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BELL SYSTEM TECHNICAL JOURNAL 



about .01 db, while a variation in load from 60 milliwatts to 6 milli- 

 watts causes a change in gain of about .4 db. 



The input and output coils in the amplifier and, in the case of the 

 regulating repeater, the retardation coil also, tend to delay the trans- 

 mission of low-frequency currents more than those of high frequency; 

 an action which is due to the inductance of these coils shunting the 

 circuit. As this reactance becomes less at the lower frequencies, the 

 delay becomes greater. It can be reduced by increasing the values 

 of shunting inductances. It is largely to reduce this effect that 

 permalloy core coils of extremely high inductance are used, as noted 



10 



30 50 100 300 500 1000 



CYCLES PER SECOND 

 Fig. 14 — Delay-frequencj- characteristic of non-regulating repeater. 



above. The condensers appearing in series also cause delay at low 

 frequencies and must be given capacity suf^ciently great to keep the 

 delay within proper limits. Inductance in series or capacity in shunt 

 will also result in delay at the high-frequency end. However, in the 

 frequency range covered by these amplifiers there is no difficulty in 

 keeping this delay small enough to be negligible. 



The delay characteristic of one of these amplifiers is shown in Fig. 14. 

 With 40 amplifiers in tandem, the overall delay at 35 cycles is 75 

 milli-seconds greater than at 1,000 cycles, while there is no appreciable 

 difference between the delay at 1,000 cycles and the delay at higher 

 frequencies. 



