Patent GB-209037-A (GB)
Title: Improvements in the reception of radio signals
IPC: H04B7/08
Filed: 1923-10-12
Abstract: 209,037. Marconi's Wireless Telegraph Co., Ltd., (Assignees of Ranger, R. H.). Dec. 28, 1922, [Convention date]. Atmospherics and undesired signals, eliminating or limiting.-The receiving circuits are fed from two or more receiving aerials having different directional or other characteristics. The energy from one only of the aerials passes through to the detecting device, the energy from the other aerial being effective only in transforming an intermediate valve from a normally inoperative to an operative condition. Signals received upon the control aerial A are passed through a detector 4 and amplifier 6 to a twoelectrode rectifier 8, where they are manifested as an increased current flowing through a resistance 9, the negative end of which is connected through an artificial-line network 10, 12 to the grid of a triode 13. The grid of the tube 13 is so biased that normally it passes a considerable current. Simultaneously signals from the operative aerial B are applied through the tubes 4<1>, 6<1> to the grid of a triode 16. The triodes 13, 16 are fed from a common battery 15 through a highresistance choke 14. So long as the tube 13 passes its normal current, the voltage drop across the coil 14 is sufficient to reduced the applied plate voltage to 180 volts, for which value the applied grid variations from the aerial B are ineffective, as indicated in Fig. 4. When however the grid potential of the triode 13 is made sufficiently negative from the resistance 9 the plate current through that valve is reduced to such an extent that the voltage applied to the plate of the triode 16 rises to 200 volts. The signals from the aerial B are then manifested in the output of the triode 13 and are applied across a transformer 17 to the input of the valve 18, and so to the phones 19 or to any suitable type of recorder. A frequency trap 22, 23 is inserted in the plate circuit of the triode 16. The impedance of the line 12, 10 is made to equal the impedance of the tube 8 so as to reduce reflection effects. In order to eliminate static the negative end of the resistance 9 instead of being applied directly to the grid of the triode' 13 is passed by means of a switch 11 through one or more of the networks 10, 12. This introduces a time-lag, as shown in Fig. 7, whereby the static impulses S are dephased, so that they have no effect on the resultant indication, which, as indicated, reflects only signals common to both of the upper curves. Alternatively the grid of the triode 16 may be normally biased by an excessive negative or positive potential, and the output from the rectifier 8 may be utilized, either directly or through an intermediate tube, to remove the prohibitive bias and set the triode 16 back to a point on its characteristic curve at which impulses from the aerial B will be passed through to the final recorder. If the aerial B is directional and the aerial A non-directional, the latter will merely serve: to render B sensitive, but as this is directional only signals coming from a particular direction will be recorded to the exclusion of all others even of the same frequency.