GAS-DISCriARGE TRANSM IT-RECEIVE SWITCH 



51 



The radar on the U.S. S. Boise in the battle off Savo Island on October 1112, 

 1942 employed a 702A vacuum tube. 



Three developments soon led to the need for much improved TR bo.xes. 

 One of these was the rapid progress which was being made in increasing the 

 peak output power from the magnetron. The second was improvements 

 in the silicon point contact rectifier, the so-called crystal detector, which 

 increased its reliability and convenience and at the same time reduced its 

 conversion loss and noise figure as compared with the vacuum tube con- 

 verter. The third was the development of still higher frequency systems to 



? <J&*»^ Jf ^IasVS"* 



70 2 A 



Fig. 2 — The 702A and 709A vacuum tubes 



achieve either greater antenna directivity or smaller size. Since satisfactory 

 vacuum tube converters were not available for these frequencies, the silicon 

 rectifier had to be used. Unfortunately the silicon rectifier, as then avail- 

 able, was subject to permanent damage if subjected to but very small 

 amounts of power as compared with the magnetron power levels. 



An active program of work was initiated at the Bell Telephone Labora- 

 tories to obtain designs of TR boxes offering adequate protection for contact 

 rectifiers at any power levels then available or contemplated. Three tubes 

 were developed, the 721A, 724B and 1B23 vacuum tubes shown in Fig. 

 3. These tubes are used at frequencies in the vicinity of 3000 megacycles, 

 10,000 megacycles, and 1000 megacycles respectively. They arc all of the 



