Re: [DML] Radio Interference

[Paul Gress <pgress@xxxxxxxxxxxxx>]

On 07/ 4/12 07:52 PM, daveswingle2 wrote:
> There are several types of radio interference in a car.
> --Power Line - typically alternator whine that comes in through the power lead. Usually symptomatic of a bad alternator or some really crappy grounds. Not static, a definite whine noise. Can usually be filtered out at the radio, some radios have a huge external choke for this purpose although IMO that means the designer screwed up internally and applied an external fix since the parts are huge.


This is called conductive emissions.  Most manufacturers today use a filter for this which is usually a choke and capacitor.  It's usually placed between the power input and ground of the radio.



> --Ignition - Comes from the ignition system as static that increases in frequency with engine RPM. Generally comes in through the antenna.



This is called radiated emissions.  It is caused by the discharge rate (ramp) of the voltage across the spark plug being almost at the same rate as an RF signal.  A simple resistor in series with the spark plug will slow the discharge rate (ramp down) to place it out of the RF spectrum of the receiver.







[Non-text portions of this message have been removed]



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