I installed a CB radio and the antenna is picking up ignition noise. It's not alternator whine and it goes away when I unplug the antenna so I know it's not coming down the power wires. They make filters for this (capacitors) that go on the power wire to the coil but I am running an MSD 6A. Can I still use a cap to filter the noise since capacitative discharge is a whole different can of worms than the stock HEI? I don't want to fry anything or catch my car on fire lol. Thanks.

 

Are you running shielded plug wires and resistor plugs?

I would think the filter cap would be OK with the MSD, but don't know for sure.

 

i know the plugs are resistors, pretty sure the wires are too. anyone else have input? thanks

 

U-Train,

It may not be the antenna, but the power supply of the radio that is affected by the ignition noise. If you feel that is possible, try filtering the power source.

Even suppression type wires and plugs can emit some RFI and cause noise spikes on the power supply. Have you trried relocating the antenna to a different (rear) part of the car to determine it's sensitivity? You should also check grounding at the radio and the antenna lead (co-ax) shield braid/bleeders.

 

from what i've read on this (common) problem, i've determined that it's not coming from the power wires because the noise stops if i disconnect the antenna. i tried putting the antenna on the back and it didn't change the noise strength. how do i ground the antenna, i'm obviously not an electronics wiz lol. thanks.

 

The antenna itself isn't really grounded, except throught the shield braid of the cable. Make certain the coaxial cable connectiosn are reliable.

It's also likely that since the citizens' band is in AM, all noise cannot be eliminated without RF low-pass filtration on the radio tuning circuit, or an added low-pass filter in rthe antenna line. If it is a low-buck radio, chances are the filtration is minimal or the radio lacks the ANL circuits found in high-end units.

Unfortunately, adding a filter (and effectively changing the cable length) will affect the standing wave, requiring you to recalibrate the cable or retune the antenna.

If you find a low-pass RF filter, try to get one with as little cable length as possible.

 

well it's not a cheapy radio so i don't think the problem is with the radio's filtration. retuning the antenna woulnt be a problem because the radio has a built in swr meter. vader, what do you think about putting a cap on the coil? also, i got the radio used and it smelled of cigarette smoke when i got it out of the box, do you think it's possible that the chemicals from the smoke may need to be cleaned off the circuitry?

 

I've heard of people installing ground wires to the hood to help shield the antenna from the rf generated by the ignition system.
I had a fiberglass hood, so I couldn't try it.
Easy enough to try though.

Another thing you might try, pull a batt from another car and connect the CB power wires to that battery. That would isolate the noise source away from the vehicles' charging sys and elec wiring.