Patent GB-757612-A (GB)
Title: Improvements in or relating to synchronising arrangements in electric telegraph systems
Inventor: PRIOR HECTOR THOMAS
IPC: H04L7/033
Filed: 1953-11-03
Abstract: 757,612. Code telegraphy. STANDARD TELEPHONES & CABLES, Ltd. Oct. 29, 1954 [Nov. 3, 1953], No. 30338/53. Class 40 (3). [Also in Groups XXXV and XL (c)] In a synchronous electric telegraph system, the receiving circuit comprises means controlled by an oscillator for regenerating the received signals which are employed in conjunction with the regenerated signals to produce a train of unidirectional control pulses whose duration and polarity are determined by the time difference between the corresponding transitions of the received and regenerated signals and which, after integration, are used to adjust the oscillator frequency in such manner as to maintain a specified time difference between the received and regenerated signals. In the diagrammatic representation, Fig. 1, the incoming signals are regenerated at 1 under control of the oscillator 7 and the pulse generator 8 and are also applied with a delay of 10 ms., produced by a network 2, to a subtracting device 3 to produce a series of short pulses indicated at D in Fig. 2. The regenerated pulses, curve B, are applied with a delay of 10 ms. via delay network 5 to a switch circuit 4 operating so that pulses from the device 3 are reversed by the circuit 4 when the marking condition exists at the output of the network 5. The pulses from the circuit 4, which will all be of the same polarity, are integrated at 6 and applied to the oscillator to change the phase of its output so that the timing of the sampling pulses from the generator 8 is adjusted to the centre of the incoming impulses. As indicated in Fig. 2 the sampling pulses from the generator 8 occur too early. If they occur too late relative to the centres of the incoming pulses, the pulses from the switch 4 will all be negative, and the output of the integrator 6 will operate the oscillator 7 to advance the generation of the sampling pulses. To maintain synchronous operation during breaks in message transmission, the message is combined with a pulse train continuously produced from an auxiliary generator so that the transitions produced by this train serve to maintain the adjustment of the oscillator at the receiver during message cessation. The received pulse train which is modified by the auxiliary signal train is restored to its original form by an auxiliary generator at the receiving station. In order to avoid the use of unstable D.C. amplifiers, two modulators, fed with a carrier, are included respectively between the output of the network 2 and of the regenerator 1, and the input to the subtracting device 3. A demodulator fed with the same carrier frequency is included between the switch circuit 4 and the integrator 6. In operation, a space element is arranged to shift the phase of the carrier frequency by 180 degrees, and the switching circuit operates to modify the short bursts or packets of oscillations resulting from the subtracting operation so that respectively they are all in phase with, or 180 degrees out of phase with, the carrier oscillations applied to the demodulator which thereby produces a train of positive or negative pulses respectively, which are integrated and utilized as indicated in connection with Fig. 1. The circuits for the modulators, subtracting and switch devices, demodulator and integrating device are described in connection with Figs. 5, 6 (not shown). The combining circuits in which an auxiliary signal generator is employed at the transmitter and receiver are described in connection with Figs. 7, 8 (not shown).