Just as there are unused portions of the television signal, so too is there excess capacity in the FM radio system. Applications in this field were explored at the same ASIS meeting by Ed Anderson of Dataspeed. One-way distribution services based on excess FM capacity take advantage of the bottlenecks experienced in the “last mile” of telecommunications systems which use more traditional distribution means. The FM subcarrier approach piggy-backs data transmission on the unused portion of regular FM broadcast radio signals. The Federal Communication Commission's 1983 deregulation of the subcarrier industry has resulted in an expansion of the bandspace available for such activities—from one to two bands, a doubling of capacity.
In the U.S., there are 3,570 FM stations, only 1,000 of which use their FM subcarrier frequency. Radio stations that do not use this capacity themselves, may lease it to others. Current use of the capability is divided as follows: 50 percent for “Muzak” applications, 15 percent for reading services for the blind, and the rest of the usage is divided among facsimile and telemetry, the Physicians Radio Network (a service of continuing education programs for doctors), and information and news services. However, there is still a large unused capacity. The medium has the advantage of broad geographic coverage, and relatively simple and inexpensive installation of generating equipment in radio stations. Installation is simple—4 to 5 hours; low cost—less than $15,000; and the equipment has a low fixed operating cost. The receiving equipment for end users is inexpensive and unique in that it is easily portable.
Dataspeed offers several services based on FM subcarriers. Its QuoTrek Stock Market Service transmits stock market information. The information is received and decoded by a pocket device no larger than a cigarette packet with a 6-inch folding antenna. The user can program the receiver to select 40 stocks from the 150 or so offered. The required stock is accessed by punching in the appropriate code on the keypad incorporated into the receiving unit. The information is provided in real time, being transmitted over distances of 50,000 miles in half a second. The service is now available in 10 U.s. cities and will be extended to 50 by mid-1985. The unit also has limited messaging capabilities, accommodating messages of up to 40 characters in length. The messaging aspect is deliberately limited so that the information loop of data is kept short to facilitate rapid retrieval. The frequency of the receiving unit can be readily adjusted so that a Philadelphia subscriber can also access the service while in Los Angeles. Receivers cost $400 a piece and subscribers pay a monthly service fee to access the data. The company is developing plans for other similar services such as sports results and news services.
Also being developed is a “Modio” (modem-radio) which will serve as a communications device for the IBM PC, receiving data—such as stock and commodities information—distributed over the FM frequencies.
While the FM subcarrier bandwidths can be divided into an unlimited number of frequencies, speed and reliability requirements currently suggest that the two available channels can only be divided among about five different carriers.
