CB radio getting interference from dome and tail light. - JKowners.com : Jeep Wrangler JK Forum
 
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post #1 of 21 Old 04-01-2010, 11:40 AM Thread Starter
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CB radio getting interference from dome and tail light.

Hi, ive had done a search but wasnít able to find what Iím looking for so here it goes....

I just installed my CB Uniden Pro510xl CB radio using an 18' Wilson coax, and K40 antenna.
I routed the coax down the passenger side and through the factory rear hole next to a wire harness (I assume itís for the tail lights) which then passes out the bottom of the jeep. The power source for the CB radio is coming directly from the battery.
My problem is Iím getting a lot of interference from the dome and tail lights whenever they light up. I assume the coax is getting interference from the wire harness running down the passenger side.

So how is everyone routing their CB radio coax and not get any interference? Or the wire harness on the passenger side isnít my problem?

Thanks

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post #2 of 21 Old 04-01-2010, 11:58 AM
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Quote:
Originally Posted by Chris85xlt View Post
Hi, ive had done a search but wasn’t able to find what I’m looking for so here it goes....

I just installed my CB Uniden Pro510xl CB radio using an 18' Wilson coax, and K40 antenna.
I routed the coax down the passenger side and through the factory rear hole next to a wire harness (I assume it’s for the tail lights) which then passes out the bottom of the jeep. The power source for the CB radio is coming directly from the battery.
My problem is I’m getting a lot of interference from the dome and tail lights whenever they light up. I assume the coax is getting interference from the wire harness running down the passenger side.

So how is everyone routing their CB radio coax and not get any interference? Or the wire harness on the passenger side isn’t my problem?

Thanks
You are getting too much power to your CB, Try tapping into the 12v plug. Use a set of butt clamps to connect the two wires.

What type of fuse are you using?

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post #3 of 21 Old 04-01-2010, 12:24 PM Thread Starter
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Originally Posted by bodybrdng View Post
You are getting too much power to your CB, Try tapping into the 12v plug. Use a set of butt clamps to connect the two wires.

What type of fuse are you using?
I thought I was suppose to wire it directly to the battery to get the cleanest power.

I'm using a 20amp inline fuse.

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post #4 of 21 Old 04-01-2010, 12:29 PM Thread Starter
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I just pulled the coax out and routed it outside of the cab and plugged it back into the CB. It's still having interference whenever the dome or tail lights comes on.

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post #5 of 21 Old 04-01-2010, 12:30 PM
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Quote:
Originally Posted by bodybrdng View Post
You are getting too much power to your CB, Try tapping into the 12v plug. Use a set of butt clamps to connect the two wires.

What type of fuse are you using?
I am no electrician but I have also been told to run power for a CB direct off the battery, I'm not saying your wrong simply stating what I have always been told. I personally have never had a problem running it off the battery so I would say to look elsewhere. define interference, is it only when transmitting, or does the CB open squelch when the lights are on? The problem may not come from the routing of the cable so much as the cable itself, coax is very touchy if not insulated properly, cheap cable will allow interference pretty easily (not saying you have cheap shit, but you didnt specify and its something to rule out). Another major thing to troubleshoot interference is the ground, a lousy ground will cause all kinds of noise. As far as the power source is concerned, remember if you tap the plug you are tapping into the CANBUS and that is just scary territory. No matter where you grab power from 12 volts is still 12 volts the CB is only going to pull as many amps as it needs to run, I have never heard of supplying too much power to a 12 volt accessory on a 12 volt system.

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post #6 of 21 Old 04-01-2010, 12:33 PM
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ok so running the coax away from any source of interference rules that out, I would check the ground next, try ground directly to the ground of the battery, if that still doesnt fix it I would look at the antenna maybe a tuning or antenna ground issue.

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post #7 of 21 Old 04-01-2010, 02:58 PM
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Quote:
Originally Posted by Rednroll View Post
Just as a trouble shooting suggestion, try disconnecting the plug to the rear window.

I know it may sound strange, but I've got some engineering experience in this area. Basically, what happens is that the dome light, and brake light wires are bundled with the rear window defogger power wire. When power is supplied to the brake or dome lights, these signals are coupled into the rear window defogger power wire. The rear window defogger on the back window acts like an antenna and transmits this signal that got coupled into it....your CB Antenna picks up this radiated signal...you then hear the noise. Unplugging the wire harness connected to the rear window, eliminates this scenario. If this is the problem, then you will need to connect some capacitors from the rear defogger power wire to Ground to reduce the voltage spike being coupled into the defogger power wire.
or take the lazy redneck way (read: my way), and disco the rear window plug when you hit the trails or when ya need the CB

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post #8 of 21 Old 04-01-2010, 03:22 PM Thread Starter
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Originally Posted by Rednroll View Post
Just as a trouble shooting suggestion, try disconnecting the plug to the rear window.

