Patent GB-762758-A (GB)
Title: Improvements in electron velocity modulation apparatus
Inventor: BECK ARNOLD HUGH WILLIAM
IPC: H01J25/12
Filed: 1953-06-10
Abstract: 762,758. Velocity-modulated tubes. STANDARD TELEPHONES & CABLES, Ltd. June 10, 1953, No. 15935/53. Class 39(1). [Also in Group XL(c)] In a frequency changing klystron of the kind in which a carrier frequency is applied to the buncher resonator, a modulating signal to the drift tube to phase modulate the velocity modulation and in which the catcher resonator extracts energy at a sideband frequency the mean potential of the drift tube is appreciably lower than that of the buncher and catcher resonators and the beam is focused by a magnetic field. The operation preferably utilises " velocity jump amplification. The signal applied to the drift tube may be an intermediate frequency wave frequency modulated by 600 or more individual speech channels of a multichannel telephone system to give a signal of five megacycles width about a mean frequency of 60 Mc/s. With a carrier of 4000 Mc/s. in the buncher, the output from the catcher is a carrier of 4060 Mc/s. or 3940 Mc/s. frequency modulated by the group of channels while the bandwidth is unaltered. It is shown mathematically that the intermediate frequency power required is proportional to V<3>/N<2> where V is the D.C. voltage of the drift tube and N is the length of the drift tube in odd integral quarter space charge wavelengths. Therefore to minimize IF power the drift tube voltage is small and its length is made several quarter space charge wavelengths. It is assumed that the beam is fully space charge limited. In one form, Fig. 2, the input resonator 23 and output resonators 24, 25, separated by drift tubes 26, 28, are formed by discs 22 sealed through glass collars 21 and two blocks with semicircular inner faces bolted together (one block of each set is shown at 49, 55) which contact the discs via beryllium copper spring members 50. A piston tuned guide section leads out of one side of each resonator and a guide section containing coupling means leads out of the other side. Apertures (not shown) in flange 56 couple the two output resonators together. The gun comprises indirectly heated cathode 30, focussing electrode 31 and anode 32 comprising ferromagnetic pole piece member 33 and a depending ferromagnetic sleeve surrounding 30, 31. Member 33 is of an alloy suitable for sealing to glass. The collector 20 comprises copper member 37 carrying cooling fins 38 and soft iron polepiece member 39 sealed via ferromagnetic sleeve 40 to the glass envelope. The magnetic circuit is completed by two pairs of magnets 57 and yoke members 58, 59, 60. In a modification disc 33 may be omitted and the gun sealed into the tube in a manner similar to the collector 20. Dimensions and potentials of an example are given, the drift tube being 5 half plasma wavelengths in length and having a D.C. voltage of 480 volts, and the resonator voltage being 1000 volts. The transit angle between the two catcher gaps is 2#. Slight modifications of the tube and magnet construction are described with reference to Figs. 1 and 3 (not shown.) Specification 694,159 [Group XL(b)] is referred to.