard with higher voltage can induce oscillations. 2. The extreme high selectivity makes it challenging to use poly variable capacitors effectively. 3. It whistles and oscillates around a station until it is tuned. Going forward, maybe I can figure out an AGC circuit. This is an easy project to build. It Works.

Note: It is Important to be cautious of counterfeits. To ensure authenticity, I recommend visiting the official TinySA website at https://www.tinysa.org/wiki/ and checking the "Where to Buy" section located at the top left of the page. This will provide a list of authorized sellers. Personally, I purchased mine from the SeeSii store on Amazon, ensuring a genuine product with reliable support. Introduction: As a hobbyist exploring the realms of electronics and radio, I recently acquired the TinySA spectrum analyzer. This compact device has exceeded my expectations with its impressive capabilities, allowing me to analyze and generate signals across various frequency bands. In this review, I will share my firsthand experience and highlight the features that make the TinySA a must-have tool for any hobbyist. Compact Design and Inputs: One of the standout features of the TinySA is its compact design, which does not compromise on functionality. The device is equipped with two inputs tailored to different frequency ranges. The first input handles MF/HF/VHF signals with exceptional quality, covering an extensive frequency range from 0.1MHz to 350MHz. The second input, designed for UHF signals, performs admirably in the 240MHz to 960MHz range. This versatility allows me to explore a wide spectrum of frequencies and pursue diverse hobbyist projects. Flexible Outputs: Not only does the TinySA serve as a spectrum analyzer, but it also excels as a signal generator. Its two output options provide the flexibility needed for various applications. The sine wave output covers frequencies ranging from 0.1MHz to 350MHz, enabling me to generate smooth, continuous signals. On the other hand, the square wave output, which operates between 240MHz and 960MHz, allows me to experiment with different waveforms. This versatility makes the TinySA an invaluable tool for testing and prototyping electronic circuits. The Ultra Version: For those seeking even more advanced capabilities, the TinySA Ultra version is available and has even more impressive features. With its larger 4-inch screen, the Ultra version expands the spectrum analyzer's capabilities. It can operate within the 0.1MHz to 800MHz range, allowing for comprehensive signal analysis. Enabling the Ultra mode further enhances the TinySA Ultra, enabling level calibration up to an astonishing 6GHz. This wide frequency coverage grants you access to signals previously inaccessible with other devices. It can become an indispensable asset for your specialized hobbyist projects. Affordability and Availability: The TinySA's affordability is amazing. I purchased it for just US $67 on sale, prime day, around $85 normally. (plus shipping) from the Amazon Seesii Store. It is also available on other distributors and prices vary widley. It's important to be cautious of counterfeits. To ensure authenticity, I recommend visiting the official TinySA website at https://www.tinysa.org/wiki/ and checking the "Where to Buy" section located at the top left of the page. This will provide a list of authorized sellers. Personally, I purchased mine from the SeeSii store on Amazon, ensuring a genuine product with reliable support. Here is a YouTube video comparing an expensive Rigol Spectrum Anaylizer DSA 815 to the TinySA. Very surprising. https://www.youtube.com/watch?v=q8v_oh28zs0 Learning Resources: Initially, I had concerns about the learning curve associated with the TinySA. However, I was pleasantly surprised to find an abundance of learning resources available. The official TinySA website hosts a comprehensive wiki that includes a detailed manual and an introductory video. These resources provided me with a solid foundation to start using the device effectively. Additionally, YouTube proved to be a treasure trove of instructional videos, showcasing practical demonstrations of the TinySA's features and applications. These resources have empowered me to explore and expand my knowledge in the world of spectrum analysis. Conclusion: Having personally experienced the capabilities of the TinySA spectrum analyzer, I can confidently say that it is a game-changer for hobbyists and radio enthusiasts. Its compact design, versatile inputs, flexible outputs, and advanced Ultra version make it an essential tool for any electronic exploration. The TinySA's affordable price, combined with its remarkable performance, makes it a worthwhile investment. By ensuring authenticity through authorized sellers, such as the SeeSii store on Amazon, hobbyists can acquire a genuine TinySA with reliable support. Embrace the power of the TinySA, and open the doors to endless possibilities in your hobbyist endeavors. Sources: 1. tinySA | Main / HomePage. https://www.tinysa.org/wiki/. 2. tinySA Ultra Reviews: A 0.1 MHz – 6 GHz Spectrum Analyzer for $120. https://www.rtl-sdr.com/tinysa-ultra-reviews-a-0-1-mhz-6-ghz-spectrum-analyzer-for-120/. 3. Hugen Launches Portable TinySA Spectrum Analyser. https://www.electronics-lab.com/hugen-launches-portable-tinysa-spectrum-analyser/. Here is a YouTube video comparing an expensive Rigol Spectrum Anaylizer DSA 815 to the TinySA. Very surprising.https://www.youtube.com/watch?v=q8v_oh28zs0

Manhattan Style, while not Gangnam Style, is still really cool. My favorite way to build a circuit. You use little squares of either copper clad board, or buy them like I do. http://qrpme.com/?p=product&id=MESb You glue them down to a copper PCB board (Just a plain board) https://www.amazon.com/gp/product/B01MCVLDDZ/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1 You solder the part to the squares and to the ground of the board. It comes out great. And if you like, you can get close to laying it out just like the schematic. Here is a link to see the results I use an open source and free vector drawing-photo program called Krita. https://krita.org/en/ It is a very complete graphics program. It's worth learning how to use it. I set the sizes and layout my setup first before I solder it up. Here is a layout I am working on. The actual size of the board is 45mm wide x 25mm high If you work in Vector mode, easy to move parts around, and easy to check your work before you solder. Then it's really, really easy to solder up. It will be different in real life, but this will help a lot

Putting my projects together I like to dress them up. I found Front Panel Designer by Schaeffer. It's freeware at https://www.schaeffer-ag.de/en/ It's purpose is to use their service and order panels. However, you can use it and export to DXF, or PDF and otherwise play with it and it's all fine with the license. Since I will not be using their service just yet, I wanted to prototype a panel and see how I do. The measurements and print out are exact, so you can use it for a template. I positioned all the controls in the software, then print it on card stock, but paper is fine. Then you can actually check the layout. I purchased some polycarbonate that is easy to score and drill, no cracking, from Amazon to try. Search for it on Amazon "Polycarbonate Plastic Sheet 12" X 12" X 0.118" (1/8") Exact with EasyRuler Film, Shatter Resistant, Easier to Cut, Bend, Mold than Plexiglass. For Robotics Teams, Hobby, Home, DIY, Industrial, Crafts." I put the plastic on top of the printout and marked the hole spots. Using a drill press is very hard, the parallax of the plastic is hard to align. But it's good for a rough panel. I also used a plexiglass cutting tool, to the score the dial. You need to start very light and slow for it to not slip. This is not used for a final panel, but can go a long way to getting it right before you send it out. Of course, if you are simply drilling holes for parts to hang, this is great. I also tried printing on a clear stick-on label but it was a huge, huge mess. Lost of bubbles, impossible to align, and on and on. I took some pictures. Since the output is accurate, and Front Panel Designer outputs to DXF, I am taking the drawing to a local laser cutter to make my panel. I'll keep you posted as I make my way through this. Here is the output printed on a card Line up the plastic Mark the holes, scare what you want, the drill it

Here is a future radio chassis I am working on. I have not found the right size or look I wanted so I set out to make one myself. Actually, I had help, from family members that have a sheet metal business, and my son that does specialty carpentry. This chassis is made of brushed aluminum and solid walnut. It is 6 inches wide, by 3 1/12 inches high and 3 1/2 inches deep. Please tell me what you think. Hope to open a store section with stuff to buy or sell. More to come.

https://mgs4u.com/product/vernier-redu

Unusual AM Superregenerative? Receiver - The RadioBoard Forums This is a recovered file. The images in this post may be out of order, and there may be duplicates. Post by Selenium » Fri Nov 20, 2015 Transistors, IC's and other new fangled devices forum Selenium Posts: 1997 Joined: Mon Jun 10, 2013 7:59 pmUnusual AM Superregenerative? Receiver I came across this 1937 magazine article of a portable single tube AM superregenerative receiver. https://ia801405.us.archive.org/33/item ... v_1937.pdf Page 26 It is unusual because superregeneration is usually not possible at the lower frequencies which comprise the AM broadcast band because the quench frequency which turns the main oscillator on and off must be above the audio range which does not give enough time for the oscillator to start. For fun, I have drawn an equivalent FET version which would be interesting to build. The quench oscillator appears to be using a tapped choke as the Hartley quenching oscillator, while the main oscillator itself uses standard Collector feedback. Depending on the FET being used, extra biasing resistors may not be necessary because the choke in the Source lead has a finite resistance. I'm hoping some others might also take up the challenge. Attachments AM superregen.png (12.49 KiB) Viewed 3996 times Last edited by Selenium on Fri Nov 20, 2015 12:40 am, edited 1 time in total. Bob Weaver Posts: 2550 Joined: Sun Apr 08, 2007 8:02 amLocation: SaskatoonContact:Re: Unusual AM Superregenerative? Receiver Postby Bob Weaver » Fri Nov 20, 2015 12:33 am Selenium wrote:It is unusual because superregeneration is usually not possible at the lower frequencies which comprise the AM broadcast band because the quench frequency which turns the main oscillator on and off must be above the audio range which does not give enough time for the oscillator to start. Not sure what you mean by the oscillator not being able to start. But yes, the quench frequency must be above audio range. Otherwise you'll hear it. So it must be at least 15kHz, and preferably 20kHz. The problem is that the bandwidth of a superregen is double the quench frequency, meaning that this receiver will have a bandwidth of at least 30kHz. So, if you have multiple local stations, there's a good chance that you'll hear them all at the same time. If you have only a single local station, then this receiver may be worth a go. Transmitting from my bio-containment unit, deep beneath the Earth's crust. Selenium Posts: 1997 Joined: Mon Jun 10, 2013 7:59 pmRe: Unusual AM Superregenerative? Receiver Postby Selenium » Fri Nov 20, 2015 12:53 am Bob Weaver wrote:Not sure what you mean by the oscillator not being able to start. In a superregenerative receiver, the quench oscillator turns the main oscillator on and off. After it turns off, the length of time it takes to turn on is determined by the Q of the oscillator circuit. For a 20KHz squarewave quench oscillator, 1/2 the period is 25uSec. The main oscillator must start within 25uSec. But for a 1MHz receive frequency, the number of oscillator cycles to do this in 25uSec. is 25. The oscillator must reach full amplitude in about 25 cycles which is unlikely because of the Q of the main oscillator circuit. This is one reason why you will not see a crystal controlled superregenerative receiver. The information in the link below is a little convoluted, but to summarize, the length of time it takes for an oscillator to start is equal to Q cycles. If the Q of the circuit is 100, it will take approximately 100 cycles to start. https://ccrma.stanford.edu/~jos/fp/Deca ... riods.html It is possible to have a functioning low frequency superregenerative receiver by using a lower quench frequency, but the quench frequency will likely have to be in the audible range. I have seen one older patent for a superregenerative AM broadcast band receiver, but I have never seen a functioning circuit. The newer patent at the link below is interesting because it quenches the oscillator as soon as oscillation is detected. http://www.google.com/patents/US7263138 . Bob Weaver Posts: 2550 Joined: Sun Apr 08, 2007 8:02 amLocation: SaskatoonContact:Re: Unusual AM Superregenerative? Receiver Postby Bob Weaver » Fri Nov 20, 2015 1:32 am Okay that makes sense. Transmitting from my bio-containment unit, deep beneath the Earth's crust. seanvn Posts: 715 Joined: Thu Apr 14, 2011 1:10 amRe: Unusual AM Superregenerative? Receiver Postby seanvn » Fri Nov 20, 2015 1:53 am The main problem when you try to design a superregenerative receiver is trying to filter out the quench frequency from the audio stream. If you don't do that you will overload the audio amplifier with ultrasonics. Also you need to completely quench the RF oscillation in LC circuit down completely to zero, quenching it down to say 10uv isn't good enough. Maybe the best option would be using an FET as a shorting switch across the LC circuit, driving the gate of the FET negative to start the oscillation build up, and taking the gate to zero or slightly positive to quench the oscillation. Maybe the best pattern would be (quench, no feedback), (unquench, no or sub oscillation feedback), (unquench, full feedback). The middle part to allow the signal from the antenna to build up by resonance in the LC circuit, the third part to do the actual detection of that built up signal. A terrible issue though is that noise from switching can provoke the LC circuit to ring, don't use a NE555 to switch the thing! In some of the older literature they say using a sine wave to do the quenching gives the best result. seanvn Posts: 715 Joined: Thu Apr 14, 2011 1:10 amRe: Unusual AM Superregenerative? Receiver Postby seanvn » Fri Nov 20, 2015 2:10 am Actually there is an optimum resistive impedance to damp the LC circuit down to zero as quickly as possible. Critical damping I think. It's a pity a reed relay isn't fast enough, though some of the early synchronous detectors did use motor driven mechanical switching. Certainly motor driven switching at say 20Khz should be possible. Selenium Posts: 1997 Joined: Mon Jun 10, 2013 7:59 pmRe: Unusual AM Superregenerative? Receiver Postby Selenium » Fri Nov 20, 2015 3:36 am seanvn wrote: Maybe the best pattern would be (quench, no feedback), (unquench, no or sub oscillation feedback), (unquench, full feedback). The middle part to allow the signal from the antenna to build up by resonance in the LC circuit, the third part to do the actual detection of that built up signal. It is my understanding that the superregen receiver does not detect RF signals in the same way as a regen receiver. In a superregen receiver, the received modulated signal alters the startup time of the oscillator dependent on the modulation amplitude. The constantly changing, modulation dependent startup time alters the oscillator's current which when low pass filtered becomes the detected modulation. One difficulty with this detection technique is that because in real life the startup time is not necessarily a linear function of the received signal amplitude, the detected signal can have significant distortion. http://www.qsl.net/l/lu7did/docs/QRPp/R ... rativo.pdf Below is a salient quote from the article. "What this means is that, no matter how small our input RF signal Vo is, sooner or later there will be a corresponding exponentially rising waveform generated across the coil. This waveform will always have the same “shape” and amplitude, but its “rise time” or delay, if we could define such a term, will vary, and will be dependent on the amplitude of our minute source signal Vo. Left to themselves, the oscillations would carry on increasing in amplitude forever. In practice they will level out as nonlinearities in the associated circuits come into effect. The system then becomes a steady oscillator. We are not interested in this however. We are only concerned about detecting the time between the switch closure and the time at which the self-oscillations rise to a specific level or threshold. Measure these times, and we have a radio receiver." Ham-er Posts: 1926 Joined: Sun Dec 02, 2007 7:50 amRe: Unusual AM Superregenerative? Receiver Postby Ham-er » Fri Nov 20, 2015 5:09 am seanvn wrote: Maybe the best pattern would be (quench, no feedback), (unquench, no or sub oscillation feedback), (unquench, full feedback). The middle part to allow the signal from the antenna to build up by resonance in the LC circuit, the third part to do the actual detection of that built up signal. Seems there is some confusion in this thread. Quenched does NOT imply "no feedback at all". as long as the feedback is "less than 1" the "main oscillator" as you call it will not be an oscillator at all. And it shouldn't ever oscillate(ideally). REGENERATION IS NOT OSCILLATION When unquenched the "regenerative amplifier/detector" MIGHT/could possibly build up enough regeneration to oscillate, but as long as we catch and quench it before that happens, it then WONT oscillate(it could still have regeneration though)! Although the "optimum" quench frequency of an AM receiver would be in the AUDIO range it does not have to be at audio. If we have multiple quenches within only ONE AM RF cycle, things will work but the signal wont be as clean and we will not get as good a "superregeneration". Also the quench oscillator does not have to be a squarewave or any particular waveshape. That make sense? 73 kb0lxy Selenium Posts: 1997 Joined: Mon Jun 10, 2013 7:59 pmRe: Unusual AM Superregenerative? Receiver Postby Selenium » Fri Nov 20, 2015 5:58 am Ham-er wrote: Although the "optimum" quench frequency of an AM receiver would be in the AUDIO range it does not have to be at audio. If we have multiple quenches within only ONE AM RF cycle, things will work but the signal wont be as clean and we will not get as good a "superregeneration". The problem with this scenario is that because of its high Q, after quenching, the oscillator does not start immediately with a large amplitude. The oscillator's amplitude is an exponentially increasing ramp starting from zero. Unlike a regenerative receiver, a normal superregenerative receiver must start oscillating. It is the increase or decrease in startup time created by the received RF signal which is detected in this type of receiver. On some of my receivers it has been possible to put the receiver into an intermediate mod, where the receiver is regenerating but also being quenched. Superregenerative receivers are not usually run in this mode. It will take approximately Q oscillation cycles to reach full amplitude. A crystal oscillator has a Q on the order of 100,000. It would be very difficult to determine the effects of the modulation on the oscillator's startup time if the oscillator were quenched after very single cycle which had close to zero amplitude. Just for interest I was successful in tracking down the 1958 patent for a superregenerative broadcast band receiver. https://docs.google.com/viewer?url=pate ... 821625.pdf It appears to be a 10KHz audio oscillator turning on and off a regenerative receiver. Last edited by Selenium on Fri Nov 20, 2015 2:34 pm, edited 4 times in total. seanvn Posts: 715 Joined: Thu Apr 14, 2011 1:10 amRe: Unusual AM Superregenerative? Receiver Postby seanvn » Fri Nov 20, 2015 6:58 am To me quenching means stopping the LC circuit ringing, completely. That might be done by stopping feedback, but it would take a long time for the LC circuit to ring down fully (presuming it is lightly loaded). The other way to quench it is to simply short it, or better connect it to the correct resistance to critically damp it. There are a lot of tricky requirements there. Maybe a neon bulb relaxation oscillator would be good for quenching but it would be hard to get more that 20KHz out of one. Or the the same thing with a negistor. I'll think about it but it isn't easy. If you could get the 1 million fold gain Armstrong got using tubes that would be fantastic. Selenium Posts: 1997 Joined: Mon Jun 10, 2013 7:59 pmRe: Unusual AM Superregenerative? Receiver Postby Selenium » Fri Nov 20, 2015 7:41 am seanvn wrote:Maybe a neon bulb relaxation oscillator would be good for quenching but it would be hard to get more that 20KHz out of one. Many self quenching superregen receivers use a simple RC network to determine the self quenching rate. In the regenerative shortwave receiver circuit below, the receiver may be made into a superregenerative receiver by increasing the value of the capacitor in the regeneration network. Attachments Regen Front End.jpg (24.68 KiB) Viewed 3935 times gzimmer Posts: 2247 Joined: Mon Jan 14, 2008 1:15 amLocation: AustraliaRe: Unusual AM Superregenerative? Receiver Postby gzimmer » Fri Nov 20, 2015 8:01 am In the Superregen, the Squelch waveform is a pulsed Sinewave having a long tail of harmonics. Because the Squelch waveform is used to modulate the Detector, the response of the receiver will be the same as the spectrum of the Squelch waveform. (you can imaging the frequency response of a Superhet, if the Local Oscillator was "squegging" as in the Superregen) This means two things: (1) That the Superregen cannot be used to receive frequencies which are occupied by the train of Squelch harmonics, and (2) the fundamental Selectivity of the Superregen will be as wide as the Squelch pulse (eg very wide indeed). In practice this means limiting the Superregen to VHF, or trying the "soften" the Squelch waveform so that the harmonics don't intrude into the required band (eg LF or MW). But in trying to do this you drastically compromise the Sensitivity of the Set. It's the old story : TANSTAAFL seanvn Posts: 715 Joined: Thu Apr 14, 2011 1:10 amRe: Unusual AM Superregenerative? Receiver Postby seanvn » Fri Nov 20, 2015 2:24 pm The transistor superregen circuits seem very impaired compared to what Armstrong claimed. I will visit youtube to see what the evidence is regarding tube versus transistor circuits. I'd like a circuit that was giving me nice, satisfyingly high audio volume. Actually you could mix the RF from a regen with say 20 MHz from a crystal oscillator and then use a superregen as a detector, up at the higher mix frequency. Selenium Posts: 1997 Joined: Mon Jun 10, 2013 7:59 pmRe: Unusual AM Superregenerative? Receiver Postby Selenium » Fri Nov 20, 2015 8:46 pm gzimmer wrote:In the Superregen, the Squelch waveform is a pulsed Sinewave having a long tail of harmonics. Squelch or quench? I have never squelched my thirst, but I have frequently quenched it. Also the quenching waveform does not have to be a sinewave. It can be any waveform which turns the main receiver oscillator on or off, even an impulse. Some low power receivers differentiate one edge of a separate square wave quench oscillator to provide biasing to a non-biased receive oscillator, which then starts oscillating. The length of time it takes to start oscillating is dependent on the RF received energy impinging on the tuned circuit. In a separately quenched superregenerative receiver, the quenching oscillator is usually free running, although some receivers use feedback techniques to quench the circuit after a certain oscillator amplitude is reached. In a self quenching superregenerative receiver, the quenching waveform can have a variety of waveshapes dependent on how the quenching is generated. It would appear that some of those who have responded have not examined the link below which I had previously posted. It explains in detail how a superregenerative receiver operates. For any interested in the topic it is worthwhile reading. http://www.qsl.net/l/lu7did/docs/QRPp/R ... rativo.pdf . Unusual AM Superregenerative? Receiver - Page 2 Post by Ham-er » Sat Nov 21, 2015 3:54 am 21-26 minutes Transistors, IC's and other new fangled devices forum Ham-er Posts: 1926 Joined: Sun Dec 02, 2007 7:50 amRe: Unusual AM Superregenerative? Receiver Selenium wrote:The problem with this scenario is that because of its high Q, after quenching, the oscillator does not start immediately with a large amplitude. The oscillator's amplitude is an exponentially increasing ramp starting from zero. Huh What? The "main oscillator"(as you call it ) does NOT have to start oscillating. EVER! Well actually a "self-quenched" supperregen does because the oscillation is the quenching. Selenium wrote:Unlike a regenerative receiver, a normal superregenerative receiver must start oscillating. Huh? no, a superregenerative receiver's (regenerative amplifier/detector) does NOT have to start oscillating EVER. In fact we can add a separate active device quench oscillator to a regular regenerative receiver to get superregeneration. This allows us to set the Gain/regeneration higher than we would normally be able to, because the Gain gets quenched BEFORE oscillation, Preventing that oscillation. Selenium wrote: It is the increase or decrease in startup time created by the received RF signal which is detected in this type of receiver. HuH? NO it is not. A regenerative detector has no "startup time". what is detected is the same AM(all 3 parts) which are "mixed" in the detector just like any other AM detector. The AM is what gets detected. Selenium wrote: On some of my receivers it has been possible to put the receiver into an intermediate mod, where the receiver is regenerating but also being quenched. Superregenerative receivers are not usually run in this mode. That is not an "intermediate mode". That IS how most(if not ALL) superregens operate because that is basically the definition of superregeneration. I.E. Let the regenerative gain build up to a point Just Before oscillation, then Quench the regeneration before oscillation can start, so that oscillation does NOT start. If it did start oscillation, it would then be amplifying it's OWN supplied signal, Instead of the incoming signal. And that is why we Don't let it oscillate. I really don't know what one would call an oscillator quenched by another oscillator, but it isn't "superregeneration". 73 kb0lxy Last edited by Ham-er on Sat Nov 21, 2015 4:27 am, edited 1 time in total. Ham-er Posts: 1926 Joined: Sun Dec 02, 2007 7:50 amRe: Unusual AM Superregenerative? Receiver Postby Ham-er » Sat Nov 21, 2015 3:58 am seanvn wrote:To me quenching means stopping the LC circuit ringing, completely. In this context quenching means preventing oscillation by stopping regeneration before oscillation. 