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w5jag
Jun 24, 2024
In Parts
I often add a cheap part / device that piques my curiosity to my cart when I am browsing AliExpress, eBay, etc. Sometimes you get a home run, sometimes not. This part looks to be a hard foul ball right off the ankle .... I'll preface this with the admonition that my test equipment is not the greatest, so take this for what it's worth. This is a low pass filter that has recently started appearing in my AliExpress feed. It is supposed to be a 30 MHz cutoff. I swept it with my 14 bit Red Pitaya using inputs of 0.01 volt and 0.001 volt from 1 MHz to 50 MHz and got the result shown here. It looks terrible. Keeping in mind that my test equipment is not the best, these graphs anecdotally appear to agree with my perception of the ham bands over the recent field day weekend. When this device was in line to the antenna port on the DC communications receiver shown in another thread, my perception was that 20 and 10 meters were weak - 40 and 15 meters were okay. This filter looks like junk to me. cheap China filter I used a Mini Circuits RLP - 30+ smd low pass filter as the input filter to my general coverage broadcast receiver also described on this board. I took screenshots of a few frequencies after it was installed, unfortunately that was a few years before the Red Pitaya firmware offered a frequency sweep function so all i got were a few screenshots. These basically depict a 10 Mhz input at 0 dBm; 37 MHz at - 10dBm; 47 Mhz at - 45 dBm and 50 Mhz at - 52 dBm. The Mini Circuits part is a quality part. I highly recommend it. MCL RLP 10 MHz MCL RLP 37 MHz MCL RLP 47 MHz MCL RLP 50 Mhz
cheap China 30 MHz low pass filter versus MCL RLP-30+ content media
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w5jag
Apr 21, 2024
In Forum Issues & Administration
Am i in some kind of time out 😎 ? I can't add a new post to any of my existing threads. I can edit an existing post I have made, but I can't post a new comment. But apparently I can make a new thread .... Head scratcher. Win W5JAG
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w5jag
Apr 04, 2024
In Solid State Radios
I enjoy listening to the classic rock format on WRMI radio, broadcast on 5050 KHz mid evenings, and 9455 KHz late night. With the DC receiver project winding down, I have enough left over parts to ( I think ) build a simple radio for listening to WRMI under good conditions. Having inventoried what I have on hand, I think the "design" goals are going to be: 1. Simple, beginner friendly circuitry, with no complicated circuits, or unobtainium parts; 2. Self contained except for power supply, suitable for daily listening, convenient to operate, hopefully not a toy that one becomes disinterested in after a week or so of use; 3. Sounds good I've always liked the oddball look of this case that someone pretty good at 3D design designed for the bitx transceivers: BitX40 Ergonomic Enclosure by fire5ign - Thingiverse. So, I printed it up, in a really bright color to go with the fun tropical / Caribbean Sea motif that WRMI is using. That takes care of the case. I have the Si5351 based raduino built and debugged - it just needs some minor tweaks to the code, and the 1602 LCD with an I2C drive board fits without difficulty in the case as is shown. That takes care of the VFO. Two out of three already done, that just leaves the radio part. I've been thinking about the best way to go about it, and I think a single conversion superhet is the best solution to meet the design goals, For the front end, I'm choosing a single tuned circuit, because I think the chances of correctly tuning up a double tuned circuit are nil, without some type of spectrum analyzer. Tentatively, I am going with a 50 ohm input. An active antenna, or maybe even a regenerated ferrite rod, might be attempted at some point. I pulled a previously wound T-37-6 coil, and gave up on counting the turns wound on it, and just used an LC meter to measure its inductance at 3.54 uH, then calculated the capacitance necessary to resonate at 5050 Khz as 280 pF. I picked a 220 pF cap that measured out at 210 pF, and a 75 pF cap that measured 69 pF, to get the needed 280 pF. I used a 5 turn link on the toroid to go from a 50 ohm antenna to the 1500 ohm input resistance of an NE602, and assembled and swept the filter with the red pitaya. And it peaked low, by about 30 pF of stray capacitance, when I back calculated the peak. I substituted a random 47 pF cap for the 75 pF, reswept the filter, and it looked close enough. An alternate, easier, approach is to substitute a trimmer cap for the smaller cap, and just peak it for maximum atmospheric noise or signal strength. I made a simple mixer with an NE602, and tested it with an RF input of 0.01 volts at 5000 KHz, and an LO input of 0.1 volts at 5500 Khz and looked at it with the red pitaya to verify it worked. The 500 KHz IF, 5000Khz LO, and 10.5 MHz IF are plainly visible. The smaller peak at 11 MHz is probably an intermod artifact of the two IF's. The 0.01 volt RF input is very strong compared to an over the air signal. All of this is being built on the board that I abandoned when I went a different direction with the DC receiver. Only the regulators were salvaged. The NE602 is using the 8 volt regulator. That's it for now. This is a low priority project, and updates / progress may be infrequent. 73. Win W5JAG
