Infotainment System Noise From HAM Radio Transmitting on UHF

K1NRG · June 19, 2022

2015 GMC Sierra LTZ with factory Nav (full Infotainment System) with Bluetooth, Onstar, etc.

Just installed a Yaesu FTM-400XD using a Comet NMO antenna mounted on rear edge of hood. When I TX on any UHF freq with any radio (mobile or HT) I get a loud thrashing sound that pulsates through all speakers. VHF TX is quiet as a mouse. RX is also normal on both VHF and UHF. The sound is coming through the system and not just the speakers directly as there is no sound when the System is powered off.

If I hold my HT (BTech DRM-6X2) antenna (Nagoya 771) right over the middle of the dash (where the radio head is) and TX on UHF the system SCREAMS - if I hold it pointing out the rear window noise is almost gone and increases as I bring the antenna back to the dash. So there is something in the Infotainment system that is super sensitive to UHF. I tried a 19" mag mount antenna for the Yaesu and with it mounted forward on the roof (directly over the dash) I get noise (but not as bad as the NMO on the hood) which decreases to just a little when all the way back near the rear window (extended cab). The Comet NMO mounted on the rear edge of the hood is pretty close to the dash.

There are a couple of YT videos of Sierra owners showing off their HAM Radio installs and one has same antenna mounted on hood no issues. I can't believe GM would have a radio head unit that is so sensitive to UHF considering how many Sierras probably have commercial UHF radios installed. Perhaps it's just my particular unit but I have had no other issues with the truck and especially the Infotainment System. Anyone else have issues with UHF and their Infotainment System?

ftwhite · June 20, 2022

I recently installed a Midlands MXT575 in my 2018 Silverado with a factory head unit, but with aftermarket amps. It was a Bose system to start, so always a separate amp mounted on the rear cab wall. I tapped the ground into a post in the passenger fuse box, and used a fuse tap for the power. Broadcasting at high power (50w), I never got feedback. The antenna started out on the dash, and then moved to the cab top on a magnet mount near the rear brake light, and then to the top of the rear seat inside to get through a car wash.

Maybe check your ground point?

K1NRG · June 20, 2022

Ground doesn't matter - like I said, I can get really loud noise in the Infotainment System using my HT with a TX on UHF and the HT antenna anywhere near the dash, point it toward the back window and noise goes away.

ftwhite · June 23, 2022

Right. I was thinking more the grounds the truck radio uses. That's where the interference is being heard, right? I had some handhelds a while back, and they never caused interference, but I have upgraded all my grounds since "day one" based on lots of Chevy truck experiences. I was going to order a new handheld soon, so I'll try it out when it gets here. Do you like the BTech?

slj2008 · June 23, 2022

On 6/19/2022 at 2:52 PM, K1NRG said:

2015 GMC Sierra LTZ with factory Nav (full Infotainment System) with Bluetooth, Onstar, etc.

Just installed a Yaesu FTM-400XD using a Comet NMO antenna mounted on rear edge of hood. When I TX on any UHF freq with any radio (mobile or HT) I get a loud thrashing sound that pulsates through all speakers. VHF TX is quiet as a mouse. RX is also normal on both VHF and UHF. The sound is coming through the system and not just the speakers directly as there is no sound when the System is powered off.

If I hold my HT (BTech DRM-6X2) antenna (Nagoya 771) right over the middle of the dash (where the radio head is) and TX on UHF the system SCREAMS - if I hold it pointing out the rear window noise is almost gone and increases as I bring the antenna back to the dash. So there is something in the Infotainment system that is super sensitive to UHF. I tried a 19" mag mount antenna for the Yaesu and with it mounted forward on the roof (directly over the dash) I get noise (but not as bad as the NMO on the hood) which decreases to just a little when all the way back near the rear window (extended cab). The Comet NMO mounted on the rear edge of the hood is pretty close to the dash.

There are a couple of YT videos of Sierra owners showing off their HAM Radio installs and one has same antenna mounted on hood no issues. I can't believe GM would have a radio head unit that is so sensitive to UHF considering how many Sierras probably have commercial UHF radios installed. Perhaps it's just my particular unit but I have had no other issues with the truck and especially the Infotainment System. Anyone else have issues with UHF and their Infotainment System?