Alongside the RF probe Steve G0FUW provided a build document for a crystal oscillator for testing in the sudden transceiver project. This was a nice simple build and seems to be working well, I used the RF probe to check that it was working then tuned to the signal on my transceiver to verify the frequency.
As part of the QRP build group Steve G0FUW has provided build documents for a couple of pieces of test equipment. I started building this a few weeks ago but needed to get some bits – croc clips, banana plugs and finally some stiff wire. Getting the Christmas decorations last weekend I spotted some nice stiff copper wire and so finally finished off the build. It is simple and uses a multimeter for readings, but does the job.
After chatting through the noise issues with my audio amp with a club member I’ve made a couple of changes, firstly I’ve replaced the AF input cable with a jack socket (and using a shielded jack to jack cable for the input audio) and secondly I’ve grounded the cases of the potentiometers.
After adding the audio in socket I was having issues, the noise was much reduced and I was getting output when playing audio through my laptop but I wasn’t hearing anything when testing the output of the product detector, eventually I realised that my issues and confusion was because I was using a stereo cable and stereo jack socket in the audio amp but a mono jack socket in the product detector. For the audio amp of the laptop out it was fine, the ring output from the laptop socket went through the stereo TRS cable to the ring of the socket in the audio amp and then out mono through the (correctly) wired AF out socket. In the case of the product detector the audio went through the tip which was connected at the audio amp end and the ring was grounded, so no sound unless I pulled it out a little, once I rewired it the issue resolved.
For the grounding of the potentiometers I connected the three together using some old desoldering braid, perhaps a bit odd and used a lot of solder but pretty effective, I then connected the end one to the ground on the voltage regulator. This all worked fine, but then when trying to track down some remaining noise I unplugged the AF in cable and it went silent, I then replugged it and the same and no sound… after a bit of checking over the board I replaced the LM386 chip and it worked, so once again I’ve somehow fried a LM386!
Regarding the remaining noise I’ve realised that it is only present when my KSGER T12 is switched on, so I’m guessing that the noise is from the switched mode power supply and is coming in via the power in on the amp, so I’ll need to do some decoupling there, to be continued…!
The final part of the M0NTV ‘Building with Blocks’ talk direct conversion receiver. I’ve built it in a different order from the ‘building backwards’ order suggested, partly based on what I had available. I’m waiting for some DC plugs and sockets I’ve ordered to complete it, but I’ve attempted powering it up connecting power with croc clips and not managed to receive anything. I don’t have an ideal 80m antenna here, but I’d expect to hear something, particularly on the FT8 frequencies. The audio amp is very noisy and receiving signals on its own so I’ll need to sort that and then try again, watch this space…
I’ve been working on a direct conversion receiver, on and off (mainly off with a couple of spurts) for a few months now based on a talk by ‘Nick the Vic’ M0NTV, and I recently put together the 80m filter. It’s designed to be modular which is quite nice because it does mean that I can dip in and out. I’m going to put together a writeup of what I’ve done, but for now a couple of pictures.
You can see in the first picture that I’m using a ‘mint tin solder pads’ PCB which I purchased from Kanga UK, very convenient for using with my mint tin, I’ve found it great and on the reverse side it has the same but with split pads.
Finally got the audio amplifier working, there are still some tweaks required but almost there. In the end I eventually discovered that I’d somehow killed the LM386 chip, so I replaced it, but second time round used an IC holder then slid the chip in, not making the same mistake twice!! After all of the resoldering as I disconnected and reconnected wires and components to find the issues it’s not looking pretty.
Finally got round to moving the audio amplifier project on to perfboard. I actually wanted to use stripboard, but TWICE managed to order the wrong thing somehow! I really haven’t enjoyed using perfboard, I’ve been using wire-wrapping wire and have found the whole process incredible faffy and fiddly. I’ve been using small pieces of wire and offcuts of components to connect between the holes, but that again is really faffy. I’ll probably end up using perfboard again as I’ve bought a few, but wish I’d bought the stripboad.
I’m having real issues getting this to work, I’ve got very quiet audio and a lot of crackling. I’m working through the various issues at the moment, nothing like a bit of problem solving!
This is the second module I’ve built for a direct conversion receiver based on a talk by ‘Nick the Vic’ M0NTV, it’s an audio amplifier using the LM386 chip. I decided to prototype it on breadboard and have investigated various configurations using the chip which has been a great learning experience, once I settle on a final configuration I’ll transfer it to perfboard and put it together using the potentiometers.
