Unusual AM Superregenerative? Receiver

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:

1. 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).

2. 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.

3. "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:

1. No audio (far below critical threshold).

2. Weak heterodyne audio (normal regenerative reception above critical threshold; very weak due to no AF amplification).

3. 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.

4. 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.

5. 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.

6. The quench frequency rises, the received signal becomes weaker, and the number of sidebands increases.

7. 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).