- Reduced-carrier transmission
Reduced-carrier transmission is an
amplitude modulation(AM) transmission in which the carrier wavelevel is reduced to reduce wasted electrical power. Suppressed-carrier transmission is a special case in which the carrier level is reduced below that required for demodulationby a normal receiver.
Reduction of the carrier level permits higher power levels in the
sidebands than would be possible with conventional AM transmission. Carrier power must be restored by the receiving station to permit demodulation, usually by means of a beat frequency oscillator(BFO). Failure of the BFO to match the original carrier frequencywhen receiving such a signal will cause a heterodyne.
Suppressed carriers are often used for
single sideband(SSB) transmissions, such as for amateur radioon shortwave. That system is referred to in full as SSB suppressed carrier ( SSBSC) or (SSB-SC). International broadcasters agreed in 1985to also use SSBSC entirely by 2015, though IBOCand IBAC digital radio(namely Digital Radio Mondiale) seems likely to make this irrelevant. FM stereotransmissions use a double-sideband suppressed carrier ( DSBSC) signal from a stereo generator, together with a pilot toneof exactly half the original carrier frequency. This allows reconstitution of the original stereo carrier, and hence the stereo signal.
Source: partly from
Federal Standard 1037C
Wikimedia Foundation. 2010.
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