A keyer is a device for signaling by hand, by way of pressing one or more switches. Modern keyers typically have a large number of switches but not as many as a full-size
keyboard; typically between four and fifty. A keyer differs from a keyboard in the sense that there is no "board"; the keys are arranged in a cluster. A keyer may take the form of a single
telegraph key for keying
Morse code. In this use, the term "to key" means to turn on and off a
carrier wave, typically. For example, it is said that one "keys the transmitter" by interrupting some stage of amplification with a
telegraph key.
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