so i finally got around to finishing the DC receiver ive been piecing together for like 3 months. its based loosely on the NorCal design but i substituted a few parts because getting exact components shipped here takes forever. the audio is actually pretty decent on 40m, picking up SSB just fine once i got the VFO dialed in, but theres this weird heterodyne that shows up whenever i touch the enclosure or even just move my hand near the coil area. like i dont even have to touch it, just proximity sets it off.

at first i thought it was a grounding issue so i redid all the ground connections on the main board and added a chassis ground strap but its still doing it. the VFO is wound on a T50-2 core and im using a 2N3904 for the oscillator stage. shield can might be the answer but i havent fabbed one yet. or maybe my layout is just bad. the board is ugly honestly, point-to-point on perfboard which probably doesnt help anything.

anyone dealt with this before on a scratch built VFO? im wondering if i just need to bite the bullet and build a proper shield or if theres something else im missing before i go down that road.

yeah that sounds like classic hand capacitance getting into the VFO. its super common on homebrew stuff especially when the oscillator coil isnt shielded. the T50-2 is fine but an unshielded coil that close to the edge of the board is basically an antenna for your hand. before you build a full can, try wrapping the coil and the 3904 in some copper foil tape and grounding the foil, just as a quick test. if the effect reduces noticeably then you know shielding is your answer. also check if your bypass caps on the oscillator supply rail are actually doing anything — sometimes people use the right values on paper but the physical placement means theyre not really decoupling where it counts. layout on perfboard can work fine but you have to be really deliberate about keeping the RF return paths short.

i had almost exactly this problem on a 20m receiver i built last winter. drove me nuts for like two weeks. turned out part of my issue was the DC power lead running too close to the coil, was picking up noise and feeding it back in. moved the lead and added a small ferrite bead and it got a lot better. still not perfect but way more usable. the shield can did help too once i finally made one out of some scrap PCB material, just soldered strips together, nothing fancy. dont overthink the can, it doesnt have to be pretty.