Patent GB-129313-A (GB)
Title: Improvements in Methods of and Apparatus for the Amplification of Small Currents by Electron Discharge Relays.
IPC: H04B1/22
Filed: 1917-10-10
Abstract: 129,313. British Thomson - Houston Co., (General Electric Co.). Oct. 10, 1917. Wireless signalling. - Relates to systems employing a series of electron-discharge relays for amplifying small currents, such as those received in wireless signalling, and to arrangements for minimizing interference due to strays. In the arrangement shown in Fig. 1, the received currents are repeatedly amplified by four relays 3 - - 6, supplied with current from a common battery 7. The filaments are heated by current from part of the battery passing through adjustable resistances 9 - - 12, and the filament-plate circuits are connected in series with highresistances 13 - - 16 across the whole battery. The plate circuit of each amplifier is connected to the grid circuit of the next, or, in the case of the last amplifier, to the telephone 21, by condensers 17 - - 20. In order to determine the normal potential between the filament and grid of the amplifiers 4, 5, 6, they may be connected by high resistances 23, 24, 25 or by batteries of the required strength and polarity. A local source of oscillations 22 may be coupled to the telephone circuit for heterodyne working. When the received current makes the grid of amplifier 3 more positive, say, the current through the amplifier will increase, thus reducing the potential applied to the grid of amplifier 4, the current through which is therefore reduced, thus increasing the potential applied to the grid of amplifier 5, and so on. Thus, a positive impulse applied to amplifier 3, transmits a magnified negative impulse to amplifier 4, and this in turn transmits a further magnified positive impulse to amplifier 5, and so on. In order to minimize interference from strays, two successive amplifiers have their characteristics so adjusted that a strong impulse of one polarity in the grid circuit due to strays produces in the plate circuit an impulse of only the same strength that a signal impulse would produce. If the stray is of such polarity as to produce a strong impulse in the plate circuit of the first amplifier, the current limiting effect of the next amplifier, for impulses of this direction, prevents it from producing an impulse stronger than would be produced by a signal impulse. Alternatively, the characteristic of a single valve may be so adjusted, by varying the grid potential or the filament current, that a change in the signalling- current in one direction will reduce the plate current to its minimum, while a change in the other direction will increase it to its maximum. The condensers 17 - - 20 should he of gradually increasing capacity so as to increase progressively the audio-frequency component of the amplified impulses with reference to the radio-frequency component. In a modified system specially suitable for eliminating strays, the antenna is rendered aperiodic by inserting therein a resistance equal to twice the square-root of the product of the capacity and inductance of the antenna, and the grid circuit of the first amplifier is connected across this resistance. The plate circuit of the third amplifier and the grid circuit of the fourth amplifier are tuned to the frequency of the signals to be received. Reference has been directed by the Comptroller to Specifications 127,013, 127,014, and 127,G51.