1286 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1956 



Frequency Range 5,925-6,425 mc 



Power Output 5 watts 



Gain at 5 watts output 31-35 db 



Noise Figure < 30 db 



The tube is designed for use with w-aveguide input and output circuits. 

 The input voltage standing wave ratio (VSWR) is less than 1.1 and the 

 output VSWR is less than 1.4 over the 500-mc band when the tube is 

 delivering 5 watts of output. Fig. 1 shows a photograph of an MI789 

 and of an experimental permanent-magnet focusing circuit. 



In developing this tube we have endeavored to produce an amplifier 

 which could be considered "practical" for use in a transcontinental radio 

 relay system. Because such an application requires a high degree of 

 reliability and refinement in performance, the tube was rather con- 

 servatively designed. This made it possible to obtain the desired gain 

 and power output without difficulty. On the other hand, the contem- 



Fig. 1 — The M1789 traveling-wave tube and an experimental permanent mag- 

 netic circuit used to focus it. The circuit contains two specially shaped bar mag- 

 nets l)et\veen which the tube is mounted. The magnetic flux density obtained is 

 600 gauss, and the overall circuit weight is about 25 pounds. 



