Patent GB-607610-A (GB)
Title: Multiplex pulse telephony
IPC: H04J3/00
Filed: 1945-10-15
Abstract: 607,610. Pulse multiplex signalling. WESTERN ELECTRIC CO., Inc. Oct. 15, 1945, No. 26921. Convention date, Oct. 19, 1944. [Classes 40 (v) and 40 (vi)] In a pulse multiplex system in which channel pulse trains are interlaced, a synchronizing pulse of longer duration than the signal pulses is sent at channel pulse recurrence frequency and, at the receiver, the synchronizing pulses are separated to enable gating pulses to be generated for combining with corresponding signal pulses to separate and demodulate the different channel trains. Transmitter. In the embodiment described, the system provides eight channels, CK1 ... CHS, Fig. 1A, of which CH4 is described in particular. The incoming line is connected to filter 10 which separates speech and lowfrequency ringing currents. The speech passes to amplifier 11 and pulse modulator 12 and the ringing currents directly to the modulator to produce a calling signal. The pulses supplied to the modulators are derived from the master oscillator 13 which delivers a rectangular wave at channel pulse recurrence frequency. The following differentiating network 17 produces short-positive pulses to control the modulators for channels 5 to 8 and negative pulses from differentiators 14, 14<1> control channels 1 to 4, being followed first by phase reversers 15, 151 respectively. The outputs of the modulators of the even and odd numbered channels respectively are fed to a radio transmitter 19 through pulse formers 18 and 18<1>. The oscillator 13 also feeds another differentiator controlling a synchronizing pulse generator feeding the radio transmitter through an amplifier. Master oscillator synchronizing and modulator circuits. The master oscillator valve 30, Fig. 2, operates in class C and its output is squared off in valve 31, the ratio between resistances 111, 112 being selected to produce the wave-form 4a, Fig. 4. The output of valve 31 is differentiated in circuit R2, C2, the resulting short negative and positive pulses being applied to the grid of valve 26, curve 4b. Grid current greatly reduces the amplitude of the positive pulse. A tapping on the anode load R3, R9 of valve 26 is connected to the grid of valve 27, which, with valve 28, form a flip-flop multivibrator triggered by the positive pulses on said grid. The resulting grid voltage on valve 28, curve 4d, shows a relaxation point which is adjusted to occur in the middle of the appropriate channel period, in this case, channel 4. The grid of valve 28 is connected to the grid of valve 29, the anode voltage of the latter being shown in curve 4e. The steep negative-going portion of this curve causes an oscillatory circuit L2, in the grid circuit of valve 36, to ring and produce a short pulse, curve 4f, before being damped by grid current flow. Valve 36 is shared by all the evennumbered channels, so that other pulses appear in curve 4f. The following valve 37 is a squarer and feeds the radio transmitter through condenser 40. Modulation of the pulse phase is accomplished by variation of the grid potential of valve 28, by the signal, through low-pass filter 23 and limiter-amplifier valve 24. The flip-flop circuits for channels 5 to 8 comprise valve pairs, such as 41, 42, controlled directly by the positive pulse resulting from the differentiation of the master oscillator output by circuit C6, R10, and being initially triggered at the commencement of the third channel interval, curve 4g, for channel 5, for example. The wider synchronizing pulse is produced between the pulses of channel 8 and channel 1 by applying the master oscillator output through circuit C7, R12 to cut-off valve 45 for the required period starting at the negativegoing edge of the wave, curve 4a. The resulting rectangular pulse is reversed in valve 46 and passed to the radio transmitter. Calling. Low-frequency ringing currents in the line 20 are separated by the filter C3, 21 and operate relay 49 through rectifier 48, to disable the flip-flop circuit 27, 28 and suppress the channel pulses. Receiver. The radio receiver 50, Fig. 1B, passes the received pulses through amplifier 51, to amplifier 56 and individual channel resistances such as 57, to pulse converters such as 58. The signal output from 58 is passed through low-pass filter 59 and amplifier 60 to the output line 61. Gate pulses to separate the channels and demodulate the channel pulses in converters 58 are produced by generators such as 55 controlled by a master squarewave generator 54 controlled by received synchronizing pulses from amplifier 53 and selector 52. The ringing relay circuits such as 63 are held inoperative so long as pulses, rectified by rectifier 62, are delivered thereto from pulse converter 58. An appropriate ringing signal is switched to the line 61 when the channel pulses are suppressed. If the synchronizing pulses fail an alarm circuit 65, fed from the selector 52 through amplifier 64, is operated, and the ringing circuits 63 are disabled. Receiver gating and demodulating circuits. Provision is made to operate the pulse demodulating circuits from the trailing edges of the received pulses. The latter pass to a common amplifier 67, Fig. 3, followed by a valve 73, the positive pulses from which are differentiated by circuit C8, R13. The following valve 74 is biassed to respond only to the resulting negative trailing edge pulse, and its output is fed through individual high resistances such as 57 to the channel demodulators. Valve 73 and circuit C8, R13 can be removed from the circuit by switches S1, S<1>1, when it is not desired to work on the trailing edges of the received pulses. For selecting the synchronizing pulses, the combined pulse train from valve 67 is fed to valve 75 the output pulses from which charge condenser C9 to a voltage dependent upon pulse duration. Only the higher voltage values due to the longer synchronizing pulses are great enough to unblock valve 76. The resultant pulses are differentiated in circuit C10, R15 and the resultant positive trailing edge pulses unblock valve 77. Valves 78, 79 are connected as a self-running multivibrator synchronized by the output from valve 77 or valve 76, if the trailing edge control described is not desired. The anode voltage of valve 78 is shown in curve 4n and the grid voltages of both multivibrator valves in curve 4p. The individual channel gate pulse generators are exemplified by channel 4 in which valve 80 acts as a sweep voltage generator with circuit R18, C15 synchronized from the grid of valve 79, and unblocking valve 81 for the duration of the channel period, curve 4q. The resulting negative pulse at the anode of valve 81 is fed to valve 82 which produces at its anode a positive gate pulse lasting for the channel period. The grid of valve 79 also controls the gate pulse generators for channels 2 and 3. The generator for channel 1 has no delay device and consists of valve 86 only. The generator for channel 5 is similar to that for channel 1 but is controlled from the anode of valve 79, and those for channels 6, 7 and 8 are similar to that for channel 4 but are controlled from the grid of valve 78, see curve 4p. The channel selector and demodulator flip-flop valves 89, 90 are fed with all the received pulses and the channel gating pulse, curve 4s showing the resultant grid voltage of valve 89. The circuit is not triggered by the ungated pulses but the combined amplitude of the gate and selected channel pulses triggers the multivibrator, which returns to the quiescent state at the end of the gate pulse. The resulting durationmodulated pulses, curve 4t, at the anode of valve 89 are fed through a low-pass filter 94 to audio amplifier 96 and output line 98. Calling and alarm circuits. As long as signal pulses are being received on the channel, the output of valve 90, rectified at 99, blocks valve 100. When the pulses are suppressed at the transmitter for ringing purposes, valve 100 becomes unblocked to energize relay 101 and connect ringing current from source 102 to the line 98. To indicate failure of the synchronizing pulses, valve 105 is fed from the anode of valve 75, to produce negative pulses which are rectified at 106 to block valve 107. When the synchronizing pulses disappear valve 107 passes current to operate relay 108 to energize an alarm device 109. At the same time a contact 110 is opened to cut-off the current to the ringing relays and valves, e.g. 100, 101 and thus disable the ringing circuits. Specification 581,812 is referred to.