MT63ASC.ASM, Last edition: 15-AUG-1997
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 64-tone, 10 baud, DBPSK HF modem with ASCII coding
 (c) 1997 Pawel Jalocha, SP9VRC,
 e-mail: Pawel.Jalocha@cern.ch

 This software is not to be used for purposes other than amateur radio
 without a written permision of the author.
 Usage for profit or in commercial/military products is explicitly prohibited.

 Note: the frequency offset shown by the Rx quality report is NOT correct.
      I shall repair it when I am back from holidays.
 The general features of the modem:
  - the modem sends 64 tones spaced by 15.625 Hz (8000 Hz/5/512*5)
  - the modem audio occupies the range from 500 to 1500 Hz
  - tones are modulated with differential bipolar phase shift keying (DBPSK)
  - modulation rate is 10 baud per tone thus the raw data rate is 640 bps
  - the user data are 7-bit ASCII characters encoded with Walsh functions.