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Satellite subcarrier audio
Satellite subcarrier audio is audio transmitted by way of satellite that utilizes a separate analog or digital signal carried on a main radio transmission (usually video) 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.
Original analog video only has one channel per transponder, with subcarriers for audio and automatic transmission identification service ATIS. Non-multiplexed radio stations can also travel in single channel per 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 landlines to send it to an earth station 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.〔(【引用サイトリンク】title=4. A Wave of International Standardization (1970-1979) : Chronology )〕 By the early 1980s, the use of analog subcarriers for radio network distribution had become well-established.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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