AM/FM Reception

RADIO SIGNAL
The radio signal is sent from a broadcast station and is then received by an antenna. The strength of the signal received depends on the following:
^ The power output, wattage, of the broadcasting station
^ The location of the vehicle, or receiver, relative to the broadcast tower.
^ Obstacles between the tower and the receiver
^ Atmospheric conditions
^ What band, AM or FM, the station is broadcasting
^ Type of antenna and the ground plane

AM RECEPTION
The AM band has a lower frequency range than the FM band. These longer wavelengths:
^ Bend around obstacles
^ Follow the curvature of the earth
^ May reflect off the ionosphere (skip)

The AM frequencies have longer range due to the ground wave. The ground wave follows the curvature of the earth and is affected by its conductivity. Greater conductivity equates to less signal loss thus transmission over water is better than over land. The AM band has a range of 80-320 km (50-200 mi).

FM RECEPTION
The shorter wavelengths of the higher frequency FM band:
^ Reflect off obstacles
^ Are absorbed by the ground
^ Penetrate the ionosphere

Broadcasts in the FM band are limited to "line of sight" reception which is typically 40 km (25 mi). Even when out of a direct line of sight, the signal may be reflected into areas that would be in a "shadow" otherwise. Factors which affect the line of sight include:
^ Height of the broadcast antenna
^ Height of the receiving antenna
^ Terrain and buildings in the broadcast path