28 Mar
2013
28 Mar
'13
3:19 a.m.
SCA is what I was thinking of, but this sounds more like overload. From my raw notes:
If I tune to 88.500 MHz I see signals about 88.3367 and 88.662
The upper one is 162 KHz away, the lower one 163. If I click on one I hear nothing.
The same is true of WAMC(?) at 90.300 with 90.138 and 90.465 so 162 and 165.
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I don't have a screen shot and I haven't seen it happen lately.
Alan
-----
Radio Astronomy - the ultimate DX
----- Original Message -----
From: Robert Nickels <ranickel(a)comcast.net>
To: osmocom-sdr(a)lists.osmocom.org
Cc:
Sent: Sunday, March 17, 2013 12:32 PM
Subject: Re: Broadcast FM subcarrier decoding?
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?
Hi Alan,
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:
http://img208.imageshack.us/img208/5922/fmspectrum.png
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
