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Showing papers on "Band-stop filter published in 1973"


Patent
24 Sep 1973
TL;DR: In this paper, a pair of pressure transducers, one having a high response capability and the other a low response capability, are positioned in a turbofan or turbojet engine flow passage.
Abstract: A pair of pressure transducers, one having a high response capability and the other a low response capability, are positioned in a turbofan or turbojet engine flow passage. The output from the high response transducer is passed through a notch filter to isolate the frequencies of interest. The output from the low response transducer is passed through a low pass filter to provide the absolute steady-state pressure level. The ratio of the high frequency pressure signal within the frequency range of interest to the steady-state pressure signal is calculated and compared to a reference ratio signal. If the calculated pressure ratio signal exceeds the reference ratio signal, the engine is approaching a surge condition, and a warning signal is generated which can be used for rescheduling of the engine away from stall. The apparatus may be used both to anticipate surge and to sense the actual occurrence of a surge condition. The invention herein described was made in the course of or under a contract with the Department of the Air Force.

43 citations


Patent
15 Nov 1973
TL;DR: In this paper, a 2-stage Biquad notch filter was modified by adding an inverter at the input to each stage and by replacing certain of the Biquads resistors with a set of resistors in the filter circuit.
Abstract: The present invention modifies a 2-stage Biquad notch filter by adding an inverter at the input to each stage and by replacing certain of the Biquad resistors with a set of resistors in the filter circuit. The notch width, notch depth, and notch center frequency of this modified Biquad filter may now be varied independently among a set of discrete values.

30 citations


Patent
04 Jun 1973
TL;DR: In this article, a stable tunable Q bandpass filter adapted to have its parameters dynamically varied over a wide range of bandwidths and center frequencies is presented. But the performance characteristics of this filter are in part attained by the component layout and shielding techniques used, in addition to the method of circuit excitation.
Abstract: A stable tunable Q bandpass filter adapted to have its parameters dynamically varied over a wide range of bandwidths and center frequencies. The filter includes a capacitor and a network coupled in parallel across the capacitor. The network includes a plurality of operational amplifiers coupled to simulate an inductor without utilizing coils. A feature of the filter is that it can be readily made adaptive to track an input signal which may randomly vary in frequency. A further feature of the invention is to have one input of each operational amplifier coupled directly to ground to minimize stray capacitance. The performance characteristics of this filter are in part attained by the method of component layout and shielding techniques used, in addition to the method of circuit excitation.

29 citations


Patent
28 Mar 1973
TL;DR: In this paper, the authors proposed a selective video suppression scheme, which consists of a band elimination, notch filter tuned to the spectrum of a video signal to selectively suppress the video signal.
Abstract: Selective video suppression apparatus, operative on a persubscriber basis, comprises a band elimination, notch filter tuned to the spectrum of a video signal to be selectively inhibited. The filter exhibits relatively little attenuation, having only a de minimus effect per se on signal reception. However, in accordance with the principles of the present invention, filter attenuation is modulated at a rate exceeding the response capacity of a television receiver automatic gain control circuit. The resulting amplitude modulated signal reaching the television receiver is essentially unrecoverable, obviating receiver synchronization, color subcarrier recovery, and generally inhibiting video reception.

26 citations


Journal ArticleDOI
TL;DR: A canonic circuit, using the second generation current conveyor is described for realizing an all-pass or a notch characteristics.
Abstract: A canonic circuit, using the second generation current conveyor is described for realizing an all-pass or a notch characteristics.

21 citations


Patent
01 Jun 1973
TL;DR: In this article, a single sideband system for digitally processing a given number of analog channel signals, provided with a digital filter to which filter coefficients are applied, which characterized a lowpass filter having a cut-off frequency which was equal to half the bandwidth of the channel signals.
Abstract: A single sideband system for digitally processing a given number of analog channel signals, provided with: a digital filter to which filter coefficients are applied which characterized a lowpass filter having a cut-off frequency which is equal to half the bandwidth of the channel signals; a fast fourier transformer to which a number of carrier signal functions is applied, which number is at least equal to twice the number of channel signals and each of which represents a carrier frequency, each frequency being an even multiple of the cut-off frequency of the lowpass filter.

