the hum is pretty clearly 60hz related i think, goes away a tiny bit when i touch the ground plane with my hand which tells me something isnt right with grounding maybe? im powering it off a wall wart right now which is probably not helping. im wondering if anybody has gone through this with the NE602 before because everything i read says its a pretty sensitive chip and easy to overload. anyway not sure if its a shielding thing or a power supply thing or just my layout being terrible

the problem is the audio is just... rough. lots of hum and what sounds like hash, especially when i touch the cabinet or move the coax around. im using a TL072 for the audio amp stage and i wonder if thats the weak point. also my ground plane situation is kind of a mess on the ugly construction board, lots of little islands that probably arent connected as well as they should be.

anyone else fought this kind of thing on a scratch built DC rx? not sure if im chasing a grounding issue or if the audio chip is just picking up everything because the gain is so high at that stage. the LO is a colpitts oscillator running around 7 MHz and i havent shielded it at all yet which might be part of it

got it picking up a couple of the stronger AM broadcast stations no problem but i'm wondering if there's anything i can do to improve selectivity without going crazy with a more complicated design. the coil is wound with 26 gauge wire, about 60 turns, and i've got the tap set maybe a third of the way up but i'm not 100% sure i have the antenna coupling right. tried a long wire out the window maybe 30 feet or so and that helped signal strength but now everything bleeds into everything else and i cant really separate the stations at all.

anybody built one of these recently or have suggestions for the coil geometry or coupling? also wondering if i should bother adding a preselector stage or if thats overkill for what this is

turned out the issue was my ground plane situation — i was basically wiring things point to point on a piece of stripboard and the audio return path was crossing over the RF section in a really ugly way. once i rerouted the ground connections and added a proper bypass cap on the NE602 supply pin it cleaned up like 80% of the hum. the other 20% i think is just my shack being noisy, not sure.

anyway the receiver actually works now and im picking up SSB signals fine, sensitivity seems decent though i dont have a signal generator to do a proper measurement. my question is about the audio filtering — right now im just running a simple RC lowpass and it sounds kinda washed out. anybody built a audio cw filter or a decent active lowpass for something like this? i was looking at the TL072 op amp stage but havent commited to anything yet.

anyway it receives, like actually receives signals, i can hear 40m SSB pretty clearly which was shocking. the problem is theres this weird hum that follows the audio everywhere, not 60hz exactly but close, and i cant figure out if its the power supply coupling in somehow or if its a grounding issue with the audio stage. ive got a single point ground on the board but maybe i did it wrong. also the image rejection is pretty bad but i knew that going in with a direct conversion design so im not too worried about that part

has anyone dealt with this kind of hum specifically in homebrew DC receivers? i wrapped the whole thing in copper tape on the inside of the enclosure and it helped maybe 20% but its still there. using a 12v wall wart right now, maybe thats the issue, should i just slap a 7812 regulator and some filter caps on it before the board

problem is theres this weird hum coming through that i cant seem to kill. its not 60hz, sounds more like 120hz so im thinking rectified AC getting in somewhere but ive got it running off a 9v wall wart and i even tried batteries and the hum is still there. less on batteries but still noticeable. also the audio is kind of muddy, like stations that my commercial rig pulls in clean sound like theyre underwater on the homebrew. the sensitivity seems okay though, im hearing things i didnt expect to on 40m at night.

anybody built one of these and run into the hum issue? im wondering if its RF getting into the audio stage or if my ground plane is just a disaster. built it on perfboard which was probably a mistake but i wanted to see if it even worked before committing to a real PCB layout.

got the thing mostly assembled on a piece of copper clad i had sitting around, point to point wiring, nothing fancy. it actually receives something which i was honestly surprised about for a first attempt. i can hear SSB signals but theres this really annoying carrier hum that im not sure how to track down. tried twisting the leads to the audio amp section and it helped a little but its still there. also the image rejection is obviously not great but i kind of expected that with a DC receiver.

the VFO is drifting a fair bit too, probably 500hz or more over the first 20 minutes. i used whatever coil former i had in the junk box and the cap is just a crappy ceramic. thinking maybe i need to use an NP0 cap and maybe pot the coil in wax or something? anyone done that with good results. also wondering if a jfet buffer after the oscillator would help with frequency pulling when i change bands.

