Tuner for Complete UHF-TV Coverage without Moving Contacts

A tuner covering the uhf television band continuously and having essentially constant selectivity over all of this band is described. A unique feature is that the tuner employs no moving contacts in the tuned circuits, and so avoids the well-known contact troubles. The circuit consists of a double-tuned preselector, a crystal mixer, a triode oscillator, and a cascode-type first intermediate stage. The two preselector circuits and the oscillator employ balanced parallel-rod constructions, each tuned with a movable capacitor element having surfaces shaped to give a linear displacement-frequency characteristic. Shielded compartments are provided for the three tuned circuits. The tuner input matches a 300-ohm antenna, and the output is suitable for feeding the conventional "40-mc" intermediate-frequency amplifier of a television receiver. Measurements of the performance show the noise figure to be 15 db or better over the band, the image rejection at least 43 db, and the transadmittance (which is a measure of sensitivity) 11 db, or better, above 1 millimho. Oscillator signal at the antenna terminals averages approximately 43 db below 1 volt.