132 



BELL SYSTEM TECHNICAL JOURNAL 



In considering the performance of lattice type filter sections, it is 

 common practice to sketch together the frequency reactance curve of 

 the two lattice arms Z^ and Zy. This is done for one of the filter sec- 

 tions and is shown in Fig. 7. In the frequency range where the two 

 curves are of opposite sign the filter transmits, and where they are of 



1600 



1000 



10 600 



5 



O 



■Z 400 



2 -200 



-400 



-600 



-1000 



-7 -6 -5 -4 -3 -2 -I +1 +2 +3 +4 + 



FREQUENCY FROM CARRIER IN KILOCYCLES 



Fig. 8 — The large reflection losses occurring within the transmission band of the 

 filters and near the edges of this band has the effect of narrowing the width of the 

 transmission band. 



the same sign there is attenuation. At the point where the two curves 

 intersect there are attenuation peaks of very high loss. The reactance 

 curves of Fig. 7 are for the filter section accountable for the pair of 

 attenuation peaks shown in the filter characteristic which are the closer 

 to the edges of the transmitted band. For the other section the cross- 



