ELECTRICAL WAVE FILTERS EMPLOYING CRYSTALS 



241 



network of Fig. 17B results. On account of the paralleling of the 

 — Z and + Z the lattice arm vanishes and the network reduces to 

 that shown in Fig. 16A. In a similar manner the other equivalences 

 result. 



The use of divided plating crystals to obtain wide band filters by 

 using series coils to widen the band is obvious. If we connect two 



(A) Cb) 



Fig. 17 — Method for proving equivalence of Fig. 16A. 



crystals as shown in Fig. 18A, one crystal being connected as shown 

 in Fig. 16A and the other in Fig. 16B, a lattice filter equivalent to 

 that is shown in Fig. 18B. In the series arms we have a crystal of 

 twice the impedance of the fully plated crystal Qi shunted by the 





2 



gNn^^TjU^y^ 



(cB+^132) 



=^c. 



^^ — Ln Lo 



— Ca+C)4|+C|42-- 



C^+C,4|+C(42 



Fig. 18 — Band pass crystal filter employing connections of Figs. 16A and B. 



capacitance C^ and the capacitance C13 of the second crystal Q2. 

 In the lattice arms we have a crystal of twice the impedance of the 

 fully plated crystal Qi in parallel with the capacitance C13 of the 

 crystal Qi. On the ends of the lattice we have capacitances Ca + Cu^ 

 + Ci42- It is obvious, then, that by using divided plate crystals w^e 

 can replace two identical crystals in the two arms with crystals having 

 twice the impedance of the fully plated crystals. This result can be 



