Cb radio interference.

HemiAlex

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I’ve got a midland 75-822 on my truck. The power is run direct to the radio and the antenna is an 18ft cable that I’ve tried to run two different ways now. I’m hearing radio interference with the antenna plugged in. I’m running a 4 ft fire stick. When I unplug either end of the antenna cable, the noise stops. The noise is 100% tied to the ignition and electrical system. I can hear the RPM and the carb fan over the radio.

I moved the antenna wire to the other side of the truck and it didn’t help it was running inline with the body harness from the alternator before and the noise was just as bad.

I’m getting pretty sick of it not being functional at all. What can I do to improve this?
 

george_tlc

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Get a Ham radio and/or a diesel :)



By direct power, I assume you mean CB power comes directly from the battery, i.e. not connected to cig lighter or other acc power.

Noise sources picked up on the antenna are typically going to be radiated noise. So, could be spark plug leads, could be alternator, does your 60 have points? Typically there would be a suppressor capacitor on the alternator (body of alternator) and to the output. If points based, there would typically be a similar style capacitor there too.

How is the antenna mounted? Coax outer braid grounded to antenna base/mount?

cheers,
george.
 

HemiAlex

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Joined
Sep 28, 2015
Messages
1,605
Location
Houston
Get a Ham radio and/or a diesel :)



By direct power, I assume you mean CB power comes directly from the battery, i.e. not connected to cig lighter or other acc power.

Noise sources picked up on the antenna are typically going to be radiated noise. So, could be spark plug leads, could be alternator, does your 60 have points? Typically there would be a suppressor capacitor on the alternator (body of alternator) and to the output. If points based, there would typically be a similar style capacitor there too.

How is the antenna mounted? Coax outer braid grounded to antenna base/mount?

cheers,
george.
The diesel would fix a few problems...and I’m ready to get a ham. This is really not functional.

I tried the cigarette lighter and then i decided to run fused leads from the battery. Just seemed better.

I’ve got an older set of denso wires. About 3 years old. No points. I’ve got a factory electronic distributor.

The antenna is mounted to a tab on my arb bumper. I’m using the firestock, their spring and quick disconnect.

Is there a wrong way to have the antenna mounted? Is there any other way of grounding it? I’m wondering if I need to buy the actual firestik cable.

If I disconnect the cable from the antenna; the noise doesn’t stop unless I move around with the cable away from the engine bay.
 

george_tlc

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I'd be checking to see if there is a capacitor on the alternator. Presumably you can hear change in pitch based on RPM, this would point to alternator or plug wires as the most likely source.

You don't need the 'firestick' cable - you are paying for nothing special. Just make sure you have decent 50 ohm coax and it is properly crimped/soldered at the RF connector that plugs into the back of the CB. The antenna end it would be the same, center of coax to antenna and braid to mount/ground on the ARB bar tab.

cheers,
george.
 

1911

chupacabra
 
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Make sure that your radio power wires do not follow the same path as the antenna coax.

You can put a capacitor on the alternator as @george_tlc mentioned.

You can put ferrite chokes on your coax (need to get the right ferrite mixture for the frequencies you are trying to attenuate).

You can add ground straps from your exhaust to the frame, i.e. "bonding".

These may help, but may not completely solve the noise issue. I had a similar problem with mine when I installed a Cobra cb radio in my FJ40; in my case, I did not achieve satisfactory results until I tried a different (Uniden) radio. Apparently, the Cobra I had was not well shielded internally. If the Midland you have is a less-expensive radio, it may have the same problem. These older trucks (40's and 60's) are very electrically noisy.
 
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Electrical interference or noise can come from a variety of reasons. As 1911 stated, avoid running your antenna coax near power wires. Specially heavy gauge wires.

These noises usually come when there's a power wires near the antenna cable, specially one which is not well insulated or has an exposed wire.

FYI, this would happen exactly the same if it were any sort of radio or any sort of engine. Coax cable is very sensitive to external current. Run it by itself.
 
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