GAS-DISCHARGE TRANSM IT-RECEIVE SWITCH 



57 



magnetron "cold" impedance docs not differ greatly from the surge imped- 

 ance of the transmission line used, it may not be possible to avoid loss of 

 reflected signal into the transmitter line. Also in some cases, an unreason- 

 able amount of adjustment must be provided in the position of the TR 

 cavity with respect to the transmitter to make up for large variations which 

 may be encountered in transmitter "cold" impedance. Both difficulties 



Fig. 8 — Series branching circuit using the 1H2S vacuum tube 



may be avoided by the use of a second gas discharge tube located between 

 the transmitter and the TR and at an odd number of quarter wavelengths 

 from the TR junction. This second tube is referred to as the anti-T-R tube 

 (usually abbreviated to ATR), or sometimes as the RT tube. The use of 

 an ATR tube was not found to be necessary in most of the systems which 

 employed the 721A tube. 



With the advent of still higher frequency systems, for which the 724B 

 tube was designed, the "cold" impedance difficulties just mentioned made 



