Patent GB-707382-A (GB)
Title: Improvements in electrical signalling systems
Inventor: BAKER GEORGE THOMAS
IPC: H04L5/24
Filed: 1950-01-30
Abstract: 707,382. Telegraphy. BRITISH TELECOMMUNICATIONS RESEARCH, Ltd. Jan. 25, 1951 [Jan. 30, 1950], No. 2388/50. Class 40 (3). [Also in Group XXXV] The invention relates to a twin-channel telegraph system in which a piece of equipment is employed which with slight modifications may be set up to function as a transmitting station, a receiving station or an intermediate station. A typical use of the system is illustrated in Fig. 1 in which four stations A, B, C and D are employed, A, B and C being close together on a line circuit and separated from D by a radio circuit. Transmitter T1 at A operates on one channel into receiver R1 at B whilst transmitter T2 at A operates on the other channel into receiver R2 at D. A further transmission takes place from transmitter T3 at B to receiver R3 at D. Station C functions to regenerate on both channels. Other arangements may be employed. For example, both of the transmitters at A may operate into D with stations B and C both regenerating. Operation at each station is controlled by a sequence unit SU, each of the units being identical apart from differences in the interconnection of their component circuits. The stations normally operate on a synchronous basis each with a local crystal-controlled pulse source which is maintained in phase with the incoming signals by an automatic control system (see Group XXXV). Operation on a start-stop basis is however possible. The signalling code employed is the normal 7-unit code comprised of 20 ms elements. The elements are, however, divided between the channels so that 10 ms is available for each. Preceding each code combination is a 10 ms space interval employed for synchronizing. Sequence unit.-Fig. 3 shows the schematic diagram. Figs. 9-12 (not shown) illustrate details of the circuits. Fig. 5 is a time-sequence diagram indicating the sequence of operation under different conditions of use. In Fig. 3, Z, SY, L and T are electronic relays comprising double-triodes cross-connected to give a circuit having two stable states. Z, L and T control polarized relays which change over with the electronic relays. Relay T is also arranged to provide a pulse on terminal TP when reset to the mark condition. S2 is a double-triode scaleof-two circuit arranged to receive pulses on both grids simultaneously and trigger alternately from one condition to the other in response to the pulses. C6 comprises three double-triodes connected to form a six-point cyclic counter. The circuits having the prefix G are gates employing rectifiers as the switching elements. The incoming signal controls gates G18 and G19 opening the gates for space and closing them for mark. A tape transmitter for channel A controls gates G1-G6, the first gate being controlled by the tape contact and the other five by the pecker bars. A gate is opened to pass a pulse to the output terminal AP if a space element is required. A second tape transmitter for channel B similarly controls gates G7-G12 to pass pulses to terminals BP. Relay T controls a teleprinter A whilst relay B controls either a teleprinter B or the outgoing line when signals are extended. Pulses occurring at 10 ms intervals appear on terminal P from the local pulse source, and the first pulse indicated at zero on the time scale, Fig. 5 triggers relay SY through normally-open gate G16. The operation of SY extends a pulse (line 4, Fig. 5) to terminal SY and also opens gate G15. The next pulse on P after 10 ms transposes S2 and extends a pulse (line 1, Fig. 5) to the A outlet gate G18. Relay Z is also triggered but the counter C6 is blocked since G14 is closed until relay Z triggers. Relay Z extends a pulse (line 5, Fig. 5) to gates G and G7. The next input pulse triggers S2 into its original position providing a pulse (line 2, Fig. 5) at the B outlet gate G19. On the next pulse, S2 is triggered to the A side and a pulse passes through G14 to the counter C6 which steps one and delivers a pulse (line 5, Fig. 5) to gates G2 and G8. The operation on succeeding input pulses is similar, each pair of pulses completing one step of the counter, the first providing an A outlet pulse and also stepping the counter to provide a pulse to corresponding gates in the groups G1-G6 and G7-G12, and the second providing a B outlet pulse. The sixth pulse from C6 re-operates Z which closes gate G14 and opens gate G17. The next B pulse re-sets SY and a cycle of operation is thus completed, the cycle time being 150 ms. Pulses for reset purposes are obtained at 10 ms intervals on terminal (A + B) R, and pulses coincident with the A and B outlet pulses are obtained on terminal AR and BR. The reset pulses are employed to move relays L and T to the mark condition but are of lower amplitude and duration than the normal operating pulses so that should a relay receive an operating and re-set pulse simultaneously it responds to the operate pulse. Twin-Channel transmitting operation. (Station A, Fig. 2).