Note 1: Usually, the instantaneous frequency is shifted between two discrete values termed the "mark frequency[?]" and "space frequency[?]". This is a noncoherent form of FSK.
Note 2: Coherent forms of FSK exist in which there is no phase discontinuity in the output signal. Synonyms frequency-shift modulation, frequency-shift signaling.
Source: from Federal Standard 1037C and from MIL-STD-188
... of gases that results when wood or other organic materials are heated in an environment with little or no oxygen. Wood gas mainly consists of molecular nitrogen (N2), ...
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