1448 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1957 



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 FREQUENCY IN MEGACYCLES PER SECOND 



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Fig. 15 — Measurement on Denver-Omaha route. Transmission characteristic 

 measured at video (a) unequalized, (b) with equalizers adjusted. 



frequency point. The "unequalized" characteristic is the circuit delay 

 distortion immediately after standard line-up procedures without video 

 equalization. The "equalized" characteristic shows the same circuit 

 distortion corrected by the addition of the transversal equalizer. The 

 first two delay terms of this equalizer were supplemented by the use of 

 319 type (linear slope) and 315A (parabolic) eciualizers. The second loss 

 term was supplemented by the use of experimental fixed parabolic loss 

 eciualizers. An attempt was made to obtain the best performance over 

 the center 10 mc of the band, corresponding to the first order modulation 

 band. 



The gain distortion was adjusted on a demodulated video basis as 

 this was the only type of sweep gain circuit available. As shown in Fig. 

 15, the unequalized circuit had more than 0.5 db per mc of slope up to 

 10 mc. The addition of the equalizer produced a flat band to about 8.5 mc. 



The effect of this equalization on cross modulation, measured by simu- 

 lating the message load with a flat band of noise, is shown in Fig. 10, 

 for two sample channels. In these curves, normal drive represents the 

 noise load whose power is 12 db below the power in a sine wa^'e giving 

 4-mc peak deviation of the TD-2 carrier. Channel A showed 5-db im- 



