The Recommendation provides in Annex 1 technical characteristics for narrow-band phase-shift keying (NBPSK) telegraphy equipment used in the HF bands of the maritime-mobile service.
ITU-R M.627-1 SPANISH-1995 history
1995ITU-R M.627-1 SPANISH-1995 Technical Characteristics for HF Maritime Radio Equipment Using Narrow-Band Phase-Shift Keying (NBPSK) Telegraphy