5 - Interior Features | Audio System
AM characteristics
AM signals bend around such things as buildings or mountains and bounce off the ionosphere.
Therefore, they can reach longer distances than FM signals. Because of this, two stations may sometimes be picked up on the same frequency at the same time.
FM characteristics
An FM broadcast range is usually about 40—50km (25—30miles) 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.
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.
Atmospheric conditions can also affect FM reception. High humidity will cause poor reception.
However, cloudy days may provide better reception than clear days.
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.
