Abstract: A double conversion tuning system for a high definition television receiver includes a microprocessor supplying first and second digital numbers to first and second local oscillators. The first local oscillator is controlled by a wide band phase locked loop that includes a programmable divider that receives the first digital number from the microprocessor and a prescaler that couples the first local oscillator signal to the programmable divider. The output of the programmable divider supplies one input of a phase detector, the other input of which is supplied with the divided down output of a crystal reference source. The output of the phase detector controls the first local oscillator frequency. The tuning of the first local oscillator is coarse and the first IF signal frequency may deviate within a predetermined range from a desired value.

Abstract: A double-balanced wide band RF mixer includes a first bifilar balun transformer coupling a high level source of RF signal to the primary windings of a pair of trifilar balun transformers. The two output windings of each trifilar transformer are connected in series with the drain-source circuits of a pair of FET transistors which are alternately activated by a symmetric local oscillator signal. An IF signal with reduced second order products of the RF signal is developed between the output windings of the two trifilar balun transformers.

Abstract: An AGC system for a double conversion type tuner for tuning digital television signals includes a quadrature coupler that has two of its four ports each terminated by a pin diode. The pin diodes are driven conductive in response to an AGC voltage and control the power transfer from the first mixer to the first IF amplifier. A series resistor is connected in circuit with each pin diode for providing a 50 ohm impedance when its associated pin diode is driven fully conductive. The pin diodes are conductively balanced to maintain impedance matching between the first mixer and the first IF amplifier.

Abstract: A wide band RF mixer includes a first bifilar balun transformer coupling a high level source of RF signal to the input winding of a trifilar balun transformer. The two output windings of the trifilar balun transformer are connected in series with the drain-source circuits of a pair of GaAs FET transistors. The source of each FET transistor is connected to ground. A local oscillator has a symmetric output signal that is coupled to a self-bias network and also to the gate electrodes of said FETs. An IF output signal is taken between ground and a common junction of the output balun windings. The arrangement provides a high level mixer with good intermodulation characteristics for ultra high frequencies.

Abstract: An RF mixer combines electrical and structural aspects to create a more efficient device. Diodes are coaxially mounted within two conductive tubes which form shields. The respective diode or diodes associated with each of the tubes are cross-connected at the LO port to the tube associated with the other diode or diodes. A capacitor compensates the inductance associated with the outer surfaces of the tubes. At their other ends, the tubes are coupled to ground and the diodes are coupled to an RF/IF bandsplitting network.

Abstract: A quadruple tuned 400 MHz IF filter comprises a rectangular substrate having a foil pattern of four inductors formed on one side thereof with four leadless capacitors and three lead type coupling capacitors interconnected between the inductors and the foil to form a filter. The inductors are arranged in a generally U-shaped configuration with the input inductor and output inductor being located at the legs of the U adjacent to each other for providing electromagnetic coupling between the input and output of the filter to sharpen the response of the filter along the skirts of the response curve. A triple tuned filter includes three helical resonators that are coupled by mutual stray capacitances. Output to input coupling is achieved with two wires connected to the input and output helical resonators and positioned adjacent to the middle helical resonator.

Abstract: A switched bandpass filter includes a plurality of triple tuned bandpass filter sections coupled in parallel between an input and an output terminal and complemented by input and output parallel resonant circuits. Each bandpass filter section includes a switch such as a switching diode by means of which the filter section is either rendered active for passing or inactive for suppressing the frequency band to which it is tuned. Portions of the inactive bandpass filter sections contribute to the resulting frequency response with notches at frequencies outside of the passband of the active filter section. Thus, some components of the inactive bandpass filter sections are reused with the active filter section to gain steep out-of-band rejection slopes. In one embodiment, the switched bandpass filter employs only one switching diode per frequency band and, by reusing two-thirds of the filter components, provides a highly efficient switched bandpass filter arrangement.

