Volvo 2005 C70 - Manual (Page 200)

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Audio systems, general information
Cross modulation
If you listen to a weak station in the vicinity
of a stronger one, both stations may be
received simultaneously. If the car is moved a
short distance, the weaker signal may be heard
more clearly.
FM - reasons for distortion
FM is affected by the electrical systems of
nearby vehicles, especially those without
suppression. The distortion increases if the
station is weak or poorly set.
The FM reception is not as sensitive to
electrical disturbance as AM.
AM - reasons for distortion
AM reception is sensitive to electrical
disturbances such as power lines, lightning,
etc.