Showing papers on "Band-stop filter published in 1969"

Diplexer for radio communication

Abstract: A diplexer enabling radio transmitter and receiver to operate simultaneously or sequentially with the same antenna with closely spaced transmitter and receiver frequencies. The diplexer consists essentially of a low pass and notch filter in the transmitter circuit, a band pass filter in the receiving circuit and series coaxial cables of predetermined lengths in the transmitting and receiving circuits which are connected to a common antenna. The electrical length of the coaxial cable in the transmitting circuit is adjusted to be a high impedance to the receiver frequency, whereas the electrical length of the coaxial cable in the receiving circuit is adjusted to be a high impedance to the transmitter frequency. The low pass filter and the receiver band pass filter may be similar to those normally used in radio communication without diplexing. The notch filter is tuned to reject the wave energy generated by the transmitter at the receiver frequency.

Filter having direct and cross-coupled resonators

Abstract: A band-pass filter is constructed from arrays of resonant elements which are coupled in a manner enabling control to be simultaneously effected over the filter''s amplitude and group delay characteristics. In each array the resonators are directly coupled in consecutive order and the resonators in one array are cross coupled to resonators in the other array. The direct and cross-coupled arrangement of resonators is in accordance with a mathematical relationship which permits selection of the filter''s group delay characteristic and the filter''s amplitude characteristic. In accordance with that relationship, multiple paths of different lengths are provided for the wave energy travelling from the input to the output.

Adjustable bandwidth optical filter

Abstract: THE OPTICAL APPARATUS USED IN A TELEVISION SYSTEM, FOR EXAMPLE, INCLUDES A SERIES ARRANGEMENT OF THREE BIREFRINGENT ELEMENTS OF DIFFERENT THICKNESS INTERSPERSED WITH TWO QUARTER WAVE DELAY ELEMENTS TO CONSTITUTE AN OPTICAL FILTER. THE FILTER IS PLACED IN THE LIGHT PATH BETWEEN AN OBJECT AND THE IMAGE FORMED AT THE PHOTOSENSITIVE ELEMENT OF A CAMERA TUBE. THE SPATIAL FREQUENCY BANDWIDTH OF THE LIGHT PASSING THROUGH THE FILTER IS CONTROLLABLE IN ONE OR MORE DIRECTIONS AND IN THE SAME OR DIFFERENT AMOUNTS IN A PLURALITY OF DIFFERENT DIRECTIONS BY SUITABLE DIMENSIONING OF THE BIREFRINGENT ELEMENTS AND/OR BY APPROPRIATE ROTATIONAL POSITIONING OF THE ENTIRE FILTER ABOUT THE OPTICAL AXIS.

N-path filter using digital filter as time invariant part

Abstract: A time division multiplexed digital filter is used as the timeinvariant part of an N-path filter. The use of a multiplexed digital filter alleviates the problem of closely matching the transmission characteristics of each of the N-paths.

L-band switchable narrow bandstop filter

Abstract: An air stripline filter has one or more loosely coupled parallel resonators. Each resonator has a shunt PIN diode tapped thereto. When the diode is forward biased by a reversible bias circuit the narrowband rejection notch of the filter is moved forward in frequency.

Discrete-time filtering apparatus

Abstract: In a discrete-time filter, sensitivity to coefficient variation is substantially reduced by using a unit delay interval, for the delay networks of the filter, which is not equal to the sampling interval. Furthermore, in realizing higher order filter systems, a plurality of such filters may be cascaded, each having a delay interval different from that of the other filters. The periods of repetition of the poles of the overall filter function are therefore different, resulting in improved filter performance.

A tuneable, Bandwidth-adjustable solid-state filter☆

Abstract: Tuneable adjustable solid state bandwidth filter using N path system for low pass to bandpass filter transformation

Musical tone-forming circuitry including filter and random noise modulation

Abstract: A whistle or grass reed sound is simulated by an electronic musical circuitry comprising a portamento-type oscillator, a tone coloring filter for providing a tone signal having predetermined harmonics as well as a fundamental, a noise generator, a low-pass filter for deriving frequency components below 30 Hz from a noise signal output of the noise generator, and a modulator for amplitude modulating the tone signal from the tone coloring filter with the noise signal components of less than 30 Hz from the low-pass filter.