Single Frequency Superhet for WRMI 5050 KHz - work in progress content media
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w5jag
Sep 19, 2023
In Parts
Is open for sales again? Dan's Small Parts and Kits (d(http://danssmallpartsandkits.net/index.html)anssmallpartsandkits.net)(http://danssmallpartsandkits.net)(http://danssmallpartsandkits.net/index.html) Always one of my favorite vendors for leaded parts. Win W5JAG
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w5jag
Oct 22, 2022
In Solid State Radios
At my second house, I have no way of listening to CW or SSB, unless I hook up my homebrew 20 meter SSB transceiver, or my FT-817 transceiver, so I’m thinking I might try to build a simple communications receiver to solve this perceived problem. My first receiver build was a direct conversion (DC) receiver, that did not work very well, but motivated me to learn how to build better superheterodynes. I’ve attached a copy of the magazine article for that first receiver. So, I’m thinking I might have a try at another DC receiver. These seem to be the new state of the art as SDR receivers. As with the general coverage broadcast receiver, commercial off the shelf parts will be used if there is an advantage to do so, and the cost is reasonable. My goal will be realized with a simple kitchen table receiver that works well for its intended purpose and can be used on a daily basis. A secondary goal is to make it a true kitchen table receiver, by doing all construction at my second house on the kitchen table, with no resort to any of the tools / equipment in my ham shack. A multi band receiver would be nice, but probably is not essential, at least at first. I have an extra working QRP Labs VFO left over from the development of my 20 meter SSB transceiver, so it will probably be used for frequency synthesis, at least in the early stages of development, if not permanently. This will be an experiment / work in progress sort of thing, sharing time with a couple of other projects I want to do. My simple SSB transceiver took three years to satisfactorily complete, and the simple general coverage broadcast receiver took another year after that, so those are the sort of time frames I operate in when tinkering / experimenting with stuff. 73, Win W5JAG
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w5jag
Jul 04, 2022
In Other Electronic Projects
SIMPLE POWER SUPPLY STATION CONSOLE I’ve been using a store bought imported power supply for the homebrew general coverage receiver, with satisfactory results, but wanted a homemade supply for use with it as a matter of principle and appearance. The power supply presented here is nothing special but provides several convenient functions: A low power regulated DC output derived from the AC mains; a rechargeable battery pack and charger; both power sources can be connected to the output connectors which can accommodate multiple loads; and a digital multifunction display. The line transformer is a Philmore miniature 7.5-0-7.5 1 amp secondary device, with the center tap unused and the ends of the secondary connected to a full wave bridge to ensure sufficient DC output voltage. 1N4007 diodes, bypassed by 100 nF disc ceramic capacitors for noise suppression, make up the bridge. The DC regulator is an LM317 device. A 200 ohm sense resistor is used between the output pin and the adjust pin, which is grounded through a 4k7 trimpot to set the desired output voltage. The small heat sink limits power output to about 600 ma or so. The circuit is completely generic - I did not even bother to draw a schematic. The Battery Pack consists of three overpriced pieces of Li-ion 18650 cells, each with a nominal voltage of 3.7 volts and 1800 mah capacity that I purchased locally at a Wal Mart lawn and garden center. Probably the best way to manage Li-ion battery packs is with one of the inexpensive battery protection boards designed especially for this purpose - they limit the charge / discharge current, charge / discharge voltage cutoffs, and probably other stuff like equalizing charge between individual cells in the pack. I tried several different types and had 100% failure rate for reasons unclear to me. So, to move forward with the project, I built a crude charger from another LM317 that limits charge current to 600 ma, about 1/3 C. More charge current would be hard on the cells, and 600 ma is about the limit from the transformer / regulator / heat sink combination. The charger module takes it’s DC input directly from the rectifier output. A trim pot sets the voltage limit on the charger, here set to about 12.3 volts, or 4.1 volts per cell ( 90% capacity ). 