CB interfere with the Display?

[Alpine Warthog]

Hey Guys, you experience any interference when using a CB radio? My GMRS radio doesn't affect the display at all, but anytime I use the CB radio, it disrupts the display and causes it to black out and restart. What could cause this?

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[Rusty PW]

Does your co-ax cable go anywhere near your display? Move the cable far away from it. What you are getting is RI interference.

 

[Alpine Warthog]

Does your co-ax cable go anywhere near your display? Move the cable far away from it. What you are getting is RI interference.

I'm kinda stuck since my CB is mounted up top on the molle overhead console. Any way to put some shielding between the cable and the mirror? The Antenna passes over the windshield frame just above the mirror,

 

[kb5zcr]

You can try these rf chokes on every cable (Antenna and power) to cut rf (radio frequency) from getting into your display. They do work but I've only used them to keep my home ham radio setup from getting into my home stereo.
Put them close to the equipment and you can loop the power cable thru each several times. Each loop thru the choke cut rf even more.
The more the better, can also be used on the stereo cables too.

https://www.amazon.com/Cedmon-Pieces-Ferrite-Suppressor-Diameter/dp/B07CWCSNW9/ref=sr_1_5?crid=23LLWD2RAAKEE&dib=eyJ2IjoiMSJ9.Sa1QrT7GfPS8avzkJEwHTwj9ejIuaOBrLpNe684jky1obwhgdS1SI277WPm_Cogjml_owAwKq1Yz8uMz9v4jRg4YY_ydCXxaKe58a4ILcLhPkJ-T0R-18IMwB9UqmAHIIOKnvz40odhxEUucJnIwoEbe2HdgxQ5GzlRhgQNZyVSeWQ5hLXwNOzaHRL9KGSVIA_c3kjuBHC8-BSsjxrJcJZRx9weqc9KGhs9wG2iJRHA.n8NmNhNJHVr5vlNTXCUDJOd_yb1MWCZkWUmX88pX9Oc&dib_tag=se&keywords=rf+choke&qid=1745300256&sprefix=rf+choke,aps,242&sr=8-5

 

[Zapper]

Yes, all sort of modern devices have the potential to receive interference from a CB. A CB at 4 watts output is actually a pretty strong radio transmitter- when compared to modern devices such as a cellphone which are around .2 to .4 watts.

As well the frequencies used by a CB are very low by modern standards, these, coupled with cheap manufacturing mean they throw off harmonics all over the place (every approx 27 Mhz). These harmonics can interfere with car electrical systems, including things like the entertainment system crashing, or check engine lights appearing, ABS warning lights, etc.

The problem you've described is likely that RF energy, which is supposed to come out of the antenna, is coming out somewhere else. The most common cause is the antenna has not been matched/tuned properly. An antenna is tuned just like a string on a musical instrument- it has a certain resonant frequency. Also like a string on an instrument, changing the length changes the resonant frequency. There's usually a segment of the antenna held on by a hex screw that allows you to slightly lengthen or shorten the antenna. if you dump power into an antenna that is not resonant with the frequency, the RF wave will not end at the end of the antenna, instead part of it will reflect back down the antenna feedline cable ("coax"). From there it will either radiate from the outer shield of the coax, radiate from the metal case of the radio or even the mic wiring, and/or radiate from the power cables.

How to address? First, find someone who can tune your antenna. There's usually guys in the local 4x4 forums with the tools. Or there might be a local 2 way radio shop who can do it for you. There's a good chance that will solve the problem. If the coax antenna cable is close to certain devices it should not be a problem if the antenna is properly tuned. All RF will be contained within the center conductor of the cable on a tuned system. It is when it is out of tune that the RF travels back over the outside shield of the coax.

Second thing, run the power cables direct to the battery. This is more about received noise, adequate power delivery and avoidance of ground loops than controlling transmitted RF but it is still good practice and can solve some strange problems.

If you still have issues, try running a ground strap from the radio case to the metal frame of the Jeep.

Another thing that can happen is the coax can break, but this is unlikely with a fresh install.

Ferrites on lines can work, but you will need a bunch of them, and they are often more masking a problem rather than fixing it. Assuming the problem is an unmatched antenna, if you fix it with ferrites, then your next issue will be that you have very little range.

 

[Alpine Warthog]

Yes, all sort of modern devices have the potential to receive interference from a CB. A CB at 4 watts output is actually a pretty strong radio transmitter- when compared to modern devices such as a cellphone which are around .2 to .4 watts.

As well the frequencies used by a CB are very low by modern standards, these, coupled with cheap manufacturing mean they throw off harmonics all over the place (every approx 27 Mhz). These harmonics can interfere with car electrical systems, including things like the entertainment system crashing, or check engine lights appearing, ABS warning lights, etc.

The problem you've described is likely that RF energy, which is supposed to come out of the antenna, is coming out somewhere else. The most common cause is the antenna has not been matched/tuned properly. An antenna is tuned just like a string on a musical instrument- it has a certain resonant frequency. Also like a string on an instrument, changing the length changes the resonant frequency. There's usually a segment of the antenna held on by a hex screw that allows you to slightly lengthen or shorten the antenna. if you dump power into an antenna that is not resonant with the frequency, the RF wave will not end at the end of the antenna, instead part of it will reflect back down the antenna feedline cable ("coax"). From there it will either radiate from the outer shield of the coax, radiate from the metal case of the radio or even the mic wiring, and/or radiate from the power cables.

How to address? First, find someone who can tune your antenna. There's usually guys in the local 4x4 forums with the tools. Or there might be a local 2 way radio shop who can do it for you. There's a good chance that will solve the problem. If the coax antenna cable is close to certain devices it should not be a problem if the antenna is properly tuned. All RF will be contained within the center conductor of the cable on a tuned system. It is when it is out of tune that the RF travels back over the outside shield of the coax.

Second thing, run the power cables direct to the battery. This is more about received noise, adequate power delivery and avoidance of ground loops than controlling transmitted RF but it is still good practice and can solve some strange problems.

If you still have issues, try running a ground strap from the radio case to the metal frame of the Jeep.

Another thing that can happen is the coax can break, but this is unlikely with a fresh install.

Ferrites on lines can work, but you will need a bunch of them, and they are often more masking a problem rather than fixing it. Assuming the problem is an unmatched antenna, if you fix it with ferrites, then your next issue will be that you have very little range.

You bring up really good points. I did tune my antenna last summer, but she's taken a beating since then so It's never a bad idea to check that. The CB is powered straight to the battery through a relay. I guess I could check the wires at the relay for corrosion. The radio isn't grounded beyond the ground to the battery so I could see about that too. I should probably check the antenna mount as well

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