In telegraphy systems, keying in which the modulating wave causes the carrier to be modulated with a single tone for the " mark " and modulated with a different single tone for the "space." ( 188 )
TWO TONE KEYING
Meaning of TWO TONE KEYING in English
Telecommunication standard terms English vocab. Английский словарь стандартных телекоммуникационных терминов. 2012