548 



BELL SYSTEM TECHNICAL JOURNAL 



were made with the set which used 13^4 cycles as the modulating 

 frequency. 



Fig. 14 shows the measured envelope delay-frequency characteristic 

 for a special open-wire circuit ■* used for a television demonstration 

 between Washington, D. C. and New York, N. Y. Curves are shown 

 for measurements on the circuit alone and for the circuit equipped with 

 its dry weather equalizer. The curves do not appear to be as smooth 

 as the curves shown in the above figures, but this is largely due to the 

 difference of the scales used for plotting the measurements. However, 



0.3 



a 

 in a. 

 a < 

 z Q 

 oz 0.; 



li 



V 



O 0.1 



111 o 



O H 



uj a 



Q. lu 



O (t 



-I a. 



lU lU 



> u. 



Z uj 



UJ (£ 



-0.1 



4.000 



8.000 



12,000 16,000 20,000 



CYCLES PER SECOND 



24,000 



26.000 



32.000 



Fig. 14 — Envelope delay characteristic for special open-wire circuit; Washington, 



D. C— New York, N. Y. 



some of the irregularity is due to the method of measurement and the 

 fact that noise on the open-wire circuits obscured somewhat the exact 

 point of balance. 



Conclusion 



It has not been the intent of this paper to include all the known 

 methods of measuring phase distortion. Various methods for measur- 

 ing phase shift are, of course, known and these can often be used to 

 indicate phase distortion. In a practical way on telephone circuits, 

 the term defined as envelope delay has certain advantages, and the 

 paper is chiefly concerned with methods of measuring this quantity. 

 In order to avoid including information which is contained elsewhere, 

 the methods have not been given in detail; but references have been 

 given, when possible, to sources where more detailed information can 



