GB215785A - Improvements in or relating to systems of receiving and indirectly amplifying radio frequency electrical oscillatory energy - Google Patents

Abstract

215,785. Jackson, W. J. Mellersh-, (Westinghouse Electric & Manufacturing Co.). May 9, 1924. Thermionic heterodyne receivers; undesired signals, eliminating. - Relates to the system of heterodyne reception described in Specification 137,271, in which incoming waves are combined with local oscillations to produce beats of lower radio-frequency; and consists in causing the beat currents to react on the input cir. cuits to obtain further amplification. The beat frequency is the resultant of the incoming frequency and an harmonic of the locally-produced frequency, as described in Specification 224,817. As shown in Fig. 1, the received oscillations are applied to a tuned circuit 4, 5 connected in the grid circuit of an amplifier 6, and the amplified oscillations are transferred by a coupling 11, 12 to the grid circuit of the local oscillator 16. The oscillator plate circuit is back-coupled by a coil 13 to a tuned grid circuit 14, 15, the frequency of which is so adjusted that one of its harmonics differs from the received frequency by a readily-amplifiable low radiofrequency. An oscillatory circuit 9, 10 tuned to this intermediate frequency is connected in the plate circuit of the valve 16 and coupled to a similarly-tuned circuit 7, 8 connected in the grid circuit of the valve 6. The intermediate-frequency currents are thus amplified by the valve 6 and are transferred through the couplings 18, 19 to the grid circuit of the detector 20, which has the telephones 21 in its plate circuit. The intermediate-frequency oscillations also react through the coupling 11, 12 on the oscillator 16, and thus increase the efficiency of the frequency conversion. The coupling between coils 8, 9 is adjustable both as regards degree and polarity, the polarity required being the opposite to that required for ordinary reaction. The coil 14 should preferably be connected between the coil 12 and the filament. Additional stages of amplification may be inserted between the coil 18 and the detector; and the process of frequency conversion may be repeated. In the modification shown in Fig. 3, a loop aerial 33 is connected through a high-pass filter 40, of one or more stages, to the grid of the first valve 41, and the beat-frequency currents are applied in the grid circuit of this vaLve by a coupling 35, 30, the secondary coil 30 being connected directly between grid and filament and tuned by a condenser 32 between the grid and the filter or aerial. The filter reduces interference by waves approximating in frequency to the intermediate or beat frequency.