Ford 1999 Taurus Owner's Manual page 71

Antenna
The antenna for the audio system is integral to the
rear window glass. The AM portion of the antenna
uses the same pattern of lines as the grid for the
rear defroster. The FM portion of the antenna uses
the top three lines on the glass, which are indicated
by the word "RADIO."
Common Radio Reception
Conditions
Several conditions prevent FM reception from being
completely clear and noise-free, such as the
following:
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 24
miles (40 km). Beyond this distance, the radio is
operating in a "fringe" area and the signal becomes
weaker. Also, "Signal Modulation" is used by some
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stations to increase their "loudness" relative to other
stations. The difference in loudness can be a result
of signal modulation as well as signal strength.
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.