Narrow Bandwidth Elliptic-Function Filters

Abstract: Although wide bandwidth microwave elliptic-function filters have previously been reported, this paper describes a circuit which provides, for the first time, a narrow bandwidth elliptic-function response at microwave frequencies. It is for narrow bandwidth applications (from 5 percent to a fraction of a percent) that the elliptic-function filter offers its most important advantages over other filter types--lower loss and greater selectivity. These features are verified by theoretical analysis and experimental data on a 1-percent bandwidth S-band stripline filter. The design of the filter, which is based upon the low-pass prototype, is simple to obtain with the relationships presented in this paper, and the elliptic-function response is readily realizable in printed or other TEM transmission lines. A waveguide elliptic-function filter is also discussed, but experimental verification of this has not yet been attempted.

Bandstop filter for the H10 mode in a rectangular waveguide

Abstract: A bandstop filter for the H10 mode in a rectangular waveguide is established by a stub in the E-plane. The enlargement of the bandwdth of this filter by a stepped pattern of the stub or by cascading of stub filters is outlined.

Tailored response microwave filter

Abstract: A multiple section microwave filter capable of being accurately tailored to special frequency response requirements over wide bandwidths in disclosed. The tailored response filter consists of an array of cascaded traveling-wave directional filters. Each filter section couples power out of a through transmission line into suitable microwave terminations. Due to the directional characteristics of traveling-wave directional filters, there is no interaction between sections. Thus the frequency response of the array is the product of the transfer functions of the individual sections. The coupling constants and the center frequencies of individual filter sections are tailored, i.e., synthesized, to result in a set of individual transfer functions which will produce the desired overall response. The tailored response filter can be used in wide bandwidth microwave systems for phase and amplitude weighting and for equalization functions.

Digital notch filters

Abstract: The letter deals with the special class of digital filters that possess a prescribed notch frequency. The present techniques for synthetising such filters rest on the bilinear-transformation method, where the designer is required to synthetise a continuous s plane notch filter, prewarp it, and then apply the transformation. It is shown here that notch filters can be synthetised directly into the z−1 plane.

Vhf filter having absorptive tuned section to eliminate narrow spurious passband

Abstract: Disclosed is a very high frequency filter for use with a high frequency radio transmitter which prevents transmission of harmonics. The filter includes an absorptive filter which eliminates spurious passbands resulting from interaction of components. The absorptive filter includes highpass filters arranged in an L-network.

A single operational amplifier notch filter

Abstract: A circuit is presented which allows the realization of a notch filter by means of a single operational amplifier. The notch bandwidth can be easily adjusted by varying the ratio of two resistors and two capacitors.

Digital filter frequency shift modulator

Abstract: Unity gain feedback places a second-order digital filter on the borderline of stability. The filter therefore oscillates in a numerical sense. Two feedback multipliers, each capable of determining a different central coefficient (and thus different oscillation frequencies) are alternatively inserted into an independent feedback path under control of an input baseband data signal whereby the output frequency is shifted in accordance with the input data. Phase discontinuities and amplitude variations due to the frequency shift are eliminated by extracting the numbers stored in the filter when a data transition occurs and reinserting new numbers representing samples of the new frequency wave, the new numbers further defining points on the new wave having the same instantaneous amplitude and phase as the wave samples defined by the extracted numbers.

Digital filter receiver for frequency-shift data signals

Abstract: Sampled FSK data signals are converted to multibit numbers and processed by a digital filter receiver which includes a band-pass filter, a dual-resonator discriminator and a low-pass filter. The dc baseband data signal is reconstructed from the receiver output number by a ''''slicer'''' which detects the sign of the output numbers. The analog-to-number conversion is simplified by limiting the multibit numbers to be processed to two values, simulating the hard limiting of analog signals. Signal harmonics introduced by the nonlinearities of the analog-to-digital converter are substantially eliminated by fixing the sampling rate to a rate which interleaves, in the frequency spectrum, the filter aliases with the harmonies. The receiver is advantageously arranged to be time-shared by a plurality of channels.

Tone channels for multifrequency receivers

Abstract: A tone channel of the type used in multifrequency receivers has in cascade an input band-pass filter that has a frequency curve similar to that of overcoupled filters, a limiter-amplifier, and an output band-pass filter that has narrow band-pass characteristics. The center frequency of both filters is the frequency of a desired incoming tone. After a signal ceases, ringing of the input filter caused by signal is at the peak response points of the input filter at either side of the center frequency, and it is therefore not effective to prolong ringing in the output filter.

