Patent GB-674743-A (GB)
Title: Improvements in signalling systems, for example for remote control purposes
IPC: G08C19/24
Filed: 1945-06-22
Abstract: 674,743. Electric selective signalling. GENERAL ELECTRIC CO., Ltd., FOOT, J. B. L., and HAWES, D. O. June 5, 1946. [June 22, 1945] No. 16042/45. Class 40 (i). [Also in Group XL (b)] Intelligence is transmitted as constantly recurrent groups of pulses, the groups differing by the number and/or time spacing of their constituent pulses, and the time spacing of the groups being greater than the maximum time spacing of any two pulses of a group. In one emodiment, the group is a pair of pulses and is distinguished by the spacing of the two pulses, Fig. 3. Oscillations at the group recurrent frequency are developed at LC, Fig. 1, and are applied to pulse generators V1, V2, one having a delay circuit R1, C1, to produce a spacing of the resulting pulses of about one quarter of the wavelength of LC. The pulses from V1, V2 are squared and amplified by valves V3, V4 and are applied to two double diodes V5, V6 which may be made conducting by earthing their cathodes at Ea, Eb. One cathode of each double diode is connected to the entrance 8 of a delay network N, the other cathodes being connected to points 6, 4 on the network. A pair of channels similar to V1, V3, V5 and V2, V4, V6 are connected to the other side of LC, one cathode of each of the final double diodes being connected to 8, and the other cathodes being connected to points 2, 0 on the delay network N. Each diode, when conducting, results in a pair of pulses appearing at O, the spacing between the pulses being individual to each diode as is the position of the pair in the train. Thus, if all the diodes are earthed, pulses a b c d, Fig. 3, are produced successively, and will continue to be produced so long as the diodes are earthed. The pulses at O are applied to a valve V7 to eliminate spurious signals, are reversed, squared and limited by valve V8 and applied over cathode follower valve V9 to a modulator T for transmission. In another embodiment, the group consists of two sets of pulses A, B, Fig. 4, in which the first and last pulses of the first set and the first pulse of the second set are always present, while the presence or absence of other pulses represents intelligence. Oscillations at the group repetition frequency from LC, Fig. 5, are applied in opposite phase to pulse generators V10, V11 from which pulses out of step with each other are applied to valves V12, V13, V16, V17, V18 connected to double diodes V14, V15, V19, V20, V21 which conduct when their cathodes are earthed. The cathodes of the diodes are taken to appropriate points on a delay network N so that the output consists of the desired train of pulses. Cathodes A10, A0, B0 are permanently earthed to provide the first and last pulses of set A and the first pulse of set B, while other pulses are selected by earthing the appropriate remaining cathodes. This system is designed to give twelve items of intelligence. A receiver designed for responding to signals of the type shown in Fig. 4, is described with reference to Figs. 6 and 7. The received signals are applied at T3, Fig. 6, connected both to one end of a delay network N and to the control grids of valves V21 ... V25, and from points 0, 2, 4, 6, 8, 10 on the network N to the suppressor grids of valves V21 ... V25. These valves are coupled through diodes V26, V27, V28, to valves V29 ... V33 which respond to the signal only when a number of pulses have been injected into the integrating circuits CR, and which operate relays 10D, 8D, 6D, 4D, 2D whose contacts are also shown in Fig. 7. As shown, the relays are de-energized. On switching on the receiver, valves V29 ... V33 conduct to operate their relays. Contact 10D2, Fig. 7, closes to energize relay E and open contact E1 thus isolating the bank of contacts ; contacts 2D10, 4D6, 6D4, 8D3, 10D3 also operate to energize a delay release relay F to close contacts F2, Fig. 7, and F1, Fig. 6. Since contacts 10D1, 8D1, 6D1, 4D1, 2D1 are open, the closure of contacts F1 does not affect valves V29 ... V33. If pulses are now received, each pulse momentarily drives all the control grids of valves V21 ... V25 positive and travels along the network, momentarily driving the suppressor grids positive in turn ; when both control and suppressor grids of any valve are simultaneously positive, the valve conducts. The first and last pulses of set A thus render .valve V21 conducting, and after a suitable number of pulses have been stored in circuit CR, valve V29 becomes non-conducting to release relay 10D ; contact 10D1 closes to earth the screen of valve 29 and maintain it non-conducting until contact Fl operates ; contact 10D2, Fig. 7, closes to energize relay E which closes contact E1 thus energizing the bank of contacts. Should any other pulses arrive the appropriate valves V22 ... V25 conduct to render the corresponding valves V30 ... V33 non-conducting thus releasing the corresponding relays 8D, 6D, 4D, 2D to operate the contacts of the bank of Fig. 7 and connecting one terminal 1 ... 12 to positive. Relay F, Fig. 6, is released by the opening of contacts 10D3, but this is a slow release relay so that contacts F1, Fig. 6, and F2, Fig. 7 are opened after the operation of slave relays connected to terminals 1 ... 12, Fig. 7. The opening of contact F1 restores the screen grid voltage of valves V29 ... V33 so that they conduct to reset the receiver for the reception of the next signal. The first and last pulses in each set prevent operation of the receiver by pulses of small amplitude, valve V21 being adjusted to be less sensitive than valves V22 ... V25. The signal of Fig. 3 may be received by a circuit similar to that of Fig. 6, and additional pulses corresponding to the.first and last pulses of set A, Fig. 4, may be added.