You know that one project you have had that never worked. Welcome to my nightmare, the QRP Labs receiver and polyphase network. Nothing wrong with the design, nothing wrong with the kit, Hans makes good stuff, even if he packs the parts in too closely together for the sane among us. But that said, let me say OH FUCK YEAH. I finally got this working and the problems were all mine. Of Course!!
Issue one, the bandpass filter was not working, I am not a fan of Han’s filter boards, to tiny, to fiddly, total pain in the arse to build, again my fault, will need to look at that again sometime later and find out where it went wrong. Issue number 2, I dumped a solder bridge over the two power pins, and guess what, one side was dry and so the flip flop was not getting power, thus no quadrature signal.
So i fixed both of those issues and set the signal generator to 7Mhz and 28Mhz plus offset and BANG it fires into life and I have a 600hz tone coming out of the headphones. Winner winner, chicken dinner. I finally have this thing working and its not got me thinking about polyphase receiver design again. Doing something similar to this one, but using a 7 or 8 stage polyphase network and getting better opposite sideband rejection. I had started drawing one up the other day in diptrace. While waiting on parts for the next build, i might just give this a try.
