MICROWAVE RADAR TESTING 481 



pulses, derived from a quartz crystal oscillator, for checking the radar range 

 pulses. A trigger pulse derived from a multi-vibrator synchronized with the 

 quartz oscillator is also provided for actuating the radar timing circuits. 

 With certain radars the calibration procedure requires an oscilloscope as well, 

 l^xtreme stability of marker pulses, better than ±.02 microsecond, is ob- 

 tained. A stop watch is included in these sets for checking rate of change 

 in range. 



Less precision is required in range calibration of search radars. For this 

 purpose the TS-5/AP calibrator provides marker pulses of |, 1, 5 or 10 

 nautical or statute miles, derived from a coil and condenser oscillator with 

 closely controlled temperature coefficients. This calibrator is designed to 

 be triggered by the radar or some other external source. 



Computer Test Sets, Etc. 



A number of radars are equipped with computers which receive the data 

 on location of target and its direction and rate of change, together with 

 essential related information on such factors as wind velocity, ground speed, 

 altitude, etc., and deliver the solution of the ballistic problem in the form 

 of a voltage which releases bombs, points the guns or serves other purposes. 

 Means for checking the accuracy of these computing devices are generally 

 required. The type of test set needed depends upon the computer design, 

 which has taken different forms according to the nature of the problem and 

 the state of the art. 



Two types of computer test set are shown in Fig. 28. TS-158/AP, de- 

 signed for use with certain airborne bombing radars, furnishes to the com- 

 puter a signal representing a target approaching at known speed and checks 

 the accuracy of bomb release. TS-434/UP, designed for several airborne 

 and ground radars, is an accurate instrument for determining the voltage 

 ratios at various points in a computer and thus checking its performance. 



Conclusion 



More than 200 different designs of test sets were developed during the 

 war by Bell Laboratories to meet the exacting requirements of radar field 

 maintenance. These differed radicall}- from previous art. Outstanding 

 features were portability, precision and generality of application. The 

 large number of designs is due partly to the varied functions of radar and to 

 the varied conditions of use. Largely, however, it results from the fact 

 that the frequency band that can be handled in any one set is limited, 

 whereas many frequency ranges and subranges had to l)e covered in all. 



Altogether more than 75,000 radar test sets were manufactured by 

 Western Electric Company and these were used in all theatres of war by the 



