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 miles). 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