GB504455A - Method of selecting electric waves without the use of resonance - Google Patents

Abstract

504,455. Wireless receiving systems; thermionic valves. GABRILOVITCH, L. Aug. 25, 1937, No. 23278. Convention date, Sept. 5, 1936. [Classes 39 (i) and 40 (v)] Selectivity is obtained by varying one of the parameters of a circuit synchronously with the carrier frequency of the modulated wave it is desired to receive. Preferably a resistance, which may be a diode, is varied and produces attenuation of the wanted frequency only. The diode may have its resistance varied by electrostatic or electromagnetic control, the former by a grid and the latter by a perpendicular magnetic field, as by coils S on opposite sides of the electron path arranged within the valve envelope as shown in Fig. 1. Fig. 3 shows two parallel signal paths each including a pair of diodes D1, D2 and D11, D12 magnetically controlled by coils BS1, BS2 and BS<1>1, BS12 fed with carrier frequency from a filter F, the path to the coils BS<1>1, BS<1>2 including a transformer Q to give a 90‹ phase shift. The modulated wave is stated to be eliminated in the path D1, D2 but to be transmitted by the path D<1>1, D<1>2 together with all incoming modulated waves. The outputs of the detectors Dt, Dt<1>, the former having carrier frequency from the filter F applied to it, and including a transformer Ti to give a 90‹ phase shift, are opposed in the transformer TBF to balance out the interference, so that the wanted frequency band which passed by D<1>1, D<1>2 and rejected by D1, D2 is obtained. Resistances, not shown, may be provided to enable the interfering currents to be balanced exactly. In a modification, Fig. 4 (not shown), electrostatically controlled diodes are. used in one channel only, the output from which is balanced against the output of an ordinary receiver channel, the detector circuits being similarly arranged to the circuit shown in Fig. 3 except that the dephasing transformer Ti is omitted. A push-pull amplifier with the valves biassed to cut-off may follow the detector and the selectivity is stated to be increased by adjusting the bias of the amplifying tubes.