Showing papers on "Band-stop filter published in 1971"

Phase-Only Complex-Valued Spatial Filter*

Abstract: A new type of phase-only filter is described for wave-front construction, in which both the amplitude and phase information necessary to construct an arbitrary image over a limited field are encoded. It is shown that this phase-only filter can duplicate the performance of an ideal complex-valued spatial filter (a filter that controls both amplitude and phase transmittance). This phase-only filter controls the amplitude transmittance by the use of a modulated high-frequency phase carrier that diffracts a controlled amount of light into the image. This type of filter is particularly useful in the implementation of computational wave-front construction, because the maximum spatial frequency that must be plotted is associated with the image and not the carrier. The performance of the filter is examined both numerically and experimentally.

Selection and processing system for signals, including frequency discriminator

Abstract: A signal selection and processing system for use with a broadband LORAN receiver in which the average of the strongest interfering signal having a predetermined duty cycle sets the AGC level and, via a special frequency discriminator, controls the frequency of a voltage controlled oscillator (VCO). The VCO output is used to shift the entire band of input frequencies so that said strongest signals fall into the attenuating notch of a notch filter while passing the other signals to the LORAN receiver.

Optical notch filter

Abstract: An optical filter system capable of transmitting light at substantially all wavelengths of incident radiation while simultaneously rejecting radiation at a single wavelength band or plurality of wavelength bands within the incident radiation is described. The system employs optically negative liquid crystal films which are the same in intrinsic rotatory sense and means for converting circularly polarized light of one sense, e.g., right handed, to circularly polarized light of the opposite sense, e.g., left handed.

Variable bandpass dynamic noise filter

Abstract: A variable bandpass filter for a dynamic noise filtering effect that reduces the perceptible noise in an audio reproduction system. The variable bandpass filter responds to peak signal levels in relatively high and relatively low frequency portions of the audio spectrum to automatically and independently vary high and low frequency cutoff points for the filter in correspondence with the level of signals at those frequencies. Low distortion and wide dynamic range is achieved in a filter configuration which comprises a forward signal path and a reverse signal path, each having a variable integration response provided by temperature compensated and linearized field-effect transistor circuits. The integration response of the two paths imparts a high and low frequency filtering effect. A further constant gain feedback path establishes a uniform middle frequency amplification for the variable bandpass filter.

Automatic tuning electric wave filter

Abstract: A band pass filter for use in RF transmitting or receiving apparatus comprises a plurality of resonant stages coupled through variable apertures whose areas are dependent on the tuning adjustment of the resonant stages whereby a substantially constant bandwidth and insertion loss are achieved over the tuning range. Tuning is effected by a servomechanism responsive to the conditions of phase and signal level at the input and output ports of the filter. The phase and signal level are sensed through directional couplers at the input and output ports of the filter. The couplers at the filter input and output act as matching sections, thereby minimizing losses.

Optimum digital filtering and inverse filtering in the frequency domain

Abstract: Two distinct filters are developed in the frequency domain which represent an attempt to increase the resolution of fine structure contained in the signal whilst keeping the expected filtered noise energy within reasonable bounds. A parameter termed the White Noise Amplification is defined and used together with a measure of the deconvolved pulse width in order to provide a more complete characterisation of the filters. Each of the two main types of frequency domain filters discussed varies in properties with respect to a single adjustable parameter. This may be contrasted with a time domain Wiener filter which in general has three variables: length, delay and an adjustable noise parameter or weight. The direct frequency domain analogue of the Wiener filter is termed a gamma-Fourier filter, and is shown to have properties which span the range from those of a spiking filter with zero least square error at one extreme, to those of a matched filter at the other extreme of its variable parameter's range. The second type of filter considered—termed the modulated Gaussian filter—is similarly shown to be a perfect spiking filter at one extreme of its parameter range, but adopts the properties of an output energy filter at the other extreme.

Effects of dielectric losses on the performance of evaporated thin-film distributed RC notch filters

Abstract: The effects of dielectric dissipation have been included in studies of distributed RC notch filter networks, and it is shown that these may have considerable influence on the magnitude of the optimum notch parameter /spl alpha//SUB 0,1/ and the location of the lowest order optimum notch frequency /spl omega//SUB 0,1/. Voltage transfer function relationships, incorporating a frequency-dependence dissipation factor B(/spl omega/), are given for uniform and exponentially tapered structures. The measured transfer responses of aluminium-silicon monoxide-nichrome evaporated thin-film notch structures were in good agreement with these values predicted. Uniformly distributed RC notch filters exhibited optimum notch attenuations of 71 dB, while exponentially tapered RC filters with taper D=+1 gave 62-dB optimum notch attenuation together with reduced rejection band width.

Coupled bandstop/bandpass filter

Abstract: This disclosure includes a four pole bandstop filter coupled to a five pole bandpass filter tuned to an adjacent band to achieve a very steep attenuation curve between the two bands and an increased bandstop width.