73 kb0lxy Ham-er Posts: 1926 Joined: Sun Dec 02, 2007 7:50 amRe: Unusual AM Superregenerative? Receiver Postby Ham-er » Sat Nov 21, 2015 4:20 am Selenium wrote:[It would appear that some of those who have responded have not examined the link below which I had previously posted. It explains in detail how a superregenerative receiver operates. For any interested in the topic it is worthwhile reading. http://www.qsl.net/l/lu7did/docs/QRPp/R ... rativo.pdf Ok Now that I have read it. It is WRONG. That is not how a superregenerative receiver works. When receiving and detecting AM; The LC circuit in a regen receiver does NOT oscillate, it is merely a frequency dependent impedance(FILTER). We are NOT quenching oscillations in the LC circuit. In fact the total loop gain is set to keep it from ringing/oscillating. It is set by the regen control manually, and actually set lower that it would/could be, if we could stop the circuit from oscillating by another means. Similarly in a superregen receiver the LC tank does NOT ring. But the loop gain set by the regen control is set too high. meaning that it WILL start oscillating if we don't do something to prevent oscillation. So what we do is "quench the gain" just before it would other wise oscillate. This has to be done very quickly, so we use an oscillator to do the quenching and unquenching for us. This allows us to have higher regeneration and gain(superregeneration) than we can achieve with a standard regen set. We are quenching Gain/Regeneration, not quenching oscillations. We are in fact preventing oscillation, it just happens to be ironic that we use an oscillator to do that quenching for us. 73 kb0lxy P.S. Only talking AM reception here not CW or SSB. seanvn Posts: 715 Joined: Thu Apr 14, 2011 1:10 amRe: Unusual AM Superregenerative? Receiver Postby seanvn » Sat Nov 21, 2015 6:23 am There are 2 reasons for quenching in a superregenerative receiver. One can be to take the loop gain of the oscillator below 1. The other reason is to empty out the LC circuit. Say the oscillation in the LC circuit reaches 1 volt, and you only damp it down to 100 uV before the loop gain exceeds 1 again, then 100uv is about the weakest signal you can receive. Any weaker signals will be swamped by what is already there. Last edited by seanvn on Sat Nov 21, 2015 7:45 am, edited 1 time in total. Selenium Posts: 1997 Joined: Mon Jun 10, 2013 7:59 pmRe: Unusual AM Superregenerative? Receiver Postby Selenium » Sat Nov 21, 2015 7:27 am Ham-er wrote: Ok Now that I have read it. It is WRONG. That is not how a superregenerative receiver works. Rather than respond to each of your unbelievably numerous incorrect assumptions about how a superregen receiver works, I felt that responding to the above quote would be sufficient. Perhaps you could write Dr. Eddy Insam and correct his errors in this document. You might also be able to assist him in correcting the information in many of his other published documents. Regarding a superregen receiver not oscillating, I wonder why the thousands of garage door and car opener superregen circuits all have RF amplifier front ends connected to their antennas? Could it be that they are oscillating and the designers want to eliminate spurious radiation? I wonder why when I put my superregen receivers near any other receiver, the receiver is swamped by RF noise. Is there any chance that the superregen receiver might be oscillating? I wonder why crystals are not normally used in superregen receivers? Could it be that their Q is so high that it would take so long for them to initialize and decay that practical voice communication with them is not possible? You can lead a horse to water ...... Last edited by Selenium on Sat Nov 21, 2015 7:52 am, edited 3 times in total. gzimmer Posts: 2247 Joined: Mon Jan 14, 2008 1:15 amLocation: AustraliaRe: Unusual AM Superregenerative? Receiver Postby gzimmer » Sat Nov 21, 2015 7:37 am > Also the quenching waveform does not have to be a sinewave. The point I was trying to make is that it's a pulse with a string of harmonics (obviously it's a pulse, and obviously it's not a sinewave as it has strong harmonics). Following on from my earlier post, the Superregen detector acts a a sampler. It operates in pulses, and so it can only take one sample per pulse. So to cover the audio band, the lowest frequency of the quench frequency must be at least twice the highest audio frequency (as per Nyquist). So that sets lower bound on the range of quench frequencies available. And FWIW, a superregen does not oscillate (or more correctly, it should not oscillate) the signal is allowed to build up to just before the point of continuous oscillation and then is quenched. Allowing it to actually begin oscillation is counter productive, as it is then saturated. So is it oscillating? Well it's building up towards oscillation, but it never actually gets there. The noise that you hear on a nearby receiver is the harmonics of the quench waveform, with perhaps some ringing at the tank frequency. Incidentally the modern software version of a supperegen is the Goertzel filter. https://en.wikipedia.org/wiki/Goertzel_algorithm At least that's how my versions of it work. ...........Zim Last edited by gzimmer on Sat Nov 21, 2015 8:20 am, edited 9 times in total. Selenium Posts: 1997 Joined: Mon Jun 10, 2013 7:59 pmRe: Unusual AM Superregenerative? Receiver Postby Selenium » Sat Nov 21, 2015 8:11 am gzimmer wrote:Further to previous, the Superregen detector acts a a sampler. It operates in pulses, and so it can only take one sample per pulse. ================================== And FWIW, a superregen does not oscillate (or more correctly, does not have to oscillate) the signal is allowed to build up to just before the point of oscillation and then is quenched. Allowing it to actually begin oscillation is counter productive. I agree with all the items in the previous post and particularly the two in the quote above. I think it is important to note that the sample does not include RF input during the entire sample period, only the start. The circuit is not acting like a regenerative receiver. Ideally, it is of no value to have the circuit have sustained oscillations during the sample period. Practically, in a self-quenching receiver, unless there is some form of threshold detector in the circuit, the simple RC networks usually used for self-quenching have no easy way of determining when a specific threshold has been reached. gzimmer Posts: 2247 Joined: Mon Jan 14, 2008 1:15 amLocation: AustraliaRe: Unusual AM Superregenerative? Receiver Postby gzimmer » Sat Nov 21, 2015 8:26 am > in a self-quenching receiver, unless there is some form of threshold detector in the circuit, > the simple RC networks usually used for self-quenching have no easy way of determining > when a specific threshold has been reached. Usually it's a simple blocking oscillator. Some mechanism (eg onset of grid current) is acting as a threshold detector. There has to be a threshold sensor, else the pulse length would be fixed, eg it wouldn't work. ....Zim Selenium Posts: 1997 Joined: Mon Jun 10, 2013 7:59 pmRe: Unusual AM Superregenerative? Receiver Postby Selenium » Sat Nov 21, 2015 1:18 pm gzimmer wrote:Usually it's a simple blocking oscillator. Some mechanism (eg onset of grid current) is acting as a threshold detector. There has to be a threshold sensor, else the pulse length would be fixed, eg it wouldn't work. Some separately quenched receivers use free running quench oscillators. Some low power receivers use unbiased oscillators which are naturally turned off. Their bias is obtained by differentiating a transient pulse from a separate quench oscillator. There is no threshold detector. Just for interest I have added two schematics for separately quenched superregen receivers in which their oscillators are not biased. The first is a micropower superregen data receiver using unbuffered CMOS devices. In this circuit the output of a free running quench oscillator is differentiated by capacitor 47 which biases the oscillator by pulling its emitter below ground. The second uses a unijunction transistor ramp voltage to provide bias to the oscillator. Attachments micropower superregen.png (33.97 KiB) Viewed 1089 timesunijunction superregen.jpg (75.33 KiB) Viewed 1089 times Selenium Posts: 1997 Joined: Mon Jun 10, 2013 7:59 pmRe: Unusual AM Superregenerative? Receiver Postby Selenium » Sat Nov 21, 2015 11:36 pm Pat Pending wrote:It does not mean that the S.R.A. is oscillating at signal frequency. Great article, good bedtime reading, thanks! http://dspace.mit.edu/handle/1721.1/58931 Regarding oscillating or non-oscillating. The article states that in logarithmic mode the oscillator has saturated. Does that not mean that it is oscillating? I am curious how many of the simple self quenching receivers have quenching circuits which are sophisticated enough to use true threshold detection that quenches the waveform before it has saturated. Likely this is highly dependent on the RC time constants used in the quenching circuit which is why in most simple regenerative receivers there is usually some means of controlling regeneration and quenching, usually a potentiometer. The separate quenching circuits in the posts above which provide bias to the oscillator circuit have no true threshold detector and it seems to me that these superregenerative receivers are in fact oscillating for at least a portion of their duty cycle. gzimmer Posts: 2247 Joined: Mon Jan 14, 2008 1:15 amLocation: AustraliaRe: Unusual AM Superregenerative? Receiver Postby gzimmer » Sun Nov 22, 2015 2:52 am > Some separately quenched receivers use free running quench oscillators. Yes, of course. > There is no threshold detector. Well, the output comes from the receiver stage, not from the oscillator, so I suspect that the receiver stage is still acting as a threshold detector, even when it is driven by a separate oscillator. Something must be creating the variable width pulse to enable it to encode the received signal strength. .........Zim Last edited by gzimmer on Sun Nov 22, 2015 8:26 am, edited 1 time in total. Ham-er Posts: 1926 Joined: Sun Dec 02, 2007 7:50 amRe: Unusual AM Superregenerative? Receiver Postby Ham-er » Sun Nov 22, 2015 3:29 am Selenium wrote: Ham-er wrote: Ok Now that I have read it. It is WRONG. That is not how a superregenerative receiver works. Rather than respond to each of your unbelievably numerous incorrect assumptions about how a superregen receiver works, I felt that responding to the above quote would be sufficient. Perhaps you could write Dr. Eddy Insam and correct his errors in this document. You might also be able to assist him in correcting the information in many of his other published documents. Selenium wrote:Regarding a superregen receiver not oscillating, I wonder why the thousands of garage door and car opener superregen circuits all have RF amplifier front ends connected to their antennas? Could it be that they are oscillating and the designers want to eliminate spurious radiation? ...... You misunderstand. The "receiver" oscillates because it's Quench oscillator does oscillate. The regenerator does NOT oscillate, at least not at the regenerated frequency. If it did that it would not be superregenerating the received signal! In A self quenching superregen, The regenerator may oscillate but it does so at the quench frequency. It does not "oscillate(by proper definition of oscillating)" at the regenerated frequency. The regenerated frequency does/can/may build up in a "ramp" until just before it would oscillate(at that frequency). Then the regenerator is quenched. Allowing the regenerator part of the "receiver" to oscillate at the desired receive frequency would be counter productive and will eliminate the "superregeneration". Selenium wrote:I wonder why when I put my superregen receivers near any other receiver, the receiver is swamped by RF noise. Is there any chance that the superregen receiver might be oscillating?...... The quench oscillator and its harmonics are strong enough at that close proximity? Selenium wrote:[You can lead a horse to water ...... True and sometimes people will misinterpret a very technical article making it seem to say what it does not. So I will guess that the ARTICLE is not WRONG if you interpret it correctly, but that YOUR interpretation of it is not correct. The regenerating part of a superregenerative receiver MUST NOT be allowed to "oscillate" at the frequency we are trying to superregenerate. If it does so we will not be superregenerating that frequency. 73 kb0lxy Ham-er Posts: 1926 Joined: Sun Dec 02, 2007 7:50 amRe: Unusual AM Superregenerative? Receiver Postby Ham-er » Sun Nov 22, 2015 3:42 am Selenium wrote: Pat Pending wrote:It does not mean that the S.R.A. is oscillating at signal frequency. Great article, good bedtime reading, thanks! http://dspace.mit.edu/handle/1721.1/58931 Regarding oscillating or non-oscillating. The article states that in logarithmic mode the oscillator has saturated. Does that not mean that it is oscillating?. Sure. The Oscillator(quench oscillator) IS oscillating. Even the SRA can be oscillating (at the quench frequency) but not at the frequency we are trying to amplify. In a sense the signal we are trying to amplify will "rise and fall" at the quench rate, but that is not the kind of "oscillating" we talk about when referring to superregen receivers. 73 kb0lxy So yes technically the gain in the SRA does "oscillate" but that is not really the radio theory we are talking about is it? seanvn Posts: 715 Joined: Thu Apr 14, 2011 1:10 amRe: Unusual AM Superregenerative? Receiver Postby seanvn » Sun Nov 22, 2015 4:09 am One reason for the confusion is that there are a number of intertwined factors and a number of different options in creating a superregenerative radio. Just for example say you had an oscillator circuit that has just started, there is say .1uv of noise in the LC circuit. Since the growth in signal amplitude is exponential (because the loop gain must be greater than 1) then after 1 time unit the amplitude could be 1uv, after 2 time units 10uv, after 3 time units 100uv, 4 TU 1mv, 5 TU 10mv, 6 TU 100 mv. Now if you started with 10 uv from an external signal in the LC circuit after 1 TU there would be 100 uv, 2 TU 1 mV, 3 TU 10 mV, 4 TU 100mv. So starting with a 10uV signal the oscillation reaches 100 mV two time units quicker than if there was no signal (just a little start up noise). So in fact you don't even need to change the gain of the oscillator amplifier if somehow you could periodically critically damp the LC circuit back to the zero energy state. That is not how a superregenerative receiver is normally done, just various options exist and you need to disambiguate them. gzimmer Posts: 2247 Joined: Mon Jan 14, 2008 1:15 amLocation: AustraliaRe: Unusual AM Superregenerative? Receiver Postby gzimmer » Sun Nov 22, 2015 8:35 am People are saying that the Super-Regen samples the received signal only at the start of the cycle. But I suspect that any signal input which is in phase with the building oscillation will cause the oscillation to ramp up more quickly. And it will cause the Oscillation to lock in phase and frequency. Sort of like the Synchrodyne. If that is the case, the S.R. is sampling the input all through the active part of the cycle. Late edit: The answer of course is that the input signal can only contribute while the exponentially rising oscillation is weak. Once the Oscillation swamps the signal, any ongoing input will have little effect. So yes, the incoming signal contributes throughout the cycle, but it can have little effect except at the beginning. ..........Zim Last edited by gzimmer on Mon Nov 23, 2015 2:02 am, edited 3 times in total. I guess you can have a different mental model where you would view the superregen as not oscillating, where you view it as taking the original signal and amplifying it by regeneration below and then above the threshold of oscillation. You can design in a different way with that view. If you use a very short regen amplifier "on" time, and you don't wait for the signal build up to hit the supply rails then the peak signal amplitude is directly related to the input signal amplitude by many, many times. Usually you do wait for the signal to be limited by the supply rails and kind of use pulse width demodulation to detect the signal. The width being modulated by the earlier onset of limiting caused by a strong input signal being present. So in a way everyone is right. seanvn Posts: 715 Joined: Thu Apr 14, 2011 1:10 amRe: Unusual AM Superregenerative? Receiver Postby seanvn » Sun Nov 22, 2015 1:05 pm So I guess the possible modes are Self quenched: 1/ Pulse width demodulation 2/ LC clearing by reducing loop gain below 1 and waiting for ring down, or fast clearing by critical damping. Externally quenched: 1/ Pulse width demodulation or in the non limiting (non clipping) case peak detection. 2/ LC clearing by reducing loop gain below 1 and waiting for ring down, or fast clearing by critical damping. Probably the second case explains how Armstrong was able to report 1 million times gain. Very likely he was able to adjust things to get peak detection but I'm not sure how he could have gotten such fast ring down of the LC circuit except by forcing the grid positive into conduction. I'll try to look at the original circuit on the Internet and see if I can figure it out. I'll try with very short "on" time method and see if I can get peak detection. I think most key-fob circuits etc. would use the pulse width demodulation to avoid any critical adjustments and also the log type response avoids the need for automatic gain control. Electrojim Posts: 39 Joined: Sun Nov 22, 2015 12:30 amLocation: Southern CaliforniaContact:Re: Unusual AM Superregenerative? Receiver Postby Electrojim » Sun Nov 22, 2015 5:41 pm Hi, Guys, I just joined the RadioBoard and was quite intrigued by this super-regen thread. There seems to be a lot of discussion regarding this mode of reception, and exactly how it works. Although I've built a good number of super-regen receivers over the years, I've really never looked deeply into the physics of the circuit, remaining blindly content with how well the circuit performs as a simple, yet sensitive (and broad!) receiver at VHF frequencies. One idea I've found useful, when using an external quench oscillator, is subtracting the quench frequency from the audio output to null the supersonic component. This allows use of a lower quench frequency and makes output filtering a lot easier. As to how the super-regen actually works, and there seems to be disagreement on this within the group, the most complete explanation I have come across is by the British writer, M.G. Scroggie, whose articles were common in Wireless World magazine over many years. Collections of his articles were incorporated in books by the publisher of Wireless World, which I believe to no longer be in business. At the possible expense of arrest, conviction and imprisonment, I have scanned and posted Scroggie's super-regen explanation here: https://www.dropbox.com/s/gwusbiqaqhqli ... n.pdf?dl=0 . Selenium Posts: 1997 Joined: Mon Jun 10, 2013 7:59 pmRe: Unusual AM Superregenerative? Receiver Postby Selenium » Sun Nov 22, 2015 5:46 pm Regarding oscillating and non-oscillating and superregenerative re-radiation. I am now curious if any participating in this thread have ever looked at the RF spectrum from a superregen receiver on a spectrum analyzer. Rather than drag out my old 100 pound Tektronix and take a picture, there are numerous examples on the Internet citing broad RF output at the LC resonant frequency with numerous sidebands displaced from the main signal at the quench frequency. The paper at the link below gives a number of analytical and graphical examples. http://essay.utwente.nl/67721/1/van%20Uem_MA_EWI.pdf I have, however, also seen some references about techniques used to minimize inband RF radiation in superrregen receivers. These techniques appear to involve altering the quench frequency characteristics. golfguru Posts: 5235 Joined: Sat Aug 18, 2007 8:52 pmLocation: AustraliaRe: Unusual AM Superregenerative? Receiver Postby golfguru » Sun Nov 22, 2015 9:15 pm Interesting read M.G. Scroggie pdf. Here is an abstract from the Strafford doc referenced. Attachments strafford.JPG (165.02 KiB) Viewed 1028 times Ham-er Posts: 1926 Joined: Sun Dec 02, 2007 7:50 amRe: Unusual AM Superregenerative? Receiver Postby Ham-er » Mon Nov 23, 2015 1:04 am Pat Pending wrote: Normally accepted understanding of amplification is to my way of thinking when a weak signal is used to control a local power source to yield a stronger faithful version of itself. S.R.A.s don't do this directly, normal regens are the best you will get for that. Define "faithfull". Even a standard regenerative amplifier does not give an exact replica of the input signal. Because there IS some phase shift between the output of the amp and its input, one cannot get exactly ZERO phase shift. You can get close but will still have some distortion, cause by adding an amplified cycle, slightly out of phase with the same cycle non-amplified. If you have 360 degree phase shift, you will be adding one cycle(now amplified) of the input, to the next cycle. With multiple 360 degree shifts, it is even less "faithfull". Take all that above and "punch holes" so to speak, in that train with a quench oscillator, and it will be even less faithfull! Still it is faithfull enough to use practically. Even with an approximately 50% duty cycle(when quench wave form is pure sinewave or squarewave) of the SRA, it can still be usefully faithfull. Yes I know that sinewave quenching wont necessarily give 50% duty cycle quenching. Additionally the waveform of a "self quenched" SRA is usually by a relaxation type oscillation and thus is nowhere near 50% on/off times. So even though an SRA may not "faithfully" amplify the input signal they still DO directly amplify the input signal, just like any other amplifier. A straight Regenerative amplifier is NOT the best you will get for that. An SRA is the best in terms of GAIN. A non-regenerative amplifier is the best you will get in terms of "faithfull" reproduction(fidelity). And No amplification at all is the best for pure fidelity. Even a non-regenerative amplifier will distort the signal a bit. 73 kb0lxy Ham-er Posts: 1926 Joined: Sun Dec 02, 2007 7:50 amRe: Unusual AM Superregenerative? Receiver Postby Ham-er » Mon Nov 23, 2015 1:25 am Pat Pending wrote: The facts are that an S.R.A. used in radio technology is a signal frequency oscillator (that is controlled by a quenching frequency), that doesn't have to oscillate continually, and is normally prevented from doing so by automatic or manual manipulation of the circuits active device's' operating point. Regards. Andy. Um NO, uh well sort of YES. A SRA is a signal frequency regenerative amplifier(based on an oscillator circuit)that is prevented from actually oscillating(at the signal frequency). It is done by automatic manipulation, because unlike a "non-super" regenerative amplifier, Manuall quenching is just not fast enough to prevent oscillation. BTW, "non-super" regenerative amplifiers are ALSO based on an oscillator circuit. 73 kb0lxy gzimmer Posts: 2247 Joined: Mon Jan 14, 2008 1:15 amLocation: AustraliaRe: Unusual AM Superregenerative? Receiver Postby gzimmer » Mon Nov 23, 2015 1:32 am Electrojim, Thanks for posting the Scroggie Super-regen article. I reckon that's the best yet... ............Zim qrp-gaijin Posts: 2822 Joined: Sun Feb 28, 2010 2:12 pmContact:Re: Unusual AM Superregenerative? Receiver Postby qrp-gaijin » Sat Nov 28, 2015 2:12 am Having read the article, I wonder why a regeneration control is needed. Isn't this supposed to be a super-regen? The article indicates that tuning may take some getting used to, and that there is interaction between the tuning and regeneration controls, but does not specify the details. So are you supposed to first tune in the station in regenerative mode, then increase regeneration until it starts to squeg, or what? Selenium Posts: 1997 Joined: Mon Jun 10, 2013 7:59 pmRe: Unusual AM Superregenerative? Receiver Postby Selenium » Sat Nov 28, 2015 2:23 am qrp-gaijin wrote:Having read the article, I wonder why a regeneration control is needed. Isn't this supposed to be a super-regen? Over the years I have built many self-quenching superregenerative receivers. Some were an afterthought where I wanted to listen to a specific shortwave station with a regen front end without adding any more audio gain. The easiest solution was to increase the size of the capacitor in the RC regeneration control network ro create a superregen receiver which meant that a regeneration potentiometer was still in place. The ability to have a regeneration control meant that it was possible to control the regeneration which also altered the quench frequency to optimize the audio output across the band and minimize heterodyning. A fixed resistor could be used to replace the regeneration potentiometer, but my experience is that for these simple receivers with a wide frequency tuning range, having a regeneration control is an asset. For any who want to experiment, the receiver below works well both as a regenerative or superregenerative receiver by changing the value of capacitor C2. The regenerative version will require significantly more audio gain to be added. Attachments simple superregen.jpg (8.41 KiB) Viewed 942 times Ham-er Posts: 1926 Joined: Sun Dec 02, 2007 7:50 amRe: Unusual AM Superregenerative? Receiver Postby Ham-er » Sun Nov 29, 2015 10:54 pm qrp-gaijin wrote: Having read the article, I wonder why a regeneration control is needed. Isn't this supposed to be a super-regen? The article indicates that tuning may take some getting used to, and that there is interaction between the tuning and regeneration controls, but does not specify the details. Get used to the idea that an amplifier(regenerative or not) DOES NOT AMPLIFY ALL FREQUENCIES THE SAME! Consider that the Impedance of reactive(capacitive and inductive) components(whether they are intentionally built in components or are stray capacitance and lead inductance), will be different at different frequencies. Therefore with a change in operational frequency, a change in GAIN may be required. * I did not read the article looking to see how wide the overall tuning range is/might be. A manual loop-gain(regeneration) control may be usefull even if not "required". qrp-gaijin wrote: So are you supposed to first tune in the station in regenerative mode, then increase regeneration until it starts to squeg, or what? Possibly. It kindof depends on how we define "squegging". I define it as: Simultaneously oscillating at more than one frequency. If one of those "oscillations" is of the relaxation type, instead of sinewave type, is that still defined as "squegging"?. I personally don't define squegging that way, but you might. I personally would call that "self quenching". Either way a Manual regen(gain) control might be helpfull if not absolutely necessary. 73 kb0lxy DrM Posts: 1027 Joined: Fri Jun 19, 2009 8:30 pmLocation: The NetherlandsRe: Unusual AM Superregenerative? Receiver Postby DrM » Mon Nov 30, 2015 9:56 am Ham-er wrote:Possibly. It kindof depends on how we define "squegging". I define it as: Simultaneously oscillating at more than one frequency. If one of those "oscillations" is of the relaxation type, instead of sinewave type, is that still defined as "squegging"?. I personally don't define squegging that way, but you might. I personally would call that "self quenching". Either way a Manual regen(gain) control might be helpfull if not absolutely necessary. Squegging is a relaxation oscillation due to large RC time constants in the RF signal and/or RF feedback paths of an oscillator. When oscillating these large time constants changes the bias conditions of the active device due to charging and discharging of the capacitor in the signal and/or feedback paths. This effect causes continuously stopping and starting again of oscillations. Especially solid-state regens in which detection and Q-Multiplying are combined into one active device, are vulnerable for squegging. Ham-er Posts: 1926 Joined: Sun Dec 02, 2007 7:50 amRe: Unusual AM Superregenerative? Receiver Postby Ham-er » Mon Nov 30, 2015 11:13 pm DrM wrote: Squegging is a relaxation oscillation due to large RC time constants in the RF signal and/or RF feedback paths of an oscillator. ............ Do you have an official "source" for that definition including the relaxation oscillation? My 1943 ARRL hand book defines squegging as "simultaneously oscillating at more than one frequency". And no further definition exactly but it goes on to talk about "squegging" being two RF frequencies as if it were an additional "sinewave" type oscillation. The RF feedback paths CAN cause that and not necessarily by "relaxation". Just like an "unintended" feedback path cause by stray capacitance and lead inductance can cause VHF "parasitic" oscillations. 