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 tunable coupling network for a frequency multiplier stage providing a passband for a desired harmonic of a fundamental frequency and rejection notches for undesired harmonic frequencies. The passband of the network can be tuned by changing the value of at least one circuit element to track the desired harmonic of the fundamental frequency over a range of fundamental frequencies. In so doing, the rejection notches also move so that they maintain fixed ratios with respect to the passband frequency as the passband moves. In one embodiment the network comprises first and second tunable circuits each including a variable reactive element. The first resonant circuit includes a variable capacitor and two fixed inductors. The second resonant circuit includes a variable inductor and two fixed capacitors. The two resonant circuits are coupled by an interstage coupling capacitor.

Abstract: An electronically tunable band reject filter rejects only frequencies of a signal that are in the reject band around its center frequency. The band reject filter includes an input directional coupler for sampling of the signal that is to be filtered and provides a first and second signal thereby. The first signal is filtered by a bandpass filter that passes only frequencies of the signal that are around the center frequency of the bandpass filter. An output directional coupler combines the second signal with the filtered signal and obtains on a difference port the difference between the second signal and the filtered signal. The frequencies of the signal that are centered around the center frequency of the bandpass filter are thereby rejected.

Abstract: A non-ringing circuit for detecting the presence of predetermined frequency components in input signals and for delivering an output signal when a predetermined component is dominant, the circuit employing plural tuned filters with different adjacent cross-over frequencies, and using coincidence detectors connected to pairs of these filters in such a way as to detect when there exists a dominant frequency component having a frequency so located with respect to said cross-over frequencies that the relative phases of the signals fed to the coincidence detectors from the filters will produce phase coincidences therein, the circuit further using multiple different paired filters having staggered cross-over frequencies such that the tendencies of these filters to ring as a result of transient excitations will produce diverse and non-coincident ringing wave forms.

Abstract: A microwave mixing circuit comprises a main transmission line having an input port for receiving an input high frequency and an output port, a band pass filter responsive to a local oscillation frequency, first and second band stop filters, and a mixing diode connected to the output port. The local oscillation frequency applied via the band pass filter to the main transmission line is prevented from being transmitted toward the input port because of the first band stop filter, while an image frequency produced by the diode is reflected by the second band stop filter to be applied to the diode.

Abstract: In modern communication systems, it has become important to provide filters, and in particular bandpass filters, which can provide substantially uniform group delay across the bandwidth of the filter while still achieving good amplitude response. In this regard, it is particularly desirable to substantially reduce the large variations in the phase characteristics found in conventional bandpass filters at the nominal band edge of the filter. To accomplish this, a filter is provided having at least one pair of lattice arms coupled in parallel to one another between the input and output of the filter. Each of the lattice arms includes a plurality of resonant LC resonators, each of the resonators having a different resonant frequency than the center frequency of the filter. In particular, within the bandwidth of the filter, the exponential damping coefficients for the resonators in each arm are set to decay at the same rate. This desired decay can be accomplished by exponential sizing of the components.

Abstract: A crossover network is coupled to each transducer in an array of acoustic ansducers, each transducer having a different frequency band, and all of the crossover networks being coupled in parallel to a single driving amplifier. Each crossover network includes a network inductance connected in parallel with a transducer capacitance to form a parallel LC circuit, the resonant frequency of such circuit being equal to the resonant frequency of a transducer RLC series circuit. The network inductance of each network is coupled to the amplifier in series with a driver inductance and a driver capacitance, which are respectively equal to the inductance and capacitance of the RLC series circuit of a transducer.

Abstract: A circuit for peak limiting an audio signal comprises a first "M" derived filter, a first clipping circuit, a second-order low pass filter, a second clipping circuit and a second "M" derived filter. Each "M" derived filter includes a series resonant shunt leg for eliminating clipping harmonics within selected frequency ranges depending upon the resonant frequency of each shunt leg.

Abstract: In an amplifier station for a trunk system, switching apparatus responsive to the absence or presence of a control signal selectively passes R. F. signals in a prescribed frequency band on a main transmission line to first and second lines. During normal operation of the amplifier relay coils are energized so as to engage second and third contacts for passing signals on the second line with amplification. When the amplifier is operating properly, PIN diodes short opposite ends of the first line for improving isolation in the station equipment. In the event of amplifier malfunction, first and third contacts are engaged thereby providing transmission along the first line. A tubular conductive member surrounds the switch contacts so as to provide capacitive coupling thereto. The tubular member is capacitively coupled to a ground plane to thereby by-pass signals which are above the desired passband of the trunk system.