Apparatus for elimination of interference from video signals

Abstract: Apparatus is described for eliminating interferences in the video signals in video telephony or in other applications where the image receiving tube at the transmitter has a short storage time. A filter circuit is described for accomplishing the elimination of such interference, and this filter circuit is preferably placed at the transmission end of the video telephone circuit. The filter basically comprises a series arrangement of a logarithmic amplifier, a band elimination filter tuned to double the power frequency, a limiter and a exponential amplifier. The video signal is clamped to the black level prior to being coupled to the aforementioned filter arrangement. After the signal has been so filtered, the necessary picture gating, line gating and synchronizing signals may be added, as necessary. Other arrangements are described in which the interference frequency is branched off from the main circuit to be mixed with the disturbed video signal. This branching may be accomplished either electrically or optically.

Automatic Photoelastimeter for Determining Very Small Dilatations

Abstract: A sensitivity of 0.03-mμ birefringence is achieved by the introduction of a plastic disk (~6-mμ birefringence) rotated at 30 Hz to modulate the birefringence at 60 Hz and a suitable detector. Two components are found in the detector signal: the one (120 Hz) that depends on the modulator birefringence is rejected; the other (60 Hz) which depends linearly on the compensator birefringence and changes phase at extinction is utilized. An A.E.I. BTH compact mercury arc (with interference filter for 546 mμ) operated on dc is the light source; a photomultiplier 1P21 is the detector. The signal is first fed into a parallel T notch filter which reduces the 120-Hz component five-hundred-fold and then into a three-stage narrow-band (5-Hz) active filter (utilizing three integrated-circuit operational amplifiers) that provides possible gain of 151 dB for the 60-Hz component. To obviate tedious manual setting of the compensator for the required traverse of the specimen, a 60-Hz servo motor is linked to the tangent screw of the analyzer and operated by a power amplifier for the active filter-output signal. Potentiometers on the specimen-translation screw and on the analyzer tangent screw permit the data to be plotted on an x-y For vitreous silica specimens 1 cm deep, 3 mm wide, irradiated with electrons of 1-mm range recorder. (0.6 MeV), the effect of a radiation-induced dilatation as small as 3 × 10−8 can be observed, equivalent to inserting an atomic sheet into a 1-cm long specimen. Alternatively, 1% dilatation of a surface layer 30 A thick can be detected.

Electrical filter circuit

Abstract: The present electrical filter circuit has a plurality of filter paths connected in parallel to each other between an input and an output. At the input side of each path there is arranged a bandpass filter which is then followed by logic circuit and bypass means interconnected in such a manner that only one path at a time is closed to the exclusion of all other paths in response to the signal level at the output of the respective bandpass filter means.

Leakage filter for frequency modulated continuous wave doppler radar system

Abstract: A leakage filter for a frequency modulated continuous wave Doppler radar system is provided. The leakage filter of the present invention replaces, with a single capacitor in each channel and with a receiver blanking switch, the complex leakage filter which has been used in the prior art systems of this general type. The typical prior art filter includes, for example, a capacitor bank in each channel and a complicated switch driver. In the leakage filter of the present invention, a single capacitor in each channel is charged at the beginning of every transition, and the receiver is blanked by the aforesaid receiver blanking switch during each charging interval, as will be described.

Band pass filter with transmission line section

Abstract: A filter circuit formed of inductive and capacitive elements and arranged to pass a predetermined band of frequencies A transmission line section having a length equal to one-fourth of the wave length of a predetermined frequency above the pass band is connected either at the filter input, the filter output, or at each end of the filter to provide high attenuation at the predetermined frequency

Acousto-optic filter having electrically variable resolution

Abstract: The optical bandpass or band reject of an acousto-optic filter is tailored in width and amplitude by tailoring the width and amplitude of a band of radio frequency acoustic waves excited in the photoelastic birefringent filter medium and on which the light beam is collinearly diffracted to produce the output light beam of the acousto-optic filter.

Dual input distributed RC notch filter

Abstract: It is shown that by using the dual-input technique in the bridged distributed RC notch filter, one can (i) obtain some amount of flexibility in the choice of the bridging capacitor, or (ii) compensate for a deviation of the bridging capacitor from the design value, or (iii) obtain a low pass filter with sharper cutoff than is possible with the distributed RC network alone.

Rc active filter apparatus

Abstract: A complex filter or filter section using an amplifier with a plurality of feedback loops which may be used for bandpass filtration or for filters requiring complex transmission zeros.

Low-pass non-linear filter

Abstract: A non-linear filter for high and low frequency signals comprises means for separating and dissipating the high frequency out-ofband energy and passing the low frequency 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. 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.

Effect of inductance on characteristics of a distributed RC notch filter

Abstract: A small notch inductance L n in a distributed RC notch filter can drastically shift the location of the optimum notch frequency. Experiments on an A1-Y 2 O 3 - NiCr evaporated thin-film filter yielded a shift of -32 percent in optimum notch frequency by the addition of L n =0.9 µH, in agreement with predictions.