73 kb0lxy aurel Re: Unusual AM Superregenerative? Receiver Postby aurel » Tue Dec 01, 2015 5:10 pm @Selenium do you really build this Poliakov circuit and which transistor u use? vladn wrote:my unverified guess is that (ii) dominates the regen control effect. The higher is the drain RF load impedance (low throttle capacitance) the larger is the amplitude of the amplified RF signal at the drain. That signal is inverted with respect to the gate signal and fed back to the gate via parasitic Cgd of the JFET. This introduces negative feedback (as opposed to the positive feedback from the source to the tank). Varying the amount of the negative feedback by changing the drain load you adjust regeneration. Again this is only a guess. Consider the following N1TEV design, which uses a fairly common Armstrong tickler and throttle capacitor arrangement with a JFET: http://www.electronics-tutorials.com/re ... ceiver.htm First, I always understood that the throttle capacitor controls the amount of current flowing through the tickler. The RFC prevents current flowing up to Vcc, so instead it flows through the adjustable throttle. Would you agree that this description is accurate for a JFET Armstrong throttle capacitor and tickler? The drain signal is inverted, so the tickler is wound, adjacent to the main coil, with its hot end (to the drain) and cold end (to the throttle capaitor) reversed with respect to the main coil, to effect in-phase feedback. Then, according to your argument above, it would seem that the reducing throttle capacitance not only reduces the current flow through the tickler (thus reducing tickler-based feedback), but it also increases the drain load impedance, which then feeds the impeded inverted signal back to the gate via parasitic capacitance, further reducing feedback beyond that aleady effected by tickler current reduction. So there are two feedback control mechanisms with the tickler and throttle cap: tickler current control and drain impedance control. Using non-inverted tickler feedback from the source, but keeping the drain throttle in place, thus prevents direct control of feedback through the tickler and leaves only drain impedance control to control feedback indirectly (through parasitics). Interesting. I have seen at least one Hartley that uses a throttle capacitor: N1TEV's 2010 design in CQ magazine. The explanation is the usual "RFC backs up the RF signal preventing it from traveling to Vcc and instead forcing it through throttle capacitor". It sounds simple enough, but perhaps there is indeed more than meets the eye. (The issue of "where do the excess electrons accumulated on the top plate of the throttle capacitor go, when the gate signal drops into a valley and constricts the JFET channel" is still bugging me; given enough time, the electrons will bleed off through the RFC, but what about when they're not given enough time as the gate signal is wiggling up and down at RF? I guess some low amount of average current leaks through the RFC, bleeding off enough electrons from the top plate such that the top plate's charge does not grow without bound.) vladn wrote:I do not quite like using device parasitics for any control (as it may not be repeatable from device to device), this is personal and subjective, indeed it may work well, it just goes against my engineering/aesthetic intuition Believe me, I want to get the gate bias regeneration control working, but it's not cooperating. So I turned to a method that I have more experience with, the throttle capacitor. I am still hammering away at getting gate bias regeneration working; now, with my almost-tilt-balanced prototype, it should be easier than with a non-tilt-balanced setup (where required gate bias would vary greatly with frequency). And speaking of design repeatability, I'm a little concerned that hybrid regen designs might not be easily repeatable due to the large amount of tweaking that needs to be done. Lack of design repeatability would be regrettable, as it would discourage casual experimentation with the very elegant hybrid feedback idea. There are many ways to "fix" a Regen. The obvious one is to add a tuned circuit in front of the Super-Regen stage it provide the necessary Selectivity. Which is what that patent seems to be doing. Very nice indeed -- as I mentioned in another thread, I'm thinking about using a superregen as an IF detector, preceded by a crystal filter to take care of the selectivity. Although the self-quenched circuit is the most attractive due to its simplicity, based on my very preliminary investigations, I'm concerned that a self-quenched circuit might not really be extinguishing the oscillations as completely as it should -- in my simulations of a 1 MHz LC superregen, there seems to be a residual waveform of a few microvolts (peak-peak) left over after every quench cycle. This residual few-microvolt signal would, it intuitively seems, therefore prevent few-microvolt signals from the antenna from being properly detected. On the other hand, even if there is a few-microvolt residual signal in the tank, an incoming signal of say 0.5 microvolts will (should) cause the build-up-time of oscillations to become faster in the next cycle, hence allowing the input signal to have an effect. I suppose the question (which may already be answered in the numerous references posted in this thread) is: what is the maximal allowed residual tank voltage Vre at the end of a quench cycle, that will not inhibit reception of incoming weak signals of voltage Vin? I saw once a reference to a calculation to this effect (how much/how long must the resonator be damped after each quench cycle), but it was beyond my comprehension (at 2am in the morning, anyway). ----- Edit: here's one reference about the importance of complete damping to avoid entering the "coherent state": https://repository.tudelft.nl/islandora ... J/download coherent.png (107.36 KiB) Viewed 720 times But it's still not exactly clear to me how to determine wither a superregen is operating in the coherent or non-coherent state... And some references to fixing the residual oscillations ("hang-over") with explicit damping: https://www.google.com/patents/US20060264196 Compared with the conventional super-regenerative receiver, the oscillation signal of the invention decays faster due to the damping of the damping resistor. The residual oscillation energy thus does not affect the subsequent oscillations. That is, the hang-over effect can be avoided. https://www.google.com/patents/US2644081 The damping resistor I2 is usually selected so that the damping of the regenerative circuit is less than critical but nevertheless sufficient to avoid carry-over or hang-over effects. That is to say, the amount of damping is usually so selected that the oscillations generated in any quench cycle of the superregenerative amplifier are clamped to a value such that they have no appreciable effect on the oscillations generated in the next succeeding quench cycle. Again, how to determine "no appreciable effect"...? I would also assume that heavier damping would lead to prolonged start-up times, which is also a problem operating at low frequencies like 1 or 2 MHz. The cross-coupled oscillator might be the easiest, fastest-starting oscillator, so perhaps a circuit might be a cross-coupled oscillator with enough damping to remove hang-over effects and enough gain to start up quickly. Then, if the cross-coupled oscillator could be self-quenched (can it?), we might have a fairly simple and sensitive superregen for 1 or 2 MHz. Mon Feb 05, 2018 8:21 am The GAIN rising(because of regeneration) and then falling(because of quenching) COULD be described as an "oscillation". But that happens at the quenching rate not at the RF rate! gzimmer wrote: ↑ Mon Feb 05, 2018 4:44 am In a Super-regen, the signal builds up in a linear Exponential fashion until it starts oscillating. Once it is oscillating, it is hard-limiting (eg is saturated). So for optimum Sensitivity, the quench should kill the energy in the coil just before it reaches saturation. ......Zim Once it is saturated, isn't this called logarithmic mode which acts as AGC? Isn't this the same as and doesn't this occur when using a low frequency quench? It seems to me that it must be oscillating and radiating very strongly at "the RF rate" by this point. In order to get a better understanding of why there appear to be misconceptions about the superregenerative process, it would be interesting if you could post your versions of how the modulation is detected in a superregen receiver. I suspect that one version will be correct and the other incorrect. Below are simulations done by qrp-gaijin and another oscilloscope view of the output of a functioning superregen receiver. The red waveform (which is likely AC coupled) when averaged or put through a low pass filter (your ears) results in the demodulated audio modulation. The waveform shown is for a separately quenched receiver. For a self-quenched receiver, the duty cycle and quench frequency change with the modulation amplitude. The last clip is a spectrum analyzer output of a functioning superregen receiver. The comments are self explanatory .http://www.amalgamate2000.com/radio-hob ... t%20HF.htm From Eddy Insam's paper http://www.eix.co.uk/Articles/Radio/Welcome.htm "Switching a negative resistance across an LC tank circuit causes positive exponential self-oscillations to be generated at its natural resonant frequency. The startup time is a function of initial conditions, namely the tiny RF currents induced in the coil from an aerial. The resulting wave growth can be easily measured by external circuitry. The negative resistance is generated by the active component used: transistor, FET, or other." And an interesting link about a crystal controlled superregen data receiver using a MOSFET for quenching. http://www.vk2zay.net/article/235 Some Ham-er quotes from earlier in the thread. Ham-er wrote: ↑ Sat Nov 21, 2015 3:54 am Huh What? The "main oscillator"(as you call it ) does NOT have to start oscillating. EVER! Well actually a "self-quenched" supperregen does because the oscillation is the quenching. ------------------- In fact we can add a separate active device quench oscillator to a regular regenerative receiver to get superregeneration. This allows us to set the Gain/regeneration higher than we would normally be able to, because the Gain gets quenched BEFORE oscillation, Preventing that oscillation. ------------------ HuH? NO it is not. A regenerative detector has no "startup time". what is detected is the same AM(all 3 parts) which are "mixed" in the detector just like any other AM detector. The AM is what gets detected. ----------------- I.E. Let the regenerative gain build up to a point Just Before oscillation, then Quench the regeneration before oscillation can start, so that oscillation does NOT start. If it did start oscillation, it would then be amplifying it's OWN supplied signal, Instead of the incoming signal. And that is why we Don't let it oscillate. ---------------- I really don't know what one would call an oscillator quenched by another oscillator, but it isn't "superregeneration". 73 kb0lxy And regarding E. Insam's paper: Ham-er wrote: ↑ Sat Nov 21, 2015 4:20 am Ok Now that I have read it. It is WRONG. That is not how a superregenerative receiver works. Sun Feb 04, 2018 12:28 am I would also assume that heavier damping would lead to prolonged start-up times, which is also a problem operating at low frequencies like 1 or 2 MHz. The cross-coupled oscillator might be the easiest, fastest-starting oscillator, so perhaps a circuit might be a cross-coupled oscillator with enough damping to remove hang-over effects and enough gain to start up quickly. Then, if the cross-coupled oscillator could be self-quenched (can it?), we might have a fairly simple and sensitive superregen for 1 or 2 MHz. Preliminary LTspice simulations indicate that the above approach appears promising. xx100.png (121.13 KiB) Viewed 1084 times Important points to note about the above circuit: R2, the 100 ohm resistor R2 in series with the tank coil, intentionally heavily damps the tank, lowering its Q and leading to much faster decay times after the onset of quenching (to remove the hang-over effect caused by residual tank energy). The cross-coupled oscillator, combined with the center-tapped coil L1/L2, provides high gain to provide fast start-up time for the oscillator to overcome the heavy tank losses. Note that when the center-tapped coil L1/L2 was replaced with a non-center-tapped coil of equivalent inductance, although the circuit still oscillated, I could not find a way to cause self-quenching; I think that the center-tapped configuration offers more loop gain for the oscillator. Again, because of the heavy tank damping (to reduce hang-over), and because we must start up the oscillator quickly (because this is a super-regen), we need all the gain we can get. "Quench waveform adjustment" resistor R3 is important to avoid heavy distortion of the oscillator waveform. Note with R3 (quench waveform adjustment) set to 100 ohms, the FFT of the overall signal clearly shows a peak at 2 MHz, indicating there is a strong 2-MHz component of the overall, periodically-quenched signal. Zooming in to the above time-domain signal we can also visually verify that the waveform doesn't appear too badly distorted. The residual energy after the quenching also appears minimal (the tank voltage drops down to almost zero thanks to the heavy damping -- contrast this with the self-quenched waveform in the last image of viewtopic.php?p=78083#p78083, where clearly more residual tank voltage is present at the end of every quench cycle). xx100z.png (72.98 KiB) Viewed 1084 times But now watch what happens if we set R3 to only 1 ohm, essentially removing the quench waveform resistor from the circuit. The FFT in the below simulation becomes flatter and no clear frequency peak is evident. xx1.png (112.19 KiB) Viewed 1084 times Zooming in to the above time-domain signal, we can see that once the self-quenching kicks in, suddenly the waveform gets seriously distorted and the natural 2 MHz response of the LC tank gets somehow overpowered by the quenching action. Sorry for the vague, hand-waving description of the mechanism, but anyway, the results speak for themselves: without the quench waveform adjustment resistor R3, serious distortion is the result. xx1z.png (51.92 KiB) Viewed 1084 times To summarise, a self-quenching cross-coupled oscillator, with heavy tank damping, would appear to be feasible as a super-regen at 2 MHz with a self-quenched quench frequency of approximately 16 kHz with the above-shown circuit constants. The one thing that I cannot verify (or do not know how to verify) from my simulations is whether or not the self-quenching is occurring too early or not (too early would mean quenching before the oscillator is reaching its "full" amplitude). On the other hand, sixtynine has commented before that self-quenched regens are always operating in logarithmic mode, and by definition logarithmic mode means the oscillator is allowed to reach full amplitude before being quenched -- so this would seem to indicate that there is no need to worry about a "too early" quench when using self-quenching. viewtopic.php?p=72688#p72688 sixtynine wrote: ↑ Sun Mar 05, 2017 4:34 am I am very fortunate to own a copy of Superregenerative Receivers by JR Whitehead printed in 1950. There are two SR operating modes , the "Linear" and so called logarithmic mode. Logarithmic mode occurs when the oscillator is self quenched, the RF gain increases exponentially untill blocking occurs. Intentionally introducing heavy damping into a resonator seems ill-advised from the normal design principle of maximising resonator Q for our radios. But we're making up for that damped Q by the cranked-up loop gain of the oscillator. I guess there will inevitably be some noise caused by the intentional resonator damping, so the question is, is that noise significant compared to the expected signal amplitudes? In particular -- assume the above scheme is used with a ferrite rod antenna for an AM BCB super-regen. Intuitively it would seem that intentionally damping the tank in this case would be a bad idea. But maybe it will work. Time to fire up the soldering iron...?Post by Electrojim » Mon Feb 12, 2018 11:58 pm 26-33 minutes Transistors, IC's and other new fangled devices forum Electrojim Posts: 39 Joined: Sun Nov 22, 2015 12:30 amLocation: Southern CaliforniaContact:Re: Unusual AM Superregenerative? Receiver Hey, Selenium, All that's good. I do have one question, however. You refer to the "Polyakov circuit" in connection with superregens, but the only circuitry I've ever seen attributed to Polyakov is the direct-conversion receiver with the local oscillator working at half the receive frequency. Is Mr. Polyakov involved with more than that DC circuit? I've just never seen his name in connection with anything else and wondered. reset Posts: 512 Joined: Sat Oct 11, 2014 3:03 amRe: Unusual AM Superregenerative? Receiver Postby reset » Tue Feb 13, 2018 12:40 am Electrojim wrote: ↑ Mon Feb 12, 2018 11:58 pm You refer to the "Polyakov circuit" in connection with superregens, but the only circuitry I've ever seen attributed to Polyakov is the direct-conversion receiver with the local oscillator working at half the receive frequency. Is Mr. Polyakov involved with more than that DC circuit? I've just never seen his name in connection with anything else and wondered. Electrojim, I saved this to read later: Super Regenerator.pdf I am not sure but I think I got it from antentop.org It's a Russian ham magazine with several of Mr Polykov's designs. Yes they use his name as if it means LO at half frequency in a DC. He has published articles on other subjects. OK I'll be running back into the cave now. 73 "If a cluttered desk is the sign of a cluttered mind what is an empty desk the sign of?" DrM Posts: 1027 Joined: Fri Jun 19, 2009 8:30 pmLocation: The NetherlandsRe: Unusual AM Superregenerative? Receiver Postby DrM » Tue Feb 13, 2018 8:43 am Selenium wrote: ↑ Mon Feb 12, 2018 9:51 pm A newer patent circuit that I have seen uses a sensing circuit and a FET to quench the oscillator just after it reaches limiting. This allows a higher quench frequency. https://www.google.com/patents/US7263138 A very interesting super regenerative receiver circuit in which the quenching action is done by periodically severely damping the tank circuit. I think that you can also use an NPN BJT in stead of using that p-channel quenching FET. The quenching transistor can be driven by a square wave generator. qrp-gaijin Posts: 2822 Joined: Sun Feb 28, 2010 2:12 pmContact:Re: Unusual AM Superregenerative? Receiver Postby qrp-gaijin » Tue Feb 13, 2018 10:02 am Electrojim wrote: ↑ Mon Feb 12, 2018 11:58 pm Hey, Selenium, All that's good. I do have one question, however. You refer to the "Polyakov circuit" in connection with superregens, but the only circuitry I've ever seen attributed to Polyakov is the direct-conversion receiver with the local oscillator working at half the receive frequency. Is Mr. Polyakov involved with more than that DC circuit? Oh yes, much more. viewtopic.php?p=35508#p35508 vladn wrote: ↑ Mon Apr 23, 2012 6:02 pm Anyway at least few of these circuits came from (or derived from) the book by Polyakov RA3AAE on crystal, TRF and regen receivers. (This one was written with novice in mind. BTW he also wrote several excellent books and papers on DC receivers/transceivers and FM receivers). Unfortunately the book is only available in Russian and is not sold on Amazon, otherwise I would have recommended to just buy it. The book is unofficially (AFAIK) available here in the web format (you can use google translate): http://amfan.ru/ The left column is the clickable content. You may want to browse the entire book for some nice schematic ideas (including some cool RF powered sets). But the particular circuits related to your application are: http://amfan.ru/usovershenstvovannye-pr ... noj-cepyu/ http://amfan.ru/usovershenstvovannye-pr ... -priemnik/ the next one should be used with a double tuned option: http://amfan.ru/usovershenstvovannye-pr ... -priemnik/ auto-regen by Kovalenko (I've seen a separate paper in Russian on this RX, if I find it I'll post it here) http://amfan.ru/sinxrodiny/kb-sinxrodin-s-kovalenko/ Also see viewtopic.php?t=5804, topic titled "2010 article on regens by the famous Polyakov (RA3AAE)". gzimmer cleaned up the document and made it more accessible for English-speakers: download/Polyakov-Regen.pdf . As to your specific inquiry about the "Polyakov circuit", see here: http://amfan.ru/avtodiny/prostoj-regenerator/ Image from the above page: My first exposure to this circuit was via a reference from vladn, who also attributed it to Polyakov: viewtopic.php?p=28151#p28151 vladn wrote: ↑ Tue Jan 18, 2011 7:47 pm Yet another approach for detuning-resistant semiconductor regen (more suitable for SW) was suggested in the book by RA3AAE. It is the simplest transistor regen I've ever seen and operates in micro-power mode (can run at <1V). The detector operates with Vcb=0 for DC which minimizes detuning. Tangential note: as for the minimal-detuning aspect of the Polyakov regen circuit, see here: viewtopic.php?p=60108#p60108 . Back on-topic, here are Polyakov's machine-translated (from Russian) comments about the super-regenerative capabilities of this circuit: Moreover, if the capacitance of the blocking capacitor C2 is significantly increased, the intermittent generation process is observed and the device becomes a simple superregenerator with very high sensitivity. The frequency of the "flashes" of generation is established by selecting the capacitance of the capacitor C2 and the resistance of the resistor R2 of the order of 15-50 kHz. For example, in one experiment, this device provided sensitivity in the super-regenerative mode better than 0.6 μV at a frequency of 46 MHz when receiving AM signals. The frequency of flares was established on the order of 15 kHz, and the bandwidth was about 60-70 kHz. In comparison with the known super-regenerators, this device is easier to set up, more sensitive and stable in operation. qrp-gaijin Posts: 2822 Joined: Sun Feb 28, 2010 2:12 pmContact:Re: Unusual AM Superregenerative? Receiver Postby qrp-gaijin » Tue Feb 13, 2018 1:35 pm DrM wrote: ↑ Tue Feb 13, 2018 8:43 am A very interesting super regenerative receiver circuit in which the quenching action is done by periodically severely damping the tank circuit. I think that you can also use an NPN BJT in stead of using that p-channel quenching FET. The quenching transistor can be driven by a square wave generator. I've been running some simulations to this effect (trying to use a BJT to damp the tank) but results are inconclusive so far. You need to be careful not to cause severe distortion in the waveform at the beginning or end of a quench cycle. I couldn't quite achieve that yet. I will run some simulations with a JFET as well (probably on the weekend). Indeed, now that we know a fixed damping resistor enables the superregen to work with higher quench frequencies at MW, the next challenge seems to be to design the simplest circuit that enables dynamic damping of the tank at the start of each quench (and, again, that does not introduce severe waveform distortion when quenching). Selenium Posts: 1997 Joined: Mon Jun 10, 2013 7:59 pmRe: Unusual AM Superregenerative? Receiver Postby Selenium » Tue Feb 13, 2018 5:01 pm Just a comment about the tap position in the Polyakov superregen. Using a standard ferrite rod antenna with a low impedance tap, I had success as a superregen receiver only when the low impedance winding with fewer turns was connected to the Collector. I also connected the tuning capacitor C1 between the Base and ground. Also, the variable resistor R1 is not necessary in a regen version of this receiver, but it will be useful to test to see if it improves the performance of the superregen version by altering the shape of the quench waveform. Attachments 5.19.jpg (16.51 KiB) Viewed 1243 times Selenium Posts: 1997 Joined: Mon Jun 10, 2013 7:59 pmRe: Unusual AM Superregenerative? Receiver Postby Selenium » Wed Feb 14, 2018 5:05 pm Just another piece of information about this receiver. I have built shortwave versions of this receiver many times both as a regen and superregen versions and when used as a regen receiver an extra audio amplifier stage is required to increase the audio to a usable level. The superregeneration version does not require an extra audio amplifier stage. I have also built a number of MW superregen versions and have discovered that when using the high input impedance audio amplifier shown below, it doesn't load the quench capacitor which alters its performance slightly compared to if a low impedance audio amplifier is used. The result is that with the values shown, the superregeneration starts abruptly with a very low quench frequency which may be increased with the regen control so that it is above the audio range and the receiver may be tuned across the band without any further adjustment of the regen control. If the regen control is adjusted just before superregeneration starts, however, the receiver behaves somewhat similar to a regen receiver except with a very large detected audio output with no background heterodyning or whistles. In this mode the effect is seen over only about a 200 KHz range and the regen control must be readjusted if the receiver is tuned beyond this range. Selectivity in this mode is very good and I had no problem separating a strong local station with a much weaker station 20 KHz away. From this behavior, it appears that the 100 Ohm damping resistor also alters the receiver's performance when in regen mode, significantly softening the regen control and it is my intention to try adding the damping resistor to the shortwave superregen version to see if it also boosts the detected audio out just before superregeneration occurs effectively creating a regen version with a much higher detected audio output. For its simplicity this is a very high performance MW receiver. With the minor inconvenience of infrequently having to readjust the regen control, who needs a superhet? Attachments am superregen polyakov 100 33.jpeg (12.39 KiB) Viewed 1191 times Electrojim Posts: 39 Joined: Sun Nov 22, 2015 12:30 amLocation: Southern CaliforniaContact:Re: Unusual AM Superregenerative? Receiver Postby Electrojim » Wed Feb 14, 2018 7:27 pm Good work, Sel. It's good to have someone who does reduce the design to a working circuit. I may give this a try myself, and thanks for keeping us updated. That's certainly an interesting audio amp; reminds me of some circuit I saw in an SCR handbook years ago. Any idea of the voltage gain in dB, or its equivalency to a more traditional 2- or 3-transistor amp? Selenium Posts: 1997 Joined: Mon Jun 10, 2013 7:59 pmRe: Unusual AM Superregenerative? Receiver Postby Selenium » Wed Feb 14, 2018 11:02 pm Electrojim wrote: ↑ Wed Feb 14, 2018 7:27 pm That's certainly an interesting audio amp; reminds me of some circuit I saw in an SCR handbook years ago. Any idea of the voltage gain in dB, or its equivalency to a more traditional 2- or 3-transistor amp? The TL431 is a shunt regulator with an internal 2.5V reference. Used in the self biased configuration shown with the 1M resistor, because of its high input impedance, the DC voltage on its output will always be just slightly above 2.5V which may be raised if it clips by adding another large value resistor from its input to ground forming a voltage divider. By comparison to an LM386 audio amp in single input mode and with the gain enhancing capacitor, the TL431 has a similar voltage gain of about 100 or 40 dB. Apart from its simplicity, 2 key advantages are its high input impedance and low output impedance which enables it to drive a standard pair of 32 Ohm earbud phones to good volume. I have also used it successfully in a simple MW regen-reflex receiver. viewtopic.php?f=4&t=6733&p=64253&hilit=tl431#p64253 Attachments tl431 regen reflex 2.jpg (30.59 KiB) Viewed 1133 times qrp-gaijin Posts: 2822 Joined: Sun Feb 28, 2010 2:12 pmContact:Re: Unusual AM Superregenerative? Receiver Postby qrp-gaijin » Thu Feb 15, 2018 6:49 am Selenium wrote: ↑ Tue Feb 13, 2018 5:01 pm Using a standard ferrite rod antenna with a low impedance tap, I had success as a superregen receiver only when the low impedance winding with fewer turns was connected to the Collector. Same behaviour observed here, running off of 1.2v with a 2N3904. It makes sense I suppose: since the tank is so heavily damped, we need to provide more feedback voltage (higher-Z winding) to the amplifier input (base) to sustain oscillation. Selenium wrote: ↑ Wed Feb 14, 2018 5:05 pm One thing I just noticed is that the quench waveform resistor only needs to be a small value. And the emitter capacitor looks large enough to pass some audio. So I wonder what would happen if we tried to insert a 32-ohm headphone in place of the quench waveform resistor. Would we get enough audio output to be usable? Only an experiment will tell... (EDIT: maybe the emitter capacitor of 10 nF will not pass enough audio into a low-Z headphone load, as its reactance at 2 kHz is 8k ohms.) My current lash-up looks like the above circuit minus the AF amp, and plus a crystal earphone connected across the emitter and ground. (I didn't try to press the crystal earphone into double-duty by trying to replace the emitter cap/resistor with the crystal earphone as was suggested in an earlier post.) Incidentally my results were that I could hear some AM stations with a single transistor, a 1.2v battery, a crystal earphone, and a ferrite rod antenna. That's pretty impressive. The superregeneration seemed rather abrupt and the quench frequency sometimes dropped into the audio range as I tuned the tuning capacitor. So my circuit wasn't yet well-behaved (hence I did not yet feel it was worth making a video yet), but this circuit definitely is worth further investigation. Also there may very well be a difference in the regeneration threshold behaviour, when using series damping vs. parallel damping. In theory, using a low-value parallel-connected damping resistor should be more effective at evening out the regeneration level as the set is (capacitively) tuned (reference: http://www.kearman.com/vladn/hybrid_feedback.pdf, p. 7, in the notes for the "Rp-dominant loss model"). I may try using a parallel damping resistor (maybe between 1k and 10k) to see if that makes my set better-behaved. I have some ideas floating around now for a truly crazy minimalist receiver, combining both regenerative and superregenerative stages. I shall start another thread when the ideas have solidified slightly... qrp-gaijin Posts: 2822 Joined: Sun Feb 28, 2010 2:12 pmContact:Re: Unusual AM Superregenerative? Receiver Postby qrp-gaijin » Thu Feb 15, 2018 12:31 pm When playing with my version of this damped AM superregen, I have finally been able to reproduce a curious phenemenon that was described several years ago by Selenium: viewtopic.php?p=44579#p44579 viewtopic.php?p=44583#p44583 Selenium wrote: ↑ Thu Aug 08, 2013 6:40 am Adjusting the regen control will result in a slight hissing sound as the circuit begins to oscillate. Maximum regen sensitivity occurs just before this point. As the regen control is advanced further there is an intermediate position before superregeneration occurs in which the quench frequency in combination with the received carrier results in sidebands at multiple positions on the dial. Recovered audio is much greater in this condition without affecting selectivity. Increasing the regeneration control further results in superregeneration with much larger audio output, but significantly poorer selectivity. [...] In intermediate mode, the oscillator is being "softly" or partially quenched and the regen receiver is still able to detect RF in its normal manner. That is it is being partially turned on and off or effectively modulated by a quench waveform with very low harmonic content. Because the transistor is a non-linear device it acts as a mixer with the incoming RF frequency and mixes with the quench frequency forming 2 or more sidebands on each side of the carrier frequency. These sidebands may be tuned and because of the mixing gain result in significant audio output. I just now experienced this phenomenon, except it occurs after superregeneration starts. Specifically, when adjusting the regeneration control from low feedback (high emitter resistance) to high feedback (low emitter resistance), I observe the following behaviour, in this order, as regeneration is slowly advanced: No audio (far below critical threshold). Weak heterodyne audio (normal regenerative reception above critical threshold; very weak due to no AF amplification). Superregenerative mode, with an audible quench frequency of about 1 kHz. Received signal audio is weakly discernible and very distorted due to low quench frequency. No multiple sidebands are yet present. The quench frequency gets somewhat higher and signal audio becomes clearer and louder as the quench frequency becomes high enough to allow sample the signal's AF content. AF content however is still distorted due to the audible quench. At some point, as the quench frequency continues to rise, audio begins to decrease, and few but multiple "sidebands" emerge, i.e. multiple "copies" of the signal appear below and above the real carrier frequency of the signal, and these copies/sidebands can be received with decreasing strength as the set is tuned further away from the real carrier frequency. The quench frequency rises, the received signal becomes weaker, and the number of sidebands increases. The set stops oscillating and no audio at all is heard. (emitter resistance has become too small to support regeneration and/or superregeneration) Because this multiple-sideband mode is described above as being due to "soft" or "partial" quenching, perhaps my tank damping is insufficient which prevents full quenching. I shall have to try increasing my damping resistor to see if it has any