GB514685A - Improvements in or relating to negative resistance circuit arrangements - Google Patents

Abstract

514,685. Valve circuits; artificial lines. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., RUST, N. M., and BRAILSFORD, J. D. April 14, 1938, No. 11572. [Classes 40 (iii) and 40 (v)] A negative-resistance circuit arrangement comprises a natural or artificial line with a negative resistance consisting of a pair of crosscoupled pentodes, acting as its termination. The arrangement is particularly applicable to the production of oscillations, the stabilising of oscillations, and the provision of controlled reaction. Fig. 2 shows the negative resistance circuit comprising two pentode valves 6, 3 reciprocally coupled by condensers 4, 8. The suppressor grids 19, 18 may be connected to adjustable tappings on cathode resistances 17, 16, respectively to ensure that the negative resistance does not vary greatly with signal amplitude. Negative resistance Zn is produced between the control grid of valve 6 and an adjustable tapping 10 on a resistance 11 connected between earth and a negative source. Control of the negative resistance is effected by varying the tapping between the control grid of valve 3 and resistance 9. Fig. 4 shows an oscillation generator comprising a quarterwave concentric line 1, with the conductors connected together and to earth at one end and to a negative resistance Zn at the other. With the line conductors open at one end, the line will act as a half-wave line. Tuning of the oscillator may be affected by connecting a variable reactance across the end of the line remote from the negative resistance. An actual line may be made of the required length by the addition of a phase-changing network. Oscillation at the fundamental or a desired harmonic frequency may be determined by the addition of a tuned circuit. Fig. 12 shows an artificial line terminated by a negative resistance Zn employed to stabilise a reaction oscillator 28. In such a case to ensure oscillation at a desired harmonic, the part of resistance 9, Fig. 2, between tappings 12, 10 may be replaced by a tuned circuit. Fig. 14 shows the application to the provision of controlled reaction to improve selectivity in a radio receiver. A tap on the aerial inductance 32 is connected through one concentric cable 1c, a tunable circuit 34, 35 and a second concentric cable 2c terminated by a negative resistance Zn, to a wide-band amplifier 37. Control of the reaction can be affected by varying resistance r, Fig. 2, or the grid bias on valves 6, 3. In other embodiments, the single-tuning circuit 35, Fig. 14, is replaced by a circuit with two tuning condensers. The invention may also be applied to lines which are not a quarter-wave or a multiple of a quarter-wave length to obtain variable reactive effects at the remote end of the line.