so this has been a project ive been sitting on for a few months now. i got a schematic from some guy on qrz who swore up and down that bypassing the stock preamp switching and wiring in an external LNA before the first mixer stage would give me a noticeable improvement on 6m and up. i figured worst case i brick a radio i paid too much for, right

anyway i did it last weekend and honestly the noise floor did drop a little bit, im seeing maybe 2-3dB improvement on 6m when i compare it against my buddys stock 7300. but here's the thing — somewhere in the process i think i messed with a ground trace near the PA section because now on 40m specifically i get this weird harmonic artifact showing up about 15kHz above wherever im transmitting. its not horrible but i can see it on the waterfall and im sure other people can hear it

anyone dealt with something like this after messing with the front end? im wondering if i disturbed something or if maybe theres a cold solder joint somewhere. i dont have a spectrum analyzer good enough to really nail down where its coming from, just using the built in waterfall which is obviously not ideal for self-diagnosis

not really sure what my question is exactly, more just throwing this out there to see if anyone else has gone down this road

yeah the harmonic thing on 40 is almost definitely a grounding issue, ive seen similar stuff happen when people disturb the shielding inside the 7300. that radio is pretty sensitive to any kind of ground loop near the PA because of how the board layout is. id start by just going over every ground point you touched with a magnifying glass and a good light, cold joints near RF sections can look totally fine visually but still cause garbage like this

also worth checking if the artifact tracks with your transmit frequency or stays fixed — if it moves when you change freq its almost certainly intermod or harmonic from the PA, if it stays put its probably oscillation somewhere which is a different problem. the bypass mod itself shouldnt be causing anything on 40 since youre modifying the receive path, so im guessing something incidental got disturbed during the work

i did something similar on an older 746 like 3 years ago, not quite the same mod but i was poking around the front end and knocked a tiny SMD cap off a ground trace and spent two weeks wondering why my audio had a buzz on certain bands. turned out to be that one cap. SMD rework in those rigs is no joke, you basically need a stereo microscope or youre flying blind

the 2-3dB on 6m sounds about right for what your describing btw, i wouldnt expect miracles from that kind of mod but its real improvement if you're chasing weak signal stuff