effect. Here are the circuit constants of my current lash-up. The self-quenching emitter RC network is 100 ohms in series with 10 nF. The regeneration control is a 100k pot in parallel with the self-quenching RC network, and in series with the emitter. The tank damping resistor is 100 ohms. A crystal earphone is connected through 100 nF to the emitter. Quite interesting stuff -- I'm experiencing higher audio than I ever thought possible with a single transistor receiver powered off of 1.2 volts. The audio isn't loud by any means, but the stations are audible. If I slowly play around with the regeneration control, it is possible to find a setting with a fairly high (almost inaudible) quench and definite, properly-behaving superregenerative behaviour, with a rushing noise where no stations are present, and a quieting effect when a station is tuned in. Selenium Posts: 1997 Joined: Mon Jun 10, 2013 7:59 pmRe: Unusual AM Superregenerative? Receiver Postby Selenium » Thu Feb 15, 2018 6:20 pm I think it would be worthwhile if you coupled the receiver to a high input impedance audio amplifier which doesn't load the quench capacitor. As I mentioned in a previous post, with the values shown on my schematic, if the regen control is set just before regeneration which is very abrupt, there is a significant increase in audio output with no heterodyning or whistles. The only caveat is that this increased sensitivity occurs over a relatively narrow portion of the band (200KHz wide) and the regen control must be readjusted if the receiver is tuned outside this range. It appears that the negative resistance from the oscillator transistor is significantly decreasing the losses even before oscillation or superregeneration is achieved. qrp-gaijin Posts: 2822 Joined: Sun Feb 28, 2010 2:12 pmContact:Re: Unusual AM Superregenerative? Receiver Postby qrp-gaijin » Thu Feb 15, 2018 11:40 pm Selenium wrote: ↑ Thu Feb 15, 2018 6:20 pm I think it would be worthwhile if you coupled the receiver to a high input impedance audio amplifier which doesn't load the quench capacitor. I will try adding a common-emitter AF amp and see if that changes anything. I'm interested in particular in the logarithmic superregenerative mode of operation, because its inherent AGC action might be utilised to good effect as part of the IF strip in a shortwave superhet. And to achieve tight, adjacent-channel selectivity, ahead of the superregenerative detector I'm considering using either a crystal filter or -- here comes the crazy idea -- a regenerative stage acting as Q-multiplier. In other words, the architecture could look like: single-transistor frequency converter, followed by a fixed-frequency, fixed-regeneration-level, single-transistor Q-multiplier (for IF selectivity and gain), followed by a single-transistor superregenerative stage (for extremely sensitive detection and inherent, volume-equalising AGC action). In short: a 3-transistor "regenerative superregenerative superheterodyne" receiver -- with inherent AGC! Having verified that reasonably-well-behaved logarithmic superregenerative behaviour could indeed be observed at MW BCB frequencies -- with apparent AGC action (rushing sound where no signals are present, quieting behaviour when a carrier is tuned in) -- I think the above plan could be feasible with an IF of 2 MHz. Taming the unwanted interactions between the stages will probably be the biggest challenge. qrp-gaijin Posts: 2822 Joined: Sun Feb 28, 2010 2:12 pmContact:Re: Unusual AM Superregenerative? Receiver Postby qrp-gaijin » Sat Feb 17, 2018 3:53 am This post is to link to relevant information from a previous thread: Selenium wrote: ↑ Thu Feb 15, 2018 6:20 pm As I mentioned in a previous post, with the values shown on my schematic, if the regen control is set just before regeneration which is very abrupt, there is a significant increase in audio output with no heterodyning or whistles. The only caveat is that this increased sensitivity occurs over a relatively narrow portion of the band (200KHz wide) and the regen control must be readjusted if the receiver is tuned outside this range. It appears that the negative resistance from the oscillator transistor is significantly decreasing the losses even before oscillation or superregeneration is achieved. Pat Pending reported a similar if not identical phenomenon: viewtopic.php?p=72685#p72685 Pat Pending wrote: ↑ Sun Mar 05, 2017 1:07 am I've noted in the past when playing with self quenching SRA's that if the cap controlling the quench frequency is reduced in value you can adjust regeneration to a point where just before the receiver goes dead, (goes into oscillation, the point that the circuit would normally superregenerate), the gain is very much greater than normal for a regen, though difficult to maintain. I didn't pursue it at the time as all I needed the receiver for was slow data and the SRA was more stable and sensitive than a plain regen, selectivity was also relatively unimportant. I believe I am occasionally seeing the same phenomenon, as described by Pat Pending, in my current lash-up. After regeneration starts, but before super-regeneration starts, there seems to be some almost-superregenerative region with louder volume. What is interesting is that Selenium reports that this region occurs before the onset of any oscillation, whereas Pat Pending and I observe it after oscillation starts, but before superregeneration starts. Selenium Posts: 1997 Joined: Mon Jun 10, 2013 7:59 pmRe: Unusual AM Superregenerative? Receiver Postby Selenium » Sat Feb 17, 2018 4:59 am While investigating the excellent performance of the receiver with the regen control set just before oscillation, I was able to retain the effect over the full tuning range without having to adjust the regen control by adding a resistor with a value of about 8K to 10K as shown below. The result is a very nice regen receiver with large audio output which when the regen control is set below oscillation may be tuned across the band without a further change in the regen control. When the regen control is set just after oscillation is obtained, the circuit will heterodyne when tuning with maximum sensitivity and selectivity, but the heterodyning will be suppressed as a station is received and the effect is consistent across the band without having to readjust the regen control making what appears to be an excellent candidate for a DX receiver. When the regen is advanced further, superregeneration will occur, but with poor performance. Attachments am regen polyakov 8K2.jpeg (12.57 KiB) Viewed 940 timesDrM wrote: ↑ Tue Feb 13, 2018 8:43 am A very interesting super regenerative receiver circuit in which the quenching action is done by periodically severely damping the tank circuit. I think that you can also use an NPN BJT in stead of using that p-channel quenching FET. The quenching transistor can be driven by a square wave generator. I've been running some simulations to this effect (trying to use a BJT to damp the tank) but results are inconclusive so far. You need to be careful not to cause severe distortion in the waveform at the beginning or end of a quench cycle. I couldn't quite achieve that yet. The following circuit looks promising. The quench oscillator (an RC phase shift audio oscillator) generates a sine wave and is powered by a separate 9v battery. I couldn't figure out how to get the quench oscillator to work off of 1.2 volts, but that's a minor issue. The important thing is that the idea of using a shorting BJT does seem to work. In the below circuit, notice the damping resistor has been reduced to around 6 ohms for an inductor Q of about 100 at 2 MHz -- in other words, no additional damping. (However, the BJT, even when off, will probably damp the tank slightly). Also notice the emitter resistance is around 20k, which is somewhat but not vastly past the oscillation threshold. In other words, the oscillator is basically a normal regenerative oscillator adjusted to be strongly oscillating, and with no additional tank damping. Then, thanks to the external quench oscillator and the shorting BJT, we get almost ideal and perfect superregenerative behavior: high-Q (but somewhat time-consuming) build up of oscillations in the non-damped tank, and extremely fast damping of the tank thanks to the shorting BJT. And this is at 2 MHz, a fairly low frequency for superregens. exq1.png (148.87 KiB) Viewed 1576 times Zooming into the waveform we can confirm the fast build-up time and fast decay time. exq2.png (69.02 KiB) Viewed 1576 times This might be a good juncture to reference a previous thread here on TRB that generated very little discussion: viewtopic.php?p=47596#p47596 . I shall quote a relevant part of that post here: qrp-gaijin wrote: ↑ Thu Jan 09, 2014 1:47 am Here is an interesting patent that claims to have made a selective and sensitive AM BCB superregen: https://docs.google.com/viewer?url=pate ... 821625.pdf. Further, the signal applied by the quench oscillator to the detector is of asymmetrical wave shape which provides longer periods of regeneration than of quenching action. This permits the regeneration or gain to build up to a maximum extent while the quenching action is more abrupt. This basically seems to be the same approach (if I am understanding it correctly) as the Q-quenching approach referenced in Selenium's post at viewtopic.php?p=78347#p78347 -- in other words, allow full Q during the start-up phase for increased sensitivity and selectivity, but then suddenly damp the tank during the quenching phase. Back to my circuit. Next, watch what happens if we reduce the oscillation amplitude slightly by increasing the emitter resistance to 30k. In this case, the oscillator gain is lower, and hence the oscillator takes longer to build up to its final value. But the quench frequency is unchanged -- therefore, we can graphically see that the quench is kicking in before the oscillator reaches full amplitude. In other words, this configuration (weaker oscillation with lower gain and 30k emitter resistance) exhibits linear, not logarithmic, behaviour. (Also see seanvn's comments on linear mode superregens here: viewtopic.php?p=63275#p63275 .) exq3.png (142.2 KiB) Viewed 1576 times exq4.png (55.68 KiB) Viewed 1576 times As a final note, observe what happens if we try to drive the quenching/shorting BJT with a square wave. exq5-badsquare.png (63.72 KiB) Viewed 1575 times The first unquenched build-up of oscillations occurs naturally with normal exponential build-up of the oscillator amplitude. But after quenching, when the oscillator is trying to recover and the tank is un-quenched (the BJT is turned off), there is a huge voltage spike across the tank, which surely will greatly disrupt the all-important start-up behaviour of the oscillator -- with a disrupted (noisy) start-up behaviour, sensitivity will likely severely be degraded. I believe this problem, when using a square-wave quench, is exactly what seanvn said earlier in this thread when he commented that "noise from switching can provoke the LC circuit to ring", hence recommending a sine wave (over a square wave). viewtopic.php?p=63113#p63113 seanvn wrote: ↑ Fri Nov 20, 2015 1:53 am A terrible issue though is that noise from switching can provoke the LC circuit to ring, don't use a NE555 to switch the thing! In some of the older literature they say using a sine wave to do the quenching gives the best result. Selenium Posts: 1997 Joined: Mon Jun 10, 2013 7:59 pmRe: Unusual AM Superregenerative? Receiver Sounds good! From qrp-gaijin's experiments in this thread, it appears that it is not the startup time which is an issue in a superregen receiver, but the decay and recovery time. One of the patents in this thread suggests dumping the energy in the tank at the end of the quench cycle with a FET across the oscillator tank which should improve sensitivity. https://patents.google.com/patent/US7263138 Seeing as you already have a 555 quench oscillator running, it would be interesting to drive a FET across the oscillator tank to quench the oscillator in order to determine its benefits compared with quenching by altering the biasing. The circuit in the patent uses a comparator to determine the optimum trigger point, but it seems likely that altering the quench frequency might also give reasonable results. Attachments force quench (1).png (16.56 KiB) Viewed 1024 times qrp-gaijin Posts: 2822 Joined: Sun Feb 28, 2010 2:12 pmContact:Re: Unusual AM Superregenerative? Receiver Postby qrp-gaijin » Sat Apr 07, 2018 1:31 pm Selenium wrote: ↑ Sat Apr 07, 2018 1:04 pm From qrp-gaijin's experiments in this thread, it appears that it is not the startup time which is an issue in a superregen receiver, but the decay and recovery time. However, if I am not mistaken, Mjones is experimenting with a receiver at VHF, whereas most of the discussion in this thread (including my experiments) was focused on MW frequencies. At VHF, I would speculate that neither startup nor decay times would be much of an issue, since the oscillation frequency is so much higher than the quench frequency. That's just my speculation though, having done almost no experiments with VHF superregens. Selenium Posts: 1997 Joined: Mon Jun 10, 2013 7:59 pmRe: Unusual AM Superregenerative? Receiver Postby Selenium » Sat Apr 07, 2018 1:53 pm qrp-gaijin wrote: ↑ Sat Apr 07, 2018 1:31 pm At VHF, I would speculate that neither startup nor decay times would be much of an issue, since the oscillation frequency is so much higher than the quench frequency. Good point, but in thinking about it, it seems to me that quenching the tank at a very high quench frequency just after full oscillation started would improve sensitivity. There is some information in the first few paragraphs of the patent description. https://patents.google.com/patent/US7263138 Mjones Posts: 456 Joined: Mon Jan 01, 2018 10:47 amRe: Unusual AM Superregenerative? Receiver Postby Mjones » Sat Apr 07, 2018 9:52 pm Thanks both, clearly I have a lot of homework to do now! I'll try to get it working satisfactorily with the quench applied to the bias, then I'll try a shorting FET. qrp-gaijin Posts: 2822 Joined: Sun Feb 28, 2010 2:12 pmContact:Re: Unusual AM Superregenerative? Receiver Postby qrp-gaijin » Sat Aug 04, 2018 3:40 am qrp-gaijin wrote: ↑ Thu Feb 15, 2018 12:31 pm When playing with my version of this damped AM superregen, I have finally been able to reproduce a curious phenemenon that was described several years ago by Selenium: viewtopic.php?p=44579#p44579 viewtopic.php?p=44583#p44583 Selenium wrote: ↑ Thu Aug 08, 2013 6:40 am Adjusting the regen control will result in a slight hissing sound as the circuit begins to oscillate. Maximum regen sensitivity occurs just before this point. As the regen control is advanced further there is an intermediate position before superregeneration occurs in which the quench frequency in combination with the received carrier results in sidebands at multiple positions on the dial. Recovered audio is much greater in this condition without affecting selectivity. Increasing the regeneration control further results in superregeneration with much larger audio output, but significantly poorer selectivity. [...] In intermediate mode, the oscillator is being "softly" or partially quenched and the regen receiver is still able to detect RF in its normal manner. That is it is being partially turned on and off or effectively modulated by a quench waveform with very low harmonic content. Because the transistor is a non-linear device it acts as a mixer with the incoming RF frequency and mixes with the quench frequency forming 2 or more sidebands on each side of the carrier frequency. These sidebands may be tuned and because of the mixing gain result in significant audio output. Recently, while investigating regenerative detectors that can smoothly transition between regenerative and superregenerative modes (required by cool386's audio-based automatic regeneration control method described at viewtopic.php?f=4&t=8298), I was able to reproduce the above "soft quenching" phenomenon in LTspice. Regeneration just past critical (pot at 60% of maximum) yields stable oscillation with no quenching. soft0.png (61.99 KiB) Viewed 855 times ----------------------------- ----------------------------- Advancing regeneration farther (pot at 61.5%) yields very soft partial quenching. soft1.png (71.04 KiB) Viewed 855 times Zooming in: soft1zoom.png (65.95 KiB) Viewed 855 times ----------------------------- ----------------------------- Advancing regeneration farther still (pot at 61.7%) yields moderate but still partial quenching. soft2b.png (85.12 KiB) Viewed 855 times Zooming in: soft2bzoom.png (79.87 KiB) Viewed 855 times ----------------------------- ----------------------------- Advancing regeneration again farther (pot at 65%) yields hard quenching. soft3.png (84.17 KiB) Viewed 855 times The mechanism seems obvious to me now that I've seen the graphs, but when I first read about the phenomenon it was hard for me to visualise what was going on. I hope the above simulation results might help clarify this "intermediate" mode of operation between the regenerative and super-regenerative states. Selenium Posts: 1997 Joined: Mon Jun 10, 2013 7:59 pmRe: Unusual AM Superregenerative? Receiver Postby Selenium » Sat Aug 04, 2018 11:43 am Great stuff! One of my future intentions has been to amplitude modulate a regenerative receiver with a variable amplitude sinewave quench signal from a signal generator with the amplitude able to be increased up to the point of superregeneration. I am particularly interested in its spectrum as would be shown on a spectrum analyzer. My real life experience has been that in this intermediate mode a large number of sidebands may occur each containing the received modulation information. My head begins to hurt, however, when I try to think about what occurs to the spectral response as the tuning of the regen receiver is varied. qrp-gaijin Posts: 2822 Joined: Sun Feb 28, 2010 2:12 pmContact:Re: Unusual AM Superregenerative? Receiver Postby qrp-gaijin » Sat Aug 04, 2018 12:02 pm Selenium wrote: ↑ Sat Aug 04, 2018 11:43 am I am particularly interested in its spectrum as would be shown on a spectrum analyzer. My real life experience has been that in this intermediate mode a large number of sidebands may occur each containing the received modulation information. My head begins to hurt, however, when I try to think what occurs to the spectral response as the tuning of the regen receiver is varied. Yes, I spent some time thinking about this today and re-reading your posts on the subject. It could be argued that this scheme is actually a one-transistor regenerative superhet receiver! Say the regen is tuned to 7320 kHz and is partially quenched at 20 kHz. The "LO" signal is the relaxation oscillation that causes the partial quenching (e.g. the 20 kHz sine wave). This LO signal mixes with an incoming RF signal at 7300 kHz. This incoming RF signal is not the same as the regen's frequency, but it is nearby, so it will get somewhat amplified regeneratively. This somewhat-amplified RF signal gets mixed with the "LO" to produce new sidebands (the "IF") at 7320 kHz and 7280 kHz, and as you have suggested before, perhaps conversion gain occurs, such that these produced sidebands (the IF) actually end up becoming greater in amplitude than the original signal. The regen, being tuned to 7320 kHz, is therefore tuned to one of these sidebands (the IF), where perhaps it can phase lock to it for synchronous AM reception. But we must remember that the regen is oscillating and mixing everything that comes in, so the produced sidebands again will be subject to the mixing process. For example, wouldn't the generated IF of 7320 kHz again mix with the LO of 20 kHz to produce sidebands at 7340 kHz and 7300 kHz -- where, interestingly, 7300 kHz is the original signal frequency, meaning that the IF signal (at 7320 kHz, and with conversion gain) is reinforcing the original signal (at 7300 kHz) somehow? The mind boggles at the possibilities.... LTspice simulations can only reveal so much, because when you start to think about self-reinforcing processes occurring at vastly-different timescales (20 kHz mixing with 7300 kHz), simulation time takes several hours/days and tiny phase shifts in signals (due to limited numerical precision) can skew or ruin the simulation results. Perhaps someone with an oscilloscope and spectrum analyser could run some real tests on this kind of a circuit. (On the other hand, perhaps this kind of analysis might be able to be done analytically from first principles.) Selenium Posts: 1997 Joined: Mon Jun 10, 2013 7:59 pmRe: Unusual AM Superregenerative? Receiver Postby Selenium » Sun Aug 05, 2018 4:24 pm I wanted to offer a slightly different scenario that it would be interesting to try. Receive a signal at 7300 kHz and tune the oscillating receiver to the same frequency 7300 kHz. Use a much higher frequency 100 kHz sinewave for partial quenching. Initial sidebands will be produced at 7200 kHz and 7400 kHz and then also at 7100, (7300, 7300), 7500 and so on. It appears as you had mentioned that the originally 7300 received signal could be reinforced by the new sideband generation. Now try tuning the receiver to one of the new sidebands (7400). Because in this scenario the partial quench frequency is so far from the original carrier, as the receiver is tuned, the original carrier will significantly diminish in amplitude even before the previously generated new sideband at 7400 is reached. In this scenario, with a much higher partial quench frequency, the original received signal would appear to be enhanced only when the receiver oscillation frequency is the same as the received signal frequency. qrp-gaijin Posts: 2822 Joined: Sun Feb 28, 2010 2:12 pmContact:Re: Unusual AM Superregenerative? Receiver Postby qrp-gaijin » Thu Aug 16, 2018 12:28 pm This may have been mentioned before, but here are some more AM BCB superregenerative receivers on p. 41 of this document: https://www.americanradiohistory.com/Ar ... tor-RX.pdf amsup.png (216.1 KiB) Viewed 604 times ----- EDIT: some old discussion here: viewtopic.php?t=5318 And here's another tube-based AM BCB superregenerative receiver, which I think has not been discussed here on TRB before (in German): https://www.radiomuseum.org/forum/super ... enger.html The above trace covers about 45 microseconds of time. The use of a separate quench oscillator helps ensure the oscillations and any residual ringing in the tank are completely damped before the start of the next sampling period. Selenium Posts: 1997 Joined: Mon Jun 10, 2013 7:59 pmRe: Unusual AM Superregenerative? Receiver Postby Selenium » Thu Aug 16, 2018 5:18 pm Earlier in this thread I posted my circuit using 2 voltage regulators in a simple superregenerative medium wave broadcast band receiver. This the only self-quenching superregen receiver which I have built that has had a high enough quench frequency in the MW band to be listenable (at least to my ears). This would imply that the tank is quickly quenched allowing a higher quench frequency. Using a standard ferrite rod antenna coil, no external antenna is required for local stations. For fun, I just built another one and placed it into a plastic kitchen container. It works well and with my scope intend to investigate the oscillator waveform. It would be interesting to hear back from any who have tried this circuit. Attachments 78L05 Regen 3 (1) (1).jpeg (19.28 KiB) Viewed 570 times golfguru Posts: 5235 Joined: Sat Aug 18, 2007 8:52 pmLocation: AustraliaRe: Unusual AM Superregenerative? Receiver Postby golfguru » Thu Aug 16, 2018 9:12 pm Have you been able to determine if selectivity is an issue? Thanks. ...... Selenium Posts: 1997 Joined: Mon Jun 10, 2013 7:59 pmRe: Unusual AM Superregenerative? Receiver Postby Selenium » Thu Aug 16, 2018 10:35 pm golfguru wrote: ↑ Thu Aug 16, 2018 9:12 pm Have you been able to determine if selectivity is an issue? Thanks. ...... The receiver can separate powerful locals 40 KHz apart. Its performance cannot be compared to a good regen receiver, but its simplicity, the fact that it doesn't need an intermediate audio stage and the fact that it doesn't need the regen control varied across the band still make it a useful small pocket receiver for strong local stations. I frequently use it to listen to local news and an oldies radio station. Selenium Posts: 1997 Joined: Mon Jun 10, 2013 7:59 pmRe: Unusual AM Superregenerative? Receiver Postby Selenium » Fri Aug 17, 2018 2:13 pm For any who are interested in a simple MW superregen receiver, the circuit below which was posted earlier in this thread works well. The variable resistor in series with the inductor damps the Q of the tuned circuit and permits a higher quench frequency. Its value may be set for optimum performance which will likely depend on the inductor used. Although maximum audio is detected at quench frequencies in the audio range, varying the regen potentiometer so that the quench frequency is above my hearing ability, detected audio is still adequate. Your ears may vary. The sensitivity and selectivity of this circuit appears slightly better than the version using the 78L05 voltage regulator. Attachments am superregen polyakov (1).jpeg (12.33 KiB) Viewed 484 times Last edited by Selenium on Fri Aug 17, 2018 5:16 pm, edited 2 times in total. qrp-gaijin Posts: 2822 Joined: Sun Feb 28, 2010 2:12 pmContact:Re: Unusual AM Superregenerative? Receiver Postby qrp-gaijin » Fri Aug 17, 2018 2:59 pm Selenium wrote: ↑ Fri Aug 17, 2018 2:13 pm For any who are interested in a simple MW superregen reciver, the circuit below which was posted earlier in this thread works well. The variable resistor in series with the inductor damps the Q of the tuned circuit and permits a higher quench frequency. Its value may be set for optimum performance which will likely depend on the inductor used. This is just a hunch, but for the moment I think self-quenched circuits might be able to achieve the same performance as externally quenched circuits. In general, perhaps, quenched circuits probably can damp the tank faster because the external quench oscillator robs energy from the oscillating tank. But maybe with the proper choice of self-quenching components, a self-quenching superregen can also damp the tank quickly enough without the need for an external damping resistor. In particular, the above receiver (as well as most of my simulated circuits in this thread) does not use a choke in the emitter. But in my recent simulator experiments I found that the choke seems to provide for better, more controllable quenching action. It is possible that with judicious choice of the choke and RC network that a combination might be found that allows for quicker self-quenching at MW frequencies without the need for the damping resistor. golfguru Posts: 5235 Joined: Sat Aug 18, 2007 8:52 pmLocation: AustraliaRe: Unusual AM Superregenerative? Receiver Postby golfguru » Fri Aug 17, 2018 9:17 pm (I think) there was mention of the possibility of using a zener to short the tank when the required voltage level was reached. Has any experimenting or simulation been done with regard to that concept? Thanks. Post by Selenium » Fri Aug 17, 2018 9:40 pm 6-8 minutes Selenium wrote: ↑ Fri Aug 09, 2019 5:41 pm Is it necessary to have the RC sinewave filter network? I think yes. If I remove it, I think the square wave switching is provoking the tank to ring at the beginning of each unquenched oscillation period, which is a bad thing that seanvn warned against previously. Previously I had simulated a perfect square wave generator in LTspice and used that to switch the shorting BJT. It resulted in noisy tank ringing as shown below. viewtopic.php?p=78477#p78477 I now tried simulating the new circuit -- using the shorting diode instead of the BJT, and using the multivibrator to generate the square waves instead of using an idealised square-wave generator. At first glance, the result "looks" like it might be OK. However, the changing DC bias voltage at the top of the "tankHot" node causes the varying (instead of constant) voltage across the tank, making it difficult to confirm whether or not undesired tank ringing is occurring or not. If we instead look at the current flowing through the tank capacitor C10, we get a better idea about what is happening inside the resonant LC tank. And we see that at the beginning of each unquenched oscillation cycle, there is a highly undesirable spike of current through the tank capacitor, caused by the square-wave switching, which provokes the tank to ring. This will disturb the start-up behavior and make the superregen's start-up time dependent not only on the input signal (good), but also dependent on the self-generated impulse (bad). ring.jpg (110.65 KiB) Viewed 314 times If we look at the current through the tank capacitor C10 in the case of sine-wave quenching (damping), we see there is no such spike. noring.jpg (106.85 KiB) Viewed 314 times As mentioned earlier in this thread, another idea is to use an asymmetrical quench waveform: a slow sine wave to allow quiet and unshocked start-up of oscillations, followed by a sudden and drastic shorting of the tank after start-up has finished (since any noisy impulse after the start-up phase shouldn't matter). viewtopic.php?p=47596#p47596 qrp-gaijin wrote: ↑ Tue Feb 20, 2018 1:40 pm Here is an interesting patent that claims to have made a selective and sensitive AM BCB superregen: https://docs.google.com/viewer?url=pate ... 