GB548095A - Modulation system for oscillation generators or amplifiers employing velocity modulation tubes - Google Patents

Abstract

548,095. Modulating systems ; frequency modulation. STANDARD TELEPHONES & CABLES, Ltd. June 6, 1941, No. 7172. Convention date Sept. 19, 1940. [Class 40 (v)] Modulation is effected in a generating or amplifying system employing a velocity-modulated tube and an associated resonant chamber, by coupling a variable impedance to the chamber and applying the modulating voltage to vary this impedance. This gives frequency modulation in the case of a generator, and amplitude modulation in the case of an amplifier. Fig. 1 shows a generator tube of known type comprising resonant chambers 2, 3, associated respectively with the control grids 8, 9 and the pick-up grids 11, 12, and with feed-back provided by the coupling conductor 19. Output is taken by the loop 15 and lead 16, and modulation is effected by a variable capacity 25, 26. The plate 25 is connected to a loop 20 sealed into the chamber 3, and the plate 26 is flexibly and conductively connected to the housing 23 and is vibrated by a moving-coil device 30 connected to the source MV of modulating voltage. The coupling of the loop 20 may be adjusted by varying its size or orientation. For amplitude modulation, the feed-back conductor 19 is omitted, the input oscillations are fed to the chamber 2 by a loop conductor, and the modulating-capacity 25, 26 is associated with a loop by which the output is taken to the load (Fig. 2 not shown). In a further modification, the capacity 25, 26 is replaced by a known thermionic reactance tube, the modulating-voltage being applied to one of its grids (Fig. 3 not shown). The impedance varied by the modulating voltage may itself be coupled to the resonant chamber.