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Satellite subcarrier audio is audio transmitted by way of
satellite
A satellite or artificial satellite is an object intentionally placed into orbit in outer space. Except for passive satellites, most satellites have an electricity generation system for equipment on board, such as solar panels or radioi ...
that uses a separate
analog
Analog or analogue may refer to:
Computing and electronics
* Analog signal, in which information is encoded in a continuous variable
** Analog device, an apparatus that operates on analog signals
*** Analog electronics, circuits which use analog ...
or
digital signal carried on a main radio transmission (usually video) on a specific satellite
transponder
In telecommunications, a transponder is a device that, upon receiving a signal, emits a different signal in response. The term is a blend of ''transmitter'' and ''responder''.
In air navigation or radio frequency identification, a flight trans ...
. 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.
Original analog video only has one channel per transponder, with
subcarriers for audio and automatic transmission identification service
ATIS. Non-multiplexed
radio station
Radio broadcasting is transmission 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 radi ...
s can also travel in
single channel per carrier
Single channel per carrier (SCPC) refers to using a single signal at a given frequency and bandwidth. Most often, this is used on broadcast satellites to indicate that radio stations are not multiplexed as subcarriers onto a single video carrier ...
(SCPC) mode, with multiple carriers (analog or digital) per transponder. This allows each station to transmit directly to the satellite, rather than paying for a whole transponder, or using
landline
A landline (land line, land-line, main line, home phone, fixed-line, and wireline) is a telephone connection that uses metal wires or optical fiber telephone line for transmission, as distinguished from a mobile cellular network, which uses ...
s to send it to an
earth station
A ground station, Earth station, or Earth terminal is a terrestrial radio station designed for extraplanetary telecommunication with spacecraft (constituting part of the ground segment of the spacecraft system), or reception of radio waves fr ...
for multiplexing with other stations.
Analog subcarriers
Satellite subcarrier audio was initially transmitted in analog form. This method of audio transmission was first employed by
Fujitsu in 1973 as part of a data line between the United States and Spain.
By the early 1980s, the use of analog subcarriers for radio network distribution had become well-established.
Standard subcarrier audio
Initially, satellite subcarrier audio was tuned using commercial receivers or consumer-grade
TVRO
Television receive-only (TVRO) is a term used chiefly in North America, South America to refer to the reception of satellite television from FSS-type satellites, generally on C-band analog; free-to-air and unconnected to a commercial DBS prov ...
"big dish" satellite receivers. The audio ranged in frequency from 5.0 to 8.5
MHz
The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose expression in terms of SI base units is s−1, meaning that one he ...
for both left and right audio channels. Fine tuning options included monaural and discrete stereo tuning with three bandwidth modes: narrow (130 kHz), normal (280 kHz) and wide (500 kHz).
Single channel per carrier (analog SCPC)
Single channel per carrier (SCPC) refers to using a single
signal
In signal processing, a signal is a function that conveys information about a phenomenon. Any quantity that can vary over space or time can be used as a signal to share messages between observers. The '' IEEE Transactions on Signal Processing' ...
at a given
frequency
Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is eq ...
and
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 ...
. Most often, this is used on
broadcast satellite
Broadcasting is the distribution of audio or video content to a dispersed audience via any electronic mass communications medium, but typically one using the electromagnetic spectrum ( radio waves), in a one-to-many model. Broadcasting bega ...
s to indicate that
radio station
Radio broadcasting is transmission 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 radi ...
s are not
multiplexed
In telecommunications and computer networking, multiplexing (sometimes contracted to muxing) is a method by which multiple analog or digital signals are combined into one signal over a shared medium. The aim is to share a scarce resource - a ...
as
subcarriers onto a single video
carrier, but instead independently share a
transponder
In telecommunications, a transponder is a device that, upon receiving a signal, emits a different signal in response. The term is a blend of ''transmitter'' and ''responder''.
In air navigation or radio frequency identification, a flight trans ...
. It may also be used on other
communications satellite
A communications satellite is an artificial satellite that relays and amplifies radio telecommunication signals via a transponder; it creates a communication channel between a source transmitter and a receiver at different locations on Earth ...
s, or occasionally on non-satellite
transmissions. In an SCPC system, satellite bandwidth is dedicated to a single source.
