Zenith Electronics Corporation

Harmon P Vaughter

Michael S Cruz

Francis F Tong

A tunable/switchable notch filter adapted for use in the front end of a television receiver removes an image frequency on the low side of the UHF passband without degrading desired frequencies. The tunable/switchable notch filter can be switched out when in a VHF mode so as not to degrade VHF performance and switched in for UHF operation for filtering out a difference image frequency which varies with and is a predetermined frequency less than the desired UHF signal.

Tunable UHF filter for switchable VHF/UHF receiver

A UHF oscillator circuit includes a plurality of first leadless, or 'chip', surface mounted components machine positioned on a first side of a printed circuit (PC) board and a plurality of second lead-bearing components mounted on a second side of the PC board and coupled in circuit through the PC board to the chip components in an arrangement which substantially reduces circuit fabrication costs. Comprised of a majority of automatically positioned surface mounted chip components and making use of a minimum number of lead mounted discrete components, the low Q values of the surface mounted components are compensated for by an external surface mounted feedback capacitor coupled across the collector-emitter junction of a common base transistor to provide oscillator tuning over a frequency range greater than an octave.

Surface mounted component UHF oscillator

A tunable notch filter for the front end of an RF receiver includes magnetically coupled input and output tunable stages each responsive to a tuning voltage provided thereto. Each of the input and output stages includes a respective series and parallel resonant circuit wherein the parallel resonant circuits are tuned to a selected RF frequency and the series resonant circuits are tuned to a frequency approximately equal to that of a local oscillator. By using the series resonant circuits to create a notch at a frequency approximating that of the local oscillator, conducted local oscillator leakage from the receiver's antenna is substantially reduced and local oscillator image frequency rejection is substantially improved.

Tunable notch filter for image frequency and conducted local oscillator

A UHF tuning system for providing linear high gain operation over the entire UHF band comprises a field effect transistor (FET) amplifier coupling a received RF signal to a mixer for developing an IF signal, the IF signal being coupled to an IF processing stage by a signal regulating diode. An AGC control signal is derived from the IF stage for controlling the gain of the FET amplifier which, in turn, is utilized to control the conduction of the regulating diode so as to provide a substantially constant level IF signal to the IF processing stage. The novel arrangement of the present invention permits the field effect transistor to operate at a lower voltage for more efficient thermal operation and increased reliability while providing a high, flat gain characteristic over the entire UHF band.

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Evanston, IL, United States of America

Harmon P Vaughter