146 



BELL SYSTEM TECHNICAL JOURNAL 



circuit. This also shows a similar effect. The initial pulse contains most of 

 the receiver characteristic, while the curve which follows is mainly de- 

 pendent on the leakage constants. 



Curve 9 is taken on a high-pass filter of the characteristic shown. It may- 

 be proved that this curve is the inverted image of the corresponding low-pass 

 filter characteristic, of which a similar curve is shown as curve 10. 



+5 

 



-5 



D 



-10 

 -15 

 -20 



2 



NDICIAL RESPONSE 



Fig. 9— String oscillograph characteristics — frequency response and indicial response with 

 different amounts of damping. 



The curves 7, 8, and 9 show that when the low frequencies are absent, the 

 indicial response becomxs too difficult to interpret. We must restrict our 

 measurements to systems which are ideal at the low frequencies in order to 

 interpret the indicial admittance by inspection. 



Curves 10 and 11, Fig. 7, are low-pass filter characteristics, the former 

 being a measured curve of a typical filter, while the latter is a calculated 

 curve for an ideal filter. The two curves check reasonably well and indicate 

 the effect of a very sharp cutoff as compared to those of the receivers shown 



