CB Radio Interferance? - Diesel Truck Forum - TheDieselGarage.com
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post #1 of 12 (permalink) Old 06-29-2009, 06:33 PM Thread Starter
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CB Radio Interferance?

Ok, I've got a CB radio in my truck that gets a ton of interferance. I cant quite tell where it is coming from, however I know it is coming through the antenna. I have switched several antennas, coax, and even changed the mounting of the antenna. The reason I know it is radio interferance through the antenna is if the antenna is unplugged, the noise goes away. The noise only occurs when the ignition switch is in the "run" position, not the "acc" position. I think it might be the computer making all that racket, but I am not sure. It isnt alternator noise, and obviously not ignition system noise. have any of you ever run into this problem before? It's driving me nuts.

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post #2 of 12 (permalink) Old 06-30-2009, 06:36 AM
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I think that you have found it.

Possible helps
a good or excellent ground at the radio and the antenna
a twisted pair power wire to the battery, greater than 2 turns per foot
do a full ground for radio frquency to the hood, fenders, fender liners and cab

Last thing to try - metal shield to the computer wiring, without a field strength meter covering the nodes. An Opto Scout is around $400 and will survey for freq and signal streingth

The SWR on the ant is also on the list

keydl

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post #3 of 12 (permalink) Old 07-12-2009, 04:02 AM
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May need to fiddle with the RF Gain and Squelch switches as well. Some areas around here are worse than others for background interference. I live in a high traffic area where 5 interstate highways converge. Get out in the sticks and a lot of it goes away.

High tension power lines or being near some electrical sub-stations, it can be pretty bad. Import radios with really good "ears" can pick a LOT of that noise.

Another possibility, is that you may need a noise filter on the power supply, if you don't get power directly from the battery. What you may picking up is from something in the engine compartment, like the alternator. I have to run a filter on 2 trucks. They pick up the noise from the injectors.

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post #4 of 12 (permalink) Old 07-13-2009, 03:53 AM
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Dropping noise from an environment that supplies digital without a shield can most times be cured without filters by using the marine practice of twisting the ground and power wires more than 2 turns per foot. If you have a specific frequency computing the length of twist can use the standing wave to remove interference.

Cat 5 cable can be used - it is pre twisted by the pairs - one of each pair for ground and the other for power.

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post #5 of 12 (permalink) Old 07-13-2009, 02:29 PM Thread Starter
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Nope, its not environmental interferance, and not the alternator, because it does it when the motor is not running, and it doesnt change with RPM. My power wires go directly to the battery. I will try twisting them to see where I get with that. SWR is 1.1 on Channel 1, and 1.2 on Channel 40. Hood, fenders, bed, doors, tailgate, and even the exhaust is gounded with 1/2" braided ground strap.

1992 W250-P-pump and some extra air, gone, but not forgotten.

2003 SVT Cobra

1984 Chevy K10


Last edited by BigRed Cummins; 07-13-2009 at 02:32 PM.
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post #6 of 12 (permalink) Old 07-14-2009, 05:01 PM
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Filtering the PCM with a big capacitor on the power lead to the PCM is a possibility, if that reduces the interferance but some is left a choke will help.

The capacitor goes from the 12 v switched power to ground, the choke is in the line.

keydl

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post #7 of 12 (permalink) Old 07-14-2009, 09:20 PM
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the day i graduated high school
i know this is stuiped but where do you have the main wire running to i know i had a cb in a old chevy hook the power in the cig. lighter and i could hear the motor on it and also too it does in it your fuse box too

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post #8 of 12 (permalink) Old 07-14-2009, 11:11 PM Thread Starter
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power comes directly from the battery

1992 W250-P-pump and some extra air, gone, but not forgotten.

2003 SVT Cobra

1984 Chevy K10

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post #9 of 12 (permalink) Old 09-11-2010, 12:29 AM
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Do you have a Cell Phone charger that only comes on when you start the truck? Mine makes a lot of noise, as does my cell phone.

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post #10 of 12 (permalink) Old 09-11-2010, 12:30 AM
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Or an electric fuel pump under the bed!

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IF YOU HAVE TO TIE PLASTIC BALLS ON IT,IT CAN"T BE MUCH OF A TRUCK!!!
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