1996 Ford Explorer Owner's Manual - Page 242

2. Terrain The terrain (hilly, mountainous, tall buildings) of the area over which the signal travels may prevent the FM signal from being noise-free. If there is a building or large structure between the antenna and station, some of the signal "bends" around the building, but certain spots receive almost no signal. Moving out of the "shadow" of the structure will allow the station to return to normal. When the radio waves are reflected off objects or structures, the reflected signal cancels the normal signal, causing the antenna to pick up noise and distortion. Cancellation effects are most prominent in metropolitan areas, but also can become quite severe in hilly terrain and depressed roadways. To minimize these conditions, a stereo/mono blend circuit has been incorporated into this system. This feature automatically switches a weak stereo signal to a clearer monaural signal, which improves the quality of reception. Several sources of static are normal conditions on AM frequencies. These can be caused by power lines, electric fences, traffic lights and thunderstorms. Another reception phenomenon is Strong Signal Capture and Overload. This can occur when listening to a weak station and when passing another broadcast tower. The close station may capture the more distant station, although the displayed frequency does not change. While passing the tower, the station may switch back and forth a few times before returning to the original station. When several broadcast towers are present (common in metropolitan areas) several stations may overload the receiver, resulting in considerable station changing, mixing and distortion. 242