630 BELL SYSTEM TECHNICAL JOURNAL 



while the absolute magnitude is given by 

 200 



M^l = 



1 \/10' + co' 



1 + WVV 102 /\ 2002 + C02 



200 



(7.4) 



The Nyquist diagram of (7.2) is shown in Fig. 8. To emphasize the im- 

 portant features, radial magnitudes have been plotted on a logarithmic 



Fig. 8 — Nyquist diagram of —fiP. 



scale. ^ The arrows indicate the direction of traversal as w is varied from 

 — CO to + 00 . The infinite arc traversed as co varies through zero is indi- 

 cated symbolically by the dotted semicircle in the right half plane. ^ As 

 is the case for any physical system, the plot for negative values of w is 

 simply the mirror image of the positive frequency plot. 



Since the polar plot does not encircle or intersect the "critical" point — 1,0, 



^ Except in the immediate neighborhood of the origin, where a hnear scale must be em- 

 ployed to plot the value nfi = 0. 



* The exact shape of this arc is of no consequence. 



