WAVEGUIDE TESTING WITH MILLIMICROSECOND PULSES 



43 



TO RECEIVER 

 \ 



TE° IN 3"DIAM copper GUIDE (ISO FT LONG) 



Fig. 6 — Waveguide arrangement and oscilloscope trace photos showing pres- 

 ence and location of defective joint. The dominant mode (TEn) was used with its 

 polarization changed 90 degrees for the two trace photos. 



from the pulse generator through branch 4 to the short circuit and then 

 to the receiver as shown by the long dashed line. This pulse has traveled 

 8 feet farther in the waveguide than the first pulse. This would be equiva- 

 lent to seeing separate radar echoes from two targets about 4 feet apart. 

 Resolution tests made in this way \vith the pulses from the regenerative 

 pulse generator, and from the double-gated pulse generator, are shown 

 on Fig. 5. With our video amplifier and viewing equipment, there is 

 no appreciable difference in the resolution obtained using either type 

 of pulse generator. 



The measuring range is determined by the power output of the gated 

 amplifier at saturation and by the noise figure of the first tube in the 

 receiver. In this equipment the saturation level is about 1 watt, and the 

 noise figure of the first receiver tube is rather poor. As a result, received 

 pulses about 70 db below the outgoing pulse can be observed, which is 

 I enough range for many measurement purposes. 



5. DOMINANT MODE WAVEGUIDE TESTS 



Fig. 6 shows the use of this equipment to test 3'^ round waveguides 

 such as those installed between radio repeater equipment and an an- 

 tenna. This particular 150-foot line had very good soldered joints and was 

 thought to be electrically very smooth. The signal is sent in through a 

 transducer to produce the dominant TEn mode. The receiver is con- 

 nected through a directional coupler on the sending end to look for any 



