Topaz L4-140 2.3L HSC (1984)
FIGURE 20
Reception Characterstics
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The AM signal, being of comparatively low frequency, has a long wave which can bend around obstacles and skip along the ground. This bending
characterstic also means that the AM signal will be reflected by a layer in the atmosphere called the ionosphere and bent back to earth. These
characterstics combine to give AM long range reception (Figure 20).
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FM range is limited to 20-25 miles, except for high power stations. Monaural FM stations have greater range than stereo FM. Range for FM does
not depend on time of day. As the station signal gets weaker, volume stays about the same, but noise increases. FM signals follow a "line-of-sight"
path and are not reflected by the ionosphere (Figure 20).
FIGURE 21
FLUTTER
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FM flutter can be best described as repeated pops and hissing bursts heard in the speaker during an otherwise good broadcast. Flutter can be
caused by numerous reasons: antenna design, fringe areas, etc. and is not the receivers fault. Flutter may be noticed, not only in fringe areas, but
near the station because of the "line-of-sight" characterstic of FM radio waves. FLUTTER occurs when a building or large structure is between
you and the station. AM has no flutter (Figure 21).
FM Multipath Cancellation and Capture, Fading and Static