GB561323A - Arrangements for the frequency modulation of a high-frequency oscillation - Google Patents

Abstract

561,323. Automatic control systems. PATELHOLD PATENTVERWERTUNGS- & ELEKTROHOLDING AKT.-GES. Oct. 6, 1942, No. 14016. Convention date, Oct. 28, 1941. [Class 38 (iv)] [Also in Group XL]. An arrangement for the frequency modulation of a high-frequency oscillation, consists of at least one oscillatory circuit, which comprises at least one condenser with mechanically non- displaceable coatings and a mechanically non-displaceable blocking layer, the capacity of which is dependent upon a bias voltage and to which a lowfrequency control voltage is supplied, so that the tuning varies in accordance with this lowfrequency voltage. Fig. 1 shows a valve V arranged as a back-coupled oscillator, the frequency of which is determined by an inductance L and adjustable condenser C shunted by a potential variable condenser K of the blocking layer type. The output, taken at 3, 4 is at a frequency which is variable in accordance with fluctuations in a voltage e which is applied at 1, 2 through a high-frequency choke L0 to vary the capacity of condenser K. The invention is also applicable to oscillators in which the tuned circuit has Bee point connection to the electrodes of the valve, Fig. 2 (not shown), while in a further embodiment, the fluctuating control potential is applied directly across the potential variable capacity, Fig. 3 (not shown). Fig. 5 shows the invention applied to a frequency modulation transmitter comprising a generator G, the output of which is modulated by a microphone M by means of an amplifier A1 applying a voltage to a potential variable condenser forming part of the frequency determining circuit Q of the generator. The output from G is passed through a frequenoy doubler F and amplifier A2 to the aerial. In order to keep the mean frequency constant, the output from F is heterodyned at M1 to give a difference frequency which is fed to a discriminator circuit D which produces a voltage which varies in magnitude and sign according to deviations of the difference frequency from its assigned value. This voltage is fed to the potential variable condenser at Q to maintain the frequency constant.