Yes, SCA is what I was thinking of. I used to be an electronics technician in consumer electronics back in the 70s and this was on licensing exams, aside from seeing them in catalogs. Being from a rural area it was just something I read about, I never actually saw one. I had forgotten the L-R signal was on a 19 KHz subcarrier, I was looking for a 1.9 KHz, which makes no sense since it would be in the audio passband.
If I run into it again I'll grab a screen shot, but what I was probably seeing was an overload condition on my poor little NooElec dongle. There's a 2 meter repeater about 20 miles away, but line of sight. When that keys up I see peaks all over the 2 MHz range that SDRSharp shows me for 2 meters, but they all go away when it unkeys. The FM broadcast station I was thinking of is a little farther away but of course a lot more powerful. When I look for them now I can't find them. I remember checking one to see if it was 1.9 KHz away from the main peak, but it was several times that, maybe around 8 KHz. Enjoyed the QST article, my copy came about a week after my dongle. I built one of the upconverter kits from Hayseed Hamfest, and it works, but it's deaf as a post. Even on my 150 foot longwire I can only hear the stronger stations. AM broadcast stations and the strong bible beaters are about it. Tuning the HF ham bands, I've rarely heard hams and then only 1 side of each QSO. The SA612 data sheet I've got (Philips) is skimpy on specifics but I wonder about the oscillator injection level. I've been trying to decide whether to put a pot in there to adjust or a dual gate mosfet broadband preamp on it. It seems like the oscillator level should be close to the signal level. I've got some BF998 FETs I was going to use because I can put a pot on the gate 2 voltage to control the gain. 73, Alan, AB1JX ----- Radio Astronomy - the ultimate DX >________________________________ > From: Robert Nickels <[email protected]> >To: >Cc: [email protected] >Sent: Monday, March 18, 2013 11:31 AM >Subject: Re: Broadcast FM subcarrier decoding? > >On 3/17/2013 11:32 AM, Robert Nickels wrote: >> 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 in >addition to the prominent 19 KHz stereo pilot. 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 > >Another subcarrier is used for RDS (Radio Data System) or RDBS in the US >digital data channel which can easily seen at 57 KHz on stations utilizing >this service. In the US The arithmetic sum of all multiplex subcarriers may >not exceed 20% modulation and different rules apply than for the primary >broadcast channel. > >73, Bob W9RAN > > > >