Digital filter arrangement which alternatively filters two signals differing in frequency

Abstract: A plurality of telephone lines which convey frequency-shift signals and a corresponding plurality of data machines, which send and receive do baseband data are interconnected via a time-shared digital (filter) circuit receiver and digital circuit modulator under the supervision of a common central processor. A low-pass digital filter is arranged to filter the incoming signals to detect ringing or, alternatively, to filter the sum of the signaling frequencies to detect carrier. To detect the low frequency ringing, the response of the filter is modified by limiting the rate at which the input signals are applied thereto and by "holding" the processed signals in the filter for the prolonged interval between the input signal applications.

Transmission-line graphical analysis of a distributed RC notch filter

Abstract: A simple method is given for obtaining the optimum notch conditions for a uniformly distributed RC filter. It is also shown that the transmission-line analysis can readily be extended beyond the conventional open-circuit voltage transfer function condition.

Pseudonoise echo ranging system with improved range resolution without increase of transmitted code word repetition frequency

Abstract: An echo ranging system comprising a code generator, the output of the code generator is used to bi-phase modulate a carrier frequency signal. The modulated signal is then transmitted towards a target from a system antenna. A return echo signal is delayed with respect to the transmitted signal by the effective target range. Further, the output of the code generator is delayed so as to be phase aligned with the transmitter leakage or spillover signal at a mixer. The code on the leakage signal is then removed and the carrier is attenuated in a notch filter. The coded echo signal is not reconstituted since it is not in time synchronization and is coded a second time at the mixer. With a round trip range equivalent to a half word code period, the doubly coded echo will appear as if it were generated by an oscillator at twice the frequency. The twice frequency coded echo signal then passes through the notch filter virtually uneffected and is coupled to a second receiver demodulator. The second input to the demodulator is the code originally generated but at a frequency twice that of the original coder clock frequency. The higher frequency coded echo is then demodulated.

Radio-frequency band-pass filter wherein magic-tee arms are coupled to cavities and resonators

Abstract: A radiofrequency band-pass filter having a flat amplitude response and a substantially constant group delay characteristic in the passband, these being obtained by the integrated combination of a magic-tee terminated with reflecting cavities, and input and output transmission resonators, the integration of the components being essential to achievement of the above characteristics. For the same complexity this filter has a higher stop-band attenuation and smaller midband insertion loss than a conventional nonintegrated filter/phase-equalizer combination.

Combined contiguous filter and acceleration and velocity analyzer for radar

Abstract: A single filter to replace a set of parallel filters in an O-T-H radar coising a prelimiting filter connected to amplifying and limiting means and quenching means for shorting out said prelimiting filter at appropriate times. The prelimiting filter is connected to receive the output of the mixer of one range bin of the velocity-and-acceleration analyzer of the radar and the predetection filter of the analyzer receives the output of the amplifying and limiting means. The quenching means also receives the output of the amplifying and limiting means and provides a quenching signal to the predetection filter.

An improved distributed RC notch filter and its application to an extremely insensitive bandpass amplifier

Abstract: A distributed RC notch filter with an improved frequency selectivity is described. An extremely insensitive bandpass amplifier can be obtained by use of such a filter.

Extraction of signals from noise through Wiener filtering

Abstract: This paper deals with the problem of finding a Wiener filter when the length of the filter output in not larger than the length of the filter input. Measure for the efficiency of a filter is defined in terms of the relation between the desired filter output and the actual filter output. This measure, called the filter efficiency, is used to find the optimum length of the filter memory function. The relation between the signal-to-noise-ratio (SNR) of the filter input and the SNR of the filter output is discussed. It is shown that there is always some improvement in the SNR through the use of a Wiener filter.

Theory and performance of N-path filters

Abstract: : The paper has five major sections. In the first, the periodic time varying network with N-identical paths operating between modulators is examined theoretically by the use of Laplace transforms. The transfer function is derived generally and then expanded for sinusoidal and rectangular modulation. In both cases the low-pass to band-pass characteristic is retained assuming low- pass elements in each path. The next section investigates theoretically, the effects of using other than low-pass elements in the N-paths. The results are such that, if a high-pass, first order all-pass, or a simple band-pass are used in the N-paths the resultant transfer function became a variable attenuator, a notch filter or a pair of adjacent band-pass filters respectively. The third major area is that of switching variations. A more practically oriented configuration is introduced, its transfer function variations are determined and then parallel switching is discussed. In the last sections, the real world tolerances and other variations of the components are accounted for in the transfer function of the N-path filter and their effects are noted in five disturbance categories, most serious of which are the variations in the modulating waveforms. Then finally there is a detailed implementation of an N-path filter for use in an IF of an AM/FM receiver which was introduced earlier in the literature. This application makes use of electronic bandwidth and frequency variations.

Filter and substitute for resonant reed relay

Abstract: A monostable multivibrator is connected to a differential amplifier to perform the following functions: signal limiter, band-pass filter, low-pass filter, high-pass filter and frequency modulation detector.

An RC all-pass filter†

Abstract: An RC all-pass network with a differential input amplifier and a notch filter is described It is also shown that an appropriate choice of the notch network can introduce certain advantages in the derived network