NEED HELP Interference/noise from the CB radio unit on all times hot 12v

SpitShine_PL

Original poster
Member
May 26, 2023
36
Poznan, Poland
Ran into an electrical issue on my 2002 K1500 Burb.

There are several accessories that installed. They are powered from an aftermarket junction block hooked to the battery posi clamp using a thick AWG wire and include front and rear park sensors, two additional 12v outlets in the cargo compartment, rear fog lights (these are obligatory in Europe), and all-times-hot power feed for a CB radio I installed in the console section where the factory CD lived. All grounds are wired to an aftermarket junction bar, which itself is connected to chassis ground and the battery neg clamp, also using a heavy gauge wire.

The issue is electrical noise/whine through the CB unit speaker. I will detail the conditions under which this problem is present:
1. The CB unit is powered by an all-times-hot 12v source coming from the 12v junction block and a 10 amp fuse. The CB unit ground wire goes back to the ground junction bar, so the entire circuit is a loop which includes the car's battery.
2. When powered on, the CB unit gives a steady pitched, continuous electrical noise. I can cut it off with the squelch control;
(a) I can definitely hear other CB users through the noise -- the antenna picks their transmissions, but the sound is garbled by the noise.
(b) The noise is steady and _does not_ change with the engine off, ignition on, or the engine (and the alternator) running, so I can definitely rule out alternator noise. No power wiring running close to the CB antenna cable injects any interference, as the noise is the same, no matter the voltage to such wiring powered off or on; the antenna cable shield is properly grounded.
(c) The noise gets a higher pitch when I turn on the rear fog lights; they are LED, so I suspect they inject electrical noise; remember that the fog lights are powered from the same 12v junction block and grounded to the same ground junction bar as the CB unit.

What should I do?
1. I could install a 12v socket plug on the CB unit's cable and plug it into one of the three 12v outlets that are factory installed in the dash, below the HVAC controls to try to replicate the problem.
2. I could also hook up a second CB unit, which lives in my other car and is known to be good, to the CB antenna on the truck and plug it into one of the three 12v outlets to see if the problem persists.
3. One possible solution would be grounding the CB unit directly to the chassis, instead of the battery neg pole.
I'm also wondering if the UEC has a stud that would provide a noise-free 12v source for the CB unit.
The solutions considered in items 1 and 2 would also allow me to rule out a busted PCB of the CB unit in the truck, which is a possibility that I haven't looked into yet.
4. I could try an aftermarket noise filter. Those exist, they are cheap (approx. 15 bucks a pop), but they are also known to be ineffective, which probably heavily depends on the wiring setup and electrical noise sources. I'm not cheap, but I don't feel like spending dollars on something with an odd chance of being ineffective because of "God knows why".
5. One possible solution for a clean 12v source would be a 12v-to-12v DC/DC power supply; though I would have to build one, they are not readily available.
 

mrrsm

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Oct 22, 2015
7,851
Tampa Bay Area
FWIW... This Video shows a Dude explaining how he installed and set up his CD radio Unit with details concerning his Coaxial Antennae Cable(s) and their Mounting Positions that could prove instructive in your situation since his arrangements involve making this all work on a Chevrolet Silverado:


...and another Truck involving the use of Citizens' Band Whip Antennae:

 
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59840Surfer

Member
Apr 19, 2020
89
Montana
I believe your antenna is picking up the LED cyclic digital pulse because of a ground-loop problem.

I had the same problem with my GMRS and my new 40/AM/USB-LSB CB.

It's not the coax - although it figures into the solution.

Try a temporary alligator clip ground at the base of the antenna --- try to at least attach it to the PL-235 ferrule and see if it goes away.

What I believe happens here is the coax becomes the only ground for the antenna - which happens at the other end of the coax where it attaches to the radio itself.

That makes the ground sheath a really long and unprotected antenna too - at least until it gets back to the radio where it will migrate to ground through the negative battery wire - which most people merely ground to a screw in the sheet metal - although you stated this is not the way you grounded your rig.

Still-n-all ---> the ground for the antenna is too far away to keep any noise out of the reception and the whole length of the shield brings that signal into the radio itself as it tries to go to ground.

I also tried power chokes (not very good) on the power supply and ferrite beads (not good at all) on the power sides (positive and negative) with NEXT TO ZERO good results.

I started thinking "Where else can a stray signal inject itself?" (the answer became obvious once I cured it).
 

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