problem is the output looks kind of rough on the scope. i was expecting something close to a sine but what im seeing has this weird shoulder on the rising edge, almost like a little pre-ringing thing before the main waveshape settles. power output seems ok, im getting around 4-5 watts into a dummy load, but something about that waveform bugs me. ran it into a spectrum analyzer app on my phone (yeah i know, not ideal) and there seem to be some harmonics that are a bit high.

the lowpass filter i built uses the values from the ARRL book for 40m, toroids wound on T50-2 cores. i double checked the turns counts but maybe i screwed something up there. anyone dealt with this kind of thing before?

the LM386 circuit is basically straight out of the datasheet, 250uf cap from pin 7 to ground, gain set to 200 with the 10uf cap between pins 1 and 8. i'm wondering if that's actually too much gain and it's just amplifying everything including noise. or maybe my audio filter is wrong. i did slap a 0.047uf cap from the output to ground which i thought would kill the RF but maybe it's also cutting too much of the audio band.

anyone built one of these and can tell me where the muddy audio usually comes from? power supply is a 9v wall wart, i haven't checked how clean it is yet

the problem is the RF front end is just terrible. im getting a ton of breakthrough from broadcast AM stations even though im running a 40m bandpass filter i wound myself on a T50-2 toroid. tried adjusting the coupling capacitors and i can reduce it a bit but it never totally goes away. also hearing a weird birdie around 7.150 that i think might be from the VFO getting into the mixer somehow. shielding is pretty minimal right now, just some copper tape i had laying around.

not sure if its worth trying to add a preamp stage or if that would just make the broadcast problem worse. anyone dealt with this kind of thing with the NE602? im also wondering if my bandpass filter design is just off — wound it for 7MHz center but honestly my inductor measuring setup is pretty janky so who knows if the inductance is actually right.

ive checked the plate voltage and its sitting around 280v which should be fine, grid bias looks okay, and the pi network is tuned to a fairly sharp dip on the plate current. neutralization i honestly am not 100% sure i did right, the tube is triode-connected in some variants i read about so maybe thats not even the issue.

the thing that really bugs me is the plate current at dip is only pulling like 55ma when loaded. i feel like that number should be higher. could be the tank coil, i wound it myself and im not totally confident about the number of turns i ended up with after trial and error. anyway anyone dealt with this on a similar build, would love some ideas before i start poking around with the RF probe again

Transmitter uses balanced modulator approach with MC1496 generating DSB, followed by crystal filter for sideband selection. Getting about 25W output with IRF840 in the final stage, class AB configuration. ALC circuit keeps things clean and prevents overdrive.

Next challenge is integrating the synthesized VFO - building Si5351-based design that covers 7.000-7.300 with 1Hz resolution. Planning to use Arduino for band/mode switching and frequency display.

Construction is modular approach with separate boards for each function connected via short coax jumpers. Keeps RF stages isolated and makes troubleshooting much easier.

the problem is the audio coming out of it sounds like garbage. not like weak or anything, i can hear stations, but theres this really annoying hum and also kind of a motorboating sound when i turn the volume up past like halfway. i put a 100uF cap on the power supply rail to the audio stage which i thought would help but it really didnt do much. using an LM386 for the final audio amp stage.

also the whole thing is really microphonic, like if i tap the bench the audio freaks out. im guessing thats the VFO being sensitive but not sure. anyone dealt with this kind of thing before? its my first homebrew receiver so i might just be in over my head here

it picks up a few AM broadcast stations which is cool but the selectivity is pretty terrible — two of the stronger stations are bleeding into each other pretty bad. i added a small variable cap i pulled from an old transistor radio to tune it and that helped a bit but not much. using a long wire out the window, maybe 15 meters or so, and a ground to the water pipe.

not sure if the coil needs more turns or if the problem is just the antenna being unbalanced or what. anyone actually built one of these that can point me in a direction? i know its a simple circuit but clearly im missing something

the rf side seems fine, i can hear signals and the sensitivity is decent, tuning around i can pick up plenty of SSB and CW. but the audio is this weird bassy muddy sound and theres a constant low hum in the background, not 60hz exactly, more like 120hz so im guessing its power supply ripple getting in somewhere. also when i touch the volume pot the hum changes which is making me think its a grounding thing maybe.

