2006 Saab 9-5 Owner's Manual - Page 110

110 Saab 9-5 Audio System FM AM IB387 IB390 Shadow effect Because FM radio waves travel in straight lines from the transmitter, a shadow effect can occur when tall buildings or hills obstruct the propagation path from the transmitter to the car. Cross modulation If 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 is needed to provide good reception. AM waves, on the other hand, are reflected off the ionosphere, thus greatly extending their range. IB388