MEASUREMENT OF DELA Y DISTORTION 



263 



measurements were made with an early model of the measuring equipment. 

 Smoother curves are obtained with the apparatus shown in Fig. 11. 



In Fig. 15 the top row shows the distortion of a square top pulse by the 

 ampUfier of Fig. 12 for 1, 10, and 30 trips through the amplifier without the 

 equalizer. The lower row shows a similar set of pictures of the pulse when 

 the distortion was reduced by a phase equalizer as shown in Fig. 14. The 

 improvement due to the eUmination of phase distortion is clearly illustrated. 

 These pictures were obtained by the circulated pulse^ technique which 



1 TIME 



10 TIMES 



30 TIMES 



AMPLIFIER ALONE 





AMPLIFIER WITH EQUALIZER 



Fig. 15 — Oscillograms showing the improvement in the square wave response of the 

 amplifier of Fig. 12 obtained by delay equalization. The numbers above the traces indi- 

 cate the number of times the test pulse has passed through the amplifier and equalizer. 



permits the observation of a pulse after it has passed a number of times 

 through the same amplifier. 



Conclusions 



Two measuring circuits have been described which are suitable for 

 measuring the small variations in relative transmission time which are 

 present in wide band microwave repeaters. K sufficient care is exercised 

 in setting up these circuits an accuracy of better than dblO""^ seconds can 

 be realized in relative delay measurements. The circuit of Fig. 5 measures 

 the relative phase shift as a function of frequency. It has the advantage 

 of requiring less signal power and fewer important parameters for absolute 



^Testing Repeaters with Recirculated Pulses, A. C. Beck and D. H. Ring. 

 I.R.E. Nov. 1947, 1,226-1,230. 



Proc. 



