1996 Ford Thunderbird Owner's Manual - Page 164

Common Radio Reception Conditions Several conditions prevent FM reception from being completely clear and noise-free, such as the following: 1. Distance/Strength The strength of the FM signal is directly related to the distance the signal must travel. The listenable range of an average FM signal is approximately 25 miles (40 kilometers). Beyond this distance, the radio is operating in a fringe area and the signal becomes weaker. NOTE: Always make sure your antenna (whether you have a power antenna or a manually adjustable antenna) is fully extended to the maximum length for proper reception. If your antenna is not fully extended, you may experience signal loss while traveling in fringe reception areas. 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. 161