Improvements in and relating to band filters

摘要

544,775. Band-pass filters. AKT.-GES. BROWN, BOVERI, & CIE. Oct. 22, 1940, No. 15560. Convention date, Sept. 11, 1939. [Class 40 (iii)] A filter comprises a pair of tightly coupled tuned circuits such as l1, C1, and l2, C2 loosely coupled to a third tuned circuit l3, C3, the damping of which is adjustable as by a shunt resistance W3 or a series resistance, to vary the band width. The shape of the attenuation curve can be adjusted by varying the tuning of the third circuit and the value of the coupling condenser C4. The latter may be fixed and associated with the third circuit by means of a potentiometer or may be replaced by a resistive coupling in the form of a bridged T-network. In a further modification, the coil ls is coupled to both coils l1, l2. The coupling l1, C1 and l2, C2 may be capacitive or galvanic.