GB236979A - Improvements relating to apparatus for use in electrical signalling - Google Patents

Abstract

236,979. Bolitho, J. B. March 17, 1924. Thermionic amplifiers.-Superregenerative systems, of the kind in which maintained oscillations are initiated by input currents and intermittently quenched, are applied to the amplification of low frequency currents or varying direct currents. The apparatus shown in Fig. 1 is similar to that described in Specification 156,330, except that instead of a high frequency input coil coupled to the coils 4. 7, 14, a low frequency transformer 2 is connected in the grid circuit of the valve 1; or the transformer 2 may be replaced by a resistance or other impedance coupling. The output is taken at 9 from the valve 1 whose grid circuit or anode circuit or each of these is tuned to a high frequency such as 10,000,000 y. The grid of the valve 1 is connected to the grid of the quenching valve 11 so that when the plate of the latter has a positive mean potential, oscillations at 10,000,000 y occur in the coil 14 in such phase as to oppose and quench the natural oscillations of the valve 1. The mean potential of the plate 11<a> is however varied at a medium frequency, such as 20,000 y, under the control of an oscillator 12, so that the quenching action is rendered intermittent. This action is enhanced by the variation at quenching frequency of the effective resistance of the grid circuit of the valve 11, which shunts that of the valve 1. Each of the intermittent groups of oscillations therefore builds up until quenched, its maximum amplitude depending on the mean potential of the grid 1<b> as determined by the low frequency input from the transformer 2. The potentiometer 3 may be adjusted so that anv desired part of the characteristic is utilized. In modifications, other known super-regenerative systems are similarly adapted for use as low frequency amplifiers. Thus as in Specification 182,135 the oscillator 12, Fig. 1, may be abolished and the plates 1<a> and 11<a> may be directly connected, the plate 11<a> being retroactively coupled to its grid through circuits tuned to the frequency of quenching. Alternatively the valve 11 may be abolished, and the quenching-frequency oscillations of the valve 12 may be applied across part of the grid coil 4. The Specification also describes and illustrates a system comprising a high-frequency super-regenerative amplifying and rectifying stage as described in Specification 156,330, and a low-frequency amplifying stage as shown in Fig. 1, a common quenching-valve being provided for the two amplifiers. Super-regenerative amplification may be applied to a duplex cable telegraph system by substituting an impedance forming part of the system for the input transformer, and substituting a telegraphic detector for the output transformer.