Fm Reception Characteristics; Fm Reception Differs From Am; Fading Out - Eclipse CD5425 Owner's Manual

How to operate the tuner

FM reception characteristics

In general, FM has much better tonal quality than AM. However, FM and FM
stereo reception encounter several characteristic problems not encountered
with AM. FM is more difficult to receive than AM in a moving vehicle. The
following are explanatory notes on what to expect from FM reception and on
how to get satisfactory performance.

FM reception differs from AM

A characteristic of transmitted signals is that lower frequencies
travel further. FM frequencies are much higher than AM's (similar to
a ray of light): they won't bend but they will reflect. Often, they will
be interrupted by tall buildings, mountains, etc., taking direct and
indirect paths to your vehicle's antenna. The distance at which FM
stations can be received satisfactorily is usually not nearly as far as
that which AM stations can be received.
AM Radio Waves

Fading out

In weak signal or "fringe" reception areas, FM stations may fade out
completely, or fade in and out. When driving in weak signal areas,
such as near hills, through valleys or tunnels, among tall buildings,
etc., you may encounter unusual noise interference. THIS IS NOT A
TUNER PROBLEM. In this case, you can only wait until you are in a
better reception area, tune to a stronger station, or reduce the treble
level.
Ionosphere
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FM Radio Waves
Ionosphere