20 BELL SYSTEM TECHNICAL JOURNAL 



version loss. Crystals with large conversion losses are less susceptible 

 to impedance changes from reactions in the radio frequency circuit than are 

 low conversion loss units. 



The level of power to which the rectifiers can be subjected depends upon 

 the way in which the power is applied. The application of an excessive 

 amount of power or energy results in the electrical destruction of the unit 

 by ru{)ture of the rectifying material. Experimental evidence indicates 

 that the electrical failure may be in one of three categories. The total 

 energ}^ of an applied pulse is responsible for the impairment when the 

 pulse length is shorter than 10~' seconds, the approximate thermal time 

 constant of the crystal rectifier as given by both measurement and calcula- 

 tion. For pulse lengths of the order of 10~^ seconds the peak power in the 

 pulse is the determining factor, and for continuous wave operation the 

 limitation is in the average power. 



In performance tests in manufacture all units for which burnout tolerances 

 are specified are subjected to proof-tests at levels generally comparable 

 with those which the unit may occasionally be expected to withstand in 

 actual use, but greater than those to be employed as a design maximum. 

 The power or energy is applied to the unit in one of two types of proof-test 

 equipment. The multiple, long time constant (of the order of 10" seconds) 

 pulse test is applied to simulate the plateau part of a radar pulse reaching 

 the crystal through the gas discharge transmit-receive switch.^ This test 

 uses an artificial line of appropriate impedance triggered at a selected 

 repetition rate for a determined length of time. The power available to 

 the unit is computed from the usual formula, 



4Z' 



where P is the power in watts, V is the potential in volts to which the pulse 

 generator is charged, and Z is the impedance in ohms of the pulse generator. 

 In general, where this test is employed, a line is used which matches the 

 impedance of the unit under test at the specified voltage. 



The second type of test is the single discharge of a coaxial line through 

 the unit to simulate a radar pulse spike reaching the crystal before the 

 transmit-receive switch fires. The pulse length is of the order of 10~^ 

 second. The energy in the test si)ike mav be computed from the relation 



where E is the energy in ergs, C the capacity of the coaxial line in farads, 

 and r the potential in volts to whicli the line is charged. 



"A. L. Samuel, J. W. Clark, and W. W. Mumford, "The Gas Discharge Transmit- 

 Receive Switch," Bell Sys. Tech. Jour., v. 25 No. 1, pp. 48-101. Jan. 1946. 



