VHF/UHF Radio Interferes with Car Radio

Phil KF4RAF · August 16, 2019

I have a 2019 Silverado, Crew Cab LT and have installed a VHF/UHF amateur radio in it. Upon keying up the VHF, (i.e...146.520 MHz) side of the radio on 50 watts the car radio volume decreases to no volume at all. It only does it on distant broadcasting stations and not local stations. Also if I remove the car antenna it doesn’t do it either.

He is my setup and attempts to troubleshoot.

Main VHF/UHF radio unit is under rear seat.
External amateur radio antenna located on driver side rear bed rail.
VHF/UHF radio running off of external battery power not car battery.

Troubleshooting,

Replaced car radio antenna with shorter stubby antenna (No difference).
Placed a handheld (HT), VHF/UHF on 5 watts near external car radio antenna. (Volume decreased like before).
My friend has a Ford F-150 and I put my handheld next to his external car radio then keyed up the (HT) radio and it didn’t decrease his car radio volume at all.

My last thoughts are that the VHF/UHF Radio Frequency (RF) is getting into the front end of the car radio and overloading it. Or the car antenna is not grounded or shielded properly against RF interference. Also the car was purchased with aftermarket window tint so I’m not sure if it is causing any increase in RF.

Any suggestions would be greatly appreciated and thanks in advance,

Phil - KF4RAF