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<div class="moz-cite-prefix">On 3/17/2013 9:48 AM, Alan Corey wrote:<br>
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<div><span>This might be a better question for the Gnuradio
list, but for years I've known that some broadcast FM
stations actually transmit a second audio program which is
somehow modulating a subcarrier in the main transmission.
It probably carries mostly elevator music type junk but is
rumored to be commercial-free (a rare thing in the US!). I
remember seeing dedicated receivers advertised for this, but
never actually bought one because I wasn't sure it was
active in my area. These date back to Lafayette Electronics
days I think and ever since so 40 years or more.<br>
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<div style="color: rgb(0, 0, 0); font-size: 16px; font-family:
times new roman,new york,times,serif; background-color:
transparent; font-style: normal;"><span>I've noticed (in
SdrSharp) that on some FM stations I can see what look like
they might be subcarriers on either side of the main
signal. Anyone decoded those?</span></div>
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<div style="color: rgb(0, 0, 0); font-size: 16px; font-family:
times new roman,new york,times,serif; background-color:
transparent; font-style: normal;"><span> Alan<br>
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<div>-----<br>
Radio Astronomy - the ultimate DX<br>
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<br>
Many, if not most, FM stations US have subcarriers, if only to carry
the stereo (L-R) signal and the bit that turns the "stereo"
indication on. On the two SCA channels for alternate programming,
you will find "elevator music," news broadcasts, audio books for the
blind, and alternate language programming on them. Since they're
usually done up as a subscription service, they don't have
commercials. I've never decoded them, but I used to work at the
transmitter site for an FM radio station. Our SCA's carried
"ambient music" (for which I had to change the tape if one ran out)
and some sort of agricultural news broadcast.<br>
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