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Signed space diagrams are described which show the pattern of amplitude and phase variation for several kinds of modulated carrier signals commonly used in digital data transmission. Such diagrams illustrate important similarities and differences among the various modulation methods. Oscilloscope pictures of actual data signal patterns are presented, and it is shown that these patterns can be used to detect the presence of amplitude and delay distortions in the transmission channel.
J. R. Davey (Sun,) studied this question.