AM Radio Interference in car

[dau]

Hello,
I like to listen to AM Radio in my car (Skoda 1998). Every time the motor runs it interferes with an ugly noise in the loudspeaker. An interim seperate supply of the radio lowered the noise level by approx. 50%. So I guess the rest is introduced by antenna pick-up. An LC-low pass filter inserted in the car-battery-supply to the radio has almost no effect. Has anyone a tip/idea?
Rolf

 

[VEBill]

It is simple to confirm that the interference is entering via the antenna - just unplug the antenna connector from the back of the radio. Unfortunately the same approach doesn't work quite so well with the power leads... ;-)

If you listen to the noise, you should be able to hear if it is sparkplug (popping), alternator (whine), whatever...

If it is the sparkplugs, then make sure that you have the appropriate resistive spark plug cables. It is quite common for people to fit non-resistive cables.

 

[BrianR]

Further to what VE1BLL said, check that the shielded lead from the antenna has its shield well grounded at the antenna end. If it is and the noise goes away when the antenna is unplugged you need to service the ignition system which might include any or all of the folowing: in order..

Replace wire HT leads with resistive leads.
Replace resistive leads with new ones.
Replace the spark plugs.
Move the antenna to the other end of the vehicle.

 

[Higgler]

Bring a separate AM radio into your car that's battery powered. I'm sure you have one lying around your place. That way you can tell partly if it's coming over the airwaves or over the power lines. You may want to connect the car antenna to this radio antenna to see if noise pick up occurs. It may sound silly, but having an external am radio having an earphone plug on it, then plugged into an external FM modulator ($30 in most stores) could have you play your AM over your FM radio in the car.
Kevin.