so ive been wanting to build something from scratch for ages and finally sat down last weekend and threw together a direct conversion receiver for 40m based on a design i found in an old ARRL handbook from like 1994. got the LO running with a NE602 and a colpitts oscillator, output goes into an LM386 audio stage. it actually receives signals which i was honestly not expecting on the first try.

the problem is the audio is really badly affected by every little thing. like if i touch the volume pot the whole receiver kind of chirps, and theres a low hum thats always there even with nothing connected to the antenna port. i tried adding some bypass caps near the 386 supply pins like everyone says to do but it didnt really help much. also the image rejection is basically nonexistent which i know is kind of the nature of DC receivers but its worse than i expected. anyone gone through this with a similar build and figured out what the actual culprit was, because im going in circles a bit

the hum and the microphonics on the pot are almost certainly a grounding issue. with the 602 and 386 combo you really need a solid ground plane, if youre building this on perfboard with point to point wiring it picks up everything. also check that your LO isnt bleeding into the audio stage through the supply rail, they share power and the 602 can inject a lot of crud if theres no decoupling between the two sections. i usually put a small ferrite bead in series on the VCC line to the 602 and a 10uF tantalum right at the pins, that cleans it up a lot. the image thing is just what it is with a DC receiver, you can add a simple low pass filter on the RF input to knock out the image band a bit but youll never fully fix it without going to a superhet. but honestly for a first build getting audio at all on the first try is pretty good, the grounding stuff is fixable

i had almost exactly this happen with an NE602 build a while back. ended up being that my audio stage was oscillating at RF frequencies, the 386 is notorious for that. there's a 10 ohm resistor and 0.047uF cap in series that you put from pin 7 to ground on the chip, most designs leave it out but it makes a huge difference with stability. might not be your exact issue but its worth trying before you tear the whole thing apart