FM broadcasting
VHF Radio waves do not travel far beyond the visual horizon, so reception distances for FM stations are usually limited to 30–40 miles (50–65 km) They can also be blocked by hills or buildings.
Broadcast range
The "primary service area" is the area served by a station's strongest signal. The "city-grade contour" is 70 dBµ (decibels relative to one microvolt per meter of signal strength) or 3.16mV/m (millivolts per meter) for FM stations in the United States, according to Federal Communications Commission (FCC) regulations. This is also significant in broadcast law, in that a station must cover its city of license within this area, except for non-commercial educational and low-power stations.