Hybrid filter for two-way transmission over a single line

Abstract: A hybrid filter is disclosed wherein the characteristics of a hybrid coupler and high and low pass filters are combined. Each port of the hybrid filter exhibits a constant input impedance that is independent of frequency. The hybrid filter provides a common, low pass and a high pass port, thus providing both frequency and power isolation between branches.

A Tunable Absorbing Band-Stop Filter: The Field Rotation Filter

Abstract: A study has been made of the propagation of the first-order modes in a structure obtained by placing a thin magnetized ferrite slab against a broad wall of a rectangular waveguide. The numerical solution of the characteristic equation shows that, with a suitable choice of parameters, it is possible to realize an electrically tunable band-stop filter. An experimental investigation carried out on a component constructed in this way has given results in full agreement with the theoretical analysis and has allowed an estimate to be made of the influence of the parameters on the selectivity characteristics and tunability of the filter.

Divergent filter system

Abstract: An electrical, easily microminiaturized filter system which exhibits a very steep rolloff, substantially rectangular response by obtaining the divergence or algebraic summation between the positively half-wave rectified response of a band-pass filter and the negatively half-wave rectified response of a band reject filter, both band filters having the same center frequency and bandwidth. Also provided is a synthesizer, including an emitter coupled monostable multivibrator, which is input bias controlled and output modulated to further enhance filter system response rectangularity through the controlled production of low amplitude narrow pulses in the region of rolloff and high amplitude broad pulses at the center of the band.

The Values of the Parameters of a Distributed RC Null Network

Abstract: Distributed RC notch filter normalized constants for dominant and nondominant transmission zero

Polylithic crystal bandpass filter having attenuation pole frequencies in the lower stopband

Abstract: A bandpass crystal filter of the type which uses coupled resonators and has a shunt capacitor at the junction between pairs of coupled resonators exhibits a stopband loss-frequency characteristic which is approximately symmetrical and monotonic In some applications, it is necessary to sharpen up at least one side of the filter and this extra loss could be obtained if one or more frequencies of infinite loss could be added in the adjacent stopband By connecting the parallel combination of a capacitor and a two-terminal quartz resonator across the junction between pairs of coupled resonators, the loss-frequency characteristic may be modified to include frequencies of infinite loss in the lower stopband

Simple notch filter using a negative-impedance convertor

Abstract: A simple easily designed notch filter is presented, which is a single RC ladder section, in association with a negative-impedance convertor. The sharpness of rejection obtained is not affected by loading.

Improved self-tuning filter for low frequencies

Abstract: An improved method for introducing self-tuning features in an active filter for detection of weak signals in a noisy background is described. The filter, which works at low frequencies (100Hz-10kHz), is provided with facilities for search and tracking. During an experiment, the filter was able to detect a sinusoidal signal of 1mV r.m.s. in a 10kHz-bandwidth background noise of 3mV r.m.s.

Carrier supply for multiplex communication system

Abstract: A carrier frequency supply including frequency dividers serves to receive a master frequency and form low frequency pulses having a high harmonic content. Filter means receive said pulses and filter out unwanted frequencies including the fundamental. The output of the filter is applied to a single harmonic amplifier which amplifies the harmonic frequencies and supplies the same to individual filters, each of which selects a carrier frequency from the harmonic frequencies.

A Nonadaptive Processing of Radar Pulse Trains for Clutter Rejection

Abstract: The problem of detecting coherent pulse trains with uniform amplitude in a clutter-plus-noise environment is considered. A radar processor for detecting targets moving radially with respect to the clutter is proposed. The minimum interpulse spacing of the transmitted signal is assumed long enough that returns are not received simultaneously from different ranges within a region of extended clutter, and the central frequency of the clutter power spectrum is postulated to be known. The processor is singled out as the linear filter, orthogonal to the clutter central frequency component, which yields the maximum ratio of peak signal power to average noise power. The filter can be implemented by slightly modifying the structure of the conventional matched filter. The performance of such a filter is compared with that achievable if full a priori knowledge of the input interference were available and with that of the conventional matched filter. This comparison is made on a signal-to-interference power ratio basis after assuming a transmitted signal consisting of equally spaced pulses and an interference characterized by an exponential covariance matrix.

Range-gated doppler filter

Abstract: A range-gated doppler filter having a balanced input switch with cancelling feedback supplied to the switch from a following lowpass filter section