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Some FM stations used to have a signal only a few could get - along with radios that could only receive one channel.
(And some stations still use it.)
Subcarrier Signals: The Unsung Heroes of the FM Dial
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Subcarriers weren't restricted to FM radio. For many years, in the analog days, Citytv used a subcarrier for a one-way intercom (IFB) out to their "Live Eye" truck. The return intercom path was on a subcarrier on the microwave signal back to the station.
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I remember them on my old C-Band satellite dish. You could get radio stations, alternate audio and in one memorable case, the control room audio of a major sporting event for some reason. Lots of great listening back then and it was all free.
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Would SAP on analog TV signals count as a subcarrier?
I can remember CFMT airing 680 News on its SAP at one time.
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MJ Vancouver wrote:
Would SAP on analog TV signals count as a subcarrier?
I can remember CFMT airing 680 News on its SAP at one time.
yes SAP (aka MTS) was a 76kHz subcarrier (mono only).
The "intercom" subarrier, known as "PRO" and not generally available to the public, was at 102kHz
Stereo TV, which used a system similar to FM radio, had a L-R difference channel (or subacrrier) at 31kHz