Re: [DML] Radio Interference

["daveswingle2" <swingle_dmc@xxxxxxxxxxx>]

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. 

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

--Other sources - Comes from things like the microswitches on the engine, window switches etc. This is what the capacitors sprinkled all over the car are trying to prevent. This can come in either via power line or the antenna. 

The radio can have quite a bit of impact on this, and modern radios are much better that 30-year-old radios. 

AM radio has its own set of problems as ignition and "other source" noise is AM in nature, it can't be filtered out and still have a radio that works! Putting the radio antenna near the engine in a car with a plastic hood and a poor antenna ground was not a good idea from an engineering perspective. Since few people really use AM at this point it is not considered a big deal to most. 

FM radio, on the other hand, can be designed for very high AM signal rejection, which is what modern FM receivers do well. Since satellite radio is essentially digital, it is even better at noise rejection, in fact excessive noise into a satellite radio will more likely be heard as holes in the sound (due to loss of signal/receiver desensitization) rather than interference. 



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