47 C.F.R. § 80.219
NB-DP and data transmission equipment installed in ship and coast stations before October 1, 1990, that operates on the frequencies in the 4,000-27,500 kHz bands must be capable of operation in accordance with the technical requirements of either ITU-R M.476-5 or ITU-R M.625-3 (both incorporated by reference, see§ 80.7 ), and may be used indefinitely. Equipment installed on or after October 1, 1990, must be capable of operation in accordance with the technical requirements of ITU-R M.625-3, 1995 (incorporated by reference, see § 80.7 ). NB-DP and data transmission equipment are additionally permitted to utilize any modulation, so long as emissions are within the limits set forth in § 80.211(f) and the equipment is also capable of operation in accordance with ITU-R M.625-3 (incorporated by reference, see § 80.7 ).
47 C.F.R. §80.219