21 citations


Journal ArticleDOI
TL;DR: It is shown how an E -filter can be designed to filter out superimposed "noise" on a signal, leaving the large peaks of the signal unattenuated.
Abstract: A new type of nonlinear filter, called the E -filter, is introduced that involves a transformation of the independent variable of the input function. It is shown how an E -filter can be designed to filter out superimposed "noise" on a signal, leaving the large peaks of the signal unattenuated. Unlike a Iow-pass linear filter, the low-pass E -filter is almost frequency independent and so does not affect the amplitudes of large sharp peaks of the signal. It is shown that the E -filter can be realized in real time and that a wide class of E -filters have a filtering action which is independent of the dc level of the input signal.

15 citations


Patent
07 Dec 1973
TL;DR: In this article, a voltage controlled nonlinear filter for high and low frequency signals comprises means for separating and dissipating the high frequency out-ofband energy and passing the low freqeuncy in-band energy.
Abstract: A voltage controlled non-linear filter for high and low frequency signals comprises means for separating and dissipating the high frequency out-of-band energy and passing the low freqeuncy in-band energy. The filtering in a low-pass filter is achieved without phase shift both in- and out-of-band by use of conjugate high- and low-pass filters located before and after the dissipating means, respectively. A hard clipper is used to perform the dissipating function, and its reference clipping level is provided so that the maximum amplitude of the in-band signal arriving at the input to the clipper is slightly less than the clipping level. The output of the low-pass filter may be fed back to set the clipping level so that this level can track the in-band signal amplitude. The clipping level may also be controlled by a bias control voltage. A sensing resistor between the clipper and the means to set the clipping level senses the high frequency information and thus, the non-linear filter can serve as a high-pass filter with no phase shift when only the low-pass filter is used after the dissipating means.

15 citations


Patent
13 Jul 1973
TL;DR: A high-Q active notch filter includes only one operational amplifier employing resistive positive feedback and reactive negative feedback as mentioned in this paper, which can be selectively changed to convert the notch filter to an oscillator operating at the notch frequency.
Abstract: A high-Q active notch filter includes only one operational amplifier employing resistive positive feedback and reactive negative feedback. The positive feedback resistance can be selectively changed to convert the notch filter to an oscillator operating at the notch frequency.

11 citations


Patent
Gittinger N1
02 Jan 1973
TL;DR: In this article, a hybrid filter having the characteristics of a hybrid coupler and band pass and band stop filters combined is proposed, which provides a band pass port and a band stop port to which a number of frequency filters are connected.
Abstract: A hybrid filter having the characteristics of a hybrid coupler and band pass and band stop filters combined. The hybrid filter provides a band pass port and a band stop port to which a number of frequency filters are connected. A predetermined frequency range of a spectrum of frequencies applied to the hybrid filter is isolated and confined to the band pass port. The frequencies other than the band pass frequency range are transmitted to the band stop port. The hybrid filter provides a constant impedance at all frequencies by employing reactive elements of critical values. A high attenuation exists at all frequencies between the band pass and band stop ports.

10 citations


Patent
13 Dec 1973
TL;DR: In this article, a bridged-T construction is used for a pair of semiconductor rectifiers in back-to-back relationship, and an oscillation voltage is applied to the junction of the rectifiers to vary their reverse biases and the junction capacities.
Abstract: The filter is of a bridged-T construction, and includes a pair of semiconductor rectifiers in back-to-back relationship. An oscillation voltage is applied to the junction of the rectifiers to vary their reverse biases and the junction capacities they exhibit. The variations in notch frequency which result are selected to overlap possible drift in filter tuning and provide continued signal rejection in the presence of such changes.

Journal ArticleDOI
TL;DR: It is shown in this paper that a multimode waveguide-represented by a ray model-acts like a low-pass filter with respect to the modulation.
Abstract: It is shown in this paper that a multimode waveguide-represented by a ray model-acts like a low-pass filter with respect to the modulation. The response function is calculated and discussed in the case of an ideal, straightlined, loss-free system.

