So ive had this Yaesu FT-7900 mounted in my truck for about 8 months now and lately its been doing this weird thing where it just drops mid-transmission. Like im talking to a guy on the local 2m repeater and the audio just cuts for half a second and comes back. Sometimes it does it a few times in a row. Doesnt seem to happen when im parked but on the highway it gets bad, especially when i go over bumps or rough pavement.

My setup is a NMO mount on the roof with a Diamond NR770H dual band whip. The coax run goes through the door jamb and under the center console to the radio. I torqued the NMO mount down good when i installed it but maybe the coax connection at the base is getting loose from vibration? I havent pulled the antenna off to check yet because its a pain to get to on my truck.

Has anyone dealt with something like this before? My first thought is the PL-259 at the radio end or maybe the NMO connector itself is the culprit. Just wanted to ask before i tear everything apart this weekend.

yeah that sounds exactly like a coax connection issue, been there. on my old Silverado i had the same thing with a lip mount and the center pin on the PL-259 had worked loose just enough to cause intermittent contact. drove me crazy for like a month. id start at the radio end first since thats the easiest to get to, then work your way back toward the antenna. if you have a multimeter you can check continuity from the center pin at the radio end all the way up while someone wiggles the antenna — if it drops out you found your problem pretty quick.

also worth just double checking the NMO mount itself. sometimes the nut underneath the roof sheet metal works loose even if you think its tight. a little loctite on the threads isnt a bad idea once you find the culprit.

could also be the power connection honestly. i know it sounds unrelated but my FT-7900 was doing something similar a while back and it turned out one of the ring terminals on my battery leads hadnt crimped all the way. under load on transmit it would just dip enough to cause weirdness. the highway thing makes sense too because vibration can make a marginal connection go from annoying to actually dropping.

not saying its not the antenna but worth checking the whole chain before you pull the NMO apart. those Diamond mounts are usually pretty solid in my experience.