GB507495A - Improvements in oscillatory circuit arrangements for modulated ultra-short waves - Google Patents

Abstract

507,495. Valve circuits for modulation and wireless reception. RADIOAKT.- GES. D. S. LOEWE. Dec. 15, 1937, No. 34742. Convention date, Dec. 21, 1936. [Class 40 (v)] A tunable coupling circuit for television signals comprises an inductance 1 arranged in series with the inter-electrode valve capacity 3 and the variable tuning condenser 2. The inductance is preferably shunted by a damping resistance equal to half the impedance of the inter-electrode capacity at the maximum modulation frequency. Fig. 3 shows a grid modulating arrangement in which the carrier source is coupled to the inductance 1 and the modulating potential is applied through a choke 9 of small reactance compared with the reactance of the tuning condenser 2. Fig. 4 shows a push-pull arrangement in which the damping resistances may equal the impedance of the inter-electrode capacity 3 at the highest modulating frequency and the tuning condenser 2 is isolated from earth. Fig. 5 shows a superheterodyne receiver. The coupling between the amplifier 8 and the frequency changer 18 comprises a band-pass filter utilizing two series resonant circuits so tightly coupled as to give the necessary band width and with the windings so arranged that the capacitative coupling assists the magnetic coupling so that the band width is maintained throughout the tuning range. A double humped characteristic may be produced and compensated for by the use of a single series resonant circuit in cascade. The condensers of the band filter and of the additional circuit may be gang tuned with, if desired, the condenser 19 of the local oscillator.