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BELL SYSTEM TECHNICAL JOURNAL 



became the key piece in the enormous development of radar equipment for 

 still higher frequencies during the war. However, at the beginning of 1941 

 there were still many unsolved problems in 3000 mc radar other than that 

 of the transmitter tube. On the other hand, the systems problems had 

 been quite satisfactorily solved in the 700-mc region. The decision was 

 therefore immediately made to extrapolate the British design down to 



Fig. 30— Mark 3 & 4— transmitter 



700 mc in order to obtain a higher powered and more satisfactory oscillator 

 for the existing systems. This was done at top speed and a picture of the 

 resulting tube is shown in Fig. 29. This was the first type of multi-cavity 

 magnetron to go into production in this country. Concurrent with the 

 design of the new magnetron the vacuum tube department of the Lab- 

 oratories developed an improved tetrode modulator tube which was many 

 times as efficient for radar pulse service as the triodes formerly used. This 

 tube was designated W.E. 701-A. 

 A new transmitter using the magnetron and two of the new modulator 