Abstract: A device to suppress the generation of second harmonic frequencies in a power amplifier tank circuit such as may be used in a radio frequency transmitter. The present invention employs a device connected between the outer conductor (which is normally at ground potential) and the inner conductor. Specifically, the device utilizes a metal strap, such as a copper strap, which is connected to the inside surface of the outer conductor in an electrically conductive manner and which is also connected to a capacitor disk movably mounted with respect to the inner conductor. The capacitor disk is mounted to an insulating arm or rod and may be projected back and forth within the space between the outer and inner conductors, thereby adjusting the impedance of the device. By sliding the rod toward the inner conductor, the loop formed by the copper strap becomes more straightened thereby changing the inductance of the circuit.

Abstract: The invention is an electrical energy storage type filter which is useful for attenuating harmonic distortion, modulation at high frequencies, line voltage transient sags and surges. The invention structurally consists of a inductance capacitance tank circuit having resistive components and with a resistive element connected in series with the tank circuit. The circuit is tuned to include in its bandwidth the fundamental frequency of the power source and includes in its design consideration of the reactance of the source.

Abstract: A power source system, which comprises a converter for converting AC power on an AC bus into DC power, a damped filter connected between the AC bus and ground and including a capacitor and an inductor, a diode-rectifying circuit for taking out and rectifying fundamental and harmonic waves produced across the inductor in the damped filter and a circuit for connecting a DC output circuit in the diode-rectifying circuit in series with a DC output circuit in said converter, and in which the rectified output is regeneratively added to the output of the converter.

Abstract: A two terminal electronic filter network is provided for connection across TV antenna input terminals to reduce interference from noncommercial FM radio stations operating within a frequency band near the TV channel 6 frequency band. The two terminal electronic filter circuit which exhibits a rapid change of reactance for changes in frequency, and having a resonant frequency provides sufficient FM signal rejection without significant attenuation of any VHF channel by the provision of a highly reactive network tuned below the resonant frequency of the filter network as a whole.

Abstract: A method of tuning a trap circuit to a desired frequency is provided. A constant amplitude signal is applied to the trap circuit in a progression of successively different frequency increments. The frequency increments cover a frequency range including the desired frequency. The amplitude of the signal, as modified by the trap circuit is detected and stored at each of the different frequency increments. Successive ones of the stored amplitude values are compared until an amplitude difference is found which is greater than a predetermined minimum difference and is of a polarity indicative of an increase in amplitude with the progression, and is a successor of an amplitude difference which is greater than the predetermined minimum difference and of a polarity indicative of a decrease in amplitude with the progression. The frequency at which the inflection point occurs, as indicated by the two-named amplitude differences, represents the null frequency of the trap circuit.

Abstract: A network is provided for attenuating the adjacent channel sound carrier signal in a television receiver. First and second trap circuits are serially coupled intermediate the R.F. mixer and the first I.F. amplifier. One of the trap circuits is tuned to a frequency in the vicinity of and above the nominal frequency of the adjacent channel sound carrier, and the other is tuned to a frequency in the vicinity of and below that of the adjacent channel sound carrier. The two trap circuits are mutually coupled to a degree necessary to produce a composite response curve exhibiting a substantially constant level of maximum attenuation in the vicinity of the nominal frequency location of the adjacent channel sound carrier. The trap circuits provide attenuation in excess of that required to eliminate adjacent channel sound carrier interference over a bandwidth sufficient to encompass expected carrier deviation due to frequency modulation, carrier mislocation, and trap mistuning.

Abstract: An R.F. resonant cavity filter for connection in a transmission line and multicouplers utilizing same, said filter adapted to pass only signals of a predetermined frequency into and out of a branch transmission line, to block signals of said predetermined frequency from propagating down said transmission line in one direction but not the other, and to pass all other signals substantially undisturbed.

