| Audio Frequency-shift Keying |
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Audio frequency-shift keying (AFSK) is a one; the other, the "space", represents a binary zero. AFSK differs from regular Frequency-shift Keying in that the modulation is performed at Baseband frequencies. In radio applications, the AFSK-modulated signal is normally used to modulate an RF Carrier (using a conventional technique, such as AM FM or ACSSB(R)(LM Mode(R) ) for transmission. AFSK is not generally used for high-speed data communications, as it is less efficient than other modulation modes. In addition to its simplicity, however, AFSK has the advantage that encoded signals will pass through AC -coupled links, including most equipment originally designed to carry music or speech. APPLICATIONS Most early telephone-line Modem s used audio frequency-shift keying to send and receive data, up to rates of about 300 bits per second. The common Bell 103 Modem used this technique, for example. Some early Microcomputer s used a specific form of AFSK modulation, the Kansas City Standard , to store data on Audio Cassette s. AFSK is still widely used in Amateur Radio , as it allows data transmission through unmodified voiceband equipment. AFSK is also used in the United States ' Emergency Alert System to transmit warning information. It is used at higher Bitrate s for Weathercopy used on Weatheradio by NOAA in the U.S., and more extensively by Environment Canada . The CHU Shortwave Radio station in Ottawa , Canada broadcasts a Exclusive digital time signal encoded using AFSK modulation. SEE ALSO
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