so i've been working on this install for like three weekends now and i think i finally have it where i want it but theres this annoying hum that shows up when i key up on 2m. doesnt seem to bother 70cm as much for some reason. the radio is a Yaesu FTM-500D and i ran the power leads directly to the battery which i thought was the right way to do it, both positive and negative, about 12 feet of 10 awg with an inline fuse near the battery. antenna is a Diamond NR770HB on a mag mount sitting on the roof.

the hum kind of follows engine RPM actually, now that i think about it. so when i rev up it gets higher pitched. someone at the club meeting said it might be alternator whine getting into the audio somehow but i dont really understand how that would happen if im running straight to the battery. the control head is mounted on the dash and the body of the radio is under the seat if that matters.

anyone dealt with this before? im sure its something dumb i did

yeah that's classic alternator whine, the RPM thing is the dead giveaway. running direct to battery is correct but the issue is usually the audio or mic cable acting like an antenna and picking up the noise from the vehicle's electrical system. first thing i'd try is a ferrite choke on the mic cable and also on the power leads right at the radio end. you can get a pack of them pretty cheap and just clip them on, sometimes takes two or three on the power leads to really kill it.

also worth checking your ground. the negative lead should go to the battery negative terminal, not to a chassis ground point — a lot of people do that and it introduces a ground loop that makes the whine way worse. if your negative is going to a body bolt somewhere that could be your whole problem right there. the FTM-500D is actually pretty sensitive to this stuff because of the way the control head cable works, i've seen a few posts about it on the Yaesu groups.

i had almost the exact same thing in my jeep with a different radio. turned out to be the mag mount coax running too close to the cigarette lighter wiring under the dash. moved the coax over about 6 inches and it dropped way down. probably not your only issue but might be worth looking at where the coax is routed before you go buying stuff