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

NHAT4 · August 21, 2019

I'm running a VHF 154Mhz, in my AT4... radio mounted to dash, left or steering wheel. antenna on DS hood... no issues but on my old truck 2013 Dmax would get some mild interference when it was mounted in center console...

Can you shield the antenna cable more or up the antenna ground?

slj2008 · August 22, 2019

On 8/16/2019 at 10:17 AM, Phil KF4RAF said:

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

Phil - did you also run the ground cable from batt ?? also unhook your antenna from radio , remove antenna from mount and take a meter a check the cable - center wire to ground should not move > That what I found on by system , replace PL-259 , work's great . Good Luck Steve n0oow

Edited August 22, 2019 by slj2008

Phil KF4RAF · August 22, 2019

Hi Steve,

I have since hard wired the radio to the car battery. GM owners manual states Do Not connect any accessories to the negative side of the battery. The battery has a sensor which monitors the battery voltage connected to the negative side of the battery and could be damaged. There is a grounding post adjacent to the battery which is used to attached your jumper cables in the event you have to jump start your car. So I grounded the negative side of the radio to that. I also took a ground wire and attached one end to the base of the car antenna and the other end to the ground post. It seemed to help a little bit but it still does it on weaker stations.

I took it to the GM dealer and I could not duplicate it, Go Figure... They had never heard of an external source causing my problem except for maybe an amplifier causing to much EMI and to shielded the antenna with EMI tape. They also told me my radio is working as it should and there was nothing more they could do about it. Well, that was the answer I was expecting to hear anyway. However, The mechanic did say it should not damage any other equipment, such as the onboard computers or electrical equipment. While driving home the radio volume decreased again on weaker FM stations on 50 watts. I think I’m going to have to live with the fact this is a cheap radio with poor front end filters and try loading it up with ferrite beads along the AM/FM radio antenna.

I did do an Ohm’s check on both mag mount and bedrail antennas for continuity and both were good.

Thanks, again,

Phil

Edited August 22, 2019 by Phil KF4RAF

slj2008 · August 22, 2019

6 hours ago, Phil KF4RAF said:

Hi Steve,

I have since hard wired the radio to the car battery. GM owners manual states Do Not connect any accessories to the negative side of the battery. The battery has a sensor which monitors the battery voltage connected to the negative side of the battery and could be damaged. There is a grounding post adjacent to the battery which is used to attached your jumper cables in the event you have to jump start your car. So I grounded the negative side of the radio to that. I also took a ground wire and attached one end to the base of the car antenna and the other end to the ground post. It seemed to help a little bit but it still does it on weaker stations.

I took it to the GM dealer and I could not duplicate it, Go Figure... They had never heard of an external source causing my problem except for maybe an amplifier causing to much EMI and to shielded the antenna with EMI tape. They also told me my radio is working as it should and there was nothing more they could do about it. Well, that was the answer I was expecting to hear anyway. However, The mechanic did say it should not damage any other equipment, such as the onboard computers or electrical equipment. While driving home the radio volume decreased again on weaker FM stations on 50 watts. I think I’m going to have to live with the fact this is a cheap radio with poor front end filters and try loading it up with ferrite beads along the AM/FM radio antenna.

I did do an Ohm’s check on both mag mount and bedrail antennas for continuity and both were good.

Thanks, again,

Phil

What radio do you have ? also If you have a two-way radio shop in your area , tell the your problem - They may have a answer for you .

Phil KF4RAF · August 22, 2019

I have an Icom ID4100 and a Yaesu FT400 installed. I do have a Comm. Shop down the street from me. However, I think I found part of the problem. I have install a video camera and had the wiring from the camera running down the “A” pillar next to the broadcasting antenna. Also I was getting power for the camera from the fuse box next to the passenger side door where the antenna wire was going into the radio unit itself. I think the proximity of the camera wire and antenna wire magnified the signal and overloading the radio. Since I relocated all the camera wire and power feed to the drivers side the radio seems to have low volume on one distant station now and its not completely gone like before.

This is the only mod I have done to the truck. I went to my neighbors house who has a 2018 Silverado and parked next to theirs. With their permission I had them tune to the same FM station I was on. I then keyed up my 2 meter radio and they had no decrease in their volume whatsoever.

Well, I’m getting there and perhaps will have to live with it.

Thanks for all the help,

Phil

Phil KF4RAF · August 25, 2019

SUCCESS AT LAST!!!

I finally fixed the audio problem I was having. I ended up putting ferrite beads on the AM/FM radio antenna. One bead on the base of the antenna and two beads where it goes into the back of on the radio. I also taped up both ends with electrical tape which were acting like strain reliefs.

I hope this helps anyone else with similar problems. Thanks to all those who replied.

73,

Phil - KF4RAF

Edited August 25, 2019 by Phil KF4RAF