18650 Li-ion cells should not be discharged below a certain point, generally about 2.75 volts per cell, so a protection circuit or voltage monitoring should be used to protect the pack from over discharge. An inexpensive front panel digital voltmeter allows for monitoring of the battery pack charging and discharge voltages, and adjustment and monitoring of the output voltage of the DC supply from the mains. The display also contains a 24 hour clock with battery backup, and a temperature sensor, as well as the DC voltmeter. It is a two wire device, meaning no independent DC supply voltage is required. The display can cycle through its various functions at a programmed interval, or continuously display one selected parameter. The attached video shows the display cycling. A series of simple mechanical switches allow: turning the AC power on / off; connecting the battery pack to the charger or the load control switch, or complete disconnection of the battery pack; connecting the output load connectors to the battery pack or the DC output derived from the mains; and connecting the voltmeter to monitor the battery pack voltage or DC output of the mains AC supply, or disconnected ( display off ). Banana / Binding posts are used for the output connectors - only two pairs are presently installed, but the case is fitted for three more pairs if needed. A two wire polarized line cord is used with a 1 amp fast blow fuse inline on the hot side before the switch. The chassis and small contrasting finish bezel around the display are designed on TinkerCad and 3d printed. The display and bezel are press fit into the opening on the chassis; a green display is installed at present - I may change it out to another color. Connectors are used for a mostly modular design - the battery pack and DC supply / charger module can be installed / removed without need to solder / unsolder any connections. 73 and happy building, Win W5JAG
Simple ( low ) Power Supply  content media
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w5jag
Jun 26, 2022
In Other Electronic Projects
Here are a couple of simple IF amplifiers using obsolete linear IC's. They are not my circuits ( I think - the 3028/3053 might be ) but I have used them successfully and might save someone some research time hitting the books. CA/LM 3028 and 3053 are basically the same chip, the '3028 version being good for much higher frequencies than the '3053, although both are completely suitable for HF frequencies. The '3053 in its day was the less expensive chip, although decades later that has reversed. Neither chip is especially common these days, but are still available. The '3028/3053 can probably be duplicated with discrete components, although I have not tried that. These are through hole parts only. A much higher gain amplifier can be made by using the third transistor, but the circuit here does pretty well gain wise, and is easily made stable. Both '3028 and '3053 were commonly duplicated by proper connection of the transistors in CA/LM 3046 and 3086, the latter being the premium VHF version of the chip. LM3046 was in production until a year or so ago, so should still be readily available in through hole. SMD parts were made, but might be dicier to locate now. The MC1350 is supposed to be long out of production, and to my knowledge was never offered in SMD, but there are still commercial devices in production that use it, and I see them available in through hole and SMD variants on AliExpress, so I'm not sure what is going on with this part. They could be counterfeits or licensed production, or both. I have a lot of old through hole in stock, so I haven't purchased any in years. I'm tempted to try some of the SMD parts. Note that on the MC1350 sheet, VR2 is an adjustable gain control. MC1350 is made for low VHF use and it is capable of substantial gain there and at HF, so caution is warranted in using it. Also note that MC1350 and CA3028 have opposite AGC control voltage action. 73, Win W5JAG
Simple IF amplifiers using obsolete IC's content media
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w5jag
Jun 16, 2022
In Solid State Radios
If so, I can write one up. 73, Win W5JAG
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w5jag
Jun 16, 2022
In Other Electronic Projects
