Methods of communication
From Megawiki
Radio amateurs use a variety of modes of transmission to communicate with one another, all based on three basic means of communication phone (voice); image; and data.
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Phone
In the terms of Amateur radio, phone simply means to modulate a signal with sound and is usually applied to voice communications. Common forms of phone modulation include Amplitude Modulation (AM); Single Sideband (SSB); and Frequency Modulation (FM).
Image
Amateur radio operators send images over radio using standard television, called Fast Scan Television (FSTV); by Slow Scan Television (SSTV) which is similar to a slide show of still images; or by Facsimile (FAX).
Data
Various means of sending data over radio have been devised, the first being Interrupted Continuous Wave (ICW) or commonly just CW where an unmodulated signal is sent and keyed on or off, most commonly this radio telegraphy is sent in Morse Code. Most other forms of data are sent and decoded using computers or dedicated devices such as Radio Teletype (RTTY), Packet Radio, Phased-Shift Keying (PSK). Most commonly digital signals are used to encode text based data however any type of data may be sent.
Bandwidth
The amount of radio spectrum needed to send any given signal is directly proportional to the amount of information the signal is encoding. A simple keyed carrier in Morse code may require as little as 50 Hz of bandwidth whereas a fast scan television signal may require as much as 6 MHz.
