High-frequency bandpass filter circuit for television tuner

摘要

The circuit includes primary and secondary parallel oscillatory circuits (P,S) with inductance (L,L1) and capacitance (C0,C11) augmented by capacitive diodes (D0,D1). The tuning voltage is applied through resistances (R5) to the junctions of both diodes and capacitors. Additional inductors (L2,L3) are coupled between the earth connection and the secondary coil (L1) and the earth connection and the capacitance (C11) respectively. The conductors are formed by a few millimetres of printed conductive track and have a comparatively low impedance of about 4 nH for the UHF band, or 6 nH for the high VHF.