I’m not an antenna expert but the mag mount grounds to the metal vehicle body under the magnet. If you took the mag mount off the car the radio wouldn’t work at all. They generally ground fine without sanding off the paint.
Try this experiment - unscrew the PL-259 antenna connector from the back of the radio {{Do NOT transmit while doing this}}, and try your brakes with the radio on. If the noise goes away, we can discuss antenna placement. If the noise is still there, you may need try first, looping your B+ (red power) wire through a ferrite choke coil (look on the power cord of some of your home electronics for one you can borrow, or order one off ebay or somewhere). If that still doesn’t cure it, you may need to run a shielded wire to the battery for power.
Are all the wires shielded? If not, the wires will act as an antenna and generate noise. Either unshielded wires can be replaced or you can slide a shield over the existing cables. Make sure to ground the shield to the connectors if you add a shield.
This comment got to thinking that when I used a CB antenna as a teenager, and had an interference problem on reception, I’d also usually have a SWR problem on transmitting too. The cause for both was usually a loose connection somewhere between the radio and the antenna, either the signal wire or the ground/shield wire. Does OP’s radio indicate any SWR problems during transmitting?
No need to guess. Suggest OP follows the instructions that came with the antenna. I’ve never used a magnetic base version of a CB antenna; my truck’s CB antenna mount has a designed in lug for connection to chassis ground. That has to be grounded properly, otherwise reception is impaired and SWR problems on transmit occur. Nevada is correct that the antenna lead itself is not grounded there, but the shield for the cable definitely is. Ideally, for best reception, the ground connection would occur right at the center of the roof, but most folks think that would appear a little gauche … lol … plus the roof would leak.
I used a few different mag mounts when I first installed my CB a long time ago. One didn’t work well at all, but the other 2 worked great. None of them were expensive models.
The mag mount has a wire soldered to like a piece of foil under the magnet, that makes a ground to the body through the paint somehow. It might not seem like a great ground but they normally work fine. I went with the permanent mount later just because I didn’t like the wire running down the roof and I had the mag mount get knocked off by tree branches a couple times.
Never figured out why, but on am for stations between 800 to 1200 on my 03 trailblazer with 170k miles, hit the bakes and at a stoplight I get a whistle over the radio, and it starts out high, and gets lower the longer I am stopped.
I am noting this because I do not know all the ins and ousts of circuits, I wish you luck, sure I actually had to get a ham radio operator license to use a cb in the olden days, but being a little up on technology, maybe there is an app for that, otherwise you can look at old school soldering a capacitor on the ground side.
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This is just a thought. Is your center brake light LED? Could this cause interference?
No need to know much about circuits. Only necessary to understand some simple physics, mainly that anytime a current flow in a wire changes from one amperage to another, anywhere in the car, that change in current flow also transmits an rf signal pulse. Any near by receiving antenna will easily pick it up. A natural wonder is how a radio works at all in a car, since currents are flowing and changing all over the place in the car’s wiring harness. Car design engineers at the manufacturer have to worry about all that. For example they sometimes place the spark plugs down in deep holes in the cylinder head. And they purposely add some resistance to the spark plug wires. And they’ll use shielded or twisted pairs in the wiring harness. Shielded, no explanation needed. Twisted pairs work for either transmit or receive, b/c one of the pair has current going in one direction, and one in the other. Along with the fact of their orientation (due to the twisting) w/respect to each other, the interference from one of the wires in a twisted pair tends to cancel out the other.
Maybe upgrade to a CB that has built in NB and ANL filters. I know if i don’t have those turned on I get noise from turn signals and wiper blades. I run a Corbra 29LX in my Freightliner and a Cobra 29 WX NW ST in my pick up. Maybe getting a radio tune up at a good CB shop will help. Mine is quiet as a mouse now. Bad SWR’s from an untuned antennas don’t cause noise.
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