2000 Saab 9-3 Owner's Manual - Page 108

108 Saab 9-3 Audio System FM AM IB980 Cross-modulation When the radio is tuned to a weak transmitter in the vicinity of a stronger one, the car's antennas will receive signals from both. Such interference is apparent when the unwanted broadcast can be heard faintly in the background. Radio waves, FM/AM FM radio waves radiate in straight lines from the transmitter. Because such waves do not follow the curvature of the Earth, their strength becomes weaker the further they travel. That is why a large number of transmitters are needed to provide good reception. AM waves, on the other hand, are reflected off the ionosphere, thus greatly extending their range. IB388 Sources of AM interference AM reception is prone to interference, e.g. from electrical systems on other vehicles, high-tension power lines and lightning. IB981