We're all spoiled by the ready availability and ease of use of the 78XX type voltage regulators, my self included. I generally stock a wide variety of 78LXX regulators, and 78MXX., as well as the LM317 types. When I was working on the power supply for my general coverage receiver still in development, I decided to kill an afternoon making voltage regulators the old fashioned way - with a zener diode and a pass transistor. The very simple circuit, likely in countless textbooks, is attached along with some of my practical observations. I do not advocate using this type of circuit in place of a 78LXX circuit, but with a sample book or assortment pack of zener diodes, one can cover pretty much every regulated voltage one might ever need. This can be important for someone like me, who travels between two houses, as it enables me to make maximum use of the limited number of parts I can carry with me to my second house, where I do most of my building these days. I used this circuit for several weeks to power a Si5351 VFO and illuminated 1602 LCD, and it works reliably as long as heat from the pass transistor is adequately dissipated. In that regard, the transistors can survive running a lot hotter than you would ordinarily think. I expect a bigger transistor would pass more current, but all I had that afternoon were puny TO-92 and SOT-23 devices. You can get several hundred milliamps out of a TO-92, so they can bridge the gap between a 78LXX and the physically larger 78XX types if space is an issue. Comments, criticisms, and suggestions welcome. 73, Win W5JAG
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w5jag
Apr 30, 2022
In Solid State Radios
This radio was previously described on the old RadioBoard forum under the title “A Simple Superhet”, and is re-presented here in more detail than previously. It is a general coverage broadcast receiver. OVERVIEW: The radio features digital tuning and frequency readout with memory channels, a low VHF first intermediate frequency for good image rejection, and broadband circuits eliminating alignment. No unobtainium parts are used. Commercial products are used where there is an advantage to do so. The radio is constructed modularly. Three 50 x 80mm BusBoard systems SMD prototype boards ( 200 x 100 format ) hold the RF and audio circuits. The power supplies are on simple perfboard. The completed modules and VFO are installed on a breadboard “chassis” designed on TinkerCad and printed on a simple and inexpensive 3D printer with PLA plastic, thus no complicated metal work is required. A rotary encoder is used for tuning, and directly mounted to the front panel, eliminating the tricky mechanical alignment problems associated with obsolete LC or Varactor VFO’s. The main tuning knob is also 3D printed. Volume is set by an electronic attenuator controlled by a simple DC voltage, eliminating cumbersome shielded wiring to the front panel. The heart of the radio is a commercially produced QRP Labs VFO kit, available for about $33 USD, using the now ubiquitous Si5351 frequency synthesizer chip. The VFO can generate a tunable LO well past 200 MHz, quadrature output if required, tuning steps as fine as 1 Hz, at a square wave level sufficient to drive commercial level 7 mixers without additional amplification. A digital frequency readout and memory channels are provided. Further, an additional fixed frequency local oscillator is provided. The firmware allows the frequency displayed to account for the IF offset from the tunable oscillator. The kit is supplied with a white on blue background LCD, but 5 volt type 1602 LCD readouts are available in a wide variety of color combinations. My radio at this time uses a black LCD with red digits. The Si5351 has many good features and one, perhaps two, significant drawbacks - there is a degree of cross talk between the oscillator channels that is inherent to the device. The output is a square wave, by definition harmonic rich. This is ideal for diode mixers. The Si5351 has a DC component on its output, so a DC blocking capacitor of 10 or 100 nF should be used in circuits where this DC component cannot be tolerated. For up converting superheterodyne receivers, the general rule of thumb is that the first intermediate frequency should be at least 1.5 X the highest frequency to be received. The intermediate frequencies in this receiver are 45 MHz and 450 KHz. Crystal filtering is used at the first IF, and a ceramic filter is used at the second IF. The use of a low VHF first IF, greatly simplifies the construction of the receiver, while enhancing its performance compared to older design techniques. Tunable LO injection is 45 MHz higher than the frequency to be received. The use of the low VHF IF puts the image frequency 90 MHz above the received signal, thus a simple low pass filter is satisfactory to protect a strong first mixer, while eliminating front end alignment and tracking issues. The low pass filters and diode double balanced mixers used are commercial products by Mini Circuits. The IF amplifiers are 50 ohm broadband amplifiers. A TDA1072 Integrated Circuit handles final IF amplification, AM detection, AGC, and provides a meter output voltage that is used for signal strength indication and an additional AGC loop. Audio output is from a DA7052A BTL Integrated Circuit. Each of the modules in the radio will be described in further detail in subsequent posts. 73, Win W5JAG
Digitally Tuned General Coverage Superhet content media
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