Improvements in or relating to time-multiplex pulse modulation signalling systems

摘要

675,454. Multiplex pulse code signalling. PHILIPS ELECTRICAL INDUSTRIES, Ltd. Oct. 13, 1950 [Oct. 17, 1949], No. 25028/50. Class 40 (v). In a time division pulse multiplex communication system, in which the time interval between the pulse of one channel and that of the previous channel characterizes the signal to be transmitted in the former, the mean time interval for each channel is increased when that channel is made busy. At the receiver a warning device is thereby operated. A sine wave generator 30, Fig. 2, at the transmitter controls a pulse generator 29 operating at channel group recurrence frequency. These pulses trigger a flip-flop synchronizing pulse generator 19, the pulses from which are of greater duration than the channel pulses. The trailing edge of the synchronizing pulse triggers the first channel pulse generator and modulator 20, of the series 20 ... 27, each of which triggers the next. Each of these channel circuits such as 21 comprises a flip-flop valve pair 31, 311 producing a pulse, the duration of which is modulated by valve 48, fed from microphone 44 and having an anode resistance 321 which is common to valve 311. The duration-modulated pulse at the anode of valve 31 is fed to the next modulator 22, which is triggered by its trailing edge, and is also differentiated and clipped in circuit 51, 52, 53, the resulting trailing edge pulse being amplified in valve 54 to provide the transmitted pulse fed to the common output conductor 65. The synchronizing and channel pulses are passed to the radio transmitter 66, 67, 68. When a channel is idle, the microphone switch 74 is open and part of the cathode resistance 47 of the modulating valve 48 is short-circuited. The pulses produced by circuit 21 are thus of minimum length. When the channel is brought into operation, the microphone switch 74, in addition to connecting the microphone 44 to valve 48, also completes the circuit of relay 69 to remove the short-circuit on part of the resistance 47. The mean duration of the pulses generated in circuit 21 is thereby increased. Alternatively, the relay may connect a condenser in parallel with the time-constant condenser 33 of the flip-flop circuit, or a resistance in series with resistance 34. At the receiver, the channel pulses at the output of the radio circuit 85, 86, Fig. 3, are passed to the channel demodulators 88 ... 95, the first of which, 88, is triggered by the synchronizing pulses derived from the separator circuit 98. The demodulator flip-flop, 97, 971, is restored by the next channel pulse and at the same time triggers the next demodulator, producing duration modulated pulses which are fed to the reproducer 103. A low-pass filter 109, 110 feeds a threshold relay 104 which responds to the increased signal output when the channel is brought into operation to energize the signal lamp 107.