MICROWAVE REPEATER RESEARCH 235 



energy from entering the 65-megacycle transformer compartment. The 

 converter developed for the New York-Boston circuit, complete with 

 sideband filter, spacer, mounting brackets and d-c. leads, is shown in Fig. 

 V-13.* 



R. F. Amplifier** 



Prior to the war, a considerable arfiount of research had been applied in 

 the Bell Telephone Laboratories to electron tubes operating on the velocity 

 modulation principle, with the expectation that such tubes would find ap- 

 plications in radio-relay systems. Although this work was interrupted 

 by the war, enough information had been obtained to make it apparent, 

 upon resumption of the radio relay work, that such tubes were the only 

 ones then known which showed promise of meeting the stated requirements. 



Velocity modulation tubes have been described by several authors,^^' ^^' ^^ 

 and the theory of their operation has been discussed adequately in several 

 places.^2, 33. 34, 35 However, a review in 1939 of the structures then known 

 had led to the decision that a new type of construction would be necessary 

 to obtain a satisfactory amplifier tube for radio relay purposes. To keep the 

 tube voltages within reasonable limits it is desirable to make the input and 

 output gaps as small as possible. Resonant circuits external to the evacu- 

 ated envelope are desirable to enable coverage of as large a frequency range 

 as possible with a single tube, and to facihtate addition of broad-banding 

 circuits. Grids on the input and output gaps are undesirable because of 

 the large interception of current and the dififtculty and expense of construc- 

 tion. 



With the above considerations in mind, decision was then made to explore 

 the possibiHties of focussed beams, and of gaps comprised of copper discs 

 sealed through a cylindrical glass vacuum envelope. The latter technique 

 had been developed at the Bell Telephone Laboratories in connection with 



* Developed by H. C. Foreman and W. W. Halbrook. 



** This section prepared by A. G. Fox and A. E. Bowen. Messrs. Fox and Bowen, in 

 collaboration with A. L. Samuel, A. E. Anderson, and J. W. Clark of these Laboratories, 

 did the major part of the research which resulted in this amplifier, 



29 Varian, R. H. and Varian, S. F., "A High Frequency Oscillator and Amplifier", 

 Jour. Applied Physics, vol. 10, No. 5, pp. 321-327, May 1939. 



'» Hahn, W. C. and Metcalf, G. F., "Velocity Modulated Tubes", Proc. I. R. E., vol. 

 27, No. 2, pp. 106-116, Feb. 1939. 



31 Harrison, A. E., "Klystron Tubes", McGraw-Hill Book Co., New York, 1947. 

 (Book) 



32 Hansen, W. W. and Richtmyer, R. D., "On Resonators Suitable for Klystron Os- 

 cUlators", Jour. Applied Physics, vol. 10, No. 3, pp. 189-199, March 1939. 



33 Hahn, W. C, "Small Signal Theory of Velocity Modulated Electron Beams", G. E. 

 Review, vol. 42, No. 6, pp. 258-270, June 1939. 



3^ Hahn, W. C, "Wave Energy and Transconductance of Velocity-Modulated Elec- 

 tron Beams", G. E. Review, vol. 42, No. 11, pp. 497-502, Nov. 1939. 



36 Ramo, S., "The Electronic-Wave Theory of Velocity Modulation Tubes", Proc. 

 I. R. £., vol. 27, No. 12, pp. 757-763, Dec. 1939. 



