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Subsidiary Communications Authorization (SCA) in the United States, and Subsidiary Communications Multiplex Operation (SCMO) in Canada, is a subcarrier on a radio station, allowing the station to broadcast additional services as part of its signal.
Subsidiary Communications Authorization is the United States Federal Communications Commission's official designation for this type of service. SCA was deregulated in 1983; since then, both AM and FM licensed broadcast stations have been allowed to use subcarriers in the United States in general without requiring separate authority; authorization is only required for some uses which are still otherwise regulated, such as common carrier or Land Mobile Radio Service transmissions. [1] The fidelity (bandwidth) of SCA channels on FM is generally quite limited compared to that of the main program material, resulting in audio quality similar to AM radio broadcasting. By extension, the already limited bandwidth of AM means that it is impossible to multiplex any secondary audio service on an AM signal; any SCA usage would be limited to text.
The Canadian Radio-television and Telecommunications Commission (CRTC) calls this service Subsidiary Communications Multiplex Operation (SCMO). SCMO for internal uses by the radio station, such as internal monitoring and cue control, are allowed under the normal broadcasting certificate. Non-broadcasting uses are allowed when the type of use is authorized[ clarification needed ] under other radio and telecommunications acts, and may require a fee. [2]
In Australia, the service is called Ancillary Communications Service (ACS) and the Radio Data System is specifically addressed by government guidelines. [3]
Subcarrier channels falling under the description of SCA are usually on FM at 67 kHz and 92 kHz from the main carrier, and 67 kHz is the most common. Major uses of SCA include:
Venture Technologies, which owns a large number of analog low-power television stations with audio subcarriers that operate as FM radio stations, proposed using SCA rules to continue transmitting those analog audio services along an ATSC 3.0 signal. [5]
Most programming transmitted by SCA/SCMO is usually pay/subscription-based, making unauthorized reception of such programming illegal, but programming which is not commercial in nature, such as reading services, can be received legally.[ citation needed ]
Companies in the past such as Norver, ComPol, Mani National Corporation, McMartin, & Dayton Industrial; and current companies such as Metrosonix make radios and adapters for receiving SCA/SCMO channels. It can be difficult to keep the main channel's FM stereo difference subcarrier from interfering with such SCA decoders, as the stereo signal is a much stronger signal, and distortions due to multipath can also cause problems.[ citation needed ]
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 comprise all the spectral components of the modulated signal except the carrier. The signal components above the carrier frequency constitute the upper sideband (USB), and those below the carrier frequency constitute the lower sideband (LSB). All forms of modulation produce sidebands.
In telecommunications, frequency-division multiplexing (FDM) is a technique by which the total bandwidth available in a communication medium is divided into a series of non-overlapping frequency bands, each of which is used to carry a separate signal. This allows a single transmission medium such as a microwave radio link, cable or optical fiber to be shared by multiple independent signals. Another use is to carry separate serial bits or segments of a higher rate signal in parallel.
Radio broadcasting is the broadcasting of audio (sound), sometimes with related metadata, by radio waves to radio receivers belonging to a public audience. In terrestrial radio broadcasting the radio waves are broadcast by a land-based radio station, while in satellite radio the radio waves are broadcast by a satellite in Earth orbit. To receive the content the listener must have a broadcast radio receiver (radio). Stations are often affiliated with a radio network that provides content in a common radio format, either in broadcast syndication or simulcast, or both. Radio stations broadcast with several different types of modulation: AM radio stations transmit in AM, FM radio stations transmit in FM, which are older analog audio standards, while newer digital radio stations transmit in several digital audio standards: DAB, HD radio, DRM.
Radio Data System (RDS) is a communications protocol standard for embedding small amounts of digital information in conventional FM radio broadcasts. RDS standardizes several types of information transmitted, including time, station identification and program information.
In-band on-channel (IBOC) is a hybrid method of transmitting digital radio and analog radio broadcast signals simultaneously on the same frequency. The name refers to the new digital signals being broadcast in the same AM or FM band (in-band), and associated with an existing radio channel (on-channel). By utilizing additional digital subcarriers or sidebands, digital information is "multiplexed" on existing signals, thus avoiding re-allocation of the broadcast bands.
A subcarrier is a sideband of a radio frequency carrier wave, which is modulated to send additional information. Examples include the provision of colour in a black and white television system or the provision of stereo in a monophonic radio broadcast. There is no physical difference between a carrier and a subcarrier; the "sub" implies that it has been derived from a carrier, which has been amplitude modulated by a steady signal and has a constant frequency relation to it.