-The connection set up between the terminals are as shown in the first part of Fig. 4 (Transmitter, Two in). A tape is inserted in each tape transmitter the holes being as indicated in part two of Fig. 5 (Typical transmitter operation). At time 0, the SY pulse is generated, and this is connected through to relay L which is moved to space to provide the synchronizing signal. At 10 ms the reset pulse from (A + B) R to LR attempts to restore relay'L but since the tape contact of the A transmitter is closed the Z pulse passes through gate G1 and holds relay L at space. This provides the A channel start signal. Simultaneously the Z pulse passes through gate G7 opened by the tape contact of the B transmitter and operates relay T to space. At 20 ms, a reset pulse is applied to both L and T, the latter re-acts but in so doing applies an operate pulse to TP, and since this is connected to L, the relay is held at space. Thus the next 10 ms transmits the B channel start signal. At 30 ms, the counter applies a pulse to gate G2 but since this is closed by the tape relay L restores to mark on the reset pulse. The other tape holds G8 open so that relay T operates. The 40 ms reset pulse has no effect on L but restores T to mark to operate L through TP. Subsequent elements read from the tapes by gates G1-G12 under the control of the counter operate relays L and T in like manner, the condition of the first tape being transmitted to line immediately whilst that of the second is stored on relay T for 10 ms and then transferred. Twin-channel receiving operation.-(Station D, Fig 1). The connections set out between the terminals are shown in the second part of Fig. 4 (Receiver, two out). The automatic control system maintains the local pulse source displaced in phase by 5 ms from the received signal. No action takes place at 0 in response to the synchronizing signal. At 10 ms, at the centre of the A channel start element, the first A pulse passes to gate G18 and since the line relay is at space a pulse passes to relay T which operates and extends a start signal to teleprinter A. At 20 ms, at the centre of the B channel start element, a B pulse passes to gate G19 and since the line relay still indicates space a pulse passes through to operate relay L and extend the start signal to teleprinter B. In a similar manner during receipt of the succeeding signal elements tests are made on the line conditions at the centre of the element and transferred to relays Land T. All the signals to the teleprinters are completely regenerated and 20 ms in length. Re-set pulses coincident with the A and B pulses are applied from terminals AR and BR. Tandem operation.-(Station B, Fig. 1). The connection set up between the terminals are shown in the third part of Fig. 4. (Tandem, one in, one out, one through). The A channel incoming signal operates the A channel teleprinter whilst the B channel signal is regenerated and extended together with a further transmission originated from the local A tape transmitter. The test on the A section of the incoming signal takes place as described above for the twin-channel receiving operation and controls the T relay to provide the output to the A teleprinter. The A portion of the outgoing signal is derived from the tape transmitter via terminal AP as described above for the twin-transmitting operation. 10 ms re-set pulses are applied to relay L from (A + B) R so that the tape reader controls only the first half of the outgoing signal. The second 10 ms is provided by testing the second half of the incoming signal via terminal BL. This signal is thus regenerated and passed to line as received. A connection is taken from SY to insert the synchronizing signal. Regeneration on both channels.-(Station L, Fig. 1). The connections set up between terminals are shown in the fourth part of Fig. 4 (Regenerator, two through). Pulses received on terminals AL and BL as a result of testing the incoming line signals control relay L in turn, re-set pulses being applied at 10 ms intervals from (A + B) R. A connection is taken from SY to insert the synchronizing signal. Automatic alignment of receiving equipment.- Normally gate G16 is open and the equipment operates continuously in 150 ms cycles. To effect alignment of these cycles with the incoming signal cycles gate G16 is temporarily switched via terminal S/S to the incoming line relay to operate in the same manner as G18 and G19. During the absence of a message the incoming signal comprises 10 ms synchronizing pulses only and the gate G16 remains closed except during these pulses. Thus, at whatever part of the incoming cycle relay SY is re-set it remains blocked until the next synchronizing pulse. At this point gate G16 is opened and SY operates to the next 10 ms pulse at P. The equipment is now in alignment and the connection via S/S may be removed. An automatic check of alignment is provided by applying the SY pulse to hold a slow release alarm relay through a gate controlled