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DXing
Those “Secret” Subcarrier Signals On FM |
Front view of a vintage Wards Airline radio
showing SCS “in” and “out” plugs using the radio’s “MPX” out jack (a jack
not found on modern radios) and its |
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As a boy in Duluth, Minnesota, I tuned the standard 88- to 108-MHz FM band and experimented with FM DX back in 1948. The receiver was a table model Zenith AM/FM radio—all tubes, of course! Later I added an outdoor, turnstile FM antenna that increased the DX I could hear. A couple of years after that, a Yagi antenna was installed, one of the first FM-only Yagis available—a JFD brand. During this pioneering time when there was no FM car radio, the FCC authorized FM subcarrier broadcasting. It was also a period when regular FM stations were hurting financially. Many, like WWDC-FM 101.1 in Washington, DC, and WFMF 100.3 in Chicago, found that selling background music to stores was a way to stay financially afloat. I recall that WFMF, which could be DXed from Duluth, had a low-frequency tone to increase the volume of commercials or to mute certain radios, under a system called “simplex” operation. Thus, receivers in certain stores would play commercials louder than the surrounding music, while in other stores the announcements were blanked out. Eventually the FCC declared “simplex” operation not to be broadcasting, as defined by the Communications Act of 1934. The new technology, known as multiplexing had, by 1954, won approval from the Commission. Stations could “multiplex” the background music to the stores, while the public heard an entirely different program. Shortly thereafter, the FCC ordered all FM stations to stop simplex transmissions and relegate the in-store music and announcements to subcarriers. (FM’s inventor, Edwin H. Armstrong, had demonstrated how one station could send out two separate programs by multiplexing, which opened the way for FM stereo to be authorized in 1960. Armstrong’s demonstration of multiplexing occurred only a few months before he died in the spring of 1954). There was considerable broadcaster resistance to the FCC’s multiplexing edict because each station offering background music would have to invest in a subcarrier generator, priced at about $5,000, with special receivers costing about $100 each (that’s 1950s’ dollars). Instead, the FCC wanted the public to receive programs more of a “broadcast” nature, as opposed to point-to-point, like the in-store music and commercials. |
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