Broadcast FM subcarrier decoding?

Alan Corey alancorey at
Thu Mar 28 02:19:40 UTC 2013

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.

I don't have a screen shot and I haven't seen it happen lately.


Radio Astronomy - the ultimate DX

----- Original Message -----
> From: Robert Nickels <ranickel at>
> To: osmocom-sdr at
> 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: 
> 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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