so ive been putting this off for like six months but last weekend i finally got the FT-857D mounted in my F-150 and ran the power cable direct to the battery. used a 40 amp inline fuse about six inches from the battery terminal like most people seem to recommend. antenna is a Tarheel 100A-HP on the rear hitch receiver mount which i was pretty skeptical about at first but honestly the SWR is pretty flat across most of HF bands which is great.

the VHF/UHF side of it though is what im having trouble with. i put a mag mount dual band on the roof for 2m and 70cm and the receive seems decent but when i transmit on 2 meters im getting this weird buzz in my truck speakers. only happens when im transmitting and only on VHF, the HF side doesnt seem to cause any RF interference at all. grounding issue maybe? or is it the mag mount not giving a good enough ground plane? the mount is sitting on the roof pretty much dead center so i wouldnt think that's the problem but what do i know.

also wondering if anyone runs a separate dedicated dual band mobile instead of using the 857 for VHF/UHF. sometimes i feel like the 857 is overkill for just hitting the local repeaters and i might grab something like an ID-5100 or even just a cheap TM-V71 to handle 2m and 70cm while the 857 stays on HF. curious what others do.

the buzz in the speakers is almost certainly RF getting into the audio system through the power wiring or maybe the antenna feedline running too close to something. ferrite chokes on the audio wiring going into the head unit usually sorts that right out, i had the exact same issue in my Silverado with a 706 and spent way too long chasing it before someone told me to just clip a few snap-on ferrites on the speaker wires near the head unit. fixed it completely. also worth checking if your coax is routed anywhere near the vehicle's CAN bus wiring, some of these newer trucks are really sensitive to that.

on the separate radio question - yeah i eventually went that route and dont regret it at all. running a TM-D710G for VHF/UHF and the HF rig stays dedicated to HF. the D710 has APRS built in which is handy and the dual receive is actually useful on a busy commute when you want to monitor two repeaters. the 857 is a great radio but juggling bands while driving gets old fast.

not sure about the buzz thing but i just wanted to say im in the same boat kind of, just got my tech license and im looking at mobile setups and the amount of options is honestly overwhelming. everyone seems to have a different opinion on antennas especially. do you find the hitch mount for the Tarheel is pretty stable at highway speeds? thats something i keep wondering about with those bigger screwdriver antennas