240 



BELL SYSTEM TECHNICAL JOURNAL 



A method'^ of measuring the phase and group delay characteristics of 

 the repeater was worked out. This is a rather difficult measurement to 

 make because the tolerable phase and delay distortion are very small due 

 to the wide band of the system. Relative group delay through the band 

 was measured with an accuracy of about ±0.001 microsecond. This cor- 

 responds to an accuracy in relative phase shift of about zb0.35°. The 

 measured distortion agreed reasonably well with the distortion calcu- 

 lated from the constants of the various circuits. These measurements and 

 calculations showed that while the characteristics of an 8-link repeater 



24 



23 



0^' 



ai 



Q 



Z 

 - 20 



Z 





4048 4050 4052 4054 4056 4058 4060 4062 4064 4066 4068 4070 4072 

 FREQUENCY IN MEGACYCLES PER SECOND 



Fig. y-17. — Frequency response of RF amplifier. 



circuit will give acceptable television pictures, phase equalization will 

 provide a definite improvement. Longer circuits will therefore require 

 phase equalization. Equalizers were devised for both the IF and RF 

 circuits which made it possible to equalize the group delay of each compo- 

 nent of the repeater amplifier to ±0.001 microsecond over the 10-mc band. 

 An experimental repeater amplifier was set up so that the output could 

 be fed through an attenuator to the input. It was then possible to break 

 the loop and make overall tests of delay, amplitude linearity, and transient 

 response with IF measuring equipment. Transient response was measured 

 by including a 2(XX)-foot waveguide line between the input and output 

 terminals and applying the circulated pulse testing technique.^^ This 



" D. H. Ring, "The Measurement of Delay Distortion in Microwave Repeaters", 

 elsewhere in this issue of the B. S. T. J. 



» A. C. Beck and D. H. Ring, "Testing Repeaters with Circulated Pulses", Proc. 

 I. R. E., vol. 35, No. 11, pp. 1226-1230, November 1947. 



