Broadcast FM subcarrier decoding?
ranickel at comcast.net
Sun Mar 17 16:32:20 UTC 2013
On 3/17/2013 9:48 AM, Alan Corey wrote:
> I can see what look like they might be subcarriers on either side of
> the main signal. Anyone decoded those?
Depending on where you live, there could be several subcarriers
present. From your description I'm pretty sure you're referring to Sub
Carrier Authorization (SCA) which has been mainly used for background
music and an audio book reading service for the blind as well as other
voice and data services. SCA uses 67 or 92 KHz subcarriers which can
be seen on the composite FM signal. If you have a soundcard with
sufficient bandwidth you can send the output of SDR# (in NBFM, 150 KHz
mode) to another instance of SDR# *(sound card, DSB mode) using Virtual
Audio Cable. My soundcard won't go high enough but here's a set of
screen images from a system that can, where the various elements on the
upper side of the FM channel center are annotated:
The RDS (Radio Data System) or RDBS in the US digital data channel is
easily seen at 57 KHz, The level of all these subcarriers is much
lower than the stereo pilot so you'll need a strong signal for decoding.
73, Bob W9RAN
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