Patent
29 Oct 1973
TL;DR: In this article, a carrier-suppressed amplifier demodulator employing a four-quadrant multiplier was proposed, in which all of the signal generated sidebands of the carrier and the carrier frequency were multiplied times the carrier center frequency by the multiplier.
Abstract: A carrier-suppressed amplifier demodulator employing a fourquadrant multiplier in such a fashion that all of the signal generated sidebands of the carrier and the carrier frequency are multiplied times the carrier center frequency by the multiplier. A notch filter coupled to the output of the multiplier is tuned to twice the carrier center frequency and removes the multiplier doubled carrier center frequency, leaving only the signal which generated the carrier sidebands. This produces an output signal which has improved transient response and low carrier frequency ripple.

Patent
19 Nov 1973
TL;DR: In this article, an intrusion alarm system for providing an alarm indication in response to the detection of an intruder within a protected area includes Doppler radar apparatus having a transmitter for radiating energy into the protected area, a receiver for receiving DoP signals provided whenever radiated energy is reflected off a moving body within the protected areas and a signal detecting and filter circuit having a level detector circuit and a low pass digital filter circuit responsive to DoP signal in excess of a predetermined amplitude and frequency.
Abstract: An intrusion alarm system for providing an alarm indication in response to the detection of an intruder within a protected area includes Doppler radar apparatus having a transmitter for radiating energy into the protected area, a receiver for receiving Doppler signals provided whenever radiated energy is reflected off a moving body within the protected area and a signal detecting and filter circuit having a level detector circuit and a low pass digital filter circuit responsive to Doppler signals in excess of a predetermined amplitude and frequency to provide a logic level output indicative of the detection of an intruder within the protected area. In addition to the low pass digital filter circuit, there are described a high pass digital filter circuit and a digital band pass filter circuit.

Patent
07 Feb 1973
TL;DR: In this paper, a measuring device, such as a weighing scale, emits a direct current voltage signal which is supplied through a filter to a receiver, and the filter suppresses alternating current carried by the voltage signal and thereby introduces a delay in the voltage signals supplied to the receiver.
Abstract: A measuring device, such as a weighing scale emits a direct current voltage signal which is supplied through a filter to a receiver. The filter suppresses alternating current carried by the voltage signal and thereby introduces a delay in the voltage signal supplied to the receiver. To speed up the signal, the signal is differentiated and the resulting pulse is employed to close a switch which is in parallel with the filter thereby substantially eliminating the delay caused by the filter.

Patent
Morlec E1
06 Nov 1973
TL;DR: In this article, a multifrequency receiver first detects any frequency combination AiBj corresponding to the frequency combination code which is used, then invalidates that detection or not according to whether the frequency combinations received was mixed with other voice frequencies or not.
Abstract: A multifrequency receiver first detects any frequency combination AiBj corresponding to the frequency combination code which is used, then invalidates that detection or not according to whether the frequency combination received was mixed with other voice frequencies or not. At the rest state, the input signals are applied to both an A-band-pass filter and a B-band-pass filter, which are respectively followed by two limiters then by two sets of selective filters tuned on the particular code frequencies A1 to A4 and B1 to B3. As soon as a possibly valid frequency combination AiBj is detected, a band stop filter rejecting only frequencies of bands A and B is connected to the receiver input and possible noise sources are disconnected from the receiver input. The output signals from the A-band-pass filter and the band stop filter are added and the resulting signals enter the first limiter. Similarly, the output signals from the B-band-pass filter and the band stop filter are added and the resulting signals enter the second limiter. If the previously detected frequency combination was pure, the selective filter will detect it again and the first detection is validated. If not, the energy of signals Ai and Bj at the limiter outputs will not be high enough to activate the selective filters and the detection is not confirmed.

