Sca
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ka3jjz
Wiki Admin Emeritus
If you mean the subcarrier service available from some FM stations - while I guess it's possible, I don't know of anyone doing it that way. To the best of my knowledge - and I'm not a FM DXer - the only way to do it is to buy modified radios or install a kit. Dr. Bruce Elving is probably one of the better known proponents of free access to subcarrier services (many are subscription services, I understand), and his website is here....
http://members.aol.com/fmatlas/home.html
This is a question better asked on the WTFDA boards, where you're much more likely to find folks knowledgeable on the subject
http://www.wtfda.org/
73 Mike
http://members.aol.com/fmatlas/home.html
This is a question better asked on the WTFDA boards, where you're much more likely to find folks knowledgeable on the subject
http://www.wtfda.org/
73 Mike
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k8tmk
Member
SCA is piggy-backed on the regular FM carrier. The SCA audio actually rides on a subcarrier, as does the RDS data (or more correctly RBDS). RDS is what carries the information that tells an RDS-equipped radio what to show (station ID, name of song playing, etc.) on the radio's display.
One common SCA subcarrier is 67 kHz. The RDS subcarrier is 57 kHz. I believe there is yet another subcarrier at 92 kHz available. The percentage of modulation for these is no more than 10% (combined). Radio stations that use subcarriers can increase their total audio percentage by the amount used in subcarrier(s), up to a maximum 110%.
As you probably know, SCA can carry continuous music (usually different than the main music), foreign language broadcasts, educational programming, etc. Many stations have stopped using SCA music (background) programming because they could not complete with Muzak, satellite, etc., which allow you to select the genre of music you want.
SCA can be demodulated from the FM carrier with a simple phase-locked-loop (PLL) circuit. To hook up the PLL circuit, you need to attach the input of the circuit to an FM receiver prior to the de-emphasis network in the receiver's detector circuit. The output of the PLL circuit should then be connected to an ordinary audio amplifier. The PLL circuit can be breadboarded with a handful of parts, and is generally not that hard to connect if you have a schematic of the FM receiver. Ramsey used to sell a kit SCA demodulator (maybe they still do).
Since RDS is data, you could probably decode it with a computer software program.
The radio station I worked for used 67 kHz for their SCA audio and 57 kHz for paging, but they dumped both SCA and paging, and now transmit an RDS subcarrier.
Hope this helps.
Randy, K8TMK
One common SCA subcarrier is 67 kHz. The RDS subcarrier is 57 kHz. I believe there is yet another subcarrier at 92 kHz available. The percentage of modulation for these is no more than 10% (combined). Radio stations that use subcarriers can increase their total audio percentage by the amount used in subcarrier(s), up to a maximum 110%.
As you probably know, SCA can carry continuous music (usually different than the main music), foreign language broadcasts, educational programming, etc. Many stations have stopped using SCA music (background) programming because they could not complete with Muzak, satellite, etc., which allow you to select the genre of music you want.
SCA can be demodulated from the FM carrier with a simple phase-locked-loop (PLL) circuit. To hook up the PLL circuit, you need to attach the input of the circuit to an FM receiver prior to the de-emphasis network in the receiver's detector circuit. The output of the PLL circuit should then be connected to an ordinary audio amplifier. The PLL circuit can be breadboarded with a handful of parts, and is generally not that hard to connect if you have a schematic of the FM receiver. Ramsey used to sell a kit SCA demodulator (maybe they still do).
Since RDS is data, you could probably decode it with a computer software program.
The radio station I worked for used 67 kHz for their SCA audio and 57 kHz for paging, but they dumped both SCA and paging, and now transmit an RDS subcarrier.
Hope this helps.
Randy, K8TMK
B_Mitchell
Member
Every few years I will check, just to see what is still there. Each time I find less than I did the last. Last May all I could find was one audio sub (The Utah Radio Reading Service), and one data stream.
SCANdal
Silent Key
How this is being enforced...I don't know.
6,
Just a reminder...
Unauthorized reception of FM-SCAs is prohibited by the Electronic Communications Privacy Act of 1986 (as amended).
SCANdal
6,
Just a reminder...
Unauthorized reception of FM-SCAs is prohibited by the Electronic Communications Privacy Act of 1986 (as amended).
SCANdal
57Bill
Member
I don't know why any radio monitoring hobbyist would be concerned about unenforceable laws like the ECPA of 1986. Yet, there is always a posting reminding of its near useless existence.
k8tmk
Member
Reception of SCA by individuals is perfectly legal, as long as it is not for personal gain. In other words, you can listen all you want. You just cannot play it in a commercial establishment (store or housing complex, etc.).
In a somewhat different area, you can put a regular broadcast receiver in your commercial establishment that customers can hear as long as it is self-contained. But it is illegal to connect multiple speakers to the receiver. Weird, right? IF you happen to get caught by BMI or ASCAP, you could receive a monitary fine. That's why many restaurants and fast-food places now use a satellite subscription service.
Randy
In a somewhat different area, you can put a regular broadcast receiver in your commercial establishment that customers can hear as long as it is self-contained. But it is illegal to connect multiple speakers to the receiver. Weird, right? IF you happen to get caught by BMI or ASCAP, you could receive a monitary fine. That's why many restaurants and fast-food places now use a satellite subscription service.
Randy
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