GB877919A - Pulse code modulation communication system - Google Patents

Abstract

877,919. Pulse modulation systems. HYCON EASTERN Inc. June 29, 1959 [Dec. 15, 1958], No. 22314/59. Class 40(5) In a pulse-code modulation system or other system employing coded groups of pulses such as a tropospheric-scatter system in which cyclic fading occurs, for example with an interval between fading peaks of the order of <SP>1</SP>/ 10 second, each successive information pulse is converted into a pulse of duration at least equal to the interval between fading peaks. One embodiment described is a time division multiplex system in which mark, space signals, M 1 , S 1 in channel I are transmitted respectively as frequencies # 1 +#, # 1 +2#, signals S 2 , M 2 in channel II are transmitted as frequencies # 1 +3#, # 1 +4# and so on, Fig. 2B. Signals M 1 , S 1 , M 2 , S 2 &c. are converted to overlapping signals of duration T 1 , equal to the fading period, In Fig. 4, the multiplexed mark, space signals control the selection of mark or space oscillator 30 or 32 operating at 18À5 or 18À0 kc./s. respectively and supplying mixer 34 which is also fed by the output of a stepping oscillator 36 whose frequency is varied in steps of 1 kc./s. from 2 kc./s. to 120 kc./s. in synchronism with the channel selection. The output of mixer 34 is applied to recording head 56 of a pulse stretching device PS comprising a capstan 52 over which a magnetic recording tape 50 is driven by a shaft 54, the tape making one complete revolution per second and head 56 being rotated about capstan 52 by shaft 58 at a rate of 100 revolutions per second. A stationary pick-up head 60 supplies the elongated pulses to a single sideband transmitter 8<SP>1</SP>. Head 56 is tracked across the tape once every hundred revolutions by a screw so as to avoid distortion of the successively recorded signals. The receiver comprises a pulse compression device PC which is similar to device PS except that the functions of heads 56<SP>1</SP>, 60<SP>1</SP> are reversed and head 56<SP>1</SP> is not tracked across the tape 50<SP>1</SP>. The signals picked up by head 56<SP>1</SP> are supplied to a mixer 34<SP>1</SP> together with the output of a stepping oscillator 36<SP>1</SP> which is operated in synchronism with oscillator 36. The output of mixer 34<SP>1</SP> is fed to one of two envelope detectors through narrow band-pass filters 42 or 44 tuned respectively to 18À0 and 18À5 kc./s. so as to provide channel separation and mark, space recognition. The original multiplexed mark, space train is reproduced by means of a decision circuit 24<SP>1</SP> and a pulse regenerator 46.