Appendix
Radio Reception
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, 2 stations may sometimes be picked up on the same frequency at the same time.
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 2 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.
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.
Weak signal noise
In suburban areas, broadcast signals become weak because of distance from the transmitter. Reception in such fringe areas is characterized by sound breakup.
Strong signal noise
This occurs very close to a transmitter tower. The broadcast signals are extremely strong, so the result is noise and sound breakup at the radio receiver.
Station drift noise
When a vehicle reaches the area of 2 strong stations broadcasting at similar frequencies, the original station may be temporarily lost and the second station picked up. At this time there will be some noise from this disturbance.
