GB670259A - Improvements to velocity modulation tubes - Google Patents

Abstract

670,259. Velocity-modulated tubes. STANDARD TELEPHONES & CABLES, Ltd. Dec. 24, 1948 [Dec. 31, 1947]. No. 33226/47. Class 39 (i). [Also in Group XL(c)] Background noise in a velocity modulation amplifier is reduced by velocity modulating the electron beam at a pair of spaced apart regions successively traversed by the electron beam, the said regions being each defined by a gap in a transmission line or cavity resonator, the two gaps being so connected by a feed-back transmission line that the phase delay from one gap to the other along the line is one or a multiple of a complete period of oscillation of the electromagnetic waves modulating the said beam, said waves being fed into the said line at the electrical mid-point between the gaps and the said gaps being separated by a distance such that the transit time of the electrons of the beam flowing from one gap to the other is one or an odd multiple of half a period of the said oscillation. In the embodiment shown, the main amplifier tube comprises a cathode 16 and concentrating electrode 17 generating an electron beam 18 which flows through a double resonator 19, comprising two resonant cavities 20 and 21, and a catcher resonator 22 to a collector electrode 23. An auxiliary low gain amplifier tube comprises a cathode 24, concentrating electrode 25, modulation resonator 26, catcher resonator 27 and collector electrode 28. The catcher resonator 27 forms a coupling resonator and is connected by two coaxial lines 29 and 30 to the respective resonant cavities of the input resonator 19. The length of the coaxial lines is such that the above-mentioned conditions are satisfied. The low level signal to be amplified is applied to the modulation resonator 26 of the auxiliary tube and the amplified high frequency energy is picked up inside the catcher resonator 22 of the main amplifier tube.