I recently read in the paper that the FCC is looking to create a couple of hundred “microradio” stations to fill a diversity void in American radio programming. In theory, the micro stations will be less commercial and more connected to the local communities than the big coast-to-coast conglomerates. This got me thinking, which in turn got me asking, which in turn got me writing to you Dopers…
I once read that major radio broadcasters sometimes sell some “part” of their electromagnetic signal – which, presumably they don’t need in this day and age – to another broadcaster. This second station transmits on this superfluous signal. If a listener has a specially modified receiver, they can pick up this otherwise unheard signal.
The article said that many immigrant communities establish such radio stations to reach their foreign speaking listeners. I presume that’s why, when I go into an immigrant-owned business there will often be a foreign language radio station playing that I can never seem to pick up with my regular receiver.
Can someone more fully explain the science of piggybacking two radio signals in this way, or correct my explanation if I got it wrong?
NOTE: I’m NOT talking about what is commonly called “pirate” radio stations. Presumably these immigrant stations are long-established and perfectly legal.
The second-signals you are talking about are known as a “subsidiary communications authorization” (SCA), and are found on the FM band.
The standard FM channel is 200 kilohertz wide, which is more bandwidth than needed for a standard program signal. Thus, FM stations are allowed to set up a second, low-power, transmitter to make use of the remainder of their bandwidth. The SCA service goes back to the days when FM stations were struggling to get established. Originally SCAs were most commonly used to transmit office background music to subscribers. Nowadays, the most common uses are for data transmissions by commercial stations, and non-profit “talking book” services by non-commercial stations.
US law says you can’t sell FM receivers which can pick up the SCA signals to consumers–the receivers must filter the SCA signals out. Thus, only subscribers who have explicit permission to receive an SCA signal are allowed to have special receivers which can pick up specific SCA transmissions. (However, some hobbyists modify their receivers to pick up SCA transmissions.)
There is an interesting review of concerns that the proposed low-power FM stations will cause interference to the SCA talking book services at: SUPPLEMENTAL COMMENTS OF INTERNATIONAL ASSOCIATION OF AUDIO INFORMATION SERVICES
What a great link. Thank you, white.
But how is it that these foreign-language stations get to use these signals. They are obviously commercial, and entertainment – not education – oriented. Do they allow such exceptions when the radio dial is already packed and large communities are unserved?
Any chance these are just regular AM stations? NYC has had a long tradition of ethnic broadcasters on the AM band. Another possibility is some sort of new satellite broadcasting service. Other than that, I’m not sure.
Some, I’m sure, are normal AM stations as you suggested, but others aren’t. The article I mentioned was in the Times – not a paper to play fast and loose with the facts – and described the scheme as I’ve stated. I specifically recall them saying how on-the-ball immigrant guys would modify radios and sell them for about $100, I think.
I found a good overview of SCA, and how to modify a receiver to pick up SCA transmissions, at FM SCA–Subsidiary Communications Authorization or FM Subcarrier Information.
It turns out that SCA foreign language offerings go back farther and are more extensive than I knew. “Subcarrier” Radio Anyone? reports that The use of SCA’s for foreign language programming came in around 1970. Also, back in 1991, The Structure of Media in New York City reported that There are several Chinese (Mandarin and Cantonese), one West Indian, and two Italian, subcarriers in New York. To receive the SCA frequency, customers must purchase a receiver that picks up the subcarrier frequency only. This is, then, a one-time expense, ranging from $100 to $140 per unit. One Chinese broadcasting company, transmitted through the SCA, reported that it has sold over 10,000 receivers in the New York metropolitan area.
If anything, the number of foreign language SCA transmissions in the New York City area is increasing. For example, a list of Haitian broadcasts includes two SCA operations. (The site with the station list appears to be down–following is the cached copy from Google: Haitian Radio Program).
Whitetho, you’re the MAN!
Thanks for going the extra mile for me. If you want to know anything about NYC history, Broadway musicals or how to strike out with women, I’ll be there for YOU!
Thanks again, bud.