four-frequency diplex telegraphy

four-frequency diplex telegraphy

[¦fȯr ¦frē·kwən·sē ¦dī‚pleks tə′leg·rə·fē]
(communications)
Frequency-shift telegraphy in which each of the four possible signal combinations corresponding to two telegraph channels is represented by a separate frequency.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.