with capacitor 44 and varactor diode 50 the frequency of this resonant circuit is controlled by the uhf tuning voltage synthesizer output provided to the cathode of varactor diode 50 with the first and second resonant circuits respectively including varactor diodes 40 and 50 and tuned to the desired uhf signal this uhf signal is provided via rf coupling capacitor 54 to the g1 gate of a dual gate field energized transistor fet 56 grounded inductor 58 coupled between coupling capacitor 54 and gate g1 of fet 56 serves as an impedance matching coil the fet 56 also includes a g2 gate to which an automatic gain control agc input may be provided from an agc circuit 57 the output of the fet 56 is typically provided via its drain d to a mixer circuit in a uhf tuner for tuning the rf receiver to the desired uhf signal referring to fig2 there is a graphic illustration of the relationship between the notch frequency f notch and the desired rf signal frequency f desired rf as shown in fig2 there is a difference in frequency f between the rf signal which it is desired to tune to and the notch frequency of the tunable switchable notch filter of the present invention while u03b4f assumes an essentially constant value i e on the order of 122 mhz for channel 3.