Expert: Cleggsan - 8/19/2010

Question
QUESTION: I have a 2002 silverado with a JVC headunit from around 2000 hooked up to a really old alpine amp, I also have a Midland CB radio with an antenna. When i mic in to say something on the CB it comes over the radio if it is on and makes a lot of squeaking and loud noises. Do you know what would cause this interference?

ANSWER: It is a big subject.  It can be from either radio and from bad wiring in the vehicle.  It takes a global analysis to get to the bottom of rf feedback. But, it sounds like yours is unusually bad.

First check all the grounds. If you can ground the cb and the head unit and amps all at the same point.  RF running around the chassis of the vehicle is bad, bad.

Then, check for any open shields on shielded wire if any.

Then, google for radio interference in cars and you will find several web pages with various levels of instructions.   Adding caps and filters in key places can help but you have to do some divine guidance to get it right.  Praying often helps - to get inspiration on where to add a cap or filter and where to run a wire, etc.  It is often   a  trial and error proposition.

Finally, it can be a defective circuit inside one of the radios.  Replacement of the unit is usually the cure.

I don't want to brush you off, but do some more testing and checking and let me know what you find that will influence the level of rf interference.



---------- FOLLOW-UP ----------

QUESTION: I think I found the source of this interference when I unplug the cb
antenna it all worked flawless. When I pulled the antenna wire away from
the dash and plugged it in it all worked great. So i just routed that wire
different.

Answer
Very good.  Good sleuthing.  Glad you found it and glad you got a relatively easy one.

Over time some of the interference may return which will you to readjust the wire route.  Such things as an extra passenger or passing by a semi on the highway may show an increase in rf feedback but hope this works good.

Thanks.