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 ...

modulation Signal modulation is the process of varying one or more properties of a periodic waveform in electronics and telecommunication for the purpose of transmitting information. The process encodes information in form of the modulation or message ...

method using a single-sideband with a

pilot tone In telecommunications, a pilot signal is a signal, usually a single frequency, transmitted over a communications system for supervisory, control, equalization, continuity, synchronization, or reference purposes. Uses in different communication ...

, 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 am ...

that was severely compressed by the

transmitter In electronics and telecommunications, a radio transmitter or just transmitter (often abbreviated as XMTR or TX in technical documents) is an electronic device which produces radio waves with an antenna (radio), antenna with the purpose of sig ...

. 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 Bandwidth commonly refers to: * Bandwidth (signal processing) or ''analog bandwidth'', ''frequency bandwidth'', or ''radio bandwidth'', a measure of the width of a frequency range * Bandwidth (computing), the rate of data transfer, bit rate or thr ...

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. (Dolby Labs or simply Dolby) is a British-American technology corporation specializing in audio noise reduction, audio encoding/compression, spatial audio, and high-dynamic-range television (HDR) imaging. Dolby li ...

. ACSB is being used by

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 ...

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

References

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 ...

'' June 3, 1982 Radio modulation modes {{telecomm-stub