Narrow-band eight-phase modem

Details Narrow-band eight-phase modem Narrow-band eight-phase modem

1976-02-26

1977-03-08

Safourek, Benedict V.

Telegraphy

Code transmitters

Rotary contact

178 67, 325320, H04L 2722

Patent

active

040114074

ABSTRACT:
An eight-phase modem is described in which a 2900 H.sub.z carrier has eight phases each representing one of eight tri-bit symbols 000 through 111. The phase modulated carrier is restricted for transmission to a frequency band of 2900 .+-. 50 H.sub.z, and the modem can carry four time-division-multiplex 75-baud teletype channels at 250 bits per second at the upper end of a telephone voice channel without interfering with normal voice use of the channel. Or, the modem can carry eight channels at 500 bits per second in a frequency band of 2900 .+-. 100 H.sub.z. The modem operates reliably despite a carrier frequency translation or shift of up to .+-. 5 H.sub.z in the communications path. The modem extracts a carrier cycle spike from the received signal during each symbol period, and uses the spike to synchronize a locally-generated reference signal, and compares each spike with the reference signal to derive the corresponding phase-modulated tri-bit symbol information.

REFERENCES:
patent: 3737578 (1973-06-01), Mutsuo
patent: 3753114 (1973-08-01), Burley

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