so i've been putting off doing any homebrew stuff for years, always figured it was beyond me or i'd need a proper lab setup or whatever. finally just said forget it and threw together a simple direct conversion receiver for 40m using the ugly/manhattan style construction on a piece of copper clad. grabbed a NE602 and an LM386 off ebay, followed the EMRFD design pretty closely but made a few mods because i didnt have all the exact capacitor values.

anyway it actually works. like, it actually pulls in SSB signals on 40m at night which is kind of wild to me because i built it. the audio is a bit rough and there's some hum i cant chase down — probably a grounding thing or maybe my audio chain is picking up 60hz somewhere. also the LO is drifting a fair bit when it first warms up, maybe 200-300hz over the first few minutes, which makes SSB pretty annoying until it settles.

anyone else gone through the LO drift thing on a first build? i'm using a colpitts oscillator and i suspect the capacitors i used are not great — just whatever ceramics i had in the junk box. would swapping to NPO/C0G caps actually make that much difference or is there something else i should be looking at first?

yeah the ceramic cap thing is almost certainly your problem. regular disc ceramics drift all over the place with temperature and the NE602 VFO gets warm enough to cause issues. C0G/NP0 caps are a huge difference, seriously night and day for oscillator stability. also if you're using a regular carbon comp resistor anywhere in the tank circuit swap that too, they drift thermally as well. silver mica caps are even better if you have them but C0G should sort you out. the 60hz hum — check that your audio ground and RF ground are actually meeting at one point, star grounding basically, and make sure your LM386 supply is decoupled properly. 10uf electrolytic from pin 6 to ground right at the chip if you dont already have it.

nice work getting it going on a first build honestly. i remember my first dc receiver was a total disaster, took me three tries to get audio out of it at all. the drift thing drove me nuts too. one thing that helped me was just putting a small piece of foam over the oscillator section to thermally isolate it a bit while it comes up to temp — buys you a few minutes. not a real fix obviously but if you're just doing SWL or casual listening it makes it usable sooner. eventually i redid my oscillator with a DDS module which kinda felt like cheating but the stability was worth it for SSB work.