You hop in our car, flip on your radio, and never give a second thought to how what you're listening to reaches your ears. It's actually a pretty simple process: the radio station transmits its programming via a certain frequency, and your radio, when it's tuned to that same frequency, plays the broadcast. But like many things, there's more to the process.
In the United States, the FCC gives radio stations 200 kHz over which to broadcast. So if the station's frequency is 103.1 MHz, it has the frequency between 103.0 and 103.2 MHz. However, the space required for a stereo FM broadcast is actually much less than that. Rather than waste the space, radio stations will sometimes either broadcast what are called subcarrier transmissions or they can also lease out the leftover frequency. These initial transmissions are called SCA transmissions in the United States (standing for Subsidiary Communications Authority), while in Canada they're known as SCMO (Subsidiary Communications Multiplex Operations).
Most FM stations will only use about a quarter of the frequency allotted to them by the FCC. This leaves about another quarter available for subcarrier communications (the rest of the leftover frequency isn't necessarily usable). Therefore, between 67 and 92 kHz, you can sometimes find subcarrier transmissions. The types of programming you'll find includes reading services for the blind, multicultural programming, and even some music programming. In order to receive these broadcasts, you need a special type of radio and receiver that can pick up the signal.
Radio SCA makes the best SCA/SCMO/AM/FM radios available today. We combine meticulous attention to detail with keen customer service. Our radios are second to none, and our prices are hard to beat.
Commercial Free Radio
SCA FM Receivers