Subsidiary Communications Authority
Encyclopedia
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.
'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.
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 under other radio and telecommunications acts, and may require a fee.
In Australia
, the service is called "Ancillary Communications Service" (ACS) and the Radio Data System
is specifically addressed by government guidelines.
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:
Companies in the past such as Norver, ComPol, and McMartin, and current companies such as Dayton Industrial, and Metrosonix, as well as electronic kit companies such as Ramsey Electronics and North Country Radio make radios and adapters for receiving SCA/SCMO channels.
It's possible to also receive the SCA/SCMO signal using a radio that is able to tune and demodulate signals below 100 kHz in FM mode. In that case, the baseband audio (recovered from the discriminator of the FM receiver before multiplex decoding or filtering) is fed into the receiver's RF (antenna) input and the radio tuned to the subcarrier frequency (typically between 53 and 94 kHz, 67 and 92 are common) to extract the signal's contents. Alternatively, the baseband audio can be heterodyned with a suitable IF (intermediate frequency) (that is in the range of the receiver's ability to demodulate FM) and fed into the receiver (tuning it to the appropriate frequency in that case) or even fed directly into the demodulating stage (provided one has the technical knowledge required).
Subcarrier
A subcarrier is a separate analog or digital signal carried on a main radio transmission, which carries extra information such as voice or data. More technically, it is an already-modulated signal, which is then modulated into another signal of higher frequency and bandwidth...
on a radio station
Radio station
Radio broadcasting is a one-way wireless transmission over radio waves intended to reach a wide audience. Stations can be linked in radio networks to broadcast a common radio format, either in broadcast syndication or simulcast or both...
, allowing the station to broadcast additional services as part of its signal.
Background
"Subsidiary Communications Authorization" is the United States Federal Communications CommissionFederal Communications Commission
The Federal Communications Commission is an independent agency of the United States government, created, Congressional statute , and with the majority of its commissioners appointed by the current President. The FCC works towards six goals in the areas of broadband, competition, the spectrum, the...
'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
Common carrier
A common carrier in common-law countries is a person or company that transports goods or people for any person or company and that is responsible for any possible loss of the goods during transport...
or Land Mobile Radio Service
Land Mobile Radio Service
The Land Mobile Radio Service is regulated in the United States by the Federal Communication Commission in CFR 47 Part 90 for non-federal government wireless use between land-based mobile and fixed stations...
transmissions.
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 under other radio and telecommunications acts, and may require a fee.
In Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, the service is called "Ancillary Communications Service" (ACS) and the Radio Data System
Radio Data System
Radio Data System, or RDS, is a communications protocol standard for embedding small amounts of digital information in conventional FM radio broadcasts. RDS standardises several types of information transmitted, including time, station identification and programme information.Radio Broadcast Data...
is specifically addressed by government guidelines.
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:
- For talking book/radio reading serviceRadio reading serviceA radio reading service or reading service for the blind is a service of many universities, community groups and public radio stations, where a narrator reads books, newspapers and magazines aloud for the benefit of the blind and vision-impaired. It is most often carried on a subcarrier, with...
for the blind: usually carried on NPRNPRNPR, formerly National Public Radio, is a privately and publicly funded non-profit membership media organization that serves as a national syndicator to a network of 900 public radio stations in the United States. NPR was created in 1970, following congressional passage of the Public Broadcasting...
-affiliated public radio stations in the United States. In Canada, this is usually provided by VoicePrintVoicePrintVoicePrint is a Canadian 24-hour English language non-profit audio broadcast television service. VoicePrint is an audio-only service that broadcasts readings of news articles and features from more than 600 of Canada’s top newspapers and magazines, as well as audio theatre and films. It is owned by...
over television second audio programSecond audio programSecond audio program , 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 TV.-Usage:...
s instead. - As a transmitter/studio linkTransmitter/studio linkThe transmitter/studio link of a radio station or television station is a return link which sends telemetry data from the remotely-located radio transmitter or television transmitter back to the studio for monitoring purposes...
