GB529291A - Oscillation generators - Google Patents

Abstract

529,291. Thermionic valves; generating circuits. STANDARD TELEPHONES & CABLES, Ltd May 26, 1939, No. 15707. Convention date, June 28, 1938. [Classes 39 (i) and 40 (v)] A generator comprises an amplifier and a closed feed-back loop, the latter including one or more four terminal reactance networks, each proportioned to produce a phase shift of 90 degrees at the operating frequency which is stable with respect to variations of the network terminating impedances the networks together with the amplifying means producing a total phase shift of zero at the operating frequency. Fig. 6 shows an amplifying path in which network 12 produces a lead of 90 degrees and a feed-back path in which the network 13 produces a lag of 90 degrees. The phase shift of the network 12 varies slowly with frequency while the piezo-electric crystal CX in the network 13 produces a phase shift which varies rapidly with frequency. Alternatively the piezoelectric crystal may be in the shunt arm of the feed-back network in which case a grid leak is provided for the amplifier input Fig. 7 (not shown). A single valve amplifier may be used with the networks in the feedback path in cascade Fig. 8 (not shown) or a pair of valves in cascade may be used with the networks in the feed-back path Fig. 10 (not shown). In the latter arrangement the branches of the two networks are given the same magnitude so that the central impedance element formed by the adjacent shunt arms of the networks becomes infinite and may be omitted. Fig. 9 shows an arrangement in which the central impedance element LC2 is retained and an output in phase with the input is obtained and the two networks produce opposite phase shifts and the single valve 18 is arranged to produce zero phase shift by having a negative amplification constant. In this arrangement the output is connected to the space charge anode 20. U.S.A. Specifications 1,896,781 and 1,976,570 are referred to.