821625.pdf. Further, the signal applied by the quench oscillator to the detector is of asymmetrical wave shape which provides longer periods of regeneration than of quenching action. This permits the regeneration or gain to build up to a maximum extent while the quenching action is more abrupt. viewtopic.php?p=78477#p78477 qrp-gaijin wrote: ↑ Tue Feb 13, 2018 1:35 pm This basically seems to be the same approach (if I am understanding it correctly) as the Q-quenching approach referenced in Selenium's post at viewtopic.php?p=78347#p78347 -- in other words, allow full Q during the start-up phase for increased sensitivity and selectivity, but then suddenly damp the tank during the quenching phase. Selenium wrote: ↑ Fri Aug 09, 2019 5:41 pm Rather than clamping the RF oscillator with the combination of the RC network, a transistor and a diode, even if using a PNP Polyakov RF oscillator, why not try powering it [...] directly from the multivibrator? I didn't yet try simulating your proposed circuits, but my thinking is that at 500 kHz, merely cutting off the oscillator power is not sufficient to for the tank oscillations to die out before the next unquenched oscillation cycle starts, meaning there will be a hang-over effect and the superregen will be sensitive to its own residual oscillations instead of external influence. We must damp the tank at these low frequencies -- either constantly damping (by severely lowering the tank Q), or by periodic switched damping. And for periodic switched damping I think it is not possible to use the oscillator transistor to achieve this damping. I think we need a separate device (a diode switch, a shorting BJT, or a shorting FET as in the other circuit you posted at viewtopic.php?p=78347#p78347) in order to really quickly damp the tank. This also means that self-quenched, high-Q superregens at MW frequencies are probably, unfortunately, not possible (unless you could come up with a way of triggering a shorting mechanism, like a diode, from the self-generated, self-quenching voltage built up at the emitter/drain of your oscillator transistor). But self-quenched, low-Q superregens at MW (where the tank is constantly damped to kill the Q and always force the oscillations to die down quickly) do work, as we already experimentally determined earlier in this thread. It would be interesting to experimentally determine how much of a detrimental effect such constant damping has on the sensitivity and selectivity of the receiver. As we verified, at least reception of strong AM BCB stations was possible with a heavily-damped ferrite rod used in a superregen. My circuit used only a crystal earphone so it was hard to judge the sensitivity to weaker signals. Selenium wrote: ↑ Fri Aug 09, 2019 5:41 pm clamping it directly from the multivibrator? As shown above, I think a square-wave "un-damping" of the tank is bad because it disturbs the start-up of the RF oscillator. Some sort of a filter is needed after the multivibrator, so that at oscillation start-up the oscillator is slowly and gradually undamped. For reference, another experimenter found at HF frequencies that "Square wave quench mode was hopeless , the receiver performance was dismal, huge input signals were required to achieve good performance." (http://www.amalgamate2000.com/radio-hob ... t%20HF.htm) My interpretation is that the provoked tank ringing at the beginning of each unquenched oscillation cycle (caused by the square wave) reduced the receiver sensitivity. Having said all of that, I would be interested in knowing if you can come up with a simple RC filter that changes the multivibrator's square waves into something like a half-sine-wave (for slow start-up) and half-square-wave (for quick damping) waveform. I suppose what is needed is simply a sawtooth wave: assuming the tank is at Vcc potential (as it is in my previous circuits), then a smooth and linear ramp-up of the voltage at the non-tank end of the diode should slowly raise the non-tank end of the diode to Vcc potential, hence turning the diode off and allowing the RF oscillations to quietly commence; this could be followed by a sudden drop of that voltage to zero, to short the tank to ground through the diode. Selenium wrote: ↑ Sat Aug 10, 2019 5:10 am Simulation result: spikes1.jpg (86.74 KiB) Viewed 218 times The behavior within each unquenched oscillation period doesn't look like normal oscillator start-up behavior. I think the multivibrator is simply shocking the tank, and what we are seeing is the decaying waveforms after each shock. Probably, in the current circuit, Q5 is not able to oscillate on its own. I could play around with Q5 biasing some more to get Q5 to oscillate, but I think that would be futile -- the very fact that the multivibrator is shocking the tank is a bad thing. Selenium Posts: 1997 Joined: Mon Jun 10, 2013 7:59 pmRe: Unusual AM Superregenerative? Receiver Postby Selenium » Sat Aug 10, 2019 6:40 am I'm very grateful for your simulations. I'm hoping you will try the simple PNP Polyakov circuits which I posted. Attachments superregen polyakov slow attack.jpeg (15.25 KiB) Viewed 213 timessuperregen polyakov slow start diode clamp.jpeg (34.66 KiB) Viewed 213 times qrp-gaijin Posts: 2822 Joined: Sun Feb 28, 2010 2:12 pmContact:Re: Unusual AM Superregenerative? Receiver Postby qrp-gaijin » Sat Aug 10, 2019 6:49 am I haven't simulated all of them yet but I'm afraid that all of your proposed circuits would seem to allow the voltage at the Q4 collector to snap up and down from rail to rail; this will snap up and down the voltage at the diode's cathode; and this will then shock the tank as it is connected to the diode's anode. Right now I'm looking for simple sawtooth generator circuits; I think that might be the easiest way to solve this problem (use a sawtooth generator instead of a square wave generator). Then we would shock the tank only when damping it (which doesn't matter), and not shock the tank when undamping it. Selenium Posts: 1997 Joined: Mon Jun 10, 2013 7:59 pmRe: Unusual AM Superregenerative? Receiver Postby Selenium » Sat Aug 10, 2019 6:55 am Isn't it possible to slow the multivibator rise time by putting a capacitor from Collector to ground? Selenium Posts: 1997 Joined: Mon Jun 10, 2013 7:59 pmRe: Unusual AM Superregenerative? Receiver Postby Selenium » Sat Aug 10, 2019 7:10 am Another thought. An NPN Polyakov oscillator similar to your original circuit would likely not have this impulse effect. One weakness of the original diode circuit is the very large current being drawn by the quench transistor. qrp-gaijin Posts: 2822 Joined: Sun Feb 28, 2010 2:12 pmContact:Re: Unusual AM Superregenerative? Receiver Postby qrp-gaijin » Sat Aug 10, 2019 7:22 am Selenium wrote: ↑ Sat Aug 10, 2019 6:55 am Isn't it possible to slow the multivibator rise time by putting a capacitor from Collector to ground? Basically it seems like the answer is yes. That does seem to yield the desired sawtooth waves. But this then reveals yet another unforeseen problem... sawtooth.jpg (116.31 KiB) Viewed 198 times Two problems: 1. The start-up behavior of the oscillator does not look clean, when we compare it with the sine-wave-damped case I posted earlier. I think my simplistic reasoning was flawed. My flawed reasoning was that a sawtooth wave would work by not shocking the tank when un-quenching, and only shocking the tank when quenching. But with a simple sawtooth wave, the instant when we quench and shock the tank is the same instant that the oscillations again start to build up. So what we need is a slowly ramping-up voltage to slowly un-quench (undamp) the tank, followed by a sudden drop in voltage to damp the tank through the diode, and (this is the missing part) a final "resting" period where the diode voltage stays at zero (damped condition) for some time to allow residual oscillations -- including the self-induced residual oscillations caused by shocking the tank during quenching -- to completely die down, before then again starting with the gradual ramp-up voltage to quietly un-quench (undamp) the tank. Forgive the crude ASCII art, but we need a quenching waveform like this one I think: _/|_/|_/|_/|_/|_/|_/|_/|_/|_/|_/|_/|_/| Such a waveform sounds rather complicated to generate. 2. Another problem, looking at the above simulation, is that the quench frequency still seems to be too high. It looks like the oscillations are not being allowed to build up to their full amplitude before quenching kicks in. But that can probably be tweaked by adjusting the quench frequency and/or the oscillator amplitude. The bigger problem is, as mentioned above, the need to insert a "rest period" into the quenching waveform. A simple sawtooth won't cut it. qrp-gaijin Posts: 2822 Joined: Sun Feb 28, 2010 2:12 pmContact:Re: Unusual AM Superregenerative? Receiver Postby qrp-gaijin » Sat Aug 10, 2019 7:45 am Selenium wrote: ↑ Sat Aug 10, 2019 6:40 am Simulation result: interesting.jpg (98.61 KiB) Viewed 196 times Selenium Posts: 1997 Joined: Mon Jun 10, 2013 7:59 pmRe: Unusual AM Superregenerative? Receiver Postby Selenium » Sat Aug 10, 2019 8:00 am What happens if you add an extra diode to dump the charge on the Emitter? Also the 250p capacitor C1 should be grounded. Attachments interesting.jpg (90.29 KiB) Viewed 184 times qrp-gaijin Posts: 2822 Joined: Sun Feb 28, 2010 2:12 pmContact:Re: Unusual AM Superregenerative? Receiver Postby qrp-gaijin » Sat Aug 10, 2019 8:07 am Selenium wrote: ↑ Sat Aug 10, 2019 8:00 am What happens if you add an extra diode to dump the charge on the Emitter? Not much, it seems... interesting2.jpg (100.23 KiB) Viewed 183 times And with the 250 pF capacitor grounded, we get: interesting3.jpg (133.12 KiB) Viewed 181 times Perhaps a sine-wave-shaped damping is the best way to go. Even if it is damping the tank more slowly than it could, at least it doesn't provoke any unwanted ringing. I suppose if one were to use a computer to generate the quench frequency (which should be easy, since a PC sound card can easily generate 12 kHz waves of any shape desired), it might be possible to experiment with the optimum quench waveform (slow attack, fast decay, rest period). Last edited by qrp-gaijin on Sat Aug 10, 2019 8:12 am, edited 1 time in total. Selenium Posts: 1997 Joined: Mon Jun 10, 2013 7:59 pmRe: Unusual AM Superregenerative? Receiver Postby Selenium » Sat Aug 10, 2019 8:11 am Also the 250p cap C1 should be grounded. My error in my original schematic. Also in this configuration only 1/2 the tank is being dumped directly. What happens if the tuning cap is connected to ground instead of across the inductor? Attachments interesting.jpg (90.23 KiB) Viewed 178 times Selenium Posts: 1997 Joined: Mon Jun 10, 2013 7:59 pmRe: Unusual AM Superregenerative? Receiver Postby Selenium » Sat Aug 10, 2019 8:19 am Would it be possible to try this one? Attachments superregen polyakov slow attack.jpeg (15.25 KiB) Viewed 176 times qrp-gaijin Posts: 2822 Joined: Sun Feb 28, 2010 2:12 pmContact:Re: Unusual AM Superregenerative? Receiver Postby qrp-gaijin » Sat Aug 10, 2019 8:22 am Selenium wrote: ↑ Sat Aug 10, 2019 8:11 am Also in this configuration only 1/2 the tank is being dumped directly. What happens if the tuning cap is connected to ground instead of across the inductor? Things start to look better. interesting4.jpg (112.68 KiB) Viewed 176 times Unfortunately there is some parasitic or secondary oscillation happening here. interesting5.jpg (110.33 KiB) Viewed 176 times This secondary oscillation makes it hard to determine if the start-up phase of the RF oscillation is quiet enough, or if it is being noisily shocked. So I need to get rid of this secondary oscillation to continue the analysis. =================================== Edit: I fixed the secondary oscillation, caused by excessive feedback (tapping at 50% of the inductor). It looks better, but still not good enough. The tank is being shocked both on the rising and the falling edges of the multivibrator signal. smallshock1.jpg (103.86 KiB) Viewed 174 times (As a separate issue, if you look closely you can see that during oscillator startup and shutdown, the density of the RF waveform is higher during these periods than when it is heavily oscillating -- this is the undesirable frequency pulling I had mentioned earlier, where the oscillator changes its frequency as it is starting up.) If we delete the RF oscillator transistor completely and just look at the effect of the multivibrator on the tank, we can see more clearly how the multivibrator shocks the tank. smallshock2.jpg (89.98 KiB) Viewed 174 times Selenium Posts: 1997 Joined: Mon Jun 10, 2013 7:59 pmRe: Unusual AM Superregenerative? Receiver Postby Selenium » Sat Aug 10, 2019 8:40 am I think the value of the 250p cap should be larger to slow the on rise time. Selenium Posts: 1997 Joined: Mon Jun 10, 2013 7:59 pmRe: Unusual AM Superregenerative? Receiver Postby Selenium » Sat Aug 10, 2019 8:44 am qrp-gaijin wrote: ↑ Sat Aug 10, 2019 8:22 am If we delete the RF oscillator transistor completely and just look at the effect of the multivibrator on the tank, we can see more clearly how the multivibrator shocks the tank. What happens if a PNP multivibrator circuit is used, or an NPN Polyakov circuit is used? Might this eliminate the turn on impulse by keeping the tank at a constant voltage as the diode is switched when undamping? qrp-gaijin Posts: 2822 Joined: Sun Feb 28, 2010 2:12 pmContact:Re: Unusual AM Superregenerative? Receiver Postby qrp-gaijin » Sat Aug 10, 2019 8:49 am Selenium wrote: ↑ Sat Aug 10, 2019 8:44 am What happens if a PNP multivibrator circuit is used, or an NPN Polyakov circuit is used? Might this eliminate the turn on impulse by keeping the tank at a constant voltage as the diode is switched when undamping? Could you explain how that would work, or show a sample circuit? I think the reason this scheme with the diode works is that we are pulling the tank down from Vcc to zero, through the shorting diode, and then raising the diode back up to Vcc when we turn it off. How would you achieve this periodic switching of the diode, if you try to keep the tank at a constant voltage? How would you turn the diode on and off? Post by Selenium » Sat Aug 10, 2019 8:55 am 6-7 minutes So I think the easiest way to damp the tank is to use a sinusoidal damping waveform, which will never shock the tank. The next problem with a superregen at MW, which I am only now starting to grasp, is the loop gain. Previously, my line of reasoning was that the long start-up time of the oscillator was not the problem with superregens at MW; the start-up time can be decreased (I thought at the time) simply by increasing loop gain. qrp-gaijin wrote: ↑ Sat Feb 03, 2018 1:27 pm Selenium wrote: ↑ Fri Nov 20, 2015 12:53 am The information in the link below is a little convoluted, but to summarize, the length of time it takes for an oscillator to start is equal to Q cycles. If the Q of the circuit is 100, it will take approximately 100 cycles to start. https://ccrma.stanford.edu/~jos/fp/Deca ... riods.html The following LTspice simulation with tank Q of 100 indicates that the below 1 MHz oscillator has no problem reaching full amplitude in far less than 25 cycles. [...] It seems that the ability to fully and quickly extinguish the tank's oscillations (to below the system's noise floor) may be the main challenge, rather than the start-up time of the oscillator. And all of my energies after the above post have been focused on the damping/quenching part of the system. But recently I realized that as I increase the loop gain, at least with this cross-coupled oscillator topology, the oscillator is shifting its frequency as it is starting up. That is probably a bad thing for sensitivity (imagine that, just as the regenerative signal build-up is occurring, you start to detune the tank away from the signal you are regenerating). And that's not the only problem. Let's look at the tank voltages of the sinusoidally-damped circuit I posted earlier. Here's the circuit again: freqshift0.jpg (88.21 KiB) Viewed 475 times The below image shows the tank voltages when the loop gain is set very high, by reducing the emitter resistance of the cross-coupled pair to only 1k ohms. freqshift1.jpg (126.07 KiB) Viewed 475 times Clearly the space between the peaks is changing as the signal is building up. That means the frequency is shifting during the start-up phase. Thinking about this some more, I started to wonder if this kind of a distorted waveform is even useful, or not, for regenerating an incoming sinusoidal signal. Look at the currents in the tank capacitor: freqshift2.jpg (77.98 KiB) Viewed 475 times Only for a tiny period of time is there a huge pulse of current; at other times, the tank currents are rather low. The amplifier is operating in class C. Is this good for regenerative build-up of an incoming signal? In other words, will an incoming signal be able to influence the oscillator start-up time, as is necessary? I don't know, but it looks kind of suspicious to me. The fact that the amplifier is only on briefly would seem to imply that the incoming signal is only briefly amplified. And the non-sinusoidal tank voltages (and currents) would also seem to make it difficult for a small, incoming sinusoidal signal to affect the large, non-sinusoidal voltages and currents sloshing around in the tank. Also if we look at the emitter current through Q2, we again see the frequency shift and we see that the whole system has become more of an astable multivibrator (at RF) instead of a sinusoidal oscillator. freqshift3.jpg (66.25 KiB) Viewed 475 times Also of concern is the comment by Dr. Insam at http://www.eix.co.uk/Articles/Radio/Welcome.htm: Many other tricks have been used to improve detector performance. The general aim is to control the loop gain in order to keep it as small as possible at the onset of oscillations. But if we keep the loop gain low, the build-up of oscillations will be slow at MW frequencies, forcing the use of a lower quench frequency. I'm not sure from Dr. Insam's article what are the consequences of too-high loop gain at the onset of oscillations. Perhaps the design process, at MW, would be to increase the loop gain as far as possible, while still maintaining sinusoidal oscillations. That will give the fastest possible start-up time, while still trying to minimise distortion. Then pick an appropriate quench frequency that allows the oscillations to build-up to their full amplitude (for logarithmic operation) and also allows the oscillations to die down completely. Along these lines, a 6 kHz quench seems feasible at 500 kHz. Here I set emitter resistance of the cross-coupled pair to 10k, for strong, but not too-strong, oscillation. The capacitors in the quenching astable multivibrator were increased to 20 nF to reduce the quench frequency to 6 kHz. This seems to have the side effect of changing the sinusoidal quench into a triangular quench, but that is not a problem in this case (a triangular wave still does not shock the tank, unlike a square wave). With these parameters, the 500 kHz RF oscillations have enough time to build up to their full amplitude, and are also fully extinguished at the end of each quench cycle. Also the RF oscillations remain sinusoidal throughout each unquench/quench cycle. 6khzquench.jpg (120.21 KiB) Viewed 471 times 6khzquench2.jpg (115.53 KiB) Viewed 471 times The oscillator amplitude will also change with frequency; tuning the tank higher (by reducing the tank capacitance) results in more vigorous oscillation and again a distorted waveform at the tank, implying the regeneration (controlled by the emitter resistance) should be adjusted as we tune the set, to prevent too-fast start-up time (and waveform distortion) while simultaneously preventing too-slow start-up time (which would quench the RF oscillator before it had a chance to reach its full amplitude, preventing the logarithmic operation which I want).

This is a recovered file. The images in this post may be out of order, and there may be duplicates. Varactor-tuned, hybrid-feedback, low-voltage BJT regen Post by qrp-gaijin » Mon Oct 14, 2013 I've successfully built a low-voltage, varactor-tuned, hybrid-feedback Vackar-Hartley regenerative detector/oscillator and have gathered some data on the frequency-dependence of the threshold oscillation level. For those not familiar with the topic, please see the following documents (by TheRadioBoard member vladn) for background reading: viewtopic.php?f=3&t=3714 and http://www.kearman.com/vladn/hybrid_feedback.pdf The basic idea is that the threshold oscillation level can be equalized over the oscillator tuning range, a procedure referred to below as "balancing the tilt". One goal of mine from the start was to attempt to apply the hybrid feedback approach to a varactor-tuned oscillator. My initial attempts were rather ambitious and failed due to my lack of experience with the hybrid feedback adjustment method and with varactor-tuned oscillators. This time, I decided to start with a low-voltage BJT hybrid-feedback oscillator that I had successfully gotten to work with an air-dielectric variable capacitor. There were two main problems with varactors that concerned me: 1. If the tank voltages are too high, the RF can get rectified and modulate the varactor capacitance, causing an unclean oscillator signal. 2. The varactor Q will change with frequency, which could make it difficult or impossible to balance the tilt due to the varactor-induced frequency-dependent losses. Regarding problem 1, I had hoped that the low oscillator supply voltage would keep the tank voltages low enough to prevent the RF rectification problem. After building the circuit (shown below), and attempting to monitor the battery-powered oscillator's radiated signal on my station recever, I at first had some hum-related problems; the oscillator's signal on the monitoring receiver sounded like it was hum-modulated. I initially incorrectly thought this was again a problem with high tank voltages causing the oscillator to de-tune itself. But it turned out to be something else, some sort of household noise affecting my monitoring receiver and possibly somehow getting back into my oscillator circuit. I noticed this because if I happened to touch a metal part of my desk, perhaps grounding the desk against my body, the oscillator signal was suddenly clean! I "solved" the issue by shutting off all electronic devices near my circuit and running my monitoring receiver off of batteries. After taking these measures, the regen's radiated signal as monitored on the station receiver sounds like a clean sine wave, though without a scope it is hard to know for sure about the signal purity and how high the tank voltages are. I'm still not exactly clear on the design procedure to ensure that a particular oscillator's tank voltage never exceeds a specified limit; if anyone has any advice, please share. Regarding problem 2, I was pleasantly surprised to discover that the tilt is almost balanced in my prototype. The data are presented below. I will continue to attempt to improve the tilt balance. Here is the successful circuit: hybrid-varactor.png (72.66 KiB) Viewed 6377 times Note there is a 0.1 uF decoupling capacitor (not shown) from the positive terminal of the 3V supply to ground. The circuit analysis is as follows. If we choose Cv to have a modestly high capacitive reactance and choose Tr1.L2 to have a very low inductive reactance, the circuit becomes a Vackar oscillator, with Tr1.L1 being the main tank inductor, Cv being the Vackar feedback capacitor and Tr1.L2 being a short-circuit. Alternatively, if we choose Cv to have a very low capacitive reactance and choose Tr1.L2 to have a modestly high inductive reactance, the circuit becomes a Hartley oscillator, with Tr1.L2 being the Hartley feedback inductor and Cv being a short circuit for RF. Balancing the values of Cv and Tr1.L2 forms a hybrid-feedback oscillator. Tr1.L3 is a low-turn-count link winding designed to prevent the collector from loading down the tank. Earlier, I had tried connecting the collector directly to the hot end of the tank inductor Tr1.L1, and the oscillator signal was very unclean at the high-end of the tuning range (5-6 MHz). The signal was unclean even when using an air-dielectric variable capacitor, indicating the unclean signal was due not to the varactor, but instead to the BJT loading down the tank. POT3 controls regeneration by raising the emitter potential either higher (closer to Vcc) or lower (closer to ground), which in turn alters the amount of collector current that can flow. The purpose of R2 is to leave some of the RF unbypassed so that some RF can be taken off of the Q1 emitter. This is for a future experiment to take the Hartley feedback off of the emitter (which might allow easier tilt balancing with a potentiometer). It was a bit tricky getting this circuit to oscillate; the gain seems to be marginal. I could not get the circuit to oscillate in Vackar-only mode when the collector was connected to the link winding Tr1.L3. When the collector was connected directly to the top of the tank inductor Tr1.L1, the circuit could oscillate in Vackar mode, but was very noisy at higher frequencies, as mentioned above. To measure the tilt, I observed the voltage at the POT3 wiper at the barely-detectable onset of oscillation. One very confusing thing was that at lower frequencies, the regeneration control seems to have a "dead spot": the set will oscillate with the POT3 wiper voltage set both below AND above this dead spot. In other words, when adjusting the wiper voltage from low to high, the oscillation pattern, at lower frequencies, is: strong oscillation -> sudden stop of oscillation -> sudden start of weaker oscillation -> gradually weaker oscillation -> soft stop of oscillation. The "soft stop of oscillation" is the proper point to define the oscillation threshold. The dead spot problem did not appear at higher frequencies. The following graph shows the dependence of the POT3 wiper voltage, required to reach the oscillation threshold, versus frequency in kHz. varactor-hybrid-data-1.png (19.06 KiB) Viewed 6375 times I took many more measurements at the low-end of the tuning range because there initially appeared to be large non-linearity at the low-end, but that turned out to be a measurement error: the apparent low-end non-linearity was caused by incorrectly believing the "dead spot" signaled the oscillation threshold, when actually the oscillation threshold occurred at a higher POT3 wiper voltage. So we can see that the threshold-vs-frequency dependence is actually rather small, and mostly monotonic. I had feared that the threshold level would be jumping up and down unpredictably due to the varying varactor Q, but it seems not to be that big of a problem. Next, I will tweak Cv (make it smaller) to see if I can reduce the tilt further, and take further measurements. Some other miscellaneous notes: 1. Small Cv? The varactor maximum capacitance should be around 450 pF (assuming an inductor of 14.40 uH and a lowest frequency of 2000 kHz). In theory, the Vackar capacitor Cv should be at least 10 times the maximum tuning capacitance, or 4.5 nF; currently, is 1.6 nF. Nevertheless, the current tilt shows a deficiency of Vackar-style feedback, which should require yet more Vackar feedback and an even smaller Cv. So I believe Cv should be decreased, not increased. However, it is conceivable that non-linear varactor losses are being offset by non-linearity caused by an overly-small Cv, which would make it difficult to predict the effects of changing Cv. 2. Applicability to higher frequencies? I tried to get the circuit to oscillate in Vackar-only mode at higher frequencies. I used an inductor consisting of 15-turns on a T50-6 (yellow) toroidal core and a 150 pF air-dielectric variable capacitor. I connected the collector directly to the hot end of the new inductor. No oscillation was observed. Then, the collector was connected to a 6-turn coupling link instead of directly to the inductor. Again, no oscillation was observed. It may be necessary to reduce Cv for higher frequencies. Or, there may simply not be enough gain at higher frequencies with my choice of transistor, Vcc, and biasing arrangement. Conclusion: It does appear possible to largely balance the tilt in a varactor-tuned oscillator. However, the Cv value is smaller than would normally be expected. Experiments continue. Proof of existence: hybrid-circuit.jpg (151.76 KiB) Viewed 6377 times --- Edit: I tried removing one tickler turn from the Hartley feedback portion of the coil to reduce the Hartley-style feedback (instead of decreasing Cv to increase the Vackar-style feedback). This shifted the tuning frequency range upwards, resulting in oscillation from about 4 MHz to 11 MHz. (This in itself is rather startling: removal of one turn shifts the oscillator frequency up several MHz? This needs further investigation.) The upper half of the tuning range was essentially completely tilt-balanced. However the lower half of the tuning range often exhibited an aggravated version of the previously-mentioned problem of the "dead zone" where the regeneration control would snap out of oscillation at some low-wiper-voltage setting and snap back in, with weaker oscillation, at a higher-voltage setting, finally fading out properly at a yet higher-voltage setting. At some lower frequencies the weaker oscillation region "above" the dead zone (higher wiper voltage) did not seem to exist, meaning that when slowly increasing the pot wiper voltage, the set would suddenly snap out of oscillation at some low-wiper-voltage setting, and would only snap back into oscillation (with hysteresis) when the voltage was again reduced beyond the point where oscillation had suddenly stopped. This whole "dead zone"/hysteresis issue leaves me feeling a bit uneasy and has me scratching my head. What may be happening is that for whatever reason the set is losing gain (at certain frequencies) when the regeneration control is set into the dead zone, which would indicate a need for increased gain, which could be had by increasing the turns on the collector link winding Tr1.L3. Another hunch is that R2 may need to be tweaked. Finally, it may turn out that the tilt can only be balanced over a portion of the varactor's tuning range due to frequency-dependent varactor losses. As I recall, varactor Q decreases with decreasing frequency (reference: 1SV149 varactor datasheet). Edit 2: It turns out I was listening to the second harmonic of the oscillating regen, which explains why I thought the frequency had shifted up so drastically. It hadn't. Edit 3: The "dead zone" issue may simply have been caused by a physically defective potentiometer which gave unpredictable jumps in resistance when adjusted to a certain position.