, sending telemetryTelemetryTelemetry is a technology that allows measurements to be made at a distance, usually via radio wave transmission and reception of the information. The word is derived from Greek roots: tele = remote, and metron = measure...
data from a broadcast FM station's transmitter to the studio for monitoring the condition of the transmitter - For commercial paging service: sent via FM subcarrier to the subscriber with a compatible pager
- For data broadcasting: Microsoft's DirectBandDirectBandDirectBand is a North American wireless datacast network owned and operated by Microsoft. It uses FM radio broadcasts in over 100 cities to constantly transmit data to a variety of devices, including portable GPS devices, wristwatches and home weather stations....
service (used by MSNMSNMSN is a collection of Internet sites and services provided by Microsoft. The Microsoft Network debuted as an online service and Internet service provider on August 24, 1995, to coincide with the release of the Windows 95 operating system.The range of services offered by MSN has changed since its...
Direct) relies on SCA FM subcarriers; Data Broadcasting Corporation's Signal service used SCA for sending real-time stock quotes. - For closed-circuitClosed-circuit radioA closed-circuit radio is a radio that emits over a very small range, typically a college campus. This system can be achieved from two ways:*By tying into the PA System*By using existing power lines, telephones lines, pipes, etc. to transmit a carrier current...
or specialized radio programming aimed at certain markets or professions, such as the Physician's Radio Network, agricultural commodity & futures information (via voice or data), or ethnic foreign-language radio programming. - For the transmission of MuzakMuzakMuzak Holdings LLC is a company based in metro Fort Mill, South Carolina, United States, just outside of Charlotte, North Carolina. Founded in 1934, Muzak Holdings is best known for distribution of background music to retail stores and other companies....
's background music service to its subscribers (i.e., supermarkets, restaurants, etc.), which was also relayed by leased phone lines: these transmission methods have been phased out with Muzak now transmitting its programming via satelliteSatelliteIn the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....
.
Receiving the SCA Signal
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.Companies in the past such as Norver, ComPol, and McMartin, and current companies such as Dayton Industrial, and Metrosonix, as well as electronic kit companies such as Ramsey Electronics and North Country Radio make radios and adapters for receiving SCA/SCMO channels.
It's possible to also receive the SCA/SCMO signal using a radio that is able to tune and demodulate signals below 100 kHz in FM mode. In that case, the baseband audio (recovered from the discriminator of the FM receiver before multiplex decoding or filtering) is fed into the receiver's RF (antenna) input and the radio tuned to the subcarrier frequency (typically between 53 and 94 kHz, 67 and 92 are common) to extract the signal's contents. Alternatively, the baseband audio can be heterodyned with a suitable IF (intermediate frequency) (that is in the range of the receiver's ability to demodulate FM) and fed into the receiver (tuning it to the appropriate frequency in that case) or even fed directly into the demodulating stage (provided one has the technical knowledge required).
See also
- Bruce ElvingBruce ElvingBruce F. Elving was a publisher, FM-radio enthusiast, DXer, and college professor from Duluth, Minnesota. He held a bachelor's degree from the University of Minnesota-Duluth, a master's degree from Iowa State University, and a Ph.D...
, author and advocate of SCA broadcasting - Second audio programSecond audio programSecond audio program , 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 TV.-Usage:...
(SAP) — a similar service on television signals - SubcarrierSubcarrierA subcarrier is a separate analog or digital signal carried on a main radio transmission, which carries extra information such as voice or data. More technically, it is an already-modulated signal, which is then modulated into another signal of higher frequency and bandwidth...
— use of subcarriers in general - Radio Data SystemRadio Data SystemRadio Data System, or RDS, is a communications protocol standard for embedding small amounts of digital information in conventional FM radio broadcasts. RDS standardises several types of information transmitted, including time, station identification and programme information.Radio Broadcast Data...
— widespread program information standard; sometimes considered a type of SCA