A varactor diode tuner includes a tunable image frequency trap in its input circuit. The trap is part of a tunable bandpass filter and forms a tapped capacitance matching network for UHF television signal carrier frequencies and a low impedance shunt at image frequencies. The trap is formed of discrete...http://www.google.fr/patents/US4835608?utm_source=gb-gplus-shareBrevet US4835608 - Image trap filter circuit