This is a recovered file. The images in this post may be out of order, and there may be duplicates. vladn: solid state frequency-compensated regen? Post by qrp-gaijin » Sat Jun 30, 2012 Switching to this thread (since the subject is not Clapp specific). This is a continuation of this thread: viewtopic.php?t=4472 and the original thread on tube branch related to hybrid feedback regens: viewtopic.php?t=3714 I have put up two circuits illustrating a minimalistic jfet regen using the hybrid feedback. The second one adds a Vackar divider and is more suitable for SW use. Please note - I have not verified these as drawn although they are relatively close to what I used for testing (also see comments below on the gate voltage regen control): qrp-gaijin wrote:How would one calculate the appropriate capacitive divider values and ratio? I start at 1:3 ratio and adjust experimentally. The main purpose of the Vackar divider is balancing disturbances introduced by the jfet gate and drain. The secondary purpose is an additional mean of the loop gain control. qrp-gaijin wrote:In terms of device operating point and frequency shift with regeneration is there any difference to raising the gate potential as opposed to lowering the source potential? There are three subtle differences: - oscillation amplitude is better controlled with positive bias at the gate/grid (I mentioned that before somewhere in the tube section); - the RC time constant shaping AF bandwidth is fixed; - (possible) simulation shows that there is some compensatory effect of simultaneously increasing Ids and decreasing Vgd reducing frequency shift, not sure it is simulation artifact or real effect, testing is needed. qrp-gaijin wrote:I don't quite folllow how "adding a series control element will increase drain signal amplitude." Could you elaborate? jfet has a relatively high output impedance that drives a relatively low impedance feedback network, hence the signal amplitude at the drain is small. If you increase the load impedance by inserting a series element in the drain circuit the amplitude at the drain will increase. qrp-gaijin wrote:Now if only there were some way to get a handle on those higher order terms (you seem to have little trouble with them, but K3NHI did). Look, we went over this several times in other threads . Let me summarize: - I have tested the method on two very distinct circuits and got over a magnitude improvement compared to conventional feedback by removing the linear term alone. I documented this to the best of my abilities - check the graphs on pg23 and pg25 of my main report, these are actual measurements; - the remaining higher order terms are hard to predict because they depend on complex physical phenomena in the resonant circuit that determine it's Q(f); - no I do not know how to remove the remaining terms; - I do not find them objectionable in practical use, take a look at videos that I made; - there is always room for improvement in any design... Here's a brief work log of my attempts and results so far with the hybrid feedback Armstrong-Vackar topology. I don't have much to report yet; the capacitive gate divider and the means of regeneration control seem a bit tricky. The initial schematic was as follows: I started with an Armstrong topology. Q2 is a 2SK192A. Tank inductor Tr2.1 was about 40 turns on a red T50-2 toroid. Tickler winding Tr2.2 was 6 turns. C21 is a fixed "throttle capacitor". Construction was done on a solderless breadboard. Initially I started with source resistor R2=3k with the gate directly grounded through the coil Tr2.1, eliminating C3 and C4. This was a known good Armstrong regenerative detector configuration and I could confirm oscillation around 7385 kHz. Further tests, unless noted, took place at this frequency. Next I inserted the gate capacitive divider C3 and C4 and grounded the gate directly through a 1M resistor. A gate divider of 27pF/27pF caused oscillation to stop. 1000pF/27pF allowed weak oscillation. Removing C4 with C3 at 1000pF allowed stronger oscillation. Further tests were done with C3 at 1000pF and without C4. Next I inserted the VR2, R10, C20, and R18 components to allow variable gate bias for regeneration control. With source resistor R2=3k, Q2 would continue oscillations regardless of the setting of VR2. With source resistor R2=20k, oscillation was weaker and could be stopped and started by adjusting VR2. Oscillation would stop below about 7000 kHz. The range of regeneration control was very limited; full regeneration resulted in a very weak oscillation. Next I decreased gate-voltage-limiting resistor R10 to 20k, and also decreased source resistor R2 to 10k. The regeneration control was fairly well behaved, allowing smooth transition from no oscillation to full oscillation. Q2 would oscillate down to about 5615 kHz with regeneration voltage at the gate at maximum, measured at 2.689V. To try to get the set oscillating even lower, next I reduced gate-voltage-limiting-resistor R10 to 10k. Q2 would oscillate down to 5295kHz with gate voltage at 4.032V. R10 was next reduced further to 3.3k; Q2 oscillated down to 5120kHz at gate voltage 5.450V. Source resistor R2 was lowered to its original value of 3.3k. Q2 would oscillate down to 3910kHz at gate voltage 4.697V. Gate-voltage-limiting resistor R10 was reduced to 1k. Q2 oscillated down to 3850kHz at gate voltage 5.494V. Maximum oscillation frequency in this configuration was 7615kHz. At higher frequencies, due to the reduced source resistor, gate bias could no longer stop Q2's oscillation. I also tried replacing the source resistor with a 10k pot, but the regeneration control seemed more abrupt and unreliable at lower frequencies. My current conclusions: - Gate bias for regeneration control seems well behaved, but requires tweaking the source resistance as well depending on frequency. - There is little frequency shift with gate bias adjustment at oscillation threshold; frequency shift increases as gate bias is further increased and oscillation amplitude increases. - The capacitive divider at the gate caused oscillation to stop, and only a very large tapping ratio allowed oscillation to continue, over a very narrow range of frequencies. Seeing as how gate bias adjustment for regeneration control requires also tweaking source bias for reliable regeneration over only a modest range of frequencies (3.8 MHz - 7.3 MHz), I'm not sure if this gate bias regeneration scheme is usable for a wide-range regen. Since the entire point of this project is to make a regen whose regeneration level needs no adjustment over a wide frequency range, the gate bias adjustment + periodic source bias tweaking method doesn't seem completely suitable. Not sure how to proceed next. I could control supply voltage for regeneration, or continue investigating the source-bias-only regeneration. All of the above represents only incremental modifications to an Armstrong oscillator. I haven't even tried inserting the Vackar feedback capacitor yet. There are many things that can cause the set to stop oscillating, and it seems to require a rather tedious and careful step-by-step alteration of the topology from Armstrong to Armstrong-Vackar in order to discover what set of parameters will allow oscillation to continue. EDIT: Some better progress. The following Vackar-Armstrong hybrid feedback circuit oscillates from 3320 to 7860 kHz. I eliminated the capacitive divider at the gate, inserted the Vackar feedback capacitor, and also rerouted the tickler to be shunt fed instead of series fed. Making C29 variable seems to hold promise as a means of regeneration control. A polyvaricon was able to pull the set out of and into oscillation, but a very low capacitance was needed to pull the set out of oscillation. When I tried with a varactor, the minimum capacitance was too great and the set continued oscillating. Anyway: the important thing is, I have an oscillating hybrid feedback topology. Next step will be to build it properly on a copper clad board, confirm the throttle capacitor regeneration works, then attempt to minimize the tilt. I still remain open to the possibility that the varying Q of the varactor may make things more difficult than they need to be, but I still want to try using varactor tuning. Few notes related to your *last* diagram (if possible try to keep reference designators for similar components the same across variants): - the value of R21 should be >1meg, otherwise you are loosing Q; - either C27 or C29 can be removed; - gate voltage range from 0 to Vcc/2 is a good starting point for regen control; - tweak C28 for linear term minimization, this will affect total feedback as well so you have to compensate by tweaking the source resistor; - for frequencies much above 5MHz use type6 or type7 core; My suggestion is not to focus on throttle capacitor regen control at least for now, once the simple version works satisfactory with the linear term removed we can discuss options for a more sophisticated regen control. Last edited by vladn on Sun Nov 25, 2012 6:16 pm, edited 1 time in total. qrp-gaijin Posts: 2822 Joined: Sun Feb 28, 2010 2:12 pmContact: Postby qrp-gaijin » Sun Nov 25, 2012 6:16 pm Some more random ideas and questions. I realize the questions might not have clear answers at this point. Consider them research issues . 1. Regeneration control. Maybe a BJT circuit with base bias control would work. I don't have much experience with BJT regens, but base bias seems to work okay (certainly better and over a wider range than my gate bias experiments). 2. Tickler turns. Why is it necessary to reduce the tickler turns below that required for a normal Armstrong regen? Can the tickler turn ratio affect the tilt and/or the nonlinear terms? 3. Tank reactance. Is there a recommended value for Armstrong-Vackar designs? Does tank reactance affect the tilt? Last edited by qrp-gaijin on Sun Nov 25, 2012 6:35 pm, edited 1 time in total. qrp-gaijin Posts: 2822 Joined: Sun Feb 28, 2010 2:12 pmContact: Postby qrp-gaijin » Sun Nov 25, 2012 6:31 pm vladn wrote:Few notes related to your *last* diagram (if possible try to keep reference designators for similar components the same across variants): Sure, sorry about that. I was in a hurry to note down the current circuit constants and behavior so I did a copy-paste, which renumbered everything. vladn wrote:- the value of R21 should be >1meg, otherwise you are loosing Q; - gate voltage range from 0 to Vcc/2 is a good starting point for regen control; OK. I note that my orignal and somewhat unsuccessful experiments with gate voltage regen control were done with a straight Armstrong topology, not the Armstrong-Vackar. But when I changed to Armstrong-Vackar, the set seemed to oscillate more reliably over a wider range of frequencies. So I will try again with the gate voltage control, and will increase R21 to improve the Q. vladn Posts: 853 Joined: Sun Nov 02, 2008 7:15 amLocation: NJ, USA Postby vladn » Sun Nov 25, 2012 9:30 pm qrp-gaijin wrote:Maybe a BJT circuit with base bias control would work. Yes. qrp-gaijin wrote:Why is it necessary to reduce the tickler turns below that required for a normal Armstrong regen? Because the two feedback paths are additive. qrp-gaijin wrote:Can the tickler turn ratio affect the tilt and/or the nonlinear terms? Yes, and so does the value of the feedback capacitor C28. Increasing tickler turns and decreasing C28 increases the total feedback. Changing only one of the two values changes both the tilt and total feedback. Changing tickler turns and C28 in the same direction changes the tilt. qrp-gaijin wrote:Is there a recommended value for Armstrong-Vackar designs? The goal is to get the highest possible unloaded tank Q. This will ensure minimal tank coupling to the amplifier and therefore minimum frequency detuning, phase noise etc. Amidon site has some Q(f) graphs for various materials for different # of turns, this gives a good starting point. Also note that type 6 and 7 materials have a noticeably better thermal stability than type 2. qrp-gaijin Posts: 2822 Joined: Sun Feb 28, 2010 2:12 pmContact: Postby qrp-gaijin » Mon Nov 26, 2012 12:22 am vladn wrote:Increasing tickler turns and decreasing C28 increases the total feedback. Changing only one of the two values changes both the tilt and total feedback. Changing tickler turns and C28 in the same direction changes the tilt. Very interesting. However, adjusting the number tickler turns is one of those things that is easier said than done. It's one reason that I started my experiments with the Seiler-Vackar - I was hoping to be able to adjust all parameters just by swapping out some caps. But as noted in an earlier post, I couldn't get it oscillating properly over a wide range with the 1 uH coil I tried and my 500 pF varactor. Maybe I'll give it a try again with a larger-reactance coil and no Vackar capacitive divider (short circuiting your C3 in the Seiler/Vackar figure on p. 16). Have you successfully prototyped in hardware the Seiler-Vackar variant? In light of the above observations on feedback and tilt adjustment in the Armstrong-Vackar, and looking at the Seiler-Vackar figure on p. 16 of the hybrid feedback paper, is it correct to say that: increasing C5 and decreasing C2 will increase the total feedback; changing only one will change both tilt and total feedback; changing C5 and C2 in the same direction will change the tilt? Sounds nice in theory and easier than fiddling with tickler turns - if it can be made to work in practice! One idea I have is a grounded-base Colpitts oscillator (see http://www.ke3ij.com/bigloop.htm ), which is a reliable starter in my experience. The interesting thing is that the amplifier output (collector) is tuned, not the input. However if I'm understandig your paper correctly, the hybrid feedback network can be reversed, so I can treat the collector as the "input" and the emitter as the "output" I should be able to use the Seiler-Vackar feedback network as-is (it will actually be reversed in terms of input and output, but that's OK, right?). vladn Posts: 853 Joined: Sun Nov 02, 2008 7:15 amLocation: NJ, USA Postby vladn » Mon Nov 26, 2012 2:22 am qrp-gaijin wrote:However, adjusting the number tickler turns is one of those things that is easier said than done. You can adjust for tilt using C28 only and then tweak the total gain with either the source resistor or the input divider or both. Before any tilt tweaks increase the value of R21 though. qrp-gaijin Posts: 2822 Joined: Sun Feb 28, 2010 2:12 pmContact: Postby qrp-gaijin » Mon Nov 26, 2012 6:46 am I can't seem to get the gate bias regeneration control working well. Experiments continue. In the mean time, I was looking for BJT regen circuits and I found this rather interesting one. It almost looks like a hybrid feedback circuit. What do you think? http://www.theradioboard.com/rb/viewtop ... 5753#25753 vladn Posts: 853 Joined: Sun Nov 02, 2008 7:15 amLocation: NJ, USA Postby vladn » Mon Nov 26, 2012 3:26 pm qrp-gaijin wrote:I can't seem to get the gate bias regeneration control working well. Experiments continue. It would help if you describe the problem. qrp-gaijin wrote:In the mean time, I was looking for BJT regen circuits and I found this rather interesting one. It almost looks like a hybrid feedback circuit. What do you think? It is a pure class 2 (Vackar-like) feedback. Also the tank is heavily damped via R3. qrp-gaijin Posts: 2822 Joined: Sun Feb 28, 2010 2:12 pmContact: Postby qrp-gaijin » Mon Nov 26, 2012 10:24 pm vladn wrote: qrp-gaijin wrote:I can't seem to get the gate bias regeneration control working well. Experiments continue. It would help if you describe the problem. Basically I can't bring the set out of oscillation at the high end of the tuning range (7 MHz) with "reasonable" (3.3k-20k) values of source resistance and zero volts up to Vcc/2 on the gate. If I raise the source resistance up to 40k, I can bring the set out of oscillation for a very narrow and limited range of frequencies at the high end of the tuning, but as I tune lower that range the set cannot be brought into oscillation anymore. Also, at lower frequencies, as I slowly tune the set lower and nudge the regeneration control back and forth, the regeneration control drastically shifts the tuning, maybe due to the unreasonable operating point brought about by the high source bias. For instance, with source bias at 3.3k the set will tune (always oscillating regardless of gate bias) from about 3.8 to 7.3 MHz over the full range of varactor capacitance, but with 40k source bias and fiddling with the gate bias, for about 75 percent of the range of varactor capacitance, the set only tunes down to about 6.5 MHz. Then the remaining 25 percent of the varactor capacitance (at the high end of varactor capacitance) doesn't oscillate at all. So the unreasonably high source bias plus the gate bias is restricting the tuning range somehow, is pulling the frequency greatly with gate bias adjustment as frequency decreases, and allows regeneration control only for a very limited range of frequencies at the high end of the tuning range. My Vackar feedback cap at the bottom of the tank was at 100nF to make the set behave in Armstrong-only feedback mode. (Decreasing it didn't help with the regeneration control.) I've basically tried everything except reducing the number of tickler turns, which I avoided because it requires unsoldering the coil and cutting wire. But I think now I need to reduce tickler turns to reduce the amount of tickler feedback. In your experience, does gate bias regeneration control work well over a wide (several MHz) range? NOTE: I monitored oscillation strength and frequency on a nearby receiver. With 3.3k source bias I am sure I was listening to the fundamental frequency. With 40k source bias I didn't verify this, so I may in fact have been listening to the second harmonic. That could make sense: the very high bias maybe (?) is introducing a large amount of inter-junction capacitance which would both lower the oscillation frequency and the range, lowering the maximum oscillation frequency so severely (down to 3.5 MHz) that I was listening to the second harmonic instead of the fundamental at 7 MHz. Just a theory. vladn Posts: 853 Joined: Sun Nov 02, 2008 7:15 amLocation: NJ, USA Postby vladn » Tue Nov 27, 2012 4:39 am Could you post your latest schematic with component values ? It would be *very* helpful to replace the varactor with a plain air variable capacitor for now. The varactor Q varies with frequency as well as the oscillation amplitude making things really complicated. Moreover, as the oscillation amplitude rises varactor will become a rectifier overriding the "tuning" voltage and shift the frequency drastically! This is why I strongly advised again using wide tuning varactor in the initial experiments. (At the very least try a standard dual varactor circuit, it has a better dynamic range. But even then I have doubts it will work.) Regeneration control via gate bias is nearly identical to the source resistor control (although adjustment range is smaller). Other differences are subtle. qrp-gaijin Posts: 2822 Joined: Sun Feb 28, 2010 2:12 pmContact: Postby qrp-gaijin » Tue Nov 27, 2012 12:39 pm vladn wrote:Could you post your latest schematic with component values ? vladn wrote:It would be *very* helpful to replace the varactor with a plain air variable capacitor for now. OK, I will try that next. I hope I can eventually get the varactor version working though as it could make for a small and precise tuning mechanism if two ten-turn pots are used. Things left to try for this circuit, in order: 1. Replace varactor with air variable cap. 2. Reduce tickler turns. 3. Rebuild circuit properly on copper ground plane (not on solderless breadboard). If I can't get this circuit working, I may try a grounded-base BJT Armstrong or Hartley configuration, and use base bias to control regeneration. Example of a potential grounded-base Hartley regen: viewtopic.php?t=2959 , though N1TEV uses some "tricks" with that regen that might complicate transformation to a hybrid feedback topology (e.g. attempting to smooth the regeneration control by simultaneously decreasing emitter bias resistance and increasing the shunting of the tickler, or running the circuit at a very low current). Anyway, that's the backup plan - I still have some hope for the JFET circuit. millwood Postby millwood » Tue Nov 27, 2012 10:22 pm R22 is 47k? qrp-gaijin Posts: 2822 Joined: Sun Feb 28, 2010 2:12 pmContact: Postby qrp-gaijin » Tue Nov 27, 2012 11:29 pm millwood wrote:R22 is 47k? I tried values from 3.3k (reasonable) to 47k (unreasonable IMHO - the JFET must be practically at pinch off). Only with source bias around 40-47k was I able to use gate bias voltage to pull the set out of oscillation. Lower values of source resistance caused the set to continuously oscillate regardless of gate voltage. So, it looks like either too much tickler feedback, and/or the varactor is messing things up. vladn Posts: 853 Joined: Sun Nov 02, 2008 7:15 amLocation: NJ, USA Postby vladn » Wed Nov 28, 2012 2:20 am qrp-gaijin wrote:So, it looks like either too much tickler feedback, and/or the varactor is messing things up. Both. The varactor causes self-reinforcing frequency shift/snap once the oscillation amplitude grows. And you have too much feedback. The latter can be fixed by adding a divider at the gate rather than reducing the tickler coil (but it can make the varactor problem even worse as the tank amplitude can increase further with the divider). Personally I would go in this sequence: step 1 (conventional armstrong feedback) - replace varactor with an air variable capacitor; - add divider (15pf/15pf), if you have a quality trim cap use it in the divider; - ground plane; - trim the divider until you can follow the oscillation threshold over the entire tuning range with a source resistor around 10-20k; step 2 (hybrid feedback) - remove (short) C27; - reduce C28 to around 1nF, this will increase feedback, trim gain back down using the gate divider; - check tilt, adjust C28, trim gain, repeat step 2a (optional if you are building RX rather than VFO) - add RF buffer and AF stage (RF buffer may require some tilt trimming) - test the thing for reception; step 3 (varactor study) - experiment with varactor, definitely use a dual varactor circuit (but it may still fall short of expectations); - if it fails use capacitor+varactor (fine tuning) arrangement, that will definitely work; step 4 (advanced regen control study) - we can try a more advanced regen control, I have it partially tested but it needs some work; qrp-gaijin Posts: 2822 Joined: Sun Feb 28, 2010 2:12 pmContact: Postby qrp-gaijin » Wed Nov 28, 2012 4:46 am Okay, good , now I know exactly what to do next. I also have a better appreciation for just how delicate of a balancing act this is. It's quite a bit more work to set up than a plain regenerative receiver, but it's remarkable that it can be made to work at all, with the whole system perched right on the brink of instability (for under-threshold reception) even as the tank is being tuned and the changes in the complementary feedback paths are perfectly cancelling out. vladn wrote:my unverified guess is that (ii) dominates the regen control effect. The higher is the drain RF load impedance (low throttle capacitance) the larger is the amplitude of the amplified RF signal at the drain. That signal is inverted with respect to the gate signal and fed back to the gate via parasitic Cgd of the JFET. This introduces negative feedback (as opposed to the positive feedback from the source to the tank). Varying the amount of the negative feedback by changing the drain load you adjust regeneration. Again this is only a guess. Consider the following N1TEV design, which uses a fairly common Armstrong tickler and throttle capacitor arrangement with a JFET: http://www.electronics-tutorials.com/re ... ceiver.htm First, I always understood that the throttle capacitor controls the amount of current flowing through the tickler. The RFC prevents current flowing up to Vcc, so instead it flows through the adjustable throttle. Would you agree that this description is accurate for a JFET Armstrong throttle capacitor and tickler? The drain signal is inverted, so the tickler is wound, adjacent to the main coil, with its hot end (to the drain) and cold end (to the throttle capaitor) reversed with respect to the main coil, to effect in-phase feedback. Then, according to your argument above, it would seem that the reducing throttle capacitance not only reduces the current flow through the tickler (thus reducing tickler-based feedback), but it also increases the drain load impedance, which then feeds the impeded inverted signal back to the gate via parasitic capacitance, further reducing feedback beyond that aleady effected by tickler current reduction. So there are two feedback control mechanisms with the tickler and throttle cap: tickler current control and drain impedance control. Using non-inverted tickler feedback from the source, but keeping the drain throttle in place, thus prevents direct control of feedback through the tickler and leaves only drain impedance control to control feedback indirectly (through parasitics). Interesting. I have seen at least one Hartley that uses a throttle capacitor: N1TEV's 2010 design in CQ magazine. The explanation is the usual "RFC backs up the RF signal preventing it from traveling to Vcc and instead forcing it through throttle capacitor". It sounds simple enough, but perhaps there is indeed more than meets the eye. (The issue of "where do the excess electrons accumulated on the top plate of the throttle capacitor go, when the gate signal drops into a valley and constricts the JFET channel" is still bugging me; given enough time, the electrons will bleed off through the RFC, but what about when they're not given enough time as the gate signal is wiggling up and down at RF? I guess some low amount of average current leaks through the RFC, bleeding off enough electrons from the top plate such that the top plate's charge does not grow without bound.) vladn wrote:I do not quite like using device parasitics for any control (as it may not be repeatable from device to device), this is personal and subjective, indeed it may work well, it just goes against my engineering/aesthetic intuition Believe me, I want to get the gate bias regeneration control working, but it's not cooperating. So I turned to a method that I have more experience with, the throttle capacitor. I am still hammering away at getting gate bias regeneration working; now, with my almost-tilt-balanced prototype, it should be easier than with a non-tilt-balanced setup (where required gate bias would vary greatly with frequency). And speaking of design repeatability, I'm a little concerned that hybrid regen designs might not be easily repeatable due to the large amount of tweaking that needs to be done. Lack of design repeatability would be regrettable, as it would discourage casual experimentation with the very elegant hybrid feedback idea. vladn wrote:4mH is way too much, even a quality multi-section 4mH choke will have the self-resonanse frequency way below SW. At your frequencies 4mH choke will have very low and capacitive ! impedance. Really? Most regens I see use 2.5 mH chokes, and one N1TEV design I built says that the set will work all the way down to long wave with no component changes. I'll do some reading on the matter, but what is the ideal range for impedance and self-resonant frequency for chokes used in regens in the drain line? vladn wrote: qrp-gaijin wrote:L1b was about 8 turns at first, reduced to 4 turns later. Apparently that's too much. If you check my 6AS6 experiments I used 1-2 turns for L1b (~50t for L1a). In your JFET case 2 turns is a good starting value. But the interesting thing is that the throttle cap with the same number of tickler turns was able to achieve proper tilt compensation. Again, this is from memory, but I would classify my experiences as follows: 1. Inverting Armstrong-Vackar, 4 mH in drain line, gate bias regeneration control. Result: C2 reduction can properly decrease the oscillation threshold (relative to high-range frequencies at ~6 MHz) at mid-range frequencies of ~4 MHz, but cannot decrease the oscillation threshold at low frequencies at ~2.5 MHz. Oscillation requires more feedback at 2.5 MHz regardless of C2 setting. So there is significant non-linearity here: C2 can compensate tilt at 4 MHz, but not at all at 2.5 MHz. 2. Non-inverting Armstrong-Vackar and gate bias regeneration control (with Vackar capacitive divider at gate). Tried both without 4 mH choke, and with 4 mH choke bypassed by 0.1 uF. Result: same as case 1. 