44 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1956 



Fig. 7 — Defective joint caused by imperfect soldering which gave the reflec- 

 tion shown on Fig. 6. 



reflections from imperfections in the line. The overloaded signal at the 

 left of the oscilloscope trace is produced by leakage directly through 

 the directional coupler. The overloaded signal on the other end of this 

 trace is produced by the reflection from the short circuit piston at the 

 far end of the waveguide. The signal between these two, which is about 

 45 db down from the input signal, is produced by an imperfect joint 

 in the waveguide. The signal polarization was oriented so that a maxi- 

 mum reflection was obtained in the case of the lower trace. In the 

 other trace, the polarization was changed by 90°. It is seen that this 

 particular joint produces a stronger reflection for one polarization than 

 for the other. By use of the precision phase shifter in the receiver the 

 exact location of this defect was found and the particular joint that was 

 at fault was sawed out. Fig. 7 shows this joint after the pipe had been 

 cut in half through the middle. The guide is quite smooth on the inside 

 in spite of the discoloration of some solder that is shown here, but on 

 the left-hand side of the illustration the open crack is seen where the 

 solder did not run in properly. This causes the reflected pulse that shows 

 on the trace. The fact that this crack is less than a semi-circumference 

 in length causes the echo to be stronger for one polarization than for the 

 other. 



