Need a ham radio consult... interference?

[moonpup]

Hi all,

I've been having this problem since I installed my Kenwood TM-v71A in my 2018 JLU last year. What's happening is that when I'm listening to a repeater while driving, the signal meter is all over the place (up and down) with significant noise and picket fencing type symptoms. I've been told my transmit audio is solid but my receive is a lot of noise on top of the signal. Now as a comparison, when using this same radio in my old vehicle with an NMO mag mount, this was never an issue. It's only since its installation in the Jeep.

The only difference is the antenna and mount (shown below). I thought maybe I didn't have a good ground, so I added the loop of wire below to the bolt holding the bracket. The power and ground are also directly connected to the battery. The top of the antenna clears the hardtop by a good 6-8 inches. Could it simply be the antenna location or because of all the metallic tinted windows causing the problem? I've tried everything I know as a ham, but I can't seem to solve this noise/interference type problem. Any help appreciated!

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[prerunner1982]

As far as the noise, does it change pitch with the engine? Ignition components are known to create RFI though not typically as much on FM. LED head/auxiliary lights are also known to cause RFI. I have also seen dash cams and charger cables that plug into the cig/power port cause RFI.

Picket fencing is due to multipath receive and the 2nd received signal being 180° out of phase cancelling out the original signal. Where was the antenna mounted on your previous vehicle? The roof? Antenna placement may have something to do with it.....if there is metal in your tint I would imagine that may impact the antenna some, rear defrost wires and rear mounted tire (steel belts) may also create problems for tailgate mounted antennas. You might consider a fender mount antenna if for nothing else to see if the picket fencing remains the same.

As far as the ground, the antenna likely has sufficient connection with the mount, you need to make sure the mount has a good ground connection with the tailgate and even the body of the vehicle. You could run a braided ground strap inside the tailgate from the mount bolt, through the wire pass through on the tailgate to a nearby bolt on the body tub.

It's not typically needed for VHF/UHF but RF bonding is common for RF and may help reduce RFI. RF Bonding is taking braided ground strap and making sure horizontal components of the vehicle are all bonded together. Examples include hood to body, engine to body, exhaust to body with multiple straps.

 

[moonpup]

EDIT: I've ordered a front fender mount and will try relocating the antenna.

Thanks for the reply! My old vehicle was a Toyota Camry with a Larsen dual band NMO mag mount that sat on the middle of the trunk. I never had any issues with receiving local repeaters and the signal meter was always strong and constant. As for the noise, I don't think it's electrical, such as alternator whine etc. My Jeep does have the LED light package.

I believe I have everything grounded adequately, but can try adding the additional braided strap. I really think it's a multipath type issue. I suppose I can try moving the antenna to the front of the Jeep with a mount that connects under the hood. Speaking of which, any recommendations for that type of mount? Also, how are other Jeepers mounting their antennas? Any issues with what I described above?

 

[4a4c55]

EDIT: I've ordered a front fender mount and will try relocating the antenna.

Did the front fender mount help?

I really think it's a multipath type issue.

Multipath means there's multiple signal paths between the transmitting station and your receiving antenna. If that were the problem, it would exist no matter which vehicle you were using or how you mounted your antenna.

any recommendations for that type of mount?

I have a Topsy Fender Mount. I haven't installed it yet, but it looks great.

 

[Cllowe]

I used a ditch light mount on the front crown with no issues. I have always heard a rear mount by the spare is a big no no.

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