Analog SCPC subcarrier audio is received using dedicated satellite receivers. SCPC audio receivers tune a frequency range of 50 to 90 MHz with both wide and narrow bandwidth options.
Receivers in the hobbyist price range included the Heil SC-One and the Universal Electronics SCPC-100 and SCPC-200.
FM Squared (FM²)
The FM Squared satellite audio format was developed in 1986 by Wegener Communications and Subcarrier Systems (later SpaceCom Systems, Inc.).
FM Squared is a method of transmitting analog satellite audio where video would normally be transmitted on a satellite transponder. FM Squared was once used to distribute
Muzak
Muzak is an American brand of background music played in retail stores and other public establishments. The name has been in use since 1934, and has been owned by a division or subsidiary of one or another company ever since. In 1981, Westingho ...
and similar "business" music (sometimes referred to as
elevator music
Elevator music (also known as Muzak, piped music, or lift music) is a type of background music played in rooms where many people come together (that is, with no intention whatsoever to listen to music), and during telephone calls when placed on ...
) to retailers.
FM Squared audio receivers tune a frequency range of 100 kHz to 9 MHz. Receivers that fell within the hobbyist price range included the Universal Electronics SC-50.
Digital subcarriers
Although not widely used until the early 2000s, digital subcarrier audio has existed almost as long as its analog technology counterpart. In 1972, the
BBC #REDIRECT BBC #REDIRECT BBC
Here i going to introduce about the best teacher of my life b BALAJI sir. He is the precious gift that I got befor 2yrs . How has helped and thought all the concept and made my success in the 10th board exam. ...
...
deployed a digital audio transmission system linking their broadcast center to their remote transmitters.
This technology wasn't applied to satellite communications, however, until the early 1980s.
DATS and SEDAT
The first widespread digital satellite audio distribution system was Digital Audio Transmission System (DATS).
DATS was developed in 1982 by
Scientific Atlanta
Scientific Atlanta, Inc. was a Georgia, United States-based manufacturer of cable television, telecommunications, and broadband equipment. Scientific Atlanta was founded in 1951 by a group of engineers from the Georgia Institute of Technology, a ...
. The DATS distribution system was first used by the largest U.S. radio networks such as
Westwood One
Westwood One is an American radio network owned by Cumulus Media. The company syndicates talk, music, and sports programming.
The company takes its name from an earlier network also named Westwood One, a company founded in 1978. The compan ...
,
ABC Radio Networks ABC Radio may refer to:
Australia
* History of ABC Radio (Australia), the division of the Australian Broadcasting Corporation (ABC) responsible for:
** ABC Classic, a classical music radio station
** ABC Classic 2, an un-presented streaming-only c ...
and
NBC
The National Broadcasting Company (NBC) is an American English-language commercial broadcast television and radio network. The flagship property of the NBC Entertainment division of NBCUniversal, a division of Comcast, its headquarters are l ...
.
The DATS system transmitted up to four 15 kHz analog audio channels at a data rate of 1.544
Mbit/s
In telecommunications, data-transfer rate is the average number of bits ( bitrate), characters or symbols ( baudrate), or data blocks per unit time passing through a communication link in a data-transmission system. Common data rate units are mu ...
(384 kbit/s each) between their originating radio studios and a C-band earth station where they were de-multiplexed, re-multiplexed, and uplinked with additional digital audio channels using
BPSK
Phase-shift keying (PSK) is a digital modulation process which conveys data by changing (modulating) the phase of a constant frequency reference signal (the carrier wave). The modulation is accomplished by varying the sine and cosine inputs at ...
digital modulation.
The 15 kHz channels had a dynamic range of 81 dB which was suitable for FM broadcasting. The system could also support up to twice as many 7.5 kHz channels suitable for AM broadcast.
DATS was later superseded by the Spectrum Efficient Digital Audio Transmission (SEDAT) satellite audio distribution system. SEDAT allows more audio channels to be carried in the same frequency range as DATS. SEDAT, also developed by Scientific Atlanta, was primarily used by ABC Radio Networks. SEDAT transmissions ended in 2001.
