GB468756A - Improvements in or relating to modulated carrier-wave transmitters - Google Patents

Abstract

468,756. Wireless transmitting systems. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., and GREEN, E. Jan. 8, 1936, No. 709. [Class 40 (v)] In a series modulating arrangement in which the carrier frequency source R, consisting of a valve or bank of valves, is connected in series with and on the negative side of a modulating valve stage M, the grid voltage applied to the input of the modulating valve includes a fixed bias component and, in opposition to it, a component across a resistance R3 obtained by rectifying, at S, the modulated carrier energy. The arrangement is such that in the absence of modulating signals at G the fixed bias V2 applied across resistance R2 is effective to "back off " the valve M, but on the occurrence of modulating signals the total bias is reduced by the increase of the voltage across R3 and the feed current through the valve stage M is increased. The bias voltage V2 may be obtained from the H.T. supply by connecting a high resistance between the negative terminal of the supply and the junction point of resistances Rl and R2. In a modification, Fig. 3, the modulating stage consists of a bank of two valves M1, M2 in parallel. Their grids are connected to tappings on resistances R1<1>, R1<11> which are connected through condensers to the modulating source G and to tappings on resistance R2, which is coneected to the negative H.T. lead (earth) through a high resistance R5 giving the fixed bias potential. The rectified modulated carrier is applied ; after smoothing across the resistance R3 and the free terminal of the modulating source G is connected to the tapping on resistance R2 to which resistance R1<11> is connected. The Provisional Specification discloses an arrangement in which the carrier stage is on the positive side of the modulating stage and also an arrangement for obtaining fixed bias in the grid circuit of the modulating stage of a series modulation arrangement. In the latter arrangement, a high resistance in the grid circuit is connected in series with a further high resistance across the carrier stage and is shunted by a condenser sufficiently large to byepass all modulating frequencies. Specification 427,026 is referred to.