GB1122801A - Improvements in or relating to the transmission of pulse coded information - Google Patents

Abstract

1,122,801. Data transmission systems; multiplex pulse code signalling; frequency modulation. SERCK CONTROLS Ltd. 18 Aug., 1965 [19 May, 1964], No. 20571/64. Headings H3R, H4L and H4P. Data in polar return-to-zero form is transmitted by representing Mark, Space, and Zero digits by three respective frequencies. At the receiver, each positive-going transition in the received frequencies causes the generation of three gating pulses, which sample the received signal at times corresponding to the possible times of the next positive transition to determine when that transition actually occurs. The time of occurrence indicates the received frequency and hence the data level. Reference is made to a time-division multiplex system in which the Mark and/or Space frequency of one channel acts as the Zero frequency of another channel which has different Mark and Space frequencies. The modulator, Fig. 2 (not shown), comprises cross-coupled transistors having frequency determining circuits, each including a plurality of resistors which are selectively shorted by transistors controlled by the data to produce the three frequencies.