so i've been chipping away at this thing for like three months now, mostly weekends when i have time in the shack. it's a basic DC receiver for 40m, pretty much the classic NE602 mixer into an LM386 audio stage design that's been floating around forever. nothing fancy but i wanted to actually build something from scratch instead of just kit stuff.

anyway it actually works, which honestly surprised me a little after all the debugging. the sensitivity is decent, i can hear everything my commercial rig hears more or less, though the selectivity is obviously nowhere near the same. audio fidelity is pretty good considering the LM386 has a reputation for being noisy if you dont bypass it properly. spent way too long figuring out that one.

main issue i'm still poking at is a low hum that comes and goes, seems related to the local oscillator bleeding somewhere but im not 100% sure. i built the VFO as a colpitts and its drifting maybe 200-300hz over a half hour warmup which is annoying but liveable. wondering if anyone else has dealt with the hum thing in similar builds, like is it RF getting into the audio stage or something with the power supply decoupling? i've got 100uf caps on the rails but maybe that isnt enough

the hum in those LM386 builds is almost always the power supply, or RF rectifying somewhere in the audio path. 100uf is probably fine but are you also bypassing right at the IC pins? like a small ceramic, 0.1uf or so right at pin 6 to ground, not just a big cap somewhere on the board. that little cap does more than the big one in my experience. also check your layout, if the audio return path shares any ground with the LO or RF ground you'll get all kinds of weird coupling.

the 200-300hz drift on a colpitts isn't terrible honestly, i built one for 20m that drifted way worse until i stuck it in a small metal enclosure and that alone cut the drift in half. thermal stuff. also NP0 caps in the tank circuit if you aren't already using them, makes a big difference on stability.

nice work getting it on the air. dc receivers are weird to listen to at first because you hear both sidebands at once, took me a while to not find that annoying. did you put any RF filtering ahead of the 602? i skipped that on my first one and could hear everything from broadcast band mixing around in there, was a mess