"econof" wrote in message news:dElpb.70518$ao4.195390@attbi_s51...
I recently installed a cobra 29 in my Ford Explorer. I understand the
previous owner had the radio "tuned". If I key the mike while my factory car
stereo is on, I can hear it through the speakers. I called a cb shop and one
guy claimed the interference wasn't because of the increased radio power,
but rather interference through the car's factory amp. Does anyone have any
insight on this? If this is true , would bypassing the factory amp and
installing a new stereo cure this?


Thanks in advance

1) Try coiling up the excess speaker wire near the AM/FM radio and
taping it together with tape. This will change the inductance of the
wire leads and may choke off some of the RF coming down the speaker
wire. If that does not work you may need purchase some ferrite beads
or loops (Radio Shack carries them) and then wrap the speaker wire
around it to get a higher value of inductance.

2) Also try coiling up the AM/FM coax as it enters the AM/FM radio.
This will create an RF choke that will cut off "common mode" RF
signals running up and down the outside shield of the coax. It will
not affect the AM/FM radio signals you want coming down the inside of
the coax.

3) Coil up the DC power leads coming in to the AM/FM radio at the
radio. You may need a ferrite loop from Radio Shack to make this work
as well.

4) Install a high pass filter in line with the AM/FM coax going to the
AM/FM radio (available at Radio Shack).

5) Install a low pass filter in line with the CB coax.

6) Close to where your CB coax hooks to the CB antenna, coil up the
coax in a loop to stop RF from running back down the outside of the
coax and back to the radio. For 27 MHz (The CB Band) and RG-58 cable
wind just over 4 feet of cable in to 8 turns and tape it together. For
RG-8 use just over 6 feet of cable wound in to 8 turns and tape it
together.

7) Some DC noise filters may have RF noise supression built in.

Hope that helps,

Night Ranger

P.S. The information I gave you came out of ARRL's Radio Interference
Handbook, and the ARRL antenna handbook.