Double tuned band-pass filter with inductive coupling - has capacitors across coupling and between input and output defining filter attenuation poles

摘要

The filter has a capacitor and a primary filter connected in series with the input (1) and a second capacitor and secondary filter connected in series with the output (2), with the filter coupling (L12) having a parallel capacitor (C12). This capacitor (C12) defines an initial filter attenuation pole, with a second pole defined by a second parallel capacitor (C03) across the input (1) and output (2). Pref. the second parallel capacitor (C03) comprises a T network with two fixed capacitors in the horizontal arm and a variable capacitor coupled to earth in the transverse arm.