Mazda mx-5 2017 Owner's Manual page 237

FM characteristics
An FM broadcast range is usually about
40—50 km (25—30 miles) from the
source. Because of extra coding needed to
break the sound into two channels, stereo
FM has even less range than monaural
(non-stereo) FM.
FM Station
40—50km
(25—30 miles)
Signals from an FM transmitter are similar
to beams of light because they do not
bend around corners, but they do reflect.
Unlike AM signals, FM signals cannot
travel beyond the horizon. Therefore, FM
stations cannot be received at the great
distances possible with AM reception.
Ionosphere
FM wave
FM wave
100—200 km (60—120 miles)
Atmospheric conditions can also affect
FM reception. High humidity will cause
poor reception. However, cloudy days may
provide better reception than clear days.
AM wave
Multipath noise
Since FM signals can be reflected by
obstructions, it is possible to receive both
the direct signal and the reflected signal
at the same time. This causes a slight
delay in reception and may be heard as a
broken sound or a distortion. This problem
may also be encountered when in close
proximity to the transmitter.
Direct
Flutter/Skip noise
Signals from an FM transmitter move in
straight lines and become weak in valleys
between tall buildings, mountains, and
other obstacles. When a vehicle passes
through such an area, the reception
conditions may change suddenly, resulting
in annoying noise.
Interior Features
Audio System
Reflected wave
5–15