Saturday, August 13, 2011

SCA: FM Radio's Alter-Ego—The Radio the FCC Doesn't Want You to Own

By Bruce F. Elving, Ph.D.
Originally published in Monitoring Times, March 1989

It has been ignored by the consumer press. The high fidelity and stereo industry doesn't talk about it. Certainly, few FM listeners are aware of it. "It" is a medium of communication available free for the taking in almost all parts of North America—namely, FM subcarrier broadcasting.

First demonstrated in 1953 by FM's inventor, the late Edwin H. Armstrong, multiplexing of more than one program on a single station's carrier was authorized to begin in the United States by the Federal Communications Commission in 1955. Long since eclipsed in the public eye by another multiplexing development, FM stereo, subcarrier FM has been largely the province of special interest groups, instead of the public.

FM-SCA listening has enjoyed a steady growth in the last 30 years, thanks largely to magazine articles showing how to assemble FM subcarrier construction kits and to companies supplying the components and radios to make such listening possible.

Indeed, the distinction between FM-SCA and FM stereo, both of which can take place on the same FM station, is blurring. Both are "multiplexed" transmissions, and both can be enjoyed by the public in large numbers, the difference being that stereo FM is identical to the regular FM program, while SCA FM is (almost always) different from the regular FM station's programming.

Not all FM stations make use of an SCA, but I am sure more would, if the owners had personal access to SCA radios in order to explore the fascinating and often money-making things that can be done with this wonderful medium. SCA can be received as clearly and reliably in the local service area as the regular FM station.

My FM Atlas and Station Directory has publicized the existence and nature of SCA programming, and this led to curiosity as to how SCA-FM can be received. This caused us in 1977 to explore the business, legal, and technical aspects of SCA tuning-in. In the years since, we've offered SCAdapter devices to the public, as well as conversions of radios to pick up SCA transmissions.

In our early days we fought off several threats of lawsuits from entrenched SCA interests who would like to keep SCA private and out of the public's radios. More recently, the FCC deregulated SCA, allowing more uses of the SCA signal, including data services, and freeing stations from having to get specific advance approval before embracing an SCA (Subsidiary Communications Authorization). That term was changed to SCS (Subcarrier Communications Service), with this article using the letters SCS or SCA interchangeably. Canada has a similar service called SCMO.

In deregulating the medium, the FCC utilized our data showing the degree of SCA utilization nationally by broadcasters. In so doing, the FCC announced its intent to encourage broadcasters to make greater use of SCA, and it created a new SCS channel, 92 kHz, which enabled broadcasters to make greater use of their station bandwidth.

The two common subcarrier frequencies are thus 67 kHz (the granddaddy of them all), and 92 kHz. One FM station can send out all three programs simultaneously—a stereo program to its regular audience and two separate programs on SCA, such as a radio reading service to the blind at 67 kHz and foreground music on 92 kHz.

Another channel—57 kHz—is in use exclusively for data. Data includes highway-condition alerts in many metro areas and digital paging. It is a channel not favored by at-home listeners, because it is devoid of talk or music programming.


Because FM-SCA is a technology which is multiplexed and "readily available" to large numbers of the public, tuning in its transmission is no more sinister than owning and using a police radio, public service band scanner, radar detector, listening to FM stereo, or watching color television. Virtually all laws prohibiting the use of such devices have been struck down by the courts as being in violation of the First Amendment to the Constitution.

Apparently, however, government can control where you can use these devices, such as forbidding the use of scanners in private automobiles. Similarly, you should be able to listen to background music on SCA in the privacy of your home but not in a business that you own if it might deprive the music company of rental income for equipment to play the music in the store.

You enjoy further legal protection if the radio, even though modified with an SCA circuit, is a radio designed primarily to tune in other transmissions (like regular FM and AM), rather than designed solely for subcarrier reception. Anybody questioning the legality of tuning in SCA should contact local broadcasters for a letter of permission authorizing tuning in their subcarriers for noncommercial, hobby purposes.

All FM stations known to have an SCA are listed in the latest edition of the FM Atlas. The very distinction between who is an "authorized user" and who is a "pirate" is a fine one, and one that even the courts would probably shy away from.

Although at this writing the FCC is unwilling to encourage the use of tunable SCA radios, the FCC noted that the frequencies received by many electronics devices, including scanners, can be used for unprotected communications as well. "Thus, the suggestion that the Commission require that reception of certain frequencies be blocked or filtered is not a practical one." The FCC pointed out that it is not a guarantor of any electronics privacy protections. It is even legal to eavesdrop on cellular telephones, using commonly-available UHF TV sets in the channels 79-83 range.

SCA or SCS is a valuable and relatively unexploited resource available to the public and to the FM broadcaster alike. Despite the use of better transmitting equipment, some broadcasters still entertain prejudice against SCA, thinking that subcarrier use will somehow compromise the quality of their main channel signal. The FCC has helped by allowing stations to increase their overall modulation to compensate for having an SCA, and there is no evidence that having an SCS will decrease a station's ratings.

