62 



BELL SYSTEM TECHNICAL JOURNAL 



behavior after the termination of the transmitting period; and (4) the low- 

 level loss, which describes the loss of the received signal including (a) the 

 loss in the TR box itself and (b) the loss in the transmitting branch. These 

 parameters are interrelated and conflicting. For example, the interde- 

 pendence of the leakage power and the low-level loss may be computed on 

 the basis of a somewhat idealized TR box as is done in Appendix A and the 

 results presented in the form of the curves of Fig. 15. It is customary to 

 design the cavities for matched input conditions (cr = 1), for obvious reasons, 

 and for a low-level loss of one to two db. The relationship between the 

 transmitting power dissipated in the TR tube and the low-level loss is shown 



0.5 1.0 1.5 2.0 2.5 



LOW LEVEL TRANSMISSION LOSS IN DB UlO LOG ,o — 



Fig. 15 — The variation in leakage power with the low level loss adjustment 



in Fig. 16. This curve may also be used to determine the effect of the low- 

 level loss adjustment of a TR cavity on the recovery time characteristic 

 since recovery time depends upon the gas discharge power rather than upon 

 the transmitter power per se. In spite of this interdependence, it will be 

 convenient to consider the different operating parameters separately in the 

 sections to follow. The receiver protection aspect will be considered first. 

 Receiver Protection. The receiver protection problem is complicated by 

 the fact that power reaches the receiver through the TR box by three differ- 

 ent mechanisms. As shown in Fig. 17, the observed leakage power pattern is 

 composed of three parts known respectively as the spike, the normal flat 

 leakage and the direct coupling. The spike is the result of the transient 