Journal ArticleDOI
TL;DR: In this article, a new structure for realizing an all-pass transfer function is given, where two special circuits using a minimum number of capacitors are derived from the general configuration, both are capable of realizing complex poles
Abstract: A new structure for realizing an all-pass transfer function is given here. By adjusting one resistor the same configuration can realize a notch filter. Two special circuits using a minimum number of capacitors are derived from the general configuration, both are capable of realizing complex poles

Proceedings ArticleDOI
K. G. Plass1
01 Oct 1973

Patent
Langan M1
04 Sep 1973
TL;DR: In this paper, a combination involving a limiter, a first active high pass filter, and a level detector in cascade is presented, paralleled by an arrangement of second active high-pass filter and inhibit circuit in cascade.
Abstract: There is herein disclosed a combination involving a limiter, a first active high pass filter, and a level detector in cascade. The first high pass filter is paralleled by an arrangement of second active high pass filter and inhibit circuit in cascade. The first filter accepts frequencies above a first cut-off point and the second filter accepts frequencies above a higher cut-off point and the output of the inhibitor is used to inhibit the output of the first filter. The result is a band pass detector which responds to frequencies within the range defined by the cut-offs.

Patent
Bucherl E1
20 Aug 1973
TL;DR: In this article, an electrical filter with a Nyquist flank characteristic is provided for generating a vestigial sideband characterized in that two identical exact separating filters are connected in cascade in such a way that the output of one filter section in the first separating filter is connected to the input of the second separating filter, and in which a signal injected at the input passes through two filter sections having the same attenuation characteristics.
Abstract: An electrical filter with a Nyquist flank characteristic is provided for generating a vestigial side-band characterized in that two identical exact separating filters are connected in cascade in such a way that the output of one filter section in the first separating filter is connected to the input of the second separating filter, and in which a signal injected at the input passes through two filter sections having the same attenuation characteristics, and in that two of the filter sections of the separating filters are terminated in identical ohmic resistances, and in that the characteristic functions assigned to the filter sections are self-reciprocal functions.

Patent
03 Apr 1973
TL;DR: In this paper, a reference signal is applied to the input of the filter and examined for phase shift at the low-pass signal output of the filtering process, and a signal proportional to the variation in phase of the reference signal was used to alter a voltage controlled resistor, which in turn varies the pole frequency of the filters.
Abstract: In an active RC filter exhibiting a predetermined signal transfer characteristic, a reference signal is applied to the input of the filter and examined for phase shift at the low-pass signal output of the filter. A signal proportional to the variation in phase of the reference signal is used to alter a voltage controlled resistor, which in turn varies the pole frequency of the filter. The reference signal is cancelled from the signal appearing at the bandpass output of the filter to remove it from the final desired output of the filter.

Journal ArticleDOI
01 Aug 1973
TL;DR: In this paper, the effect of the shunt resistor in the distributed RC notch filter networks is investigated, and it is shown that the distributed capacitance associated with the SHunt resistor can drastically shift the location of the optimum notch frequency.
Abstract: The effect of the distributed nature of the shunt resistor in the distributed RC notch filter networks is investigated, and it is shown that the distributed capacitance associated with the shunt resistor can drastically shift the location of the optimum notch frequency.

Patent
Heinz Krause1
27 Mar 1973
TL;DR: In this paper, a network consisting of an all-pass circuit consisting of two equal frequency separating networks whose partial filters have even characteristic functions reciprocal to one another of the degree 2n (n=1, 2, 3... ) and in which between each two equal partial filters there are connected four-pole circuits which are dimensioned in such a way that the electrical properties of the entire network, except for one additional phase, agree with the prescribed electrical properties.
Abstract: A network consisting of an all-pass circuit which consists of two equal frequency separating networks whose partial filters have even characteristic functions reciprocal to one another of the degree 2n (n=1, 2, 3 . . . ) and in which between each two equal partial filters there are connected four-pole circuits which are dimensioned in such a way that the electrical properties of the entire network, except for one additional phase, agree with the prescribed electrical properties of the interposed four-pole circuits. The interposed four-pole circuits are constructed with respect to their transmission properties as equal all-pass or low-pass sections of which the one lying in the band-pass or low-pass path, is rendered a band stop circuit by quartz elements.

