GB557507A - Improvements relating to frequency modulation - Google Patents

Abstract

557,507. Automatic control systems. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Sept. 25, 1942, No. 13521. Convention date, Sept. 26, 1941. [Class 38 (iv)] [Also in Group XL] A frequency-modulating transmitter, of the kind in which the signal voltage is applied to the grids of one or more reactance valves 12, 13 connected across an oscillatory circuit 11, is stabilized as to mid-frequency by a feed-back connection from the oscillatory circuit to the reactance valve grids including (a) a network 17 providing a fixed plan shift of less than 90 degrees, and (b) a crystal or like resonant element 18 providing a further phase shift in response to frequency deviation in such direction as to correct the deviation by changing the reactance of the reactance valve or valves. When two halves are employed their plates PI, P2 are excited in phase opposition from the oscillatory circuit 11, and their grids G1, G2 are connected by a further network 16, which is arranged to produce a voltage phase on G2 lagging behind that on the plate P2 by the same angle as the voltage on grid G1 leads that on the plate P1. In this way, one valve functions as a capacitative and the other as an inductive reactance. The modulating voltage for effecting frequency modulation is applied in push-pull relation to the grids G1, G2. The resonant element 18 may be a two-terminal crystal operating at its seriesresonant frequency and connected as a series element, or it may be of the four-terminal type. The network 17 may comprise a series condenser and a shunt resistance ; and the network 16 may comprise a series condenser and a shunt inductance and resistance in parallel. Modified forms of the networks 16, 17 are described and their components may be adjustable. In another modification, the plates P1, P2 are excited in phase agreement.