RESISTANCE COMPENSATED BAND-PASS CRYSTAL FILTERS 433 



lattice filter of Fig. 12. A hybrid coil with series aiding windings con- 

 nected to two impedances 2Zi and 2Zi as shown by Fig. \2)A can be 

 shown to be equivalent to the circuit of Fig. \2>B in which a lattice 



Fig. 11 — A three-winding transformer crystal filter. 



network with the branches Zi and Zi is placed in series with the trans- 

 forming network and the series terminating inductances. Hence if the 

 hybrid coil has nearly a unity coupling between its secondary coils and 



Fig. 12 — A narrow-band lattice crystal filter. 



the remainder of the transformer is designed to work into the impedance 

 of the filter, the network of Fig. 11 is equivalent to the narrow-band 

 lattice filter of Fig. 12 with crystals removed from the lattice arms, plus 



A B 



Fig. 13 — An equivalent circuit for a three-winding transformer and network. 



