THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1953 



AGt 

 AP. 



As an example of the application of these formalas consider the effect 

 of television induced compression. The presence of the television signal 

 reduces the gain of the line amplifier. The effect is small but cumulative. 

 In the absence of regulator action it merely compresses the television 

 signal slightly and makes a negligible change in the contrast rendering 

 of the picture. However the regulators observe a gain change to the pilots 

 and attempt a correction. The very rapid changes are ignored but 60 

 cps, for example, is partially corrected. This introduces a 60 cps gain 

 change which will lag the picture and therefore must meet 60 cps bar 

 pattern requirements. This problem is solved by keeping the regulator 

 response low at 60 cps. 



For /xjS of —70 db, 90 degrees, at 60 cps a chain of 700 regulators will 

 insert a total gain change approximately one tenth that of the total 

 compression. If the m/3 were allowed to approach — 50db the total gain 

 change would equal the compression and certain types of pictures would 

 be degraded. 



The above example brings out one of the important facts: When 

 designing regulators for long systems the )U/S characteristic must be care- 

 fully controlled to losses much higher than is customary in amplifier 

 design. In a conventional feed-back-amplifier loop-cutoff the magnitude 

 and phase of /u/S is no longer of much interest after it drops below — 10 

 db. In L3 regulators the loop is of vital interest to losses of the order of 

 70 db. This is, of course, largely due to the fact that the chain action 

 increases the effective system feedback by nearly 60 db. Thus the over- 

 all system is similar to conventional amplifier practice. Loop gain (ai/3) 

 and feedback (l-n^) characteristics for the line and office regulators are 

 shown on Figs. 19, 20, 21 and 22. Note that 1,000 line regulators in 

 tandem give an over-all gain enhancement of only 1.2 db. This would be 

 even less if it were not for a 100 cps roll-off in the dc amplifier to reduce 

 noise. One hundred office regulators give 0.8 db gain enhancement even 

 with their 20 cps roll-off. 



THE DYNAMIC LINE REGULATOR 



As indicated in Fig. 23 a crystal filter is used to pick the pilot off the 

 line in the presence of the other signals. The filter impedance goes 