I know it may sound strange, but I've got some engineering experience in this area. Basically, what happens is that the dome light, and brake light wires are bundled with the rear window defogger power wire. When power is supplied to the brake or dome lights, these signals are coupled into the rear window defogger power wire. The rear window defogger on the back window acts like an antenna and transmits this signal that got coupled into it....your CB Antenna picks up this radiated signal...you then hear the noise. Unplugging the wire harness connected to the rear window, eliminates this scenario. If this is the problem, then you will need to connect some capacitors from the rear defogger power wire to Ground to reduce the voltage spike being coupled into the defogger power wire.
i tried unplugging the rear window defrost plug and theres no difference. Sorry.

I also added a ground wire from the frame to the rear tire carrier where the antenna is mounted on. i believe it cleared some of the interferance but its still there. ill play with the ground some more later.

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post #9 of 21 Old 04-01-2010, 03:47 PM
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Your antenna/coax ground may be problem. Try grounding the outside of the coax connector at the radio directly to ground. Just wrap some wire around it and hook it to ground temporarily see if it goes away. Some radios are very sensitive and need the radio grounded really well. If it goes away then you'll have to figure out how to make a more permanent ground. Just a shot in the dark most of these problems are ground related.

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post #10 of 21 Old 04-05-2010, 05:01 PM Thread Starter
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Ok i checked my grounds with a meter and everything seems good but I'm still having a lot of interference and static noises when i run the motor or power up anything inside. The CB radio is mounted to my center console and the coax runs down the passenger side inside of the cab and out the back.
This is the order i set up my CB radio...

K40 tunable fliberglass antenna SF300 - 3 FT Whip 1000 Watts
Heavy Duty Fold Down Mount
Firestik Stainless Steel Springs. med spring
Francis Stud 310-M102C Antenna Mount
Wilson Coax for a Single Antenna System

The stud is mounted to a steel tab on my tire rack that has a good ground (-)

I'm using a Uniden Pro 510XL with the positive (+) wire connected to the battery. The negative (-) is connected to the body.

My SWR tuner reads all channels above 3

do you guys have anymore suggestions on how to solve my problem?




edit:
Rednroll- I re-did the ground where the tire carrier is now grounded to the body of the jeep which didnt make any difference to the interference or the static noises from the CB radio. i also tried wrapping a wire from the ground (-) side of the stud to the body of the jeep and still no difference.
When i unplugged the coax from the antenna side the interference would go away.

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Last edited by Chris85xlt; 04-05-2010 at 05:54 PM.
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post #11 of 21 Old 04-05-2010, 11:15 PM
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Try some basic steps to determine where the noise is being received.

First remove the antenna and turn everything on and see if you still hear the noise.

Then remove the coax from the antenna mount...

Then remove the coax from the back of the radio...

This will hopefully pinpoint where the noise is from. Post up the results and we can maybe help you solve this issue. This is the first I have ever heard of "noise" from the dome light.

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post #12 of 21 Old 04-06-2010, 12:14 PM Thread Starter
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Quote:
Originally Posted by Rednroll View Post
Try this to see if this helps as a trouble shooting scenario. Where the coax cable connects to the antenna, unscrew that cable and then try to just insert the cable far enough so that the center pin of the cable makes contact with the antenna connection but NOT the outer part where it screws on to the antenna. If the center pin is not long enough to make a connection to the antenna without letting the outer part touch any metal then, you might have to clip a paper clip or a small nail to that center pin and then insert it into the antenna. The key here is to make sure the outer connector of the coax does not touch any metal. Once you do that, then see if the problem goes away or if it gets worse.

If it gets better, then you should physically disconnect the braided wires of the coax cable from the end connector.
i disconnected the coax cable from the antenna stud. then did what u said where have only the inner pin of the coax cable touch the center of the stud.
No difference in the interference but if i diconnected the coax completely from the stud, the interference went away.



Quote:
Originally Posted by jdrogers View Post
Try some basic steps to determine where the noise is being received.

First remove the antenna and turn everything on and see if you still hear the noise.

Then remove the coax from the antenna mount...

Then remove the coax from the back of the radio...

This will hopefully pinpoint where the noise is from. Post up the results and we can maybe help you solve this issue. This is the first I have ever heard of "noise" from the dome light.
Ill go do that right now.








Any of you guys run a noise filter? it looks like a large diode thats spliced into the power wire for the CB radio (i think). i was suggested by my CB radio shop.

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post #13 of 21 Old 04-06-2010, 01:27 PM Thread Starter
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update...

I now have the CB antenna stud and the CB radio both grounded to the body. Both grounds reads 00.00 loss on the meter.
Interference still there if i power anything in the car. Worse with the motor running

I then removed the antenna, fold-down mount and spring leaving just the stud mounted to the jeep. Coax is still connected to stud.
Interference still there if i power anything in the jeep. Worse with the motor running

If i disconnected the Coax from the stud.
No more interference

Im going to go pick up a noise filter from radio shack and ill report back

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post #14 of 21 Old 04-06-2010, 01:43 PM
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Quote:
Originally Posted by Chris85xlt View Post
update...