Digital SCPC and MCPC
As digital subcarrier audio encoding and modulation methods have matured, less-expensive "standard" systems of satellite audio distribution have developed. This trend started with the emergence of
VSAT
A very-small-aperture terminal (VSAT) is a two-way satellite ground station with a dish antenna that is smaller than 3.8 meters. The majority of VSAT antennas range from 75 cm to 1.2 m. Bit rates, in most cases, range from 4 kbit/s up to 1 ...
technology in 1986
and was further supplanted by leased space on
DBS systems such as
DirecTV
DirecTV (trademarked as DIRECTV) is an American multichannel video programming distributor based in El Segundo, California. Originally launched on June 17, 1994, its primary service is a digital satellite service serving the United States. I ...
and
Dish Network.
The two ''de facto'' methods for digital satellite audio transmission are digital
single channel per carrier
Single channel per carrier (SCPC) refers to using a single signal at a given frequency and bandwidth. Most often, this is used on broadcast satellites to indicate that radio stations are not multiplexed as subcarriers onto a single video carrier ...
and
multiple channel per carrier multiplexing.
In digital radio systems, several variable bit-rate data streams are multiplexed together to a fixed bitrate transport stream by means of statistical multiplexing. This makes it possible to transfer several video and audio channels simultaneously over the same frequency channel, together with various services. On communications satellites which carry broadcast television networks and radio networks, this is known as multiple channel per carrier or MCPC. Where multiplexing is not practical (such as where there are different sources using a single transponder), single channel per carrier mode (SCPC) is used. Digital SCPC differs from the older analog SCPC transmission method in that a digital SCPC signal carries more than just a single audio channel (two are used) but also coding and decoding information, ancillary and control data, and network identification data.
Digital SCPC and MCPC subcarrier transmissions use satellite broadcast standards such as
DVB-S and its successor
DVB-S2 along with
MPEG-2 and
MPEG-4 compression formats, respectively. BPSK modulation has been replaced with newer modulation schemes such as
QPSK
Phase-shift keying (PSK) is a digital modulation process which conveys data by changing (modulating) the phase of a constant frequency reference signal (the carrier wave). The modulation is accomplished by varying the sine and cosine inputs at ...
(quadrature phase-shift keying).
StarGuide
StarGuide was the second-generation system of digital audio distribution via satellite. Many of the largest U.S. radio networks upgraded from or supplanted DATS/SEDAT audio feeds with StarGuide II and III audio receivers. The StarGuide platform is a proprietary MCPC digital audio distribution system that uses proprietary MX3 multiplexing technology. The StarGuide II receiver handles data rates from 0.512 to 6.144 Mbit/s (in MX3 mode) and up to 8.192 Mbit/s in normal mode. The StarGuide III receiver can handle data rates up to 25 Mbit/s and is capable of a larger number of data and code rates than its predecessor. Both the StarGuide II and III receivers can use proprietary StarGuide Service Module expansion cards, including the ability to interface with
local area network
A local area network (LAN) is a computer network that interconnects computers within a limited area such as a residence, school, laboratory, university campus or office building. By contrast, a wide area network (WAN) not only covers a larger ...
s (LAN) using
10/100Base-T Ethernet
Ethernet () is a family of wired computer networking technologies commonly used in local area networks (LAN), metropolitan area networks (MAN) and wide area networks (WAN). It was commercially introduced in 1980 and first standardized in 1 ...
connections.
X-Digital (XDS) format
The X-Digital Systems format is (as of 2011) the newest generation of digital satellite subcarrier audio technology used by the large radio networks in the United States. In 2007, X-Digital Systems acquired specific assets and patent licensing of StarGuide Digital Networks technology from DG FastChannel, Inc.
The X-Digital Systems platform has been deployed by
Clear Channel Communications,
Premiere Networks
Premiere Networks (formerly Premiere Radio Networks, shortened as PRN) is an American media company, a wholly owned subsidiary of iHeartMedia, for which it currently serves as its main original radio content distribution and production arm. ...
(now an iHeartMedia subsidiary) and
Citadel Broadcasting
Citadel Broadcasting Corporation was a Las Vegas, Nevada-based broadcast holding company. Citadel owned 243 radio stations across the United States and was the third-largest radio station owner in the country. Only iHeartMedia and Cumulus Media ...
(who also owns the former ABC Radio Networks).
See also
*
Satellite radio
External links
ATX Networks website (parent company of the X-Digital Systems format)
References
{{reflist
Satellite radio