Electronic tuning chiyu - na null for UHF band reception

摘要

PURPOSE:To obtain a three-section UHF electronic tuner with excellent image disturbance eliminating characteristic by forming a series trap at the image frequency band over all channels at the input terminal of a mixer circuit. CONSTITUTION:An input terminal of a mixer circuit 10 is connected to a connecting point between an RF amplifier circuit 2 and a coupling capacitor 3 to tuning circuits 4, 5, 6 of the next stage via a coupling capacitor 7 having a minute capacitance. A two-series trap composing of the coupling capacitor 3, the tuning varactor diode 4, the tuning capacitor 5, the coupling capacitor 7 and a coupling line 8 is formed at the input terminal of the mixer circuit 10 by connecting the capacitor 7 in this way. The relation of ft=f0 is obtained, where f0 is the reception frequency and ft is a trap frequency. That is, a trap is formed at high frequencies than the reception frequency f0 and the signal attenuation of the image frequency band is increased and an excellent image disturbance elimination characteristic is obtained.