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In the United States, radio stations are assigned callsigns that either start with K (for those located west of the Mississippi River), or W (for those located east of the Mississippi River). AM radio stations by call sign (starting with KA–KF)
FM station class Reference (maximum) facilities for station class (ERP / HAAT) FM protected or primary service contour Distance to protected or primary service contour Distance to 70 dBu city-grade or principal community coverage contour Class A 6 kW 100 m (328 ft) 60 dBu (1.0mV/m) 28.3 km (17.6 mi) 16.2 km (10.1 mi) Class B1 25 kW 100 m (328 ft)
In the Americas (defined as International Telecommunication Union (ITU) region 2), the FM broadcast band consists of 101 channels, each 200 kHz wide, in the frequency range from 87.8 to 108.0 MHz, with "center frequencies" running from 87.9 MHz to 107.9 MHz. For most purposes an FM station is associated with its center frequency.
A coverage map may be produced to indicate the area in which a certain signal strength is delivered. [1] Even if it is 100% accurate (which it never is), a major factor on whether a signal is receivable depends very much on whether the receiving apparatus is sensitive enough to use a signal of that level.
In US broadcasting, service contour (or protected contour) refers to the area in which the Federal Communications Commission (FCC) predicts coverage.. The FCC calculates FM and TV contours based on effective radiated power (ERP) in a given direction, the radial height above average terrain (HAAT) in a given direction, the FCC's propagation curves, and the station's class.
Example of a radio map estimate using STORM, a transformer-based radio map estimator. Signal strength maps quantify signal strength at each location. Formally, a signal strength map can be seen as a function γ ( r ) {\displaystyle \gamma (\mathbf {r} )} that provides a signal strength metric for each location r {\displaystyle \mathbf {r} } .
Technologies are available that allow for switching to a different signal carrying the same radio program when leaving the broadcast range of a station. Radio Data System allows for switching to a different FM or station with the same identifier, or even to (but not necessarily from) an AM station. Satellite radio also is designed to switch ...
The FCC gave FM two boosts in the early 1960s: first by setting a technical standard for stereo broadcasts, and second by adopting the FM Non-Duplication Rule in 1964, prohibiting broadcasters with an AM and FM license in cities of more than 100,000 from transmitting more than 50% of the same programming on both stations.