[V8] Radio Theory ... and troubleshooting

[Buchholz, Steven]

... one of the reasons that alternatives to AM (Amplitude Modulation) radio
were even investigated was the issue with the noisy reception in
automobiles.  FM (Frequency Modulation) receivers are set up to clip the
amplitude variations and extract the information from the radio signal by
measuring the amount of frequency deviation from the center frequency.  FM
receivers are inherently immune to amplitude modulation effects of radio
frequency interference such as alternator noise.  If you hear any
"alternator whine" during FM operation it is not likely to be coupled in
through the antenna, rather the power and ground system of the stereo.
There is no question that the frequency of the interference created by the
alternator is modulated by the change in the speed of the engine, but this
effect is so far away from the carrier frequency of the FM station that it
is not a factor.  

When functioning properly, the window mounted antennae of the stock
Blaupunkt system are very effective, even for AM operation.  When I drove
#344 back from Colorado, I was able to listen to a San Francisco AM station
from Salt Lake City all the way across the desert into Nevada.  If you are
noticing a lot of alternator noise and poor performance in AM mode there is
probably something that can be fixed.  One of the first things to do is to
make sure that the antennae are not swapped at the deck.  Only the antenna
in the rear windshield is intended for AM operation ... if the front antenna
is attached to the connector for the rear antenna on the deck you will get a
lot of engine noise and poor AM reception.  The next thing to look at is the
antenna amplifier behind the left rear "C" pillar trim.  Make sure the
module is getting power when the radio is turned on.  You might even want to
test the antenna terminal on the amplifier by attaching and removing the lug
on the amp and antenna while listening to the radio.  You should notice a
difference in the signal when the amp is powered on and off, and when the
antenna in the windshield is disconnected.  There also appears to be some
weird coupling with the operation of the rear window defroster ... you might
even try switching that on and off while testing ... The thing that happened
on #344 was that the antenna lead from the rear antenna to the deck was
damaged while the dealer was dorking around with the airbag recall on the
car.  The best way to test for this is to measure the resistance of the
center conductor of the cable by disconnecting the connector at the
amplifier and the deck and measuring from one to the other with an ohmmeter.
If you have the factory or aftermarket RF CD changer installed this test
will not work ... 

Steve B
San Jose, CA (USA)
> 
> Actually, alternator noise is an "FM" signal, and would be 
> noticeable on the FM dial.