so i spent most of saturday running coax and power cables through the cab of my F-150 and got the FT-857D sitting in a RAM mount between the seats. runs great, TX and RX both seem fine, making contacts on the local 2m and 70cm repeaters no problem. but theres this high pitched whine in the audio that changes with engine RPM. goes higher when i rev the engine, lower at idle. classic alternator whine i think but im not totally sure since ive never dealt with it before in a mobile install.

i ran the power cable directly to the battery with an inline fuse which i thought was the right way to do it. the ground goes to a bolt on the frame pretty close to where the negative battery terminal grounds. antenna is a diamond NR770RHBK on a lip mount on the trunk lid. i dont think the antenna has anything to do with it but figured id mention it.

anyone dealt with this before? is it definitely the ground or could it be something else. i read something about ferrite cores on the power leads but wasnt sure if thats just snake oil or actually does something

yep that's alternator whine, pretty much textbook. the ferrite cores can help a little but honestly the first thing i'd check is your ground. grounding to the frame can work but its not always great depending on the truck -- sometimes theres paint or corrosion under that bolt that you cant see and it creates a bad connection. try running a dedicated ground straight from the radio chassis back to the battery negative post, short as you can make it, and see if that cleans things up. i had the exact same thing on my tacoma with an IC-2300 and that fixed it completely. also make sure your coax shield is grounded well at the antenna mount, a floating shield can pick up all kinds of garbage from the electrical system.

if you do all that and still have the whine then yeah look at a noise filter on the power line, astatic makes one thats like 12 bucks and actually works reasonably well. but ground first, seriously.

i had this same issue with my 2m radio last year and it drove me crazy for weeks lol. turned out my power cable was running right next to the ignition wiring harness under the dash and it was picking up noise from there. tried moving the cable to the other side and it helped a lot. might be worth checking how you routed everything even if the ground ends up being the main fix