the audio amp section is built around an LM386 which i know isnt the best choice but i had a bunch of them. running it at about 46db gain with the 1.2k and 10uf between pins 1 and 8. bypass cap on pin 7 is 10uf. i did add a 10 ohm resistor and 0.047uf cap on the output like the datasheet suggests to keep it stable but i wonder if my layout is part of the problem since this whole thing is built dead-bug style on a piece of copper clad.

anyone dealt with this kind of audio mess on a homebrew receiver? not sure if i should just tear out the audio section and start over or if theres a tweak i can try first

the oscillator stage is a colpitts using a 7.030 crystal and im running it off a 12v regulated supply so its not a voltage issue i think. the PA is a single IRF510 running maybe 3-4 watts out. i kept the oscillator and PA on the same board which in hindsight was probably dumb because there's definitely some heat coupling happening. anyway wondering if anyone's fought this before and what you did about it — whether its worth physically separating the stages or if there's a better fix

problem is the audio sounds kind of phasey or hollow i guess? hard to describe. SSB signals are intelligible but they have this weird quality like listening through a tin can. CW is actually fine and sounds clean which is confusing me. i double checked my decoupling caps on the 386 and they look okay, and the supply voltage is stable at 9v. wondering if maybe my IF filter is doing something weird or if theres some kind of feedback path i'm not seeing. layout is pretty loose on a piece of copper clad which probably isnt helping

anyone dealt with this before with the 602 designs? ive built a regen before but this is my first proper superhet attempt, or well i guess DC receivers arent really superhets but you know what i mean

i followed the basic schematic from Experimental Methods in RF Design which i know is kind of old but figured it was a good starting point. my power supply is a 12v wall wart, i wonder if thats the issue. the decoupling caps i used are just whatever i had in the junk box, like a mix of 0.1uF ceramics and some old electrolytics. ive been chasing this problem for days and honestly starting to wonder if the LM386 is just a garbage part or if i messed something up in the layout.

anyone been through this? what did you do to clean up the audio on a simple DC receiver like this?

it actually works which honestly surprised me a little. im hearing SSB stations and CW and the audio is decent through a pair of headphones. BUT theres this really annoying hum, not sure if its 60hz or a harmonic of it, and it seems worse when i touch the coax or get close to the board. i built it on manhattan style pads on a piece of copper clad and the layout is kind of a mess if im honest. also the LO is leaking into the antenna port i think because i can hear myself on another radio nearby when i tune around.

before i start adding a second stage or anything i want to sort out these basics. is the hum most likely a grounding issue or should i just box it up and see if that helps. and is LO leakage just something you live with on a simple design like this or is there a buffer stage i should add between the oscillator and the mixer.

the problem is the audio sounds kind of hollow and there's this low frequency rumble that comes and goes. like if i tune to a CW signal it sounds like the tone is inside a tin can. SSB is barely intelligible. i checked my LO and its sitting pretty stable on the scope, the NE602 seems to be getting the right supply voltage. audio stage is just an LM386 feeding a small 8 ohm speaker. im wondering if its an impedance mismatch between the mixer output and the audio amp input or maybe my bypass caps are insufficient somewhere but honestly im just guessing at this point

anyone built something similar and had audio issues like this? would really appreciate some direction before i start randomly swapping components

Audio output shows clean signal on 'scope but breakthrough is definitely there. Anyone experienced similar with direct conversion designs? Wondering if I need better band-pass filtering ahead of mixer or if this is oscillator isolation problem.

Using Manhattan construction on double-sided PCB material, copper pads every 0.1 inches. Supply is clean 12V with proper decoupling throughout.

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.

Using 6MHz IF with discrete mixer and crystal filter. T/R switching is done with PIN diodes. Anyone experienced similar issues after PA modifications? Wondering if increased RF leakage from the MOSFET stage is desensing the receiver during standby.

PA isolation is showing only 30dB on my homebrew directional coupler - should be closer to 60dB. Any suggestions for improving T/R isolation in QRP transceivers?

Anyone experienced similar issues? Wondering if it's insufficient isolation between stages or feedback through the power supply. Currently running 12V with 100uF + 0.1uF decoupling at each stage.

AGC is functioning properly, so I don't think that's the culprit. Would appreciate any troubleshooting suggestions from fellow homebrewers.