Amplitude-companded single-sideband (ACSB) is a

narrowband Narrowband signals are signals that occupy a narrow range of frequencies or that have a small fractional bandwidth. In the audio spectrum, narrowband sounds are sounds that occupy a narrow range of frequencies. In telephony, narrowband is us ...

modulation In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the '' carrier signal'', with a separate signal called the ''modulation signal'' that typically contains informat ...

method using a single-sideband with a

pilot tone An aircraft pilot or aviator is a person who controls the flight of an aircraft by operating its directional flight controls. Some other aircrew members, such as navigators or flight engineers, are also considered aviators, because they ar ...

, allowing an expander in the receiver to restore the

amplitude The amplitude of a periodic variable is a measure of its change in a single period (such as time or spatial period). The amplitude of a non-periodic signal is its magnitude compared with a reference value. There are various definitions of a ...

that was severely compressed by the

transmitter In electronics and telecommunications, a radio transmitter or just transmitter is an electronic device which produces radio waves with an antenna. The transmitter itself generates a radio frequency alternating current, which is applied to ...

. The pilot tone serves as a frequency reference for the receiver, eliminating the signal distortion that would occur with single-sideband suppressed carrier modulation when the receiver is off frequency. It offers improved effective range over standard SSB modulation while simultaneously retaining backwards compatibility with standard SSB radios. ACSB also offers reduced bandwidth and improved range for a given power level compared with narrow band FM modulation. The companding used in ACSB is a type of dynamic range reduction wherein the difference in amplitude between the louder and softer sounds is reduced prior to transmission. A corresponding expander circuit in the receiver inverts this transformation in order to restore the dynamic range. If a conventional SSB receiver is used to receive ACSB signals, some distortion may be noticed but generally the signals are quite intelligible. Similar techniques are used in audio noise reduction circuits such as those developed for

Dolby Dolby Laboratories, Inc. (often shortened to Dolby Labs and known simply as Dolby) is an American company specializing in audio noise reduction, audio encoding/compression, spatial audio, and HDR imaging. Dolby licenses its technologies to ...

. ACSB is being used by

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

operators, air-to-ground phones, as well as mobile-satellite services.

External links

Mobile and Mobile-Satellite Services
Milton Mueller ''The

Cato Institute The Cato Institute is an American libertarian think tank headquartered in Washington, D.C. It was founded in 1977 by Ed Crane, Murray Rothbard, and Charles Koch, chairman of the board and chief executive officer of Koch Industries.Koch Indus ...

'' June 3, 1982

References

Radio modulation modes {{telecomm-stub