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.
Second audio program (SAP), also known as secondary audio programming, is an auxiliary audio channel for analog television that can be broadcast or transmitted both over-the-air and by cable television. Used mostly for audio description or other languages, SAP is part of the multichannel television sound (MTS) standard originally set by the National Television Systems Committee (NTSC) in 1984 in the United States. The NTSC video format and MTS are also used in Canada and Mexico.
The International Telecommunication Union uses an internationally agreed system for classifying radio frequency signals. Each type of radio emission is classified according to its bandwidth, method of modulation, nature of the modulating signal, and type of information transmitted on the carrier signal. It is based on characteristics of the signal, not on the transmitter used.
HD Radio (HDR) is a trademark for an in-band on-channel (IBOC) digital radio broadcast technology. HD radio generally simulcasts an existing analog radio station in digital format with less noise and with additional text information. HD Radio is used primarily by AM and FM radio stations in the United States, U.S. Virgin Islands, Canada, Mexico and the Philippines, with a few implementations outside North America.
Datacasting is the broadcasting of data over a wide area via radio waves. It most often refers to supplemental information sent by television stations along with digital terrestrial television (DTT), but may also be applied to digital signals on analog TV or radio. It generally does not apply to data inherent to the medium, such as PSIP data that defines virtual channels for DTT or direct broadcast satellite system, or to things like cable modems or satellite modems, which use a completely separate channel for data.
The Crosby system was an FM stereophonic broadcasting standard developed by Murray G. Crosby. In the United States, it competed with, and ultimately lost to, the Zenith/GE system, which the FCC chose as the standard in 1961.
FM broadcasting is a method of radio broadcasting that uses frequency modulation (FM) of the radio broadcast carrier wave. Invented in 1933 by American engineer Edwin Armstrong, wide-band FM is used worldwide to transmit high-fidelity sound over broadcast radio. FM broadcasting offers higher fidelity—more accurate reproduction of the original program sound—than other broadcasting techniques, such as AM broadcasting. It is also less susceptible to common forms of interference, having less static and popping sounds than are often heard on AM. Therefore, FM is used for most broadcasts of music and general audio. FM radio stations use the very high frequency range of radio frequencies.
WILL-FM is a public, listener-supported radio station owned by the University of Illinois Urbana-Champaign and licensed to Urbana, Illinois, United States. It is operated by Illinois Public Media, with studios located at Campbell Hall for Public Telecommunication on the university campus. Most of WILL-FM's schedule is classical music with NPR news programs heard in weekday morning and afternoon drive times. Weekends feature classical and other genres of music, including jazz and opera.
FMeXtra is a deprecated in-band on-channel digital radio broadcasting technology created by Digital Radio Express. It was intended to allow a second all-digital signal to be simulcast with an existing analog FM radio station, offering a less noisy signal that would be particularly useful in urban environments where multipath distortion can seriously degrade analog FM transmissions. It can also support a second all-digital channel at the same frequency, allowing two channels to be broadcast by a single FM station.
Radio Maria, formally known as The World Family of Radio Maria, is an international Catholic radio broadcasting service founded in Erba, province of Como, in the diocese of Milan, Italy, in 1987.
Radio is the technology of communicating using radio waves. Radio waves are electromagnetic waves of frequency between 3 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmitter connected to an antenna which radiates the waves. They are received by another antenna connected to a radio receiver. In addition to communication, radio is used for radar, radio navigation, remote control, remote sensing, and other applications.
HMWN Radio Maria is a non-commercial Catholic broadcaster which operates as a closed circuit Subsidiary Communications Multiplex Operation (SCMO) and uses the subcarrier frequency of 67 kHz removed from the centre FM broadcast frequency of 102.1 MHz in Toronto, Ontario. HMWN's offices and studios are also located in Toronto.
Satellite subcarrier audio is audio transmitted by way of satellite that uses a separate analog or digital signal carried on a main radio transmission on a specific satellite transponder. More technically, it is an already-modulated signal, which is then modulated into another signal of higher frequency and bandwidth. In a more general sense, satellite subcarrier audio is an early form of satellite radio not intended for the consumer market but was initially unencrypted, thus receivable to satellite hobbyists.
WGYN was a radio station that last broadcast at 97.9 MHz FM in New York City. It operated from December 1941 to May 1950. Studios and transmitter were located at the Cities Service Building at 70 Pine Street.
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