Secret
Radio: The Story of FM Subcarrier Radio
In the early days of FM radio,
stations needed extra income and the Federal Communications Commission
authorized the transmission of "subcarriers" for additional
programming.
These programs continue to this
day, "hidden" on the radio signals you receive in your home and car.
The FM "subcarrier" is
an extra signal. It is broadcast on top of the audio you hear.
To imagine what a subcarrier is,
suppose that the station mixed a very high-pitched dog-whistle in along with the
music. You wouldn't be able to hear the whistle because it would be above
human hearing. However, your radio could "hear" it and use it.
You could even
"modulate" that dog-whistle, meaning you would vary its pitch slightly
to encode it with words and songs. Remaining hidden, it would carry a
second, entirely different radio program.
In essence, this is how FM
stations transmit the hidden signals.
On the subcarriers, stations
transmit background music to stores, offices and restaurants. They
transmit the reading of books for the blind. They transmit stock
quotations and other special programs.
Subscribers to these programs
must purchase or lease special radios to detect the hidden signals.
The subscription services
generally don't want hobbyists, experimenters, or curious folks listening
in. Few people know that the subcarrier exists; most have no idea how to
purchase a subcarrier radio.
One source of FM subcarrier
radios is a company called FM
Atlas.
FM
Atlas has been selling specially modified radios, along with excellent
reference guides to FM stations, for over 20 years.
FM
Atlas is a family-owned company operated by Bruce
Elving, Ph.D., and his wife Carol. You can get full information on
their products and services by clicking on the links marked above or here.
Please note that intercepting
subscription music without permission and playing it in a public place is
definitely prohibited! This article is educational in purpose only --
hobbyist, experimenters, and home users only!
You can also get general
information on FM Subcarrier Radio by entering
those words in most internet search engines.
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