GAS-DISCHARGE T RAN SM IT-RECEIVE SWITCH 



65 



discharge, it is customary to provide a "crystal gate" in the form of a 

 shutter which isolates the crystal from the TR box until after stable trans- 

 mitting conditions have been reached and until the TR tube discharge has 

 been established. The need for this additional turn-on protection is some- 

 what greater with the 724B than it is with the 721A tube. Another im- 

 portant function of the "crystal gate" is to prevent the crystal in an idle 

 radar from being damaged by energ\' from other radars operating nearby. 



o 500 1000 1500 2000 



PULSE REPETITION RATE IN PULSES PER SECOND 



P^ig. 18 — The dependence of spike on the repetition rate for the 724B tube in a cavity 

 adjusted for a 1.5 db low level loss and for a transmitter power level of 8 kw peak 



The energy in the spike is a function of the efifective size of the input and 

 output coupling windows of the TR box. A convenient method of present- 

 ing this effect is to plot the spike energy as a function of the low-level trans- 

 mission loss of the cavity which also depends upon the window sizes. Fig. 

 19 is such a plot for the 724B tube*. Comparing these experimental data 

 with the computed flat power curve of Fig. 15, one notes that the spike 

 energy varies at a more rapid rate than does the flat power. In both cases, 

 the leakage decreases as the low-level loss increases and crystal protection 

 can be purchased at the expense of receiver sensitivity. 



* Based on data taken at the M.I.T. Radiation Laboratories by F. L. McMillan. Jr. 

 and J. B. Wiesner. 



