TIME DIVISION MULTIPLEX SYSTEMS 



207 



amplitude. If we use very short contact durations in time division, we 

 should accordingly expect a large number of sidebands of nearly equal 

 amplitude. The combination of proper numbers and phases of these side- 

 bands offers a key to the realization of a time division multiplex system 

 giving good crosstalk suppression with economy of frequency band. 



Suppose that the duration of contact time is made sufficiently small to 

 realize approximately the limiting values Ami — 2Ax/N, Bm\ = 2Bx/N in 

 transmitting and receiving respectively for the first 2M + 1 of the side- 

 bands and that by means of a low-pass filter with linear phase shift and 



4 5 10 20 30 40 50 



NUMBER OF SIDEBANDS TRANSMITTED 



Fig. 2 — Crosstalk between adjacent channels of ten-channel time division multiplex sys- 

 tem with on-and-off switching. No attenuation or phase distortion in pass band of line 



uniform attenuation in its pass-band all other sidebands are removed from 

 the line. The expression (23) then becomes: 





1 + 2 £ cos Irrnrik - j)/N 



TO=1 



1 -f 2M 



1, k=j 



sin (2M + DttU - j)/N 



^(2M-f l)sin7r()fe-y)/iV 



,k9^j 



(24) 



In particular, if 



