cardiagn.com (c) Fade out is caused by objects (buildings, mountains, etc.) that deflect away part of a signal, resulting in a weaker signal when the object is between the transmitter and vehicle. High frequency radio waves, such as FM broadcasts, are easily deflected by obstructions. Low frequency radio waves, such as AM broadcasts, are much more difficult to deflect. 4. NOISE PROBLEMS (a) Technicians must have a clear understanding about the noise problems of the customer's vehicle. Use the following table to diagnose the problems.
RADIO WAVE CONDITION IN WHICH NOISE OCCURS PRESUMABLE CAUSE AM Noise occurs in a specific area Strong possibility of foreign noise AM Noise occurs when broadcasting is faint Same program may be broadcasted from various local stations If the program is the same, one of those may be tuned in AM Noise occurs only at night Strong possibility of beats from distant broadcasting FM Noise occurs at a specific place during driving Strong possibility of multipath noise and fading noise caused by changes of FM frequency. HINT: When the noise does not match the examples above, refer to ''Reception Problems''. Check the descriptions about phasing and multipath.