Amplitude-shift keying (ASK) is a form of modulation which represents digital data as variations in the amplitude of a carrier wave.
Amplitude-shift keying - Encoding.
The simplest and most common form of ASK operates as a switch, using the presence of a carrier wave to indicate a binary one and its absence to indicate a binary zero. This type of modulation is called on-off keying, and is used at radio frequencies to transmit Morse code (referred to as continuous wave operation).
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ASK is the simplest kind of modulation that can be used to send data through a channel. It has several bad points:
it can be used only when the signal-to-noise ratio is very high, because most of the signal is transmitted at reduced power, so it would be hard to recover.
it needs A/D converters working at a frequency that could be higher than necessary: for example, if the bandwidth between 100 and 101 MHz is used for the transmission, the spectrum of the signal will be only 1 MHz wide, but the A/D converter will need to work at 101*2 = 202 MHz. In QAM modulation, ...
The simplest and most common form of ASK operates as a switch, using the presence of a carrier wave to indicate a binary one and its absence to indicate a binary zero. This type of modulation is called on-off keying, and is used at radio frequencies to transmit Morse code (referred to as continuous wave operation).
More sophisticated encoding schemes have been developed which represent data in groups using additional amplitude levels. For instance, a four-level encoding scheme can represent two bits with each shift in amplitude ...
