GB502013A - Improvements in electric wave signal transmitting apparatus - Google Patents

Abstract

502,013. Wireless transmitting systems. STEWART, J. C. June 7, 1937, Nos. 15767, 15758, and 15759. Convention dates, June 6, 1936, July 24, 1936, and Nov. 5, 1936. [Class 40 (v)] In a carrier wave signalling system the supply voltages are so controlled by the signal that up to an arbitrary signal value the carrier component of output voltage is reduced from the no signal valve and above this valve it is increased. Modulation of carrier from 0 is effected in the stage MA by the series modulator value VM and the modulated carrier is amplified by the stage PA. Modulating potentials are supplied at M and a constant but reduced negative bias at GBM while means RM which may be a rectifier fed with signal energy at X provides a negative bias proportional to the envelope value of the signal voltage. Anode supply for the modulated stage is obtained from a constant voltage source EC in series with a variable voltage source EV which comprises a bank of rectifiers fed with a variable alternating input voltage from the regulating means ER. In the regulator ER each leg of the polyphase mains has a transmission network of iron-cored inductors L1, L2 with secondary windings LS1, LS2 associated therewith. The windings LS1, LS2 are connected to rectifiers V1, V2 in series with which are valves V3, V4 which are controlled by signal energy supplied at Y, rectified at the biassed smoothed rectifier RVR and supplied to the grids through a D.C. amplifier DCA and driver stage DS. A voltage derived from a potentiometer R and proportional to the excess of plate supply voltage over the "nosignal" value of plate supply voltage is applied in series with and in opposition to the output of RVR to DCA. Similar arrangements EC2, EV2, EC3, EV3 and ER2 are provided for the anode and grid bias supplies to the stage PA As the signal input rises from zero the carrier output falls due to the increased negative bias provided by means RM and by reason of biassing the rectifier RVR and its counterpart in the regulator ER2 are rendered inoperative until a predetermined level of signal voltage is reached. When this arbitrary level is exceeded the grids of V3 and V4 are made more positive and the resultant increased unidirectional current tends to saturate the inductors L1, L2 so that the input voltage to EV is increased with consequent expansion of the high tension and grid bias voltages and the carrier component of output current. In a modified method for controlling the voltage fed to the variable sources, Fig. 4 (not shown), the secondaries of two transformers, whose primaries are connected to the mains, are connected in series in the leads from the regulator ER to the source EV. These secondaries deliver voltages in quadrature which together subtract vectorially from the voltage output of ER so that in the " no-signal " state the voltage fed to EV.may be adjusted to zero or any desired value. Instead of the arrangement of rectifiers and valves shown in Fig. 1 for producing the saturation of the inductors, grid controlled gas discharge tubes may be connected across each secondary of the inductors and phase shifting grid control devices operated by the rectified signals may control the discharge tubes. Various modified arrangements for deriving the controlling potentials from the signals are described. In Fig. 5 (not shown), two rectifiers with output circuits of different time constants are fed with the signals, one rectifier being connected in series with the bias means of the other. In an alternative arrangement a constant bias source is provided to replace the potentiometer R across the high tension supply for supplying a voltage to the output of rectifier RVR. Other alternative effects for producing the controlling potentials are the variations occasioned by grid current flowing in an amplifier and variations of plate current in such an amplifier. Specifications 283,264, [Class 40 (v)], 427,508, 466,831, and 471,423 are referred to.