single frequency network (SFN)
Common wave networks or common wave radio (GWF) are terrestrial transmitter networks with several transmitters that all transmit on the same frequency. The transmitters ' antennas can be positioned to illuminate a specific transmission area, regardless of topographical features. In addition, they operate in a frequency-efficient manner because, unlike single-transmitter systems, the received field strength is not dependent on radiated power, antenna mast height, or distance.
The individual transmitter signals of a common wave network do not interfere with each other, but interfere with each other by amplifying each other. If no or only limited reception is possible in certain regional areas due to the topology of the terrain, in tunnels or buildings, this can be compensated for by so-called filling transmitters.
The topology of common wave networks consists of a control center and several common wave converters, all transmitting in the same frequency band and on the same frequency.
Regardless of whether the network is serving stationary receivers or a mobile receiver, within the transmission area a radio receiver receives the same radio frequencies from several different transmitters. Since the receivers receive the same frequency from several transmitters at the same time, frequency overlaps and interference occur. For these reasons, receivers work with this diversity and suppress transmitters that come in with low received field strengths. This is called the FM suppression effect(capture effect), which ensures proper radio coverage even in the overlapping areas of a common wave. It is important that all transmitters must not have any differences in carrier frequency, frequency dev iation and phase.
Common wave radio is used in public safety radio (authorities and organizations with security tasks), amateur radio, terrestrial digital TV, DVB-T, DVB-H and digital broadcasting.