Patent GB-693862-A (GB)
Title: Improvements in or relating to electric pulse signalling systems
IPC: H04J3/06
Filed: 1951-04-09
Abstract: 693,862. Multiplex pulse code signalling. GENERAL ELECTRIC CO., Ltd., and STENNING, L. C. Feb. 13, 1952 [April 9, 1951], No. 8243/51. Class 40 (v). In a pulse signalling system, phasing of the receiver equipment is determined by a received pulse train having a characteristic modulation and at least three monitoring means, to which are fed pulse signals occurring in adjacent pulse intervals, and which produce outputs from the characteristic signal which provide phase correction voltages unless the signal is fed to a predetermined monitor circuit. In the system described, there are twelve five-unit binary on-off code channels, the channel recurrence frequency being 8 kc/s. so that pulse positions recur at the rate of 480 kc/s. The last pulse positions of the groups of one channel are utilized to carry pulses defining a characteristic modulation. At these positions there is alternately a pulse and no pulse so that the pulses defining the characteristic modulation have a recurrence frequency of 4 kc/s. For this purpose, at the transmitter the coder 1, Fig. 1, feeds the output terminal 4 through a gate circuit 2, which suppresses any pulses occurring in every sixtieth pulse position, that is the fifth and last pulse position in one of the twelve channels. The gate circuit 2 is controlled by a pulse generator 3 which also supplies pulses to the output terminal 4 having a recurrence frequency of 4 kc/s. so phased that they occur at alternate time positions when the gate circuit 2 is non-conducting. At the receiver, the pulse code signal from terminal 11, Fig. 2, is fed to the decoder 12, the operation of which is determined by the phase of oscillations supplied, through a variable phase-shifter 13, by an oscillator 14. The frequency of oscillator 14 is controlled by the code signal from terminal 11. Five monitors, 15... 19, are responsive to pulses having the characteristic modulation and are supplied with pulses from the signal occurring at every sixtieth position, the monitors being supplied with such pulses derived from a group of five adjacent pulse positions. For this purpose terminal 11, and four tappings on a delay line 21 fed therefrom are connected respectively to the five gate circuits 22 ... 26, the tappings being spaced by a period equal to that between adjacent pulse positions. A common gating signal is fed to the gate circuits from the pulse generator 27, which is controlled by the oscillator 14 and phase-shifter 13, so that the gates pass the signal component occurring at every sixtieth pulse position. Taking the monitor 17 for example, the signal from gate 24 is passed through a band-pass filter 28, adapted to pass oscillations of 4 kc/s. frequency, to an amplifier 29 and rectifier 31, controlling relay C. The relay C is operated if the gate 24 is passing the pulses having the characteristic modulation. Similarly relay A, B, D or E in monitor 15, 16, 18 or 19 respectively, is operated if gate 22, 23, 25 or 26 respectively is passing these pulses. For normal operation, the receiver is arranged to require the relay C to be operated by the characteristic signal in order correctly to phase the decoder 12. This opens contacts C<SP>1</SP>, C2 to cut off the supply to relays F, G, which control the supply, and its polarity, to a motor 33 provided to operate the phaseshifter 13. If, when the phasing is incorrect, relays A or B are operated, contacts A<SP>1</SP> or B<SP>1</SP> are closed to energize relay F which cuts off the supply to relay G at contact F<SP>2</SP> and energizes the motor 33 at contact F<SP>1</SP> for one direction of rotation. The resulting adjustment of the phase-shifter 13 is such as to alter the phase of oscillations supplied to the decoder 12 and pulse generator 27 towards the desired condition when the pulses having the characteristic modulation are applied to the monitor 17 to operate relay C. If relays D or E are operated, due to incorrect phasing, the motor 33 is energized at contact G<SP>1</SP> to rotate in the opposite direction, by energization of relay G through contact D<SP>1</SP> or E<SP>1</SP>. At the same time, the circuit of relay F is broken at contact G<SP>2</SP>. While adjustment is taking place, instants may occur when none of the relays A ... E is operated, so that a holding circuit for relays F and G is provided through contacts 34, 35 which are closed while the phaseshifter 13 is being operated. Energization of relay C subsequently, will de-energize motor 33 and open contacts 34, 35. Automatic phasing is thus accomplished if the received signal slips one or two pulse positions either forward or backward. For the initial setting up of the receiver, a timing signal, as described in Specification 693,859, may be transmitted thereto. If a slip of more than two positions has occurred, an alarm signal may be automatically produced, for transmission back to the transmitter, and operated by a circuit containing additional series-connected normally-closed contacts of the relays A ... E. Instead of using the fifth pulse position in every group of one channel, that position may be used only in every fourth group, for example, to reduce the degradation of the intelligence transmitted over the channel. If the invention is applied to a pulse time modulation system, the transmitted signal also contains periodically recurring pulses having a characteristic modulation.