- See also phase-shift keying (PSK).
Frequency-shift keying (FSK) is a method of transmitting digital signals. The two binary states,
logic 0 (low) and 1 (high), are each represented by an analog
waveform. Logic 0 is represented by a wave at a specific frequency, and logic 1 is represented by a wave
at a different frequency. A modem converts
the binary data from a computer to FSK for transmission over telephone lines, cables, optical fiber, or wireless media. The modem also converts incoming FSK signals
to digital low and high states, which the computer can "understand."

The FSK mode was introduced for use with mechanical teleprinters in the
mid-1900s. The standard speed of those machines was 45 baud, equivalent to about 45 bits per second. When personal computers
became common and networks came into being, this signaling speed was tedious. Transmission of
large text documents and programs took hours; image transfer was unknown. During the
1970s, engineers began to develop modems that ran at faster speeds, and the quest for
ever-greater bandwidth has continued ever
since. Today, a standard telephone modem operates at thousands of bits per second.
Cable and wireless modems work at more than 1,000,000 bps (one megabit per second or 1
Mbps), and optical fiber modems function at many Mbps. But the basic principle of FSK
has not changed in more than half a century.
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27 Jul 2001
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