Abstract: Circuit for the compensation of harmonic currents in a network, including a wideband highpass filter having a choke connected in parallel with a damping resistor and a capacitor connected in series therewith, and a harmonic converter connected to the highpass filter.

Abstract: AC to DC converters used in high-voltage direct-current power transmission lines produce objectionable harmonics. The composite filter herein described is actively tuned for the eleventh and thirteenth harmonics in addition to providing a low impedance path for the higher order harmonics, thereby eliminating such undesired harmonics so that they will not be transmitted over power lines where they can cause telephone interference, undesired heating of electrical equipment and other difficulties.

Abstract: The present video bandpass filter passes a sinusoidal video output in response to a square pulse input. The video band-pass filter rejects d.c. and low frequency signal components as well as noise and spurious signals generated at the transmitting source. The video bandpass filter is comprised of an M-derived filter, a series-tuned notch filter, and a final d.c. blocking series-tuned filter which, together, pass the desired video with minimal distortion.

Abstract: A mixer circuit employing a distributed constant circuit using a strip line includes a strip line for applying a high frequency signal and a local oscillation signal to a diode. The strip line is provided with a filter for exclusively blocking the local oscillation signal and a filter for exclusively blocking the high frequency signal. The strip line further includes a line which acts as a shortcircuit for an intermediate frequency signal and as an open impedance for the high frequency signal and the local oscillation signal.

Abstract: To improve the effect of a filter circuit for the harmonics, which contains an L-C-R series resonant circuit in at least one loop, a variable supplementary current excitation which compensates the residual harmonic current in the consumer arrangement at least approximately, is coupled into the series resonant circuit, the supplementary current excitation preferably being supplied by a compensation transformer which is controlled by the current in the loop, the compensation transformer being excited by a source and controlled by an auxiliary transformer arranged in the loop.

Abstract: A cavity notch filter (1) for series connection in a transmission line is disclosed which comprises a high Q cavity (2) containing therein an inductively coupled L-C series circuit (19). The notch filter (1) acts as a high series impedance at the resonant frequency of the cavity. At frequencies off resonance, the filter is characterized by low impedance so as to produce broad lateral pass bands.A multicoupler (18) for connection of a plurality of signaling devices (15) to a single antenna (16) may be assembled to comprise two or more of the filters (1) inserted into the transmission line (17); each being tuned to resonate so as to produce a notch at the respective frequency of the signaling device (15). A different signaling device (15) is connected to each of the series connected notch filters (1) at a junction (7). Energy at all frequencies is then permitted to propagate down the line except the energy at the frequency of the respective signaling device (15).

Abstract: A nonlinear adaptive filter for improving the signal-to-noise ratio of video signals generated from images of features under analysis typically includes filtering components for attenuating low amplitude video noise excursions while passing high amplitude video signal excursions substantially without attenuation. Attenuation of the noise is provided by electrical circuitry operating as a function of the voltage input. In general, the electrical circuitry has a predetermined relationship to the value of the video signal and its noise characteristic.

Abstract: A four-terminal radio frequency interference filter is described which combines a series connected parallel tuned circuit with a pair of capacitors to form a pi network. In one refinement, a quarter wave coaxial stub and a zener diode are connected in parallel with one another and with one leg of the pi network. The series combination of a diode and a resistor are connected in parallel with the other leg. Filtering is improved by inductive coupling between the diode-resistor circuit and the coil of the tuned circuit.

Abstract: A filter for a telecommunication system, designed to suppress a signal frequency F.sub.a and to transmit an adjoining frequency F.sub.b without significant attenuation, comprises a resonant cavity of prismatic shape longitudinally traversed by a conductive coil wound on a hollow dielectric core into which an adjusting screw is inserted. One end of the coil is grounded at the cavity wall while its other end is left unconnected and forms with the adjusting screw a variable capacitance C.sub.d with distributed constants; a lumped-constant tuning capacitor C.sub.1 is connected between ground and an input lead connected to an intermediate tap on the coil, the inductance L.sub.2 " of that lead and the inductance L.sub.2 ' of the coil portion between the tap and ground forming an inductive voltage divider bridged by the lumped-constant capacitor C.sub.1. The remainder of the coil, lying between the tap and the unconnected end, forms an inductance L.sub.1 which together with the distributed-constant capacitance C.