788 



BELL SYSTEM TECHNICAL JOURNAL 



we notice that the deviation represented by Curve I at the point marked 

 by the arrow would lead to a reflection coefficient of about 50 per cent 

 even if the system were otherwise ideally terminated. Curves II and 

 III, under the same conditions, represent reflection coefficients of about 

 29 per cent and 3 per cent respectively. 



o 



N 



U 



o 



z 



a 



UJ 



o ■ 



D 



ZA 



2.0 



1,6 



1.2 



0.8 



0.4 



-0.4 



-0.8 



-1,2 



-1.6 



-2.0 



-2.4 



0.9 



1.0 



1.2 



1.3 1.4 



FREQUENCY 



IN 



1.5 1.6 



ARBITRARY 



1,7 

 UNITS 



1,8 



1.9 



2.0 



2.1 



Fig. 18 — Susceptance correction of x-terminated band-pass filters. 

 I — Uncorrected Susceptance. 

 II — Susceptance after the addition of a simple auxiliary network. 

 Ill — Susceptance after the addition of a more elaborate auxiliary network. 



Improvements in Filters for Use with Modulator and Demodulator 



We have hitherto restricted our attention to the impedance charac- 

 teristics of filters within their transmitting bands since it is only in 

 this range that impedance irregularities in the circuit can produce 

 crosstalk. When a filter operates in conjunction with a modulating 

 device, however, a high modulator efficiency with low distortion de- 

 mands that the impedance of the filter to the untransmitted side band 

 be low (or high) and nearly constant. All of the correcting networks 



