Reduced-carrier transmission is an

amplitude modulation Amplitude modulation (AM) is a signal modulation technique used in electronic communication, most commonly for transmitting messages with a radio wave. In amplitude modulation, the instantaneous amplitude of the wave is varied in proportion t ...

(AM) transmission in which the

carrier signal In telecommunications, a carrier wave, carrier signal, or just carrier, is a periodic waveform (usually sinusoidal) that conveys information through a process called ''modulation''. One or more of the wave's properties, such as amplitude or frequ ...

level is reduced to reduce

waste Waste are unwanted or unusable materials. Waste is any substance discarded after primary use, or is worthless, defective and of no use. A by-product, by contrast is a joint product of relatively minor Value (economics), economic value. A wast ...

electrical power Electric power is the rate of transfer of electrical energy within a electric circuit, circuit. Its SI unit is the watt, the general unit of power (physics), power, defined as one joule per second. Standard prefixes apply to watts as with oth ...

. Suppressed-carrier transmission is a special case in which the carrier level is reduced below that required for

demodulation Demodulation is the process of extracting the original information-bearing signal from a carrier wave. A demodulator is an electronic circuit (or computer program in a software-defined radio) that is used to recover the information content fro ...

by a normal receiver. Reduction of the carrier level permits higher power levels in the

sideband In radio communications, a sideband is a band of frequencies higher than or lower than the carrier frequency, that are the result of the modulation process. The sidebands carry the information transmitted by the radio signal. The sidebands c ...

s than would be possible with conventional AM transmission. Carrier power must be restored by the receiving station to permit

, usually by means of a

beat frequency oscillator In a radio receiver, a beat frequency oscillator or BFO is a dedicated electronic oscillator, oscillator used to create an audio frequency signal from Morse code radiotelegraphy (Continuous wave, CW) transmissions to make them audible. The signal ...

(BFO). Failure of the BFO to match the original

carrier frequency In telecommunications, a carrier wave, carrier signal, or just carrier, is a periodic waveform (usually sinusoidal) that conveys information through a process called ''modulation''. One or more of the wave's properties, such as amplitude or fre ...

when receiving such a signal will cause a heterodyne. Suppressed carriers are often used for single sideband (SSB) transmissions, such as for

amateur radio Amateur radio, also known as ham radio, is the use of the radio frequency radio spectrum, spectrum for purposes of non-commercial exchange of messages, wireless experimentation, self-training, private recreation, radiosport, contesting, and emer ...

on shortwave. That system is referred to in full as SSB suppressed carrier ( SSBSC) or (SSB-SC). International broadcasters agreed in 1985 to also use SSBSC entirely by 2015, though IBOC and

IBAC Ibac is a supervillain featured in American comic book, American comic books published by Fawcett Comics and DC Comics. Primarily, versions of the character serve as parallels to Captain Marvel/Shazam and Black Adam, sharing significant histories ...

digital radio Digital radio is the use of digital technology to transmit or receive across the radio spectrum. Digital transmission by radio waves includes digital broadcasting, and especially digital audio radio services. This should not be confused with In ...

(namely Digital Radio Mondiale) seems likely to make this irrelevant. FM stereo transmissions use a double-sideband suppressed carrier ( DSBSC) signal from a stereo generator, together with a pilot tone of exactly half the original carrier frequency. This allows reconstitution of the original stereo carrier, and hence the stereo signal.

References

* {{DEFAULTSORT:Reduced-Carrier Transmission Radio modulation modes

See also

References