Broadcast FM subcarrier decoding?

This is merely a historical archive of years 2008-2021, before the migration to mailman3.

A maintained and still updated list archive can be found at https://lists.osmocom.org/hyperkitty/list/osmocom-sdr@lists.osmocom.org/.

Jonathan Guthrie jguthrie at brokersys.com
Mon Mar 18 14:47:16 UTC 2013


On 3/17/2013 9:48 AM, Alan Corey wrote:
> 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.
>
> 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?
>
>   Alan
> -----
> Radio Astronomy - the ultimate DX

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.

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osmocom.org/pipermail/osmocom-sdr/attachments/20130318/72b9ae29/attachment.htm>


More information about the osmocom-sdr mailing list