Abstract: A microwave oscillator and a combination microwave oscillator/single balanced mixer for a satellite television receiver includes a cylindrical dielectric resonator located on one side of a ground plane formed by a conductive foil on a substrate with microstrip transmission lines formed by foil patterns on the opposite side of said substrate. A gallium arsenide FET is disposed in a hole through said substrate with its source electrode connected to the ground plane and its drain and gate electrodes coupled to first and second transmission line strips, portions of which are following the contours of said dielectric resonator. Two sets of coupling slots are formed in the ground plane for permitting magnetic coupling between the dielectric resonator and the opposite transmission line strips. In one embodiment an additional coupling slot in the ground plane couples the dielectric resonator to an output transmission line strip.

Abstract: A wideband intermediate frequency (IF) amplifier including a GaAs FET input portion and a bipolar transistor output portion is disclosed. The high gain of the GaAs FET over higher frequencies is complemented by the high gain of the bipolar transistors at lower frequencies to provide high amplifier gain over a large bandwidth. The GaAs FET and bipolar portions are coupled by means of an equalizer circuit matching the two portions together only at the higher frequencies of the IF band to provide an inexpensive, high performance IF amplifier particularly adapted for use in a direct broadcast satellite receiver operating in the super high frequency (SHF) band.

Abstract: The front end of a microwave receiver includes a waveguide with one wall comprised partially of the conductive ground plane of a printed circuit board. On the opposite side of the circuit board is mounted receiver front end circuitry including packaged, discrete devices and integrated circuits. An RF probe is inserted through the circuit board and into the waveguide for picking up a signal incident thereon and providing it to the aforementioned receiver front end circuitry. Incorporated in the waveguide is a cavity also partially formed from the ground plane of the receiver circuit board and containing a dielectric resonator element which, in combination with an oscillator located on the circuit board, provides a reference frequency for mixing with the received signal in generating an IF signal which is then provided to IF signal processing circuitry.

Abstract: In an RF receiver, the unsymmetric RF input to a single balanced mixer is provided from the preceding portion of the receiver by means of a hybrid coupler to provide DC decoupling and impedance transformation at the RF and image frequencies. The hybrid coupler includes first and second microstrip conductors on the first side of a circuit board, each respectively coupled to the preceding portion of the receiver such as to a preamplifier and to the mixer and mutually electromagnetically coupled. On a second side of the circuit board is located a slot etched in the circuit board's conductive ground plane providing the single balanced mixer with a symmetric oscillator frequency source. The ground plane in which the slot is located forms one wall of a cavity in which a dielectric resonator is contained which, coupled to either end of the slot and in combination with an active device, forms the oscillator frequency source.

Abstract: A multichannel communications receiver, e.g. a CATV converter, includes a switched filter for reducing third order intermodulation distortion by limiting the number of channels processed by the receiver. In a preferred embodiment, the filter is switchable between a highpass and a lowpass configuration by a control signal supplied to two switching diodes. The input and output of the filter are coupled by a mutual inductance which partially compensates for the effect of parasitic inductance at higher frequencies.

Abstract: A method and structure is disclosed for isolating the shield of a shielded conductor system from a low frequency power source to which the shield may be connected. In one embodiment, the isolation technique includes providing an interruption in the conductor's shield and situating within the interruption dielectric and magnetically absorptive material so as to create at least a pair of capacitance across the interruption, and such that the capacitances are separated by magnetically absorptive material. In this manner, low frequency isolation is achieved and the field within the cable is shielded from ambient high frequency electromagnetic interference which could otherwise leak through the interruption into a desired high frequency signal path within the conductor. In other embodiments, at least some of the dielectric material forms part of a series resonator to improve attenuation of electromagnetic interference at low VHF frequencies.

Abstract: A single balanced mixer for use with a superheterodyne receiver or the like comprises an integrated structure characterized by a pair of opposed capacitive plates, a first mixing diode connected between the plates and a second mixing diode connected between one of the plates and a point of ground potential. A ferrite balun core is disposed between the capacitive plates and includes a first cavity receiving the first diode and a return conductor connected between two points of ground potential and a second cavity receiving the second diode and a return conductor connected between one of the plates and a point of ground potential. In another embodiment of the invention, a double balanced mixer comprises two interconnected integrated structures of the foregoing type, the diodes of one of the structures being connected having a polarity opposite that of the other.