3. Non-inverting Armstrong-Vackar, 4 mH choke in drain, 365 pF throttle capacitor for regeneration control, gate grounded through 1M resistor (with Vackar capacitive divider). Result: C2 reduction can properly reduce and reverse the tilt such that 2.5 MHz requires less feedback (less throttle capacitance) than 6 MHz. C2 enlargement can properly reverse the tilt such that 2.5 MHz requires more feedback than 6 MHz. It seems that the gate bias regeneration control method is somehow causing more energy loss at low frequencies requiring more feedback no matter how much class-2 feedback is introduced. Yes, it could be argued that I just have too much class-1 style feedback. I will test that and reduce the turns. But: the non-inverting Armstrong-Vackar with throttle cap (and with choke) worked fine with the existing tickler feedback, whereas the exact same circuit and tickler, rewired for gate bias regeneration control, didn't work properly. So it seems that something is fundamentally different between throttle cap regen control and gate bias regen control in this circuit. Again, in this non-inverting Armstrong-Vackar configuration, the C2 vapacitor has a dual role of Vackar network capacitor *and* source bypass capacitor. I suppose that the value of the C2 bypass capacitor may have some frequency-dependent effect on the required feedback level when changing the gate bias - an effect that perhaps is not present when the gate bias is fixed (at ground, relying only on source bias) and when using the throttle cap to control regeneration. This is just a guess. In the inverting Armstrong-Vackar, the source bypass cap is separate from the Vackar network cap C2. However, very similar poor tilt adjustment behavior (using gate bias) exists. qrp-gaijin wrote:Solderless without proper ground plane is not a good testing platform at HF and higher frequencies. I've seen very strange behaviour from RF circuits that work reliably and repeatably on with a proper ground. It's entirely possible my gate bias woes are due to this. My intuition seems to say there's something more, though, since the same circuit works with the throttle cap but doesn't work with gate bias. And one more data point: base bias in a BJT almost seems workable. I could reduce but not reverse the tilt using base bias (non-inverting, tuned collector, grounded-base Armstrong-Vackar). I didn't see the low-frequency non-linearity I saw with gate bias control. The tilt was reducing, across the band, but I couldn't eliminate it (too much class 1 tilt), and further C2 reduction stopped oscillation or led to parasitic oscillations (C2 is also the emitter bypass cap in this design). This would seem to suggest that reducing tickler turns (and class 1 feedback) would make the base bias regen control topology work. Again, I'll try that (reducing tickler turns even further), and maybe that will fix the gate bias problems too. The BJT base bias regeneration control worked well immediately without any capacitive divider gain adjustment (as was needed to get gate bias regeneration control working), so that may be the least-trouble, easiest topology to get working. It also has the advantage that no throttle cap or RFC are required. Anyway, more experiments will follow. Since we've got a good theoretical discussion going about both the throttle capacitor and about hybrid feedback topologies, I thought I'd mention for exploration another conceivable idea for a tilt-balanced regen. (I think I mentioned it briefly before in another thread.) It's probably much more trouble to realize in practice than the existing hybrid feedback approach (combining class 1 and class 2 feedback types), but who knows, maybe it might be interesting to analyze and/or try to implement this alternative idea. The idea: take a dual gang variable capacitor. Use one gang to control tuning and another gang to control regeneration as a throttle capacitor. Higher frequencies will automatically receive less total feedback due to decreased throttle capacitance. Therefore this scheme should be appropriate to counteract the tilt for class 1 oscillators (Hartley, Colpitts, Armstrong). To make the throttle capacitance level track exactly the regen frequency, it would be necessary to use use padders and trimmers in parallel with the throttle capacitor gang, as well as to control overall loop gain. Such a scheme presents a number of interesting questions. First of all, for a class 1 oscillator, what is the shape of the function Cth(f) that specifies the required throttle capacitance Cth to reach oscillation threshold for a given oscillator frequency f? This will depend (as being discussed in the other thread on throttle capacitor function) on device parasitic capacitance and the oscillator feedback configuration (number of tickler turns, etc.). Second, is it possible to achieve the required shape of the Cth(f) function when the physical Cth is ganged with the tuning capacitor Ctu? I can hazily imagine how one would could use a trimmer in parallel with the throttle capacitor gang, and a padder in series with the throttle capacitor gang, to achieve a desired capacitance swing for the throttle capacitance. Then the padder and trimmer might be optimized along these lines: Given: Ctu(f) = 1/(L*(6.28*f)^2) And for a capacitor with equally sized gangs, the throttle capacitance is equal to the tuning capacitance: Cth_unadjusted(f) = Ctu(f) Then, adding the padder and trimmer, the adjusted throttle capacitance is: Cth_adjusted(f) = 1 / ( 1/(Ctu(f) + Ctrimmer) + 1/(Cpadder) ) Then, find Ctrimmer and Cpadder to minimize the error between Cth_adjusted(f) and the ideal Cth(f) function. Since the ideal Cth(f) function's shape will depend on the oscillator feedback arrangement (tickler turns, gate divider, bias, etc.), these parameters all could also be optimized to minimize the error. It might also be possible or necessary to alter the relationship between Ctu(f) and Cth_adjusted(f) by adding a trimmer/padder to the capacitor gang used that is used to control oscillator frequency. This particular scheme seems impractical enough so that I probably won't be trying to figure it out anytime soon, but maybe someone is interested in pursuing and/or formalizing the matter. It seems like there should be enough information in this thread and the throttle cap thread to take a stab at the problem. Note that Dave S.'s page at http://makearadio.com/others/regenrx4.php makes a mention of this kind of "ganging" scheme for automatic regeneration control, but the idea isn't formalized. (Search that page for the phrase "automatic control of regeneration".) On a different note, it is interesting to observe that the above page refers not to a "throttle condenser" but instead to a "variable bypass condenser", so the concept of the "throttling" role of the capacitor had perhaps not yet taken hold. vladn wrote:Could you re-draw the simplified circuit with reference designators ? Second jfet is the grounded gate feedback jfet. Aha, that changes everything. OK. The following diagram (D1) is the original simplified circuit (mostly based on KR1S's diagram with a sprinkling of the Ten Tec diagram). I eliminated the RF preamp stage. I also moved the grounded-gate JFET (T2) to the lower-right corner of the diagram to emphasize the fact that it is part of the source follower output/feedback loop, not part of the input. Diagram D1: The next diagram (D2) represents my misinterpretation of your post, where I thought the "second JFET" was the input JFET (T1). Here you see what I mean that there would be three feedback paths (through T2 to tank, through tickler magnetic coupling to tank, and through tickler to Vackar capacitor C9). Diagram D2: The next diagram (D3) represents what I think is the correct interpretation of your post: eliminating the original direct-from-T2-to-tank feedback, and instead routing it through an Armstrong tickler and the Vackar cap. I agree that this looks like it would work. EDIT: Now I think this will not work. The T2 output is non-inverting, but using C9 as the Vackar cap requires an inverted output. See updated diagram D3a. Diagram D3 (EDIT: maybe incorrect due to non-inverting T2 output; see corrected diagram D3a below): Diagram D3a: updated diagram D3 to use non-inverting Vackar-style feedback. I think this is correct, and D3 is incorrect. C9 is just an RF grounding cap; C10 is the (non-inverting) Vackar feedback cap. Probably, the RFC is not needed here. The next diagram (D4) represents my proposed idea to augment the existing direct-from-T2-to-tank feedback path with an additional Vackar feedback path from T2's source into C10. Note that since the T2 output is non-inverting (with respect to the tank), we need to feed the Vackar signal into C10, not C9 (C9 is just an RF grounding cap, and C10 is the Vackar cap). I am not sure if (a) the original feedback path is class 1 (if not, then adding class 2 Vackar feedback is inappropriate), and (b) if the signal magnitude of the added Vackar feedback path will be sufficient (it doesn't go through the grounded gate amp, but is taken directly off the preceding source follower). Diagram D4 (as in D3a, probably, the RFC is not needed here): Assuming the basic idea of diagram D4 is plausible, then maybe we could add another grounded-gate amp T3 for the Vackar feedback, and try to balance the feedback paths with a potentiometer VR3, as shown in diagram D4a below. You mentioned such an idea (balancing two separate amplifier paths) at the end of the hybrid feedback paper. Diagram D4a: possible dual-feedback, dual-amplifier topology. This is starting to move beyond the realm of "simple" regenerative receiver topologies... (EDIT: added DC blocking cap between VR2 and VR3, moved RFC to T3 drain) In diagrams D3 and D4 (and variants) it does seem, as I mentioned before, that the frequency response of T2 will affect the tilt. Would you agree? Also, what is the class of the unaltered feedback mechanism in the original diagram D1? vladn wrote:BTW you can simulate it and see what happens at the higher frequencies. Just break the feedback loop at the second jfet drain and drive the V-A path with a current source. Hm, OK. I have mostly figured out how to simulate the idealized VCCS/VCVS hybrid feedback models, but I haven't tried running simulations with actual JFET models yet. Maybe soon. EDIT: added possible dual-amplifier balanced topology as diagram D4a. rp-gaijin wrote:No. For the AC sweep simulation, R2 is disabled (open circuit), I1 current source is enabled, I2 current pulse is disabled, and open-loop output is taken at point "out" on the left side of R2. For transient analysis to check if oscillation is possible, R2 is enabled, I1 is disabled, and I2 is enabled. Are you using the current source to drive the base in the AC sweep ? If so then you introduce synthetic downward tilt in the frequency response - the device Miller capacitance and the infinite impedance source forms an integrator. qrp-gaijin Posts: 2822 Joined: Sun Feb 28, 2010 2:12 pmContact: Postby qrp-gaijin » Sat Jan 12, 2013 5:05 am vladn wrote:Are you using the current source to drive the base in the AC sweep ? If so then you introduce synthetic downward tilt in the frequency response - the device Miller capacitance and the infinite impedance source forms an integrator. Yes, I am using the current source to drive the base in the AC analysis (with an open loop). Is there a better way? I assume your previous comments, about needing to run the AC sweep with the amplifier oscillator below oscillation threshold, do not apply when running with an open loop, correct? Last edited by qrp-gaijin on Sat Jan 12, 2013 5:12 am, edited 1 time in total. vladn Posts: 853 Joined: Sun Nov 02, 2008 7:15 amLocation: NJ, USA Postby vladn » Sat Jan 12, 2013 5:10 am qrp-gaijin wrote:Yes, I am using the current source to drive the base in the AC analysis. Is there a better way? Use a voltage source instead. Or a current source shunted to ground by a realistic impedance of the feedback path. In all my simulations I used the voltage source assuming that I use a transconductance amp. Bipolar is a current device but driven from a low impedance node here operates "close to" the transconductance mode (voltage driven current source). qrp-gaijin Posts: 2822 Joined: Sun Feb 28, 2010 2:12 pmContact: Postby qrp-gaijin » Sat Jan 12, 2013 6:25 am vladn wrote:Use a voltage source instead. OK. The results were: with the common-base, no change: the circuit remained tilt balanced with exactly the same circuit parameters. (As I said, the common-base is a reliably-performing circuit.) For the common emitter, first I realized that the circuit as posted has a problem when simulated in open-loop mode: the base bias is cut off when the loop is opened. I fixed this by connecting the base directly to RFC2 to Vcc, and connecting Lfb to the base in a shunt-feed instead of series-feed arrangement. The result was that the tilt could not be balanced at all: too much class-1 feedback was always present. I'll continue to experiment in the simulator, but the tentative conclusion is again that the common-base seems like the most well-behaved arrangement. Edit: After some experimenting in the simulator I realized that when opening the loop it is important to make sure that all components that affect the active device biasing or bypassing should be kept in place when opening the loop or else the active device will not act realistically when the loop is opened. So I opened the loop at the collector output where it enters the H-V network input port, drove the H-V input port with a current source, and measured output at the collector. This ensures that the parts of the network that affect base bias and bypassing remain intact. This yielded tilt balance with reasonable values of, as I recall, Lfb=3e-4 * Lt and Vackar feedback capacitor C5=12n. I think the plausible simulator results are enough to warrant a physical prototype. qrp-gaijin Posts: 2822 Joined: Sun Feb 28, 2010 2:12 pmContact:Re: Toroids and excessive class-1 feedback Postby qrp-gaijin » Sat Jan 12, 2013 3:27 pm vladn wrote: qrp-gaijin wrote:sometimes a feedback coil inductance of 0.00001 uH is needed Are you sure the loss model is realistic ? I have not observed such extremes neither in simulation nor in real circuits. You can also increase the Vackar divider ratio, the threshold condition will be achieved at higher Lf and lower Cf values. It still seems that at higher HF, e.g. covering 10 MHz-30 MHz with a 1.5 uH coil (Rs=10, Rp=200k), it may not be possible to achieve tilt balance with a toroidal inductor since the minimum one-turn feedback coil inductance is 0.05 uH and the coupling is a fixed, high value, both of which seem to introduce too much class-1 feedback. Regarding the Vackar divider ratio being able to change the required Lf and Cf at threshold, do you have an example circuit where this works? I'm not seeing it in my simulations. vladn Posts: 853 Joined: Sun Nov 02, 2008 7:15 amLocation: NJ, USARe: Toroids and excessive class-1 feedback Postby vladn » Sat Jan 12, 2013 3:41 pm qrp-gaijin wrote:It still seems that at higher HF, e.g. covering 10 MHz-30 MHz with a 1.5 uH coil (Rs=10, Rp=200k), it may not be possible to achieve tilt balance with a toroidal inductor since the minimum one-turn feedback coil inductance is 0.05 uH and the coupling is a fixed, high value, both of which seem to introduce too much class-1 feedback. Regarding the Vackar divider ratio being able to change the required Lf and Cf at threshold, do you have an example circuit where this works? I'm not seeing it in my simulations. Make C8 (on your latest diagrams) 10x larger. Then to get the circuit back to the oscillation threshold you will have to reduce C5 and increase Lfb (simultaneously, to maintain zero tilt). In my 6as6 RX I've used 1t feedback coil (50t main coil) and then adjusted Cfb to about 24nF to get the zero tilt. I used an 8pin DIP socket (high quality - round pins) with one row grounded and the other row connected to the Lfb, then put few caps in parallel in the socket. I also have a C0G trimmer in the Vackar divider. Using both a socket and a trimmer makes tilt and threshold adjustments quite easy and solderless. qrp-gaijin Posts: 2822 Joined: Sun Feb 28, 2010 2:12 pmContact:Re: Toroids and excessive class-1 feedback Postby qrp-gaijin » Sat Jan 12, 2013 4:01 pm vladn wrote:Make C8 (on your latest diagrams) 10x larger. Then to get the circuit back to the oscillation threshold you will have to reduce C5 and increase Lfb (simultaneously, to maintain zero tilt). But C5 can only be reduced down to a certain minimum value before it starts to introduce tilt non-linearities, right? I'm still not able to achieve tilt balance in my simulated common-emitter 10-30 MHz design with Lf >= 0.05, Vackar ratio increased 10x, and decreasing C5. I'll continue to see if I can get it balanced, but there may be some circuit limits that are being run up against as we move into the upper HF region. Either that or my common-emitter open loop model is still messed up (again, I'm currently opening the loop where the collector drives the H-V network, instead driving the H-V network with a current source, and measuring collector voltage). I may also try to balance the common-base in the same frequency range. I think the common-base has no Miller capacitance so maybe it's easier to adjust and/or analyze. vladn Posts: 853 Joined: Sun Nov 02, 2008 7:15 amLocation: NJ, USA Postby vladn » Sat Jan 12, 2013 4:12 pm You need to re-estimate Rp and Rs for that frequency range. Take a Q of 200, calculate both for this Q and 20MHz, then take a half of Rs and double the Rp. It is a crude model, a much more accurate one can be derived from Q(f) plots from the Amidon site. This requires an optimization software to be written and the curves to be digitized (I have the methodology but it requires work). qrp-gaijin Posts: 2822 Joined: Sun Feb 28, 2010 2:12 pmContact: Postby qrp-gaijin » Sun Jan 13, 2013 1:20 am vladn wrote:You need to re-estimate Rp and Rs for that frequency range. Take a Q of 200, calculate both for this Q and 20MHz, then take a half of Rs and double the Rp. It is a crude model, a much more accurate one can be derived from Q(f) plots from the Amidon site. This requires an optimization software to be written and the curves to be digitized (I have the methodology but it requires work). OK. I think I am starting to see the basic problem, which you again state above but which I had forgotten: Q (and physically non-observable parameters Rs and Rp) are not constant, but instead are a non-trivial function of frequency. Nevertheless: assuming use of a toroid, even if we were to use the physically-observable Q(f) plots from the Amidon site, and used some tilt optimization method that uses Q(f), is it not still possible that, for some frequency range, it may be impossible to remove the linear term of the tilt? This would be because of the physically-dictated restrictions on the to-be-optimized parameters k, Lf, and Cf. The coupling efficient k cannot be reduced at all for a toroid, so its value cannot be optimized. Similarly, lower bounds exist on the to-be-optimized parameters Lf, which cannot be reduced to less than one turn, and Vackar feedback capacitor Cf, which practically speaking probably cannot reliably be reduced below 1 pF (and lowering Cf less than max(C_tuning) will introduce tilt non-linearities, but I suppose that doesn't matter if the non-linear optimizer is taking this effect into account). Perhaps I'm just worrying too much and misinterpreting simulator results, and in practice everything will work fine, but is it correct to say that to your knowledge, no one has yet built a hybrid feedback regen for upper HF? vladn Posts: 853 Joined: Sun Nov 02, 2008 7:15 amLocation: NJ, USA Postby vladn » Sun Jan 13, 2013 4:33 am qrp-gaijin wrote:Perhaps I'm just worrying too much and misinterpreting simulator results, and in practice everything will work fine, but is it correct to say that to your knowledge, no one has yet built a hybrid feedback regen for upper HF? As far as I can tell the method is crude (hard to predict exact Lfb,Cfb without measuring Q(f)) but robust (stable to parameter variations, I was so far always able to converge to zero tilt by adjusting Lfb,Cfb and the divider ratio in hardware). It worked for MW and mid-HF. I do not see a reason for it not to work at the upper HF but I have not tested it. You should try to choose the core material / size / wire diameter / #turns such that the Q peak is inside the frequency range of interest (for many reasons, not just tilt compensation). I do however recommend getting a feel for the simultaneous variation of the divider ratio and the Lfb,Cfb pair such that BOTH the tilt and the network gain are nearly constant in the simulator before proceeding to the hardware. qrp-gaijin Posts: 2822 Joined: Sun Feb 28, 2010 2:12 pmContact: Postby qrp-gaijin » Sun Jan 13, 2013 8:17 am I had some time to work on the hardware prototype today. The BJT common-base Hartley-Vackar showed slight class 1 tilt even with no Hartley feedback inductance (cold end of inductor directly grounded). However it was very nearly tilt-balanced with 1.6nF as the Vackar feedback capacitor. Vackar divider was 4pF/47pF. Regeneration control was abrupt (snapping into oscillation). I then reworked the circuit to be the common-emitter variant. This refuses to oscillate at all. Vackar divider is 4pF/4pF. Vackar feedback cap is 1.6nF. Hartley feedback coil is two turns. The QUCS circuit simulator says it should oscillate, but it doesn't. One lingering possibility is that the fixed caps I am using may not be NP0 (though they are marked with a black dot). This would introduce unknown losses. Next time I buy parts I'll pick up some known-good NP0 or silver mica caps and will try again. Edit: Common-emitter is now oscillating. Problem was a poorly placed emitter bypass cap (it should be mounted directly on the emitter regen control pot). This was discovered by poking around the circuit randomly, always a good thing to do when an oscillator won't start. I happened to touch the wire leading from the emitter to the regen control pot, and suddenly it oscillated. By touching it I was grounding it; otherwise, it was probably picking up stray RF from the tuning capacitor nearby. Regeneration control is smooth. Hand capacitance seems about the same as with the common-base, meaning that the hand capacitance problems with the common-base were due mainly to shielding and physical chassis instability, not to the floating variable cap. Physical placement of the two RFCs in common-emitter seems noncritical (I was worried that two RFCs in close proximity might cause unwanted feedback and instability). As for tilt, there seems to be some tilt nonlinearity; mid-band requires less feedback than low/high band (currently tuning 3.5-10 MHz). I'll continue to try to tweak the tilt in this topology. qrp-gaijin Posts: 2822 Joined: Sun Feb 28, 2010 2:12 pmContact:Some tilt data Postby qrp-gaijin » Sun Jan 13, 2013 10:06 am Here's some measured tilt data from my common-emitter Hartley-Vackar prototype. Vackar divider is 4pF/4pF. Vackar feedback cap is 1640pF. Hartley feedback coil is 2 turns. Main inductor is an additional 59 turns (T50-6 yellow core). Tuning capacitor is 150 pF max. I measured the amount of emitter resistance required for a barely-detectable onset of oscillation on my nearby station receiver with an antenna of about 10 cm wire. 3500 kHz 42.0k 4500 kHz 44.6k 5500 kHz 44.5k 6500 kHz 44.7k 7495 kHz 42.4k 8510 kHz 35.5k 9495 kHz 37.4k 10500 kHz 33.6k There is some non-linearity evident; required feedback dips mid-band and rises at the band edges. A simple analysis, attempting to cancel only the linear tilt, would call for more Hartley/less Vackar feedback. Next I'll try to increase the Vackar feedback capacitance. I hope I'm not boring you all with this project. The tilt optimization certainly presents an interesting challenge to get the most out of a simple (and in my case, low-voltage) regen circuit. vladn Posts: 853 Joined: Sun Nov 02, 2008 7:15 amLocation: NJ, USA Postby vladn » Mon Jan 14, 2013 6:28 am Antenna coupling changes the frequency dependence, sometimes drastically. You may want to add an RF buffer to get a better feel for the threshold dependence. The numbers look reasonable (you should be able to reduce the remaining tilt). Yes the higher order terms are there but I think you should also get the measurement for the Vackar-only and Hartley-only configurations in the hardware and compare. qrp-gaijin Posts: 2822 Joined: Sun Feb 28, 2010 2:12 pmContact: Postby qrp-gaijin » Mon Jan 14, 2013 6:57 am vladn wrote:Antenna coupling changes the tilt. You may want to add RF buffer to get a better feel for the threshold dependence. Sorry I didn't make that clearer - the regen has no antenna connected to it yet. The 10cm antenna was connected to the monitoring receiver (FT-817ND) to pick up the onset of oscillation from the nearby regen. I have no spectrum analyzer or scope, so such crude measurement methods must suffice. Yes, I will add an RF amp. The circuit will be be the same as the RF amp in this circuit: http://www.electronics-tutorials.com/re ... ceiver.htm , with the emitter resistor adjusted for 2.5 mA of current when running off of 1.4V. Either I will use inductive coupling of the amp signal into the tank inductor, or I will just connect the amp collector to the oscillator collector below the choke (similar to your earlier proposed idea of connecting a grounded-gate amp directly to the drain RFC). vladn wrote:The numbers look reasonable (you should be able to reduce the remaining tilt). Yes the higher order terms are there but I think you should also get the measurement for the Vackar-only and Hartley-only configurations in the hardware and compare. I plan to do that. One thing that still puzzles me though is the behavior of the earlier common-base circuit I tried. Even with no Hartley feedback coil, there was some slight class-1 feedback, even with a small Vackar feedback cap (820 pF with a tuning cap of 150 pF). I can only assume that stray couplings caused by my messy wiring, and/or parasitic capacitances within the BJT, were causing the class-1 feedback even with Lfb=0. You mentioned earlier that "follower" topologies can introduce non-linear tilt when driving capacitive loads. I don't consider a common-base topology a "follower" but perhaps something similar with happening with the common-base to introduce parasitic class-1 feedback that could not be balanced. qrp-gaijin Posts: 2822 Joined: Sun Feb 28, 2010 2:12 pmContact:Biasing common-emitter BJT Postby qrp-gaijin » Mon Jan 14, 2013 10:33 am Got a question about regen biasing. My current common-emitter BJT prototype is built as follows. This was based on the following RA3AAE circuit: That RA3AAE circuit was discussed here as being detuning-resistant: viewtopic.php?p=28151#28151 vladn wrote:The detector operates with Vcb=0 for DC which minimizes detuning. You can see that in my variant, with the Vackar capacitive divider and hybrid feedback, I need to add two RFCs. This seems somewhat odd to me, although it does preserve Vcb=0, it does oscillate, and it does seem resistant to detuning as regeneration is adjusted around threshold. I was considering a way to remove RFC2. For instance, we could use feedback bias as follows: In the simulator, this does oscillate. However, Vcb is no longer 0 for DC, which was the original design feature. What would be the side effects if I were to go with the feedback bias variant? I suppose detuning with regeneration adjustment would increase. Anything else? qrp-gaijin wrote:One thing that still puzzles me though is the behavior of the earlier common-base circuit I tried. Even with no Hartley feedback coil, there was some slight class-1 feedback, even with a small Vackar feedback cap (820 pF with a tuning cap of 150 pF). A common base arrangement has a very low active input impedance at the emitter side and requires more energy recirculation (hence tighter amplifier coupling) which is why I did not study it. I don't know the answer to your question off the top of my head. I may need to run the simulator and see what happens there. On your common emitter circuit. Something I do not quite like is the inclusion of the RFC into the tank circuit with significant coupling (1:1 divider ratio or 1:4 impedance conversion). Standard RFCs usually have neither good temperature stability, nor high Q. I would either increase the divider ratio or do the opposite - connect the collector to the main coil without the divider and pull the coil middle tap to Vcc via a single RFC (the middle tap has the lowest impedance for RF). The latter will increase the effects of the collector loading but the RFC effects will be virtually eliminated. qrp-gaijin Posts: 2822 Joined: Sun Feb 28, 2010 2:12 pmContact: Postby qrp-gaijin » Mon Jan 14, 2013 10:19 pm vladn wrote:I would either increase the divider ratio or do the opposite - connect the collector to the main coil without the divider A rather annoying tradeoff: remove RFC effects but suffer increased collector loading, or decrease collector loading but suffer RFC effects. It seems that connecting the collector to an additional lower tap on the coil would be the high-Q way to solve the problem: collector loading reduced due to the low tap (replacing the capacitive Vackar divider), and no collector RFC effects (collector, and base, go to Vcc through the RFC at the Hartley tap). vladn Posts: 853 Joined: Sun Nov 02, 2008 7:15 amLocation: NJ, USA Postby vladn » Tue Jan 15, 2013 12:47 am qrp-gaijin wrote:A rather annoying tradeoff: remove RFC effects but suffer increased collector loading, or decrease collector loading but suffer RFC effects. Intuitively I think RFC is worse, but I am not sure. qrp-gaijin wrote:It seems that connecting the collector to an additional lower tap on the coil would be the high-Q way to solve the problem: collector loading reduced due to the low tap (replacing the capacitive Vackar divider), and no collector RFC effects (collector, and base, go to Vcc through the RFC at the Hartley tap). Yes, it may be a good solution, but I need to check the simulation - the inductive divider is not grounded. (edit)No go unfortunately, the divider must be between the tuning cap and the ground. It kind of works for mid-tap 1:1 ratio (with higher non-linear terms) but not for high division ratios.