Patent GB-647700-A (GB)
Title: Improvements in or relating to the production of modulated high frequency oscillations
IPC: H03C5/02
Filed: 1943-12-28
Abstract: 647,700. Valve modulating circuits ; frequency modulation. SPERRY CORPORATION. Dec. 28, 1943, No. 21768. Convention date, Dec. 30, 1942. [Class 40 (v)] [Also in Group XL (a)] An electron discharge apparatus for producing either substantially pure frequency modulation, or substantially pure amplitude modulation, or a desired mixture of both comprises means for producing a main electron beam (cathode 65, Fig. 5) and means for velocity-modulating it to establish in a cavity resonator 61 a highfrequency electromagnetic field, and means for producing one or more auxiliary beams passing through said field (cathodes 66, 67), or through a field in a resonator coupled to said field (Figs. 12, 13, not shown), without substantial energy contribution thereto ; means such as grids 52, 55, 56 are provided to modulate the main and auxiliary beams as required. To obtain pure amplitude modulation, frequency modulation due to the effect of the varying space charge in the main beam on the frequency of the resonator is eliminated by adjusting the auxiliary beams so the total space charge is always constant. To obtain pure frequency modulation, the main beam is unmodulated and the auxiliary beams are modulated to vary the frequency of the resonator. The device shown in Fig. 5 is of the kind described in Specification 630,005, [Group XL (a)], with a buncher resonator 60 and a catcher resonator 61, separate drift tubes 47, 48, 49 being provided for the main beam and the two auxiliary beams. The batteries 102, 103 adjust the velocities of the two auxiliary beams so that the bunches enter the resonator 61 in phase opposition, thus contributing no energy to it. The intensity of the auxiliary beams is adjusted by bias potentiometers 105, 106, to be half that of the main beam. Modulation 107 is applied through centre-tapped secondary of transformer 108 to potentiometers 109, 110 modulating the auxiliary and main beams respectively. For amplitude modulation, the tappings 111, 112 are on opposite sides of the centre point, the amplitude of the auxiliary modulation being half that of the main beam. For frequencymodulation tapping 111 is at the centre point and tapping 112 is at maximum. Desired mixtures of amplitude and frequency modulation may be obtained by adjusting the tappings intermediate these extreme conditions. The two resonator oscillator may be replaced by a single resonator reflex type, Fig. 6 (not shown), in which case only one auxiliary beam is needed, if it is collected after its first transit, so that it does not energize the resonator, Fig. 9 (not shown). Separate auxiliary beams, from cathodes 78, 79, Fig. 7, may be applied to the buncher and catcher resonators 90, 91, a partition 97 serving to cut off the beams so that they do not energize the resonators. The device is of the kind shown in Specification 602,164, [Group XL (a)]. The auxiliary beam may be transverse to the electric field in the resonator in either a reflex or a two resonator type, Figs. 8, 10 (not shown). The auxiliary beams may pass through separate resonators coupled by coaxial lines to the main resonators ; Figs. 12 and 13 (not shown), show such arrangements otherwise generally similar to Figs. 9 and 7 respectively. In Fig. 11, the separate resonator 181 is in the feedback path between buncher resonator 179 and catcher resonator 178. Specifications 530,869, 531,251 and 535,767 also are referred to.