I just installed a mobile CB (Uniden) into my Jeep. When the key is in auxiliary (car off, accessories on) and the squelch turned all the way down, no S/RF lights are illuminated and the background noise is relatively low. When I start the car, I can hear engine noise and the first of three S/RF lights light up (while the CB is receiving). If I turn the squelch up to block it out, operating the windshield washer (spray pump) can break squelch.

S/RF Number 1 light illuminated at engine idle

I'm new to amateur radio and CB. Is this normal? When I first installed the radio a few days ago, this was not happening.

  • $\begingroup$ Well this is where the fun starts! Did you install the radio in this car or did you install it in another car? Which band did the other radio use? In general, I'm not surprised that you're getting more noise with the car running. You have the ignition system that can be noisy and you have electrical motors that can also be source of noise. Right now, my advice would be to try to find someone to give you a readability report when the engine is running, to check if the noise is reaching Tx. $\endgroup$
    – AndrejaKo
    Commented May 26, 2015 at 7:07
  • 2
    $\begingroup$ You could also try disconnecting the antenna and checking how that affects the noise when the engine is on and off. This way, you'll know if and how much noise is coming from power installation and how much is picked up by the antenna. Edit your question with that info and tell us more about your antenna installation and which radio exactly you're using and how is it connected to power and chassis of the vehicle. $\endgroup$
    – AndrejaKo
    Commented May 26, 2015 at 7:10
  • $\begingroup$ Thanks for the help! I grounded the radio to the chassis at a main ground under the dash. I connected the hot lead to the fusebox. The radio is a Uniden 510XL. I will try to find someone to give me a mic check soon. As I say, I'm new to amateur radio. Disconnecting the coax cable reduces the noise significantly (the S/RF light is not on) but I can still hear noise that matches the engine revs. I used a multimeter to check the grounding of my mount to the vehicle body. There is good continuity from the mount to the chassis. $\endgroup$ Commented May 30, 2015 at 5:10

1 Answer 1


If your car uses petrol (gasoline) rather than diesel, then the ignition system can potentially generate a lot of noise because of the high-voltage system used to generate the sparks that ignite the fuel.

Electric motors such as those used in the windscreen washer pump and/or wipers (or electric windows, etc.), can also generate noise. This would mean that when you operate the motorised devices, the noise will show on the radio as extra 'hash', and will eventually break squelch if it reaches a high enough level.

All of this noise can get in through the power system (electrical noise), or can be received as electromagnetic radiation across a broad range of frequencies (RF noise). Any electrical noise can be reduced by using choke filters on the power supply to the radio, and RF noise is better eliminated at source.

To answer the question "is it OK for the S/RF light to be illuminated at engine idle?", the answer is that it's not completely unexpected in a noisy environment, but it's something you can probably do something about. The first thing to do (as suggested in a comment to your question) is to disconnect the antenna from the back of the radio, and see if any (even a small amount) of the noise is present when no antenna is connected. If so, then you're in luck, and some choke filters on the power leads where they enter the radio might be able to stop the problem. If not, you have the more difficult task of trying to reduce the noise generated by the multiple systems within your Jeep, at source.

  • $\begingroup$ Thanks! Removing the coax cable from the radio reduces the noise significantly but there is still some engine noise. Would running the power leads straight to the battery help in this situation? $\endgroup$ Commented May 30, 2015 at 5:14
  • $\begingroup$ That might help, and be aware that it will be possible in that case to run the battery flat if you leave the radio turned on when you switch the ignition off overnight or all day. Also DO REMEMBER to put a proper fuse between the battery and the radio - preferably one on each wire (positive and negative), as close to the battery as you can. $\endgroup$
    – Scott Earle
    Commented May 30, 2015 at 5:16

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