GB421340A - Improvements in or relating to methods of and arrangements for modulating high frequency transmitters - Google Patents

Abstract

421,340. Wireless transmitting systems. PUNGS, L., Technische Hochschule, Brunswick, Germany. June 19, 1933, Nos. 17428 and 17429. Convention dates, July 6, 1932 and Aug. 15, 1932. [Class 40 (v)] In a modulating system of the kind described in Specification 387,182 in which the mean carrier intensity is varied with variations in signal volume, and in which weak original signals are over-amplified prior to modulation, means are provided for imposing a lower limit on the carrier intensity, and a variable-mu valve is used for pre-modulation amplification of the signal. As shown in Fig. 2, signals from a microphone M are amplified at V1 and are applied by a transformer T1 to modulate the carrier wave, which is also supplied to the grid circuit of the amplifier RS from a source O. The mean carrier amplitude is determined by the bias applied to the grid of the valve RS from the potentiometer P. This is so adjusted that with no modulation present, a low limit is placed on the carrier amplitude, whilst as the signal increases in volume, the carrier grows in amplitude owing to the effect of the amplifier V2, the full-wave rectifier G and the directcurrent amplifier R. The circuits may be arranged so that a feeble signal steps up the carrier immediately to a higher level than that prevailing during pauses ; or a long pause may, by means of a time-delay switch, raise the carrier amplitude above its lower limit for the purpose of conveying an interval signal. The amplifier V1 includes a variable-mu valve arranged to amplify weak signals more than strong signals with a view to correcting the non-linear detection at the receiver. The valve has its screen-grid connected directly to its plate ; its grid is negatively biassed, and a resistance in its grid circuit causes the bias to increase with stronger signals. The output circuit may include resistance or transformer coupling.