Patent GB-202700-A (GB)
Title: Improvements relating to wireless and wired wireless telegraphy and telephony
IPC: H04B1/12
Filed: 1922-05-16
Abstract: 202,700. Bolitho, J. B. May 16, 1922. Atmospherics and undesired signals, eliminating or limiting. - The signal impulses and the disturbing impulses are impressed upon a series of valves in a balancing circuit, the grid potential being such that each valve tends to suppress the signal impulses and retains and amplifies the disturbing impulses of relatively large amplitude which are used to balance out the effect of the disturbances in the actual signal receiving circuit. In a modified method shown in Fig. 11, separate signal and balancing circuits are not used, the disturbing impulses being selectively amplified and then fed back with reverse reaction so as to neutralize partially the effect of the disturbing impulses. The method may be used in combination with the arrangements described in Specifications 156,330 and 197,077. In the system shown in Fig. 1, the aerial circuit is coupled to the signal circuit S, comprising amplifying valves 4, 5, 6 and a detecting valve 7, and to a balancing circuit B, comprising amplifying valves, 14, 17 - - 24. The normal grid potential of the valves 14, 17 - - 24, is such that weak signal impulses produce practically no change in the anode current and are suppressed, while the relatively strong disturbing impulses are retained and amplified. The anode circuit of the last valve 24 is connected to an impedance 10 in the grid circuit of valve 7 in such a way as to balance the effects of the disturbing impulses in the signal circuit S, the signal impulses only affecting the. telephones 11. The shape and amplitude of the balancing impulse may be varied by adjusting the impedance 10 or condenser 26. The last valve 24 may be a rectifying-valve, the anode circuits of valves 7, 24 being differentially connected to the telephone circuit. In the system shown in Fig. 4, the anode circuit of the last amplifying valve of the signal circuit S is connected by coils 27, 28 to a trigger valve 29 of the kind described in Specification 156,330, an impedance 10 in the grid circuit of which is connected to the last valve in the balancing circuit. The valves 14, 17 - - 21, are similar to those shown in Fig. 1, but the anode circuit of valve 21 is coulped in parallel to the grid circuits of two valves 22, 23, the anode circuits of which are coupled differentially to valve 24. The grids of valves 22, 23 are respectively negative and positive so that each valve is at a flat part of its characteristic. The combined valves have the characteristic shown in Fig. 6, weak signal impulses a being practically suppressed, disturbing impulses b, c being only partially suppressed. The anode circuit of valve 24 is coupled to a pair of valves 40, 41, arranged like the valves 22, 23 and coupled differentially to the final valve 43. Pairs of valves such as 22, 23 and 40, 41 enable the effects of disturbances of one amplitude to be modified without altering the effect of disturbances of another amplitude. The shape of the combined characteristic shown in Fig. 6 may be modified materially by choice of suitable valves and grid potentials. Pairs of valves, such as 22, 23, or a cascade of valves such as 17 - - 21, Fig. 1, may be used in the system shown in Fig. 2 of Specification 197,077. In a modified system, reaction coupling may be used in the balancing circuit, the anode circuit of valve 19, Fig. 1, being coupled to the valve 20 and also through three valves, having their grids at a negative potential, and a phase-shifter back to the grid circuit of valve 17. The anode circuit of valve 19 may alternatively be coupled to a valve in the signal circuit S in a direction to balance out the effectsof disturbing impulses, and the low-frequency current at the end of the balancing circuit may also be used to supplement this high-frequency balance. In a further system, Fig. 11, in which a separate balancing circuit is not used, aperiodic amplifying valves 61, 63, 64 are used, the anode circuit of valve 63 being coupled reversely through valves 52, 53, 54 to the grid of valve 61. The grid of valve 53 is made negative so that signals are suppressed in the reverse reaction connection, but the effects of disturbances are amplified and applied to the grid of valve 61 to neutralize partially the original disturbing impulses. In a modification the grid circuit of one of the amplifying valves in the balancing circuit may include an inductance 8, Fig. 13, and condenser 88 adjusted so as to bye-pass any undamped currents of signal frequency. In all the systems described. the grid circuits are usually tuned to the signal frequency, but in some cases they may be tuned to the frequency of an interfering transmitting station. In a further modification, a balancing circuit of the kind described in Specification 197,077 and a balancing circuit, Fig. 1, are both connected to the signal circuit, the balancing being effected before or after rectification or under both conditions. The first Provisional Specification refers to the use of a, differential relay or recorder with coils in the signal and balancing circuits respectively.