Patent
19 Jul 1973
TL;DR: In this article, the authors describe a system consisting of a Gunn oscillator, transmitting and receiving antennas, and a mixer circuit, where the signal from the mixer circuit passes by way of a filter circuit and integrator to an output alarm circuit.
Abstract: The system is of the type that comprises a Gunn oscillator, transmitting and receiving antennas, and a mixer circuit. If there is intruder motion the doppler signal from the mixer circuit passes by way of a filter circuit and integrator to an output alarm circuit. In one embodiment the filter circuit is a notch filter that exhibits infinite attenuation above a predetermined frequency, such as 120 hertz, while passing lower intruder frequency signals. The system is also provided with novel supervisory alarm circuitry.


Journal ArticleDOI
TL;DR: In this article, it was shown that if a bandpass filter is obtained from a prototype low-pass filter by the usual lowpass to bandpass transformation, the white-noise margin and the (1/f)^2 noise margin of the resulting filter will be identical to the white noise margin.
Abstract: It is shown that if a bandpass filter is obtained from a prototype low-pass filter by the usual low-pass to bandpass transformation, the white-noise margin and the (1/f)^2 noise margin of the resulting filter will be identical to the white-noise margin of the prototype low-pass filter. A method for using this general result for evaluating some types of integrals that arise in noise calculations is indicated.

Journal ArticleDOI
TL;DR: In this article, a new performance criterion for comparing high-pass filters (HPF's) is proposed; namely, E, the unit-step-response energy, which is the energy of the envelope response to the center frequency amplitudemodulated by a step function.
Abstract: A new performance criterion for comparing high-pass filters (HPF's) is proposed; namely, E , the unit-step-response energy. Increased interest in narrow-bandwidth notch filters with minimum energy of the envelope response to the center frequency amplitudemodulated by a step function prompted this choice, for this envelope energy is proportional to E of the equivalent HPF. Initially, it is shown that E is identical to the prototype low-pass filter (LPF) impulse-response energy, thus relating the transient characteristics of the two filters. It is further shown that the so-called "unknown energy" referred to in the literature is actually E . A new expression is derived for the step-response energy of a lossless passive singly terminated network, whose input impedance is minimum reactance. This formula simplifies for HPF's so that E is easily computed and then plotted for well-known responses. The noise bandwidth of an LPF is shown to be proportional to E ; thus the curves for E also yield the noise bandwidths. This consolidates much of the scattered information on this subject. It is then established that of all second-order systems, the Chebyshev filters possess the lowest value of E ; in fact, the energy decreases as the passband ripple increases.

Journal ArticleDOI
TL;DR: In this paper, a frequency-locked RC active ladder filter is proposed, which is used as a frequency discriminator by using two of the filter branch voltages to generate a control voltage, which can then be used to tune or frequency-scale the ladder filter transfer function to lock the filter to the frequency of the control tone.
Abstract: A frequency-locked RC active ladder filter is described, which is frequency-locked to a sinusoidal control tone. The tunable ladder filter is used as a frequency discriminator by using two of the filter branch voltages to generate a control voltage. The control voltage is then used to tune or frequency-scale the ladder filter transfer function to lock the filter to the frequency of the control tone. A simple linear frequency-signal control system is developed to describe the frequency-locked performance of the adaptive filter. The frequency-locked filter can be designed so that the sinusoidal control tone is rejected at the filter output, making it possible to adapt the filter transfer function during transmission of a message. A practical frequency-locked filter is given in which a frequency-locked third order elliptic lowpass filter is designed. The performance of the practical filter is analysed using a simple linear control system model.

ReportDOI
06 Mar 1973
TL;DR: In this paper, the authors present the general theory and evaluation of a commutative filter, in which presentation the effects of 'leaky' capacitors and load resistance are considered.
Abstract: : A commutative filter is a bandpass filter capable of very high Q's, large range of resonant frequency (0 to 2 megahertz that can be electronically tuned), comb-filter frequency response, small bandwidth (independent of resonant frequency), and extremely small size (can be constructed of integrated circuits since no inductors are required). The purpose is to present the general theory and evaluation of a commutative filter, in which presentation the effects of 'leaky' capacitors and load resistance are considered. An eight-channel filter is built, and laboratory and theoretical results are compared for the transfer function, bandwidth, quality factor, and sensitivity of the commutative filter. The commutative filter is also investigated from the viewpoint of enhancement of signal-to-noise ratio.