The needs of a growing population to be better informed about specialized matters will dictate more uses of SCA, rebounding to the benefit of FM stations and the public alike. By taking SCA "out of the closet," our efforts could result in SCAs being included in every FM radio sold in the United States in the future.


SCA's programming has considerably broadened since 1977, when most of the use of the medium was background music to stores. Radio reading services to the blind were just getting underway; they are now found in most metropolitan areas, or across entire states, usually on the subcarriers of public stations. Overlapping reading services can be tuned in in such areas as Wichita, Kansas, and along the Minnesota-Wisconsin borders.

It is a pity that most SCA radios are fixed tuned, getting only one station, and not allowing blind citizens who travel or who live in areas having overlapping signals to tune in all that they could. There is ethnic programming in many major markets, at either 67 or 92 kHz. Foreground or light rock music predominate on 92 kHz. Many stations have an easy-listening SCA at 67 kHz. With the demise of easy-listening from many commercial FM stations, SCA remains the only way for millions of people to hear that format on radio.

In certain areas of the country, you can tune in religion, medical news, relaying of sports and special events, or even AM stations on SCS. With many AM stations having financial troubles, it might make sense for them to direct their efforts to being on the SCA of a nearby FM station than face the prospect of ultimately closing down.

Listeners with radios so equipped could hear the regular FM program and then, flipping a switch, hear an SCA containing their favorite AM station. SCA has a monaural signal with a bandwidth up to 7,000 Hz, or about as good as the best AM stations send out. Its benefits include coverage range similar to the main station stereo signal, and the ability to broadcast a whole new program without having to create new transmitters, build new towers, or pay the power bills necessary for running a complete radio station. SCS is truly a piggyback service.

With the FCC concerned about "deregulation," and removing artificial restrictions in broadcasting, the time is ripe for broadcasters and the public alike to turn to FM-SCA. Let its crystal-clear signal peal out with music and information in clear voice—content that can inform, uplift, extoll, or even upbraid.

To computer activists, SCA offers a world of data, whose unencryption can challenge the most technically adept. Broadcasters, however, know the world of sound, and it is talk and music services which they should consider when addressing SCA opportunities. By offering alternative programming, whether for profit or not, they can complement what they are doing with their main channels.

A public station could provide music on its SCA while carrying news-magazine programs on the main channel. A commercial station could offer its regular music format while broadcasting sports on SCA, or vice versa. A rock station could offer its easy-listening or talk formatted AM signal via SCA, especially if the AM has coverage problems, or if located in areas having high concentrations of high-rise buildings with steel construction, making for poor AM reception (but unimpaired FM-SCA reception).

The fact that hundreds of thousands of folks are out there with tunable SCA radios, as is the case in the New York city area alone, should be of little concern to the stations or the SCServices. The public at large may have some curiosity about hearing the reading service station, ethnic programming, medical news, or background music, but this is a transitory interest, far eclipsed by the tunings-in of those to whom such broadcasts are intended. Indeed, this large audience is something that could be programmed to and nurtured.

Third parties can get into the SCAct by approaching the manager of a local FM station with ideas as to how its SCS could be providing a profitable or meritorious service in exchange for a nominal monthly rental to the station. SCStations are free of such FCC restrictions as the equal time requirement in political broadcasting, although ultimately the FM station licensee is responsible to the FCC for the contracts it has with the people to whom it leases an SCA, and for having a general knowledge of the nature of the SCA emanations, including foreign language or what type of data is being sent out to computers, pagers, and similar instruments.

Reading services on SCA get away with audio pornography that would not be tolerated by most stations if it were on a main carrier, and you can pick up private point-to-point messages on SCStations having tone-and-voice paging services.

To the casual listener or would-be SCA broadcaster, the opportunity is there for a new form of electromagnetic discovery. Not only are the programs different, but the reception characteristics differ. Some stations run their SCA only part of the time. Others run different services on the same channel at different times, while still others experiment with it, sometimes turning the signal on seemingly only for the engineer's amusement.

Even trying to find out information from some SCA stations can be far from routine. Not everybody employed at the station knows that an SCA exists or what it is used for—and, even if they know, they may be paranoid about it and not tell you. Yet it behooves those employed at an FM station to find out about its subcarriers. The SCA may be helping to make the station more profitable, and make possible the paying of your salary.

Listeners should be aware, too, that many a public or religious FM station that may be begging you for funds could be raking in the dollars by offering for-profit data, music, paging or other services—something they're not very likely to mention, but nevertheless a significant source of income or potential income.

Being able to tune in SCA at home, on a portable, or on a car radio is the absolute elitism in radio listening. You are in a class unlike 99 percent of your neighbors. Considering that SCS is sent out with only 10 percent of the energy that the main FM station uses, reception of SCS under most conditions is surprisingly good and uncritical when the receiving equipment is properly installed and used, although it does suffer from multipath distortion and crosstalk problems. To get good reception, place your radio in a spot getting a clear signal from the FM station with no multipath interference.

Until the day comes that you can visit your favorite store and buy an FM-SCA radio, you may have to use some ingenuity in tuning in SCA. It should be well worth the effort to familiarize yourself with this medium—and the best way to do so is with your own FM-SCS radio or adapter unit.

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