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Crossband (cross-band, cross band) operation is a method of telecommunication in which a radio station receives signals on one frequency and simultaneously transmits on another for the purpose of full duplex communication or signal relay.
To avoid interference within the equipment at the station, the two frequencies used need to be separated, and ideally on different 'bands'. An unattended station working in this way is a radio repeater. It re-transmits the same information that it receives. This principle is used by telecommunications satellites and terrestrial mobile radio systems.
Uses
Crossband operation is sometimes used by amateur radio operators. Rather than taking it in turns to transmit on the same frequency, both operators can transmit at the same time but on different bands, each one listening to the frequency that the other is using to transmit. A variation on this procedure includes establishing contact on one frequency and then changing to a pair of other frequencies to exchange messages.