(/edit) qrp-gaijin Posts: 2822 Joined: Sun Feb 28, 2010 2:12 pmContact: Postby qrp-gaijin » Tue Jan 15, 2013 4:06 am vladn wrote: qrp-gaijin wrote:connecting the collector to an additional lower tap on the coil No go unfortunately How about a low-turn-count separate coupling coil from the collector to Vcc (replacing the collector RFC), magnetically coupled to the tank? Turns count would be reduced to just sustain oscillation. One complicating factor would be that the new collector coil would be magnetically coupled to both the tank coil and the base's Hartley feedback coil. No idea what that would do to the tilt. Edit: I tried 2 simulations, one with no divider (collector goes directly to top of tank; Hartley tap goes through RFC to Vcc) and one with a new low-inductance link coupling for the collector. Both had the same problem: too much class-1 feedback unless the feedback and/or collector link inductance were reduced to the order of 1e-5 * Ltank (Vackar cap=1.6nF). Tuning range was 3.5-10 MHz, Ltank=15 uH. I'm going to focus on why the no-divider (collector directly to tank) method seems to have an excess of class-1 feedback (more so than with the 4pF/4pF Vackar divider), and if there's any way to increase Lfb to more reasonable values. Maybe extra Rs and/or Rp tank loading is one way (but I cringe at the thought of intentional tank damping). Another alternative might be to forget inductive class-1 feedback and instead try a Colpitts-Vackar. vladn Posts: 853 Joined: Sun Nov 02, 2008 7:15 amLocation: NJ, USA Postby vladn » Wed Jan 16, 2013 4:51 pm qrp-gaijin wrote:Edit: I tried 2 simulations, one with no divider (collector goes directly to top of tank; Hartley tap goes through RFC to Vcc) and one with a new low-inductance link coupling for the collector. Both had the same problem: too much class-1 feedback unless the feedback and/or collector link inductance were reduced to the order of 1e-5 * Ltank (Vackar cap=1.6nF). Tuning range was 3.5-10 MHz, Ltank=15 uH. I'm going to focus on why the no-divider (collector directly to tank) method seems to have an excess of class-1 feedback (more so than with the 4pF/4pF Vackar divider), and if there's any way to increase Lfb to more reasonable values. Maybe extra Rs and/or Rp tank loading is one way (but I cringe at the thought of intentional tank damping). Another alternative might be to forget inductive class-1 feedback and instead try a Colpitts-Vackar. Is that the exact same circuit that you posted last time ? (BTW is there a way to refer to a specific post number on this board ?) I'd like to see/check the results but I need to know precisely what you are doing and observing. If you can post (or PM) a link to your latest simulation this would help avoid bloating the thread with minute details. qrp-gaijin Posts: 2822 Joined: Sun Feb 28, 2010 2:12 pmContact: Postby qrp-gaijin » Thu Jan 17, 2013 12:12 am vladn wrote: qrp-gaijin wrote:Edit: I tried 2 simulations, one with no divider (collector goes directly to top of tank; Hartley tap goes through RFC to Vcc) and one with a new low-inductance link coupling for the collector. Both had the same problem: too much class-1 feedback unless the feedback and/or collector link inductance were reduced to the order of 1e-5 * Ltank (Vackar cap=1.6nF). I'd like to see/check the results but I need to know precisely what you are doing and observing. Let's start simply. To begin with, here is the circuit where I removed the input (Robert/Vackar) divider. Normally, the collector would go directly to the top of the tank inductor. For open loop analysis I break the loop at the H-V network input, drive the network with a current source, connect the collector to Vcc through a 1-ohm load resistor, and measure voltage at the collector. Parameters: Lt=15uH, Rs=10, Rp=200k, Ct=1*/(((6.28*f)^2)*(Lt)), f swept from 3 to 10 MHz. Q1 is a 2N3904. For Lfb=1e-4 * Lt: For Lfb=1e-5 * Lt: For Lfb=1e-6 * Lt: The only way to balance the tilt is with a tiny feedback inductance of Lfb = 1e-5 * Lt. If Lfb is larger (e.g. 1e-4*Lt), reducing Vackar cap C5 cannot compensate. I'm getting some other unexpected behavior with variants of this circuit (e..g. class 1 feedback even with the feedback coil removed), but let's address that later. First: is such a small Lfb expected? If not, what is causing the excess class-1 feedback? Parasitics? After we get this sorted out, next we might examine the circuit variant with the extra link winding on the collector for impedance transformation. vladn Posts: 853 Joined: Sun Nov 02, 2008 7:15 amLocation: NJ, USA Postby vladn » Thu Jan 17, 2013 2:20 am This is your problem: vladn wrote:You need to re-estimate Rp and Rs for that frequency range. Take a Q of 200, calculate both for this Q and 20MHz, then take a half of Rs and double the Rp. It is a crude model, a much more accurate one can be derived from Q(f) plots from the Amidon site. This requires an optimization software to be written and the curves to be digitized (I have the methodology but it requires work). Let's say the middle of your frequency range is approx 6MHz, then assuming Q=200 Rs(equiv)=2*pi*f*L/Q=2.8ohm Rp(equiv)=2*pi*f*L*Q=113k Splitting the losses in half we take the half for Rs (1.4ohm) and double the Rp (220k). You have used much higher value of Rs hence the difference in the simulation results. With Rs=1.4ohm I got flat response with Lf=0.5e-3*Lt which is doable. Again I want to emphasize that the model is crude because we do not know the exact Q(f) and use arbitrary Rp+Rs mix instead. A real circuit (albeit tube) covering this frequency range and using a toroidal type 7 iron core required much higher ratio of class 1 to class 2 feedback compared to the simulation, so you should be OK. qrp-gaijin Posts: 2822 Joined: Sun Feb 28, 2010 2:12 pmContact: Postby qrp-gaijin » Thu Jan 17, 2013 4:27 am vladn wrote:This is your problem: vladn wrote:You need to re-estimate Rp and Rs With Rs=1.4ohm I got flat response with Lf=0.5e-3*Lt which is doable. Right. I had carelessly assumed the values I was using for Rs and Rp were OK for low-HF, but I see now the values are quite critical (though physically unobservable). This is what I get with Lf=5e-4*Lt, Rs=1.4, Rp=220k. Is it close to your result? There seems to be more non-linearity than with my previous results. I suppose the previous greater Rs and greater damping smoothed out the non-linearities. Hopefully later today I will get a chance to re-simulate the collector link coupling with the more realistic loss values. As I recall, other than the low Lf needed, the collector link method seemed to return reasonable tilt behavior, so it might be a way to implement an inductive divider without using the lossy RFC at the hot end of the tank. vladn Posts: 853 Joined: Sun Nov 02, 2008 7:15 amLocation: NJ, USA Postby vladn » Thu Jan 17, 2013 5:00 am I think you have an aliasing problem. Can you add more points to the sweep command (not tuning steps but finer resolution in the sweep itself)? And use the log scale on the vertical axis if possible. qrp-gaijin Posts: 2822 Joined: Sun Feb 28, 2010 2:12 pmContact: Postby qrp-gaijin » Thu Jan 17, 2013 10:38 am vladn wrote:I think you have an aliasing problem. Good call. That fixes it, and is something I should have been and from now on will be more careful about when dealing with simulation results. Next: reducing the collector tank loading. We said before that a capacitive divider isn't ideal (as it requires a lossy RFC at the tank's high-Z point), and an additional inductive tap divider on the main coil won't work (since the resulting inductive divider is ungrounded). So, the next question is, will an additional RF-grounded link coil at the collector work? As far as I can tell, the answer is yes. The circuit (loop has been broken between collector and link coil): Lt=15uH, Rs=1.4, Rp=220k, Lfb=1e-3*Lt, Lin=1e-3*Lt (Lin=new input link into H-V network). The tilt: Any problems with this approach? And while we're on this circuit... is it possible to add a "bandwidth-compensated" bandspread control here as discussed in the other thread? Edit: looking at the circuit again... has this now become a Reinartz oscillator? vladn Posts: 853 Joined: Sun Nov 02, 2008 7:15 amLocation: NJ, USA Postby vladn » Fri Jan 18, 2013 1:33 am qrp-gaijin wrote:Any problems with this approach? I think it is OK conceptually. Requires even more complex inductor though... qrp-gaijin wrote:And while we're on this circuit... is it possible to add a "bandwidth-compensated" bandspread control here as discussed in the other thread? Yes, just add a large variable cap in parallel to the Q1 base for fine tuning. In general it should "sit" on the feedback node of the H-V network, opposite to the tuning cap. qrp-gaijin wrote:Edit: looking at the circuit again... has this now become a Reinartz oscillator? I am getting lost myself with naming conventions. Is Reinartz = Meissner ? qrp-gaijin Posts: 2822 Joined: Sun Feb 28, 2010 2:12 pmContact: Postby qrp-gaijin » Fri Jan 18, 2013 2:43 am vladn wrote: qrp-gaijin wrote:Any problems with this approach? I think it is OK conceptually. Requires even more complex inductor though... Well, it seems to be the only remaining way to reduce collector loading. If it improves oscillator stability and noise, I think an extra link coil isn't too much added complexity. And the link can be relatively easily adjusted just like a Roberts/Vackar divider - remove turns until oscillation is just barely maintained. vladn wrote: qrp-gaijin wrote:"bandwidth-compensated" bandspread Yes, just add a large variable cap in parallel to the Q1 base for fine tuning. This would be a variable cap from the base to ground? vladn wrote:Is Reinartz = Meissner ? That's something I've been wondering about for a while as well. In the context of a BJT, I'm referring to the non-inverting common-base oscillator with inductive coupling links from both emitter and collector into the tank. I've seen this arrangement referred to as both a Reinartz and a Meissner. In the latest proposed circuit, we have a tank that is coupled to the base and collector (not emitter and collector as in the normal Reinartz) and is thus an inverting configuration. In addition we've raised the cold end of the tank (and the feedback coil) above ground with the Vackar cap and have fed additional inverted feedback energy into that junction. So it seems it could be argued that this is an inverting Reinartz/Meissner configuration to which Vackar feedback has also been added. qrp-gaijin Posts: 2822 Joined: Sun Feb 28, 2010 2:12 pmContact: Postby qrp-gaijin » Sat Jan 19, 2013 5:28 pm I can confirm that the latest circuit I posted (with the collector link coupling) works in hardware. A single link turn could sustain oscillation but required very high regeneration levels (i.e. very low emitter resistance). I increased it to three turns (being careful to keep the winding sense the same as the main tank coil for proper phasing) and with a Vackar cap of 1640 pF it is very close to tilt-balannced. It seemed that the number of collector link turns affected the tilt. The almost-balanced configuration with three link turns was not balanced with one link turn. It seemed that there was excessive class-1 feedback with only one link turn. However, I'm not seeing that effect in the simulator. Maybe the extremely low emitter resistance required when using only one link turn is disturbing the tilt. Also, when using only one link turn, frequency varied quite a bit with regeneration adjustment near threshold. With three link turns, frequency shift is reduced. The collector link winding does seem, as expected, to help stability compared with connecting the collector directly to the tank top. Monitoring the regen's oscillation on a nearby receiver, there was noticeable warble if the link winding was not used. With the link winding, the impedance transformation should be about 1:413. Next I will work on the RF amp and some way of extracting audio from the regenerative stage. vladn Posts: 853 Joined: Sun Nov 02, 2008 7:15 amLocation: NJ, USA Postby vladn » Sun Jan 20, 2013 9:06 pm It looks like it is possible to use the "feedback" tap of an H-V network as a bidirectional node in a "two-point" type oscillators like negative resistance oscillators or two transistor non-inverting feedback style oscillators. The optimum values for C_fb and L_fb are different in this arrangement. One interesting property of such an arrangement is that the next (non-linear) term has the opposite sign - the frequency response curve has a sight dip in the middle of the frequency range (as opposed to a slight increase). There could be a way (at least in theory) to use this somehow to compensate the next term (but it is not an easy problem to solve). qrp-gaijin Posts: 2822 Joined: Sun Feb 28, 2010 2:12 pmContact: Postby qrp-gaijin » Mon Jan 21, 2013 4:10 am vladn wrote:One interesting property of such an arrangement is that the next (non-linear) term has the opposite sign - the frequency response curve has a sight dip in the middle of the frequency range (as opposed to a slight increase). There could be a way (at least in theory) to use this somehow to compensate the next term (but it is not an easy problem to solve). When you say "use this ... to compensate the next term" do you mean "having observed both dip and hump shapes for the second order term, design a way to control the dip/hump parameter and achieve zero for both first and second derivatives"? In one of the many BJT variants I simulated, I believe I was able to control the dip/hump (second order term sign) by altering the emitter bypass capacitance. (Not sure about if this was the parameter I altered, but I do remember that altering some parameter allowed me to change the dip into a hump.) I'll have to check and re-simulate that to make sure it wasn't an aliasing artifact. In general, I was getting very odd behavior with low values (0 pF-20 pF) of emitter bypass capacitance and no Hartley feedback inductance. Maybe parasitic Colpitts-style feedback was taking place (I was specifically trying to investigate combining inverting Vackar feedback with non-inverting Colpitts feedback). After many tries over the 3 years since this thread started, I have finally achieved an important goal: I have successfully built a hybrid-feedback, tilt-balanced, low-voltage, varactor-tuned, BJT regenerative receiver with a practically fixed regeneration level. For the background on tilt-balanced regens with fixed (equalised) regeneration level, see these links: http://www.kearman.com/vladn/hybrid_feedback.pdf http://www.kearman.com/vladn/hybrid_theory.pdf viewtopic.php?f=3&t=3714 Back to my varactor-tuned hybrid-feedback circuit - here it is: circuit-2.png (76.6 KiB) Viewed 1331 times Q1 is an RF amp to allow coupling in the RF signal while presenting the detector with a constant load; Q2 is the regenerative detector. The key to success was the use of a high-Q 1SV74 varactor. In a previous attempt at a varactor-tuned, hybrid-feedback regenerative receiver I had used a low-Q 1SV149 varactor, designed for AM BCB use and having a Q of 200 at 1 MHz, which approximately equals a Q of 20 at 10 MHz. On the other hand, the new 1SV74 varactor I am using has a Q of 50 at 50 MHz, which approximately equals a Q of 250 at 10 MHz. The disadvantage of the higher-Q varactor is a more limited capacitance swing, and hence a more limited tuning range. On the other hand, one advantage is that a limited tuning range is easier to tilt-balance than a wide tuning range. Datasheet for low-Q 1SV149 varactor: http://www.qsl.net/df7tv/datasheets/1SV149.pdf Datasheet for high-Q 1SV74 varactor: http://www.rf-microwave.com/datasheets/ ... V74_01.pdf The important thing is that the varactor Q must be higher than the coil Q, or at the very least, the varactor's equivalent series resistance should be almost constant over the entire tuning range. If these conditions are met, then the predominant losses in the tank are the Rs (serial losses) and Rp (parallel losses) of the coil, and as described in vladn's paper, the hybrid-feedback approach can passively equalise the threshold regeneration level for any arbitrary mix of Rs and Rp. The worst thing is a low-Q varactor with ESR that varies greatly as the varactor is tuned - and unfortunately the 1SV149 varactor is just such a varactor when used at HF. The circuit currently tunes from 7 MHz to 10 MHz. Here are some notes on the construction: 1. Determining the threshold regeneration level: It's easiest to connect the regen to an AF amplifier and to listen for the threshold noise as you adjust the regeneration control. Once you have found the threshold level, you can then tune the regen higher or lower in frequency and observe if you need more or less regeneration to reach threshold. One problem with this approach is if you have too much or too little feedback in the circuit (i.e. the regen is never able to oscillate, or the regen is always oscillating), then even adjusting the regeneration control you will never cross the oscillation threshold and thus you will hear nothing from the AF amplifier. 2. Determining the proper amount of feedback: I am repeating a principle stated by vladn earlier in this thread, but the principle bears repeating: Increasing L2 increases the total feedback and alters the tilt towards class-1 behavior. Decreasing C12 increases the total feedback and alters the tilt towards class-2 behavior. To increase the total amount of feedback without altering the tilt, you must increase L2 and decrease C12 simultaneously. Conversely, to decrease the total amount of feedback without altering the tilt, you must decrease L2 and increase C12 simultaneously. 3. Construction order 3a. The first thing I did was to build the circuit with L2 being a short circuit and C12 (the Vackar feedback capacitor) set to 1000 pF. Then, I could verify that the oscillation was controllable below, through, and above threshold. Furthermore, regeneration behaved as a class-2 oscillator, i.e. required regeneration to reach threshold increased monotonically with increasing frequency. 3b. Then, I set C12 to 100 nF (essentially an AC short circuit with 0 ohms reactance) and increased L2 to become 5 turns on the cold end of L1. Again, I could verify that oscillation was controllable below, through, and above threshold. Furthermore, regeneration behaved as a class-1 oscillator, i.e. required regeneration to reach threshold decreased monotonically with increasing frequency. Having verified both pure class-2 and pure class-1 behavior, I then knew I would be able to balance the two feedback paths. (Previously when using the lossier 1SV149 varactor I could only verify partial class-1 and partial class-2 behaviors.) 3c. I reduced C12 back to 1000 pF to re-introduce Vackar feedback into the circuit. This gave too much feedback. I could hear no output from the AF amplifier (no threshold noise) as I adjusted the regeneration control over its entire 100k range, and based on the principle in #2 I knew that the total circuit feedback was too much and that the circuit was always oscillating. I also verified on a spotter receiver that the regen was always oscillating no matter how I adjusted the regeneration control. 3d. I reduced L2 to 3 turns and increased C12 to 2000 pF. I could verify slight class-2 behavior (required regeneration at the low end of the tuning range was slightly lower than at the high end of the tuning range), indicating a slight excess of Vackar-style feedback. 3e. I incrementally added capacitors in parallel to C12, finally arriving at 2320 pF for almost perfectly level tilt. 3f. vladn's advice from the original tube thread is also useful when adjusting the feedback: viewtopic.php?f=3&t=3714 vladn wrote: General guidelines for feedback branch balancing: C2 should be several times bigger than maximum value of Ct. L2 should have slightly fewer turns than in conventional Armstrong regen (perhaps 80% or so). Once you get the amount of total feedback right (operating in the middle of regen pot adjustment) - tweak C2 to minimize tilt. Decrease it if the regen level pot needs to be advanced more at the bottom frequency vs top frequency of the tuning range. Increase C2 if the opposite is true. 4. There seems to be a tiny tendency for oscillation in the middle of the tuning range indicating a non-linear excess of feedback. There also seems to be a tiny bit of excess Vackar feedback. I might try adding another 100 pF in parallel with C12 to see if it helps. 5. Connecting an active antenna to the RF amp Q1, I could verify that I could set the detector below threshold and tune over the entire tuning range without the set breaking into oscillation, and I could hear several SWBC stations in this state. However, I could not hear the band noise. This indicates the detector is somewhat insensitive, which might be fixed by a separate detector stage. 6. Again using the active antenna and setting the set slightly into oscillation, I could verify that I could tune over the entire tuning range with good sensitivity and with easy phase-locking onto AM SWBC carriers for synchronous reception, thanks to the weak oscillation level maintained over the entire range by the tilt-balanced, equalised regeneration level. 6a. Adding a separate, explicit, aactive limiter stage (as in Kovalenko's automatic regeneration scheme) would help maintain the oscillation level at an even lower amplitude for better synchrnous reception. LTspice simulations indicate Kovalenko's scheme should work even when running off of 1.2 volts, as my receiver is. The combination of explicit gain limiting and passive tilt-leveling (with hybrid feedback) would then start to echo vladn's 6as6 regen design. 7. One thing I was worried about was that the heavy coupling of the collector into the tank might upset the equalised regeneration level, as it allows the BJT parasitic capacitances to influence the tank. However, this seems not to be significant enough to worry about. A smaller link coupling, magnetically coupling the collector to the main tank coil, could be used to reduce tank loading by the collector. 8. Currently the set tunes 7-10 MHz. At higher frequencies (approaching 30 MHz) parasitic BJT capacitances of #7 may upset the equalised regeneration level. Also, the 1SV74 varactor Q will be lower at higher frequencies (e.g. the 1SV74 varactor Q will be only approximately 83 at 30 MHz). In a future experiment, I may try some different VHF varactors (FV1043) with even higher Q that should have Q>300 over the entire HF spectrum (specified Q=100 at 100 MHz, i.e. Q=333 at 30 MHz, Q=3333 at 3 MHz). Datasheet for FV1043 varactors: http://aitendo3.sakura.ne.jp/aitendo_da ... FV1043.pdf 9. All potentiometers are high-quality 10-turn potentiometers. 10. C12 must consist of high-quality, RF-grade capacitor(s) such as NP0 or C0G types. 11. I'm not convinced the RF amp coupling to the detector is optimal. Setting the RF attenuator to maximum oddly seems to desensitize the receiver instead of increasing sensitivity (when using the active loop antenna). This may have to do with the fact that Q1 (RF amp) is directly coupled to the RFC of Q2 (the regenerative detector). It's probably better to have the Q1 load be another secondary winding on L1. 12. I'm allowing the varactor reverse bias to fall to 0 volts, which is generally not recommended. Varactor Q is lowest in this condition, so it's possible that limiting the minimum bias to 1 volt may reduce the variability in varactor ESR and hence improve the equalisation of the regeneration level. 13. I would guess the circuit should be reproducible, with the same circuit constants, using a variable capacitor instead of a varactor. Here's what the chaotic breadboard looks like. board.jpg (179.46 KiB) Viewed 1340 times The coil is would as shown below. The top 3 turns on the coil are L2; the rest of the turns are L1. coil.jpg (151.54 KiB) Viewed 1340 times If there is any interest I could post a video, but the current construction is not physically stable so the reception frequency is subject to warbling and microphonic effects. Big thanks again to vladn for your advice throughout this thread. From the start, I was determined to use varactor tuning and to limit myself to a 1.2-volt power supply. Finally, I have achieved this goal to my satisfaction. I plan to rebuild this receiver into a more stable and usable form. Probably for the next iteration I will focus on bandswitched coils, which will require tilt balancing for each separate coil. For future iterations I might try to mimic vladn's superlative 6as6 design and add a dynamic limiter, scale-invariant gain compression, bandwidth control, RF AGC, etc. - all running of course off of 1.2 volts. I came up with a new way of applying hybrid feedback (Colpitts-Vackar) to my simple BJT regen, and applied the hybrid feedback to a circuit with a ferrite rod and a wide-tuning 1SV149 varactor. First, I present an unsuccessful circuit: fer-armstrong-vackar.png (83.01 KiB) Viewed 1044 times This is the same circuit as the tilt-balanced Armstrong-Vackar I mentioned in my previous post. However, in the new circuit of this post I am using a shortwave ferrite rod antenna for the tank inductor instead of a T50-6 iron core. The idea was to eliminate the need for an external antenna. You can see the ferrite rod in a previous receiver here: viewtopic.php?p=50381#p50381. In this experiment I also returned to using AM BCB 1SV149 varactor, which is noticeably lossy at shortwave frequencies. The frequency-dependent losses in the varactor combined with the frequency-dependent losses in the ferrite rod antenna make for a receiver that is likely difficult to reproduce. Nevertheless, I wanted to try the combination of the 1SV149 varactor (which has a wide tuning range) plus the ferrite rod antenna, and see to what extent it was possible to use hybrid feedback to level out the regeneration level. In the above circuit I used the same approach as before of using Vackar-style feedback (via feedback capacitor C12, holding the base above RF ground) plus Armstrong-style feedback (via the L2 tickler). The good news was that with L2 being a short-circuit (no Armstrong feedback), I could verify Vackar-style tilt (required regeneration increases with frequency) over most of the tuning range. That indicates that the frequency-dependent varactor losses and the ferrite rod losses are somehow balancing each other, such that the inherent Vackar-style tilt can emerge without being distorted by the varactor and ferrite rod losses. The bad news was that adding the L2 tickler into the circuit always overwhelmed the circuit with too much Armstrong-style feedback, resulting in Armstrong-style tilt (required regeneration decreases with frequency). Even with L2 reduced to a single turn very loosely coupled to the cold end of the ferrite rod, that single loosely-coupled turn was enough to cause the tilt to shift from Vackar-style to Armstrong-style. One approach to fix this would be to increase the Vackar-style feedback by decreasing C12. Unfortunately that isn't really possible because C12 should not be reduced too small, as it should always be much lower impedance than the tuning capacitance (provided by D1, which is a maximum of about 500 pF). The other approach to fix this is to reduce the Armstrong-style feedback. Unfortunately it's not possible to reduce the feedback below a single loosely-coupled turn. So instead, I opted for Colpitts-style feedback (which has the same tilt behavior as Armstrong-style feedback) as shown below. fer-colpitts-vackar.png (81.58 KiB) Viewed 1044 times Here, I removed the tickler L2 and added a new Colpitts-style feedback path through C1, with a tiny value of 4 pF, just to add a tiny bit of Colpitts feedback from the collector back into the emitter. Note that if C1 is not present (i.e. C1 reactance is infinity), the circuit is just a Vackar-style regen. On the other hand if C1 is present (i.e. reactance less than infinite) and the Vackar capacitor C12 has near-zero reactance (e.g. a high value like 100 nF), then the circuit becomes a common-base Colpitts regen, with the Colpitts divider formed by C1/C11, the tuning capacitance D1 being in parallel with both capacitors of the divider, and the cold end of L1 being grounded through the near-zero-reactance C12. With both feedback paths C1 and C12 in the circuit, the circuit becomes a hybrid feedback regen using both an inverting feedback path (collector-base) for the Vackar feedback, and a non-inverting feedback path (collector-emitter) for the Colpitts feedback. After some theoretical investigation I had recently discovered this topology, but this is the first time I tried it in hardware. The results are good and this method does work to balance the tilt. The required regeneration adjustment tuning over the entire tuning range (~4-12 MHz) is very small. There is a slight excess of Colpitts feedback, so C1 should be reduced (reducing Colpitts feedback) or C12 should be reduced (increasing Vackar feedback). There is also some noticeable nonlinear behavior in the tilt (especially when the varactor reverse bias approaches zero volts at the extreme low end of the band) indicating that a perfectly flat regeneration level across the entire tuning range is likely not possible when using the lossy varactor and the lossy ferrite rod. Even if not perfectly flat, the mostly-flattened regeneration level does make for a much smoother operating experience with reduced need for regeneration adjustment, plus the advantage that the ferrite rod removes the need for an external antenna. This combination of ferrite rod antenna plus reduced regeneration adustment will likely make a handy portable receiver. I aim to rebuild my prototype into a usable receiver soon.

This is a recovered file. The images in this post may be out of order, and there may be duplicates. Post by vladn » Thu Dec 22, 2011 Most wideband regen RXs require substantial adjustment of regen level as you tune across the band. For example most common BCB regens using Armstrong/Hartley/Colpitts topology usually require advancing feedback at the low side of the band. This is the result of frequency dependence of both tank Q-factor and feedback path gain. But there is a solution that allows compensating at least the linear term (tilt) of the regen feedback adjustment dependence on frequency. There are at least 3 class of oscillator feedback network types (I wrote about it earlier) that have substantially different frequency dependence of the feedback gain: class 1: Armstrong, Colpitts, Hartley class 2: Vackar (basic form, fig5 in original Vackar paper [1]) class 3: Clapp/Gouriett Within each class the feedback dependence on frequency is essentially the same (but there could be substantial implementation-specific variations due to tank loading by both active device and antenna). In simulations that I've done a properly equalized loading and tank loss model results in exactly the same feedback frequency dependence within each class. I've tried building a regen based on a different class feedback network (Vackar) and found that it has a frequency feedback dependence tilted in the opposite way for a typical regen: you have to advance regen level as you go higher in frequency. According to my simulations it is tilted even more heavily in the class 3 feedback networks (not tried to build one). However it is possible to constructively combine two feedback types from two oscillator classes in a single detector to eliminate the tilt. I tried it in both simulation and a prototype. By properly adjusting/balancing branch gain I managed to get zero tilt - the lowest and highest frequency points of BCB tuning range required exactly the same regen potentiometer position. The second order term (quadratic) is still uncompensated (you need to reduce regen level somewhat in the middle of the band) but the amount of remaining adjustment is much lower than in conventional class 1 oscillator regen. The receiver that I used for testing combines Armstrong and Vackar feedback types. It is based on a battery-powered dual 1T4 tube regen that I've built with kids some time ago. The board was easy enough to modify so I used it as a testbead. Combination feedback Armstrong/Vackar is particularly easy to do - any standard Armstrong regen can be modified to operate with combined feedback. Below is the circuit diagram of the detector stage. The circuit is a bit unconventional in that it uses screed greed as virtual anode for RF feedback (mostly for legacy reasons as the donor RX was done this way). Here you can see a combination feedback from the screen grid (virtual plate) via L2/L1 coupling (Armstrong) and a current feedback to C2 (Vackar pi-network C2/L1/Ct). Few important notes: 1. Gridleak resistor R1 is connected to ground as the tank has non-zero DC potential. 2. Gridleak capacitor C3 must be rated for B+. 3. R3 is added to damp RFC/C2 resonance 4. I connected antenna to point A via 1nF capacitor but regular inductive coupling can be used as well. 5. Screed grid has low resitance path to ground for AF but not for RF - the tube is used as pentode for AF and triode for RF. General guidelines for feedback branch balancing: C2 should be several times bigger than maximum value of Ct. L2 should have slightly fewer turns than in conventional Armstrong regen (perhaps 80% or so). Once you get the amount of total feedback right (operating in the middle of regen pot adjustment) - tweak C2 to minimize tilt. Decrease it if the regen level pot needs to be advanced more at the bottom frequency vs top frequency of the tuning range. Increase C2 if the opposite is true. It is possible to build a circuit using conventional feedback from the plate of the pentode. Untested but the idea should be clear: Both circuits use Armstrong-Vackar feedback combination however mathematically they behave similarly to the "extended range" Vackar (fig6 in paper [1]). These circuits using Armstrong feedback in one of the feedback paths are a little bit more friendly in terms of implementation and conversion of existing Armstrong regens. Floating inductor (required by Vackar pi feedback) allows a simple circuit implementation with cathode detector. In this case triode gain/current can be controlled from the grid side by a high impedance network (from an optional voltage stabilizer): Even though I derived the idea of dual feedback directly from the Vackar paper quite some time ago there are other sources pointing to this arrangement. In fact recently I found some old russian RF technician textbook that shows VFO with Armstron-Vackar combination feedback used to stabilize VFO amplitude across the tuning range ([2] in russian, fig4-10, pg79), so in a way I was reinventing a long forgotten wheel here. Nevertheless this concept somehow did not get into regen builders view AFAIK. But I think it is worth exploring for both pure regens and regenerodynes or any tunable regenerative circuit. References: [1] http://n1ekv.org/Oscillators/Vackar_wholepaper.pdf [2] В.К. Лабутин, "Книга Радиомастера", издание 1955г (in russian, I have a .djvu copy, I can post the reference page if requested)