If i disconnected the Coax from the stud.
No more interference

Im going to go pick up a noise filter from radio shack and ill report back
Adding a noise filter to the power leads will not make any difference. Having the noise go away when you remove the coax from the stud indicates that the noise is related to that connection.

Usually when the antenna is removed and the noise goes away indicates that the radio is picking up "radiated" noise from some electrical component. On the TJ's (pre 2007 Wrangler) the fuel pump was a very common source of electrical noise. You can test for fuel pump noise by turning the key to on but do not start the engine. After a few seconds the fuel pump will stop because the fuel has no place to go. This was easy to test on the TJ. If it is radiated noise, you can try to move the antenna location or my must remove the source of the noise.

Since you stated the noise did not go away until you disconnected the coax from the stud, I suspect there is something wrong with that connector or with you mount. When you mounted the stud to the antenna mount are you sure you put the small plastic washer in correctly to insulate the stud from the vehicle body?

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post #15 of 21 Old 04-07-2010, 11:27 PM
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Wow, sorry to hear about your problems. I wasn't having that problem but was having problems getting the swr's down and ended up running a ground wire from the tub to the frame and it solved my problems. Good luck with your problems, Mike

Last edited by Mike; 04-08-2010 at 08:25 PM.
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post #16 of 21 Old 04-08-2010, 01:32 AM Thread Starter
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After taking everything apart and cleaning all the connections, the SWR is now around 2.25 which are not great, but much better than before.

I’m still getting some interference from when I power up anything in the jeep, but now the static noises and pulses are much more tolerable. I’ll try adding a grounding strap from the body to frame if there isn’t one already. After that I’m just going to leave it the way it is...

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post #17 of 21 Old 04-08-2010, 01:37 PM
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Quote:
Originally Posted by jdrogers View Post
When you mounted the stud to the antenna mount are you sure you put the small plastic washer in correctly to insulate the stud from the vehicle body?
I had a problem like this on my CB for my XJ. Tried everything but no luck, so I took it down to a local CB shop. The tech went straight to the antenna mount and found that I put the plastic washer in wrong. THAT WAS IT!
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post #18 of 21 Old 04-08-2010, 08:31 PM
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Quote:
Originally Posted by Chris85xlt View Post
After taking everything apart and cleaning all the connections, the SWR is now around 2.25 which are not great, but much better than before.

Iím still getting some interference from when I power up anything in the jeep, but now the static noises and pulses are much more tolerable. Iíll try adding a grounding strap from the body to frame if there isnít one already. After that Iím just going to leave it the way it is...
I just went to Napa and bought a short grounding strap and found a easy place to get under the rear of the jeep and used self tapping screws and went from frame to the tub. 2.25 is pretty high. I know it can be frusterating, I hope you get it figured out.
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post #19 of 21 Old 04-07-2012, 01:47 PM
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Thought I'd bring this thread back to life since I have a similar problem now. Mods, feel free to move it to a new thread if necessary.

I had a Midland 75-822 connected to a 12V source directly to the battery and an 18' coax cable to a 3' Firestik on my Or-Fab carrier. SWR was never great, but hovered around 1, so I never bothered tweaking it to lower than 1. Worked great and served its purpose.

I installed late last night a Uniden Pro520XL last night to the same power source, but also added a 6' coax extension to my existing 18' coax since the 18' wasn't long enough to reach above the rear-view mirror.

Now I have engine interference when I turn the CB on. When the CB is on, I hear the revs of the engine as a high-pitch whizzing sound through the CB.

It was late last night and I didn't test it with the engine on until today. I plan to disconnect the coax altogether and see if it makes the noise.

Any idea what this could be and how to resolve it? Are there in-line filters for the coax or power feeds?

Thanks.

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post #20 of 21 Old 04-08-2012, 01:04 PM
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One way to narrow it down would be unmount the antenna physically from the jeep and keep it connected to the radio. If the problem goes away, it's a ground loop problem, If it stays, it's a RFI problem.
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post #21 of 21 Old 08-01-2018, 02:22 PM
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UNIDEN 75 SW XT Static with rear LEDs

I experienced a similar problem with static when using rear LEDs. I am running a UNIDEN 75 SWXT and a Firestick antenna with a NGP coax. The CB itself is wired into an auxiliary connector off the rear of the cigarette lighter. All auxiliary lights are run through a sPOD. Static problem only occurred when i turned on the rear LEDs over the spare tire carrier. No issue with other LEDs on Jeep (headlights, fogs, floods, spots, rock lights). I checked continuity on the antenna mount. No issues. I disconnected the coax from the CB itself and the static stopped. I therefore removed the NGP coax connection from the antenna mount. Although the plastic and metal washers were in the correct order, I noted the raised plastic insulator on the NGP coax was smashed and was too close or touching the antenna mount. I made a few minor adjustments to the plastic insulator on the coax and the static stopped.
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