AflCROWAVE RADAR TESTING 477 



enced. Double moding, i.e., oscillating at different frequencies on different 

 pulses, is shown by a double trace. Frequency jumping during a pulse is 

 shown by a break in the envelope. Misfiring gives a base line under the 

 envelope. Other abnormalities in the RF envelope may result from in- 

 correct video wave shape. Observation of the RF envelope requires a 

 rectifier, usually a crj'stal, together with a suitable video amplifier. Since 

 limitation of the scope to video functions permits general application to 

 radars of all frequencies, the rectifier is generally provided externally. 



The oscilloscopes available before the war did not meet the requirements 

 of radar. Fast sweeps were necessary to permit viewing of pulses ranging 

 from several microseconds to a fraction of a microsecond. Amplifiers were 

 required for such pulses with low phase and amplitude distortion over a 

 broad frequency band. Existing methods of synchronizing and phasing 

 sweeps were also inadequate. The progress of the oscilloscope art during 

 the war is illustrated in the successive designs of field test oscilloscopes 

 shown in Fig. 25. 



The BC910A oscilloscope, gotten out as a "stop gap" not long after the 

 attack on Pearl Harbor, incorporates fast sweeps and broad-band amplifica- 

 tion. Following close upon this was the BC1087A (Navy code CW60AAY) 

 which replaced sine wave synchronization by a start-stop sweep triggered by 

 the incoming pulses. This feature made it possible to superpose the erratic 

 pulses produced by spark wheel and similar pulsers and at the same time 

 avoided external synchronizing connections. A valuable feature conjoined 

 with the start-stop sweep was a delay network in the main transmission path 

 which gave the sweep time to start before the pulse reached the cathode-ray 

 tube. This oscilloscope in original and modified form has seen wide ser\dce 

 in all theaters. However, its weight of more than 60 pounds was a handicap 

 for many uses. 



Further advances in oscilloscope circuitry and in weight limitation re- 

 sulted in TS-34/AP, weighing only 25 pounds. This combined the short 

 pulse features of the previous design with those of the conventional oscillo- 

 scope for viewing slower waves. A schematic diagram is shown in Fig. 26. 

 A redesign, coded as TS-34A/AP, incorporated variable start-stop sweeps 

 and improved mechanical design. These two oscilloscopes, TS-34 and TS- 

 34A, were produced to a total of some 12,000 and universally used by all 

 branches of the service for both radar and radio testing. Toward the end 

 of the war the trend toward shorter pulses, coupled with the need for precise 

 measurement of wave amplitude and duration, led to a new design, TS- 

 239/UP, which embodied wide advances over TS-34A4n performance and 

 versatility but with an increase in weight. 



In association with different oscilloscopes, other video devices have been 



