What Happens Differently at 8 MPH and Below on a WK2?

[Bob]

I’m trying to locate the source of strong radio interference from my 2014 GC to the installed ham radio on 147.27MHz, which happens to be a useful repeater frequency in my area.

It only occurs when the speed is at or below 8 mph while driving or when stopped, or with the engine off but the key in run position.
(I haven't yet tried to see if it happens in Sport mode, reverse, or low 4x4.)

So, what happens differently at and below 8 mph? Something with the drive train control, or ABS, or stability control, or...?

If I knew what system was involved, it would make it much easier to locate the source and try possible mitigation ideas.

[Jim]

I don't know - but if it's repeatable - can you walk around with a radio to try and locate where the interference is strongest?

If it does it while standing - key to run (or just ACC) you could start pulling fuses and see which fuse silences the interference. I think this is where I'd start.

[Tom]

I wouldn’t know where to begin. It was all much simpler back in the points and condenser days.

[Bob]

Thanks, fuse pulls are a good idea, may have to do that.

I tried walking around with an HT, but it’s pretty strong everywhere, not a lot to go on. Oddly the highest of it was at the rear view camera but the problem doesn’t correlate to camera use, and I wouldn’t expect the camera would be powered up based on speed. Could be the wiring to the camera is acting as an antenna for the noise, perhaps run in the same portion of harness as the noise maker.

Didn’t seem to be the strongest in the engine compartment. I can’t get much access underneath the car because of the skid plates, unless I take them off, which is a chore.

[Jim]

Fuse pulling just became the easier option... ;)

[Bob]

I got a major clue from jeepforum.com. There are front parking sensors in some markets so the controller turns them all on at low speed even if only the rear are present as they are on my car. So I pulled only one fuse, #95 for that circuit, and the noise disappeared.

The rear camera is part of that circuit so now I understand why the signal was somewhat stronger there. The noise is from the sensor circuit or the camera or both. Maybe the camera is powered on with the sensors but the image doesn’t show on the dash screen unless in reverse. Now I can start looking in detail at reducing the interference.

Thanks for your help!

[FINOCJ]

back in the points and condenser days.

if only you could get a good quality condenser these days....

[Jim]

Thanks for the conclusion.

So you're going to look at resolving the issue... How? Do you think the noise is from the computer or the wiring to the device or the device(s)?

Does anything else run on that circuit (that you desire to use) or could you leave the fuse out / put a switch on the dash when wheeling?

[Bob]

The back up lights are on the same circuit so I can’t remove the fuse permanently and wouldn’t feel it safe to do even temporarily. Besides, I use the backup camera all the time and sometimes the sensors are very useful. I did more observations with the hand held radio this morning and I’m fairly certain the source is the back up camera itself, not the sensors.

The first try at mitigation would be to remove the hatch trim panel and snap a ferrite bead or two of the correct frequency range around the wiring to the camera and see if the noise is attenuated. It should be to some degree. This a standard reduction technique for common mode RFI, and I’m sure you’ve seen them snapped on computer cables. Whether it would be enough to make the frequency usable depends on the bead attenuation and how much signal gets out through the plastic body of the camera.

Unfortunately there wont be a lot of extra wire to wrap around a ferrite bead or toroid, as attenuation increases as the square of the turns. If it reduces but not enough, then I would consider splicing in a length of wire to use for this purpose.

If that fails, it might be possible to perform surgery and connect some capacitors to ground at the camera output to shunt the signal to ground (car body). This might cause side effects though, possibly bad video, so it’s not a great option.

[Jim]

Would some lead "foil" to wrap around the camera body and wire do anything (even if space exists)?

[Bob]

Sometimes, and it may be worth a try, but usually shields added after the fact leak a lot of signal, or become another radiator, unless it can be done nearly completely with seams sealed with metal tape or conductive gaskets.

[RockyMtRebel]

Is the radio a Baofeng? If so, it’s the radio! I went wheelin a few months ago and the guy I went with insisted we use his Baofeng radios…… every time I hit the brakes it had major interference….. no matter what I did, it was constantly making noises and was a pain to use. Switched to my cheap-o FRS handhelds and no problems. I read since Baofeng is garbage and this is a common issue

[Tom]

Is the radio a Baofeng? If so, it’s the radio! I went wheelin a few months ago and the guy I went with insisted we use his Baofeng radios…… every time I hit the brakes it had major interference….. no matter what I did, it was constantly making noises and was a pain to use. Switched to my cheap-o FRS handhelds and no problems. I read since Baofeng is garbage and this is a common issue
Likely caused by the default baofeng squelch setup. Can be reprogrammed via chirp.

[Jim]

This is a curious turn to the issue!

[Bob]

Is the radio a Baofeng?
No, it’s a Kenwood TM-D710G dual band mobile.