Hi all,

appreciate some help with this question. Recently installed a 477mhz
(australian) CB radio in vehicle. Now getting interference on the CB
radio
which is related to how fast the wheels are spinning. I get no
interfernece if the vehicle is not moving even if I rev up the engine
(i.e. the problem is not alternator or ignition system related). I also
get the interference when I use a handheld CB which does not have power
or antenna connected to the car.

Therefore, the interference is not coming through a power or antenna
cable and the usual suggestions of "use a noise filter" will not apply
in this case.

Some people I have been speaking to have suggested that the problem
could be either:

1. Speedometer drive circuitry - It is possible that the speedo
sensor is acting as a transmitter, even with the ignition off, as it is
electro-mechanical, and may generate pulses even if there is nothing
turned on to read them.

2. ABS sensor - sends data to computer about wheel movement - could be
causing interference

3. Magetic wheels / tyres - could be creating interference.

Can anyone tell me:

1. could the speedo / ABS units be causing the interference?

2 if so, where are the speedo / ABS units located and how can I stop
this problem? I.e. can they be shielded using copper cable or can I
noise filter be applied to them.

thanks in advance

Roj