Patent GB-1364808-A (GB)
Title: Simultaneous radio communication system
IPC: H04B1/56
Filed: 1972-12-05
Abstract: 1364808 Magnetic disc recorder SENDAI TELEVISION BROADCASTING CORP 5 Dec 1972 [8 Dec 1971 18 April 1972] 56066/72 Heading G5R [Also in Division H4] In a duplex radio communication system in which transmission in each direction is on the same carrier frequency, the carriers are interrupted in opposite phase at the same period, the on-periods of the carrier waves include timecompressed information signals and the cooperating receivers have means for time-expanding the time-compressed signals. General description.-An audio signal SA, Fig. 1, is stored at 2 and read out with a time base of one half that of the signal SA under the control of a synchronizing signal PS derived from a generator 11. The time-compressed signal modulates the carrier wave which is interrupted by a control signal PQ derived at 18 from the synchronizing signal and the resulting signal is transmitted. The signals are received at 22 under the control of signal PQ<SP>1</SP> derived at 25 from the sync signals and under the control of sync signal PS stored at 23, which operates in inverse manner to device 2, and read out in timeexpanded form as signal SD, a replica of signal SA. The received signal also controls generator 11, which detects the interruptions of the carrier waves. The sync signals PS in the two stations are arranged to be in opposite phase and likewise the signals PQ, PQ<SP>1</SP> in each station. In one arrangement using magnetic storage, the audio wave itself is compressed. In a modification, the audio signal is sampled and the resulting amplitude modulated pulses are compressed in time. Magnetic disc time base compressor.-A magnetic disc 4, Figs. 2, 3, is rotated clockwise by driving means 3a and co-operates with a fixed recording head HA and a rotary playback head HB. Head HB is mounted on an arm 6 and is rotated by means 3b about axis OB, which is offset from the axis OA of the disc, at the same speed but in the opposite direction to the disc. Driving means 3a, 3b are controlled by the sync signal PS. The air gap of head HA forms a track FA and the air gap of head HB forms a track FB on the disc so that the two tracks only co-operate for a portion of each revolution and the two heads will not collide. The signal SA is supplied to the head HA and the time-compressed signal SB is supplied by the head HB. The track FA is equally divided in a clockwise direction into sections D1, D2, D3, D4, and the instants when the beginnings of these sections cross the line OA-LA are taken as t 1 , t 2 , &c., Fig. 4, the corresponding recorded signal portions being S1, S2, S3, S4, S5, ... The corresponding output from head HB is shown in Fig. 4B. The amplitude fluctuations may be made negligible by minimizing the distance between centres OA, OB, or alternatively the signal SA may be frequency or phase modulated and a limiter included. Keying of the transmitter by the signal PQ, Fig. 4C, results in the transmission of signal RS, Fig. 4D, which is the signal SA compressed. At the receiver, the signal SC is supplied to the rotary head HB of a similar device and the signal SD, Fig. 4F, is read off by the fixed head HA.