Showing papers on "Frequency band published in 1971"

Design of a New Broad-Band Isolator

Abstract: The design theory and experimental results of a proposed broad-band technique of an isolator are presented. The isolator not only has a broad-band backward loss but also a low broad-band insertion loss. The network constants and the performance are obtained in connection with the magnetic loss of ferrite, and they are confirmed by experimental data. The trial ultrawide-band isolator the performance of 20-dB isolation over the frequency band from 70 MHz to 800 MHz.

Flame detector and electrical detection circuit

Abstract: A PHOTOELECTRIC PROVIDES SIGNALS RESPONSIVE TO A FLAME, THE SIGNALS ARE APPLIED TO FREQUENCY SELECTIVE AMPLIFIERS, HAVING THEIR FREQUENCY RANGES OF AMPLIFICATION SO SET THAT THE LOWER LIMIT OF THE FREQUENCY BAND OF ONE AMPLIFIER IS NOT MORE THAN TWICE THE FREQUENCY OF THE UPPER LIMIT OF THE ORDER AMPLIFIER, PREFERABLY EACH WITH FREQUENCY BAND WIDTH IN THE ORDER OF $2, ADJACENTLY LOCATED, SO THAT HARMONICS OF SENSED FREQUENCIES ARE EFFECTIVELY EXCLUDED FROM AMPLIFICATION, WHILE SEPARATE AMPLIFICATION CHANNELS AMPLIFY FREQUENCIES OF DIFFERENT BAND WIDTH. THE OVERALL FREQUENCY BAND WIDTH OF AMPLIFICATION IS PREFERABLY BETWEEN 2 AND 40 HZ.

On the suppression of radiation nulls and broadband impedance matching of rectangular waveguide phased arrays

Abstract: Numerical solutions are obtained for the problem of radiation from an infinite array of rectangular waveguides, each of which is loaded with iris at the array aperture. It is shown that the introduction of aperture irises can remove a radiation null in the active element pattern and significantly improve the array performance over a wide frequency band.

Diversity receiver suitable for large scale integration

Abstract: The cost of a diversity receiver is reduced by providing branch circuits which can be fabricated by large scale integration techniques. To this end nonintegrable filters are eliminated and lead connections are minimized. Filtering is provided by a phase-locked loop which passes only the single frequency band to which it is locked. Channel acquisition is achieved by initially swamping all branches with an unmodulated acquisition signal at a frequency selected to cause all branches to lock on one channel. The acquisition signal, which may be introduced at numerous points, is removed after lock-on in order to permit detection of the intelligence modulation.

Frequency domain approach to automatic testing of control systems

Abstract: The system user must be satisfied that frequency domain data adequately measures the quality of his system in all the performance aspects of interest This involves the interpretation of transfer functions other than system output/input, and the acquisition of data over a wide frequency band ranging from a few percent of bandwidth to several multiples of bandwidth, the latter for the detection of secondary resonances However, only a few spot frequencies need be chosen to ensure that system response to actual operational signals is adequate Careful selection will also maximize the diagnostic potential of the measurements In noisy systems the measurement time for adequate confidence in gain and phase observations must be established before the test routine can be automated

Double octave broadband traveling wave tube

Abstract: An O-type traveling wave tube of the invention includes a slow wave structure having a broad band characteristic over a predetermined range of frequencies and in some cases is capable of broad band operation over a double octave of frequencies. In this the slow wave structure comprises a combination of a substantially nondispersive delay line, such as a helix, with a substantially dispersive delay line, such as a ring loop section. The ring loop sections complement in gain the gain drop off characteristic of the helix at the edges of the frequency band at which the gain from the helix circuit tapers off. In this the overall gain of the traveling wave tube is enhanced and extended over a frequency spectrum greater than that which is available solely with the helix construction.

Method for the synchronization of a transmission path

Abstract: A method for synchronizing apparatus on the receiving side of a time multiplex or code multiplex transmisson system with apparatus on the transmitting side of the system, in particular in a system which operates in accordance with the SSMA technique, with which system the information is transmitted in a broad frequency band compared with the base band occupied by the information wherein a rapid frequency change modulated oscillation is transmitted by the transmitter at the beginning of transmission so that each frequency element is submitted to a digital phase modulation during transmission which is characteristic therefor in such a way that the frequency band which is occupied by this signal corresponds at least approximately to the frequency band which is occupied in a normal case of operation, whereby the carrier to be transmitted is phase shift keyed by a very rapidly clocked code with a long code period. The coding of the combined frequency and phase shift keyed signal transmitted prior to communication may contain fewer elements per code period, so code-phase-synchronization can be acquired more rapidly.

A frequency division multiplex microwave communication system using polarization division multiplex technique

Abstract: A signal transmission and reception system which includes means for transmitting a plurality of information signals each of which occupies a different frequency band. The information signals, which may correspond to television signals, amplitude-modulate a carrier wave to produce single side band components of the modulated carrier wave, each single side band component corresponding to a different information signal. The components are combined into two groups of side band components each group being comprised of side band components corresponding to alternate, adjacent information signal frequency bands. The two composite signals are transmitted by transmitter means which uniquely polarize each composite signal with respect to the other. Receiving means, responsive to each of the polarized signals, detect the composite signals and apply each to a different demodulator. The demodulated signals are combined to reconstruct the information contained in the plurality of transmitted information signals.

A Continuously Variable Dielectric Phase Shifter (Correspondence)

Abstract: A stripline phase shifter is described which yields a linear variable phase shift versus frequency. The phase shift is accomplished by varying the dielectric constant of the medium through which the signal propagates. Characteristic impedance is kept constant at all phase shift settings; hence, in theory, no reflections are produced. Measurements made over the 1 to 2 GHz band show the maximum voltage standing-wave ratio (VSWR) to be 1.15. Measured values of insertion phase shift over the same frequency band show good agreement with theory (maximum difference about 2.5 percent).

Loudspeaker system having bass response range below system resonance

Abstract: The subject patent application is concerned with improvements over prior art systems relative to the processing of the speaker back-wave by acoustic networks that include a part, and the use of the back-wave to produce supporting port radiation in a frequency band below the basic resonance frequency of the system. The structure includes essentially a pair of acoustic cavities, coupled by an aperture. The speaker is mounted in the first cavity. The second cavity may be subdivided and may include damping. A port aperture is included in one of the cavities. The improvements involve relationships between acoustic elements of inertance, capacitance and resistance that result in in-phase port radiation; and in relationships whereby smooth response is obtained while maintaining and improving the phase of port radiation relative to that of the speaker front-wave in the frequency region below system resonance. The present invention concerns only the bass and lower midrange frequencies, and is intended for operation with 6 db/octave amplifier equalization in the bass range.

Theory of an ultra-broad-band optical dielectric waveguide coupler system

Abstract: A technique is described for operating a prism to dielectric thin-film waveguide system over a wide frequency band from a conventional broad-band source of the dye-laser type. The continuous coupling bandwidth can extend, typically, over a frequency range of twice to three times the center frequency. The experimental tolerances have been established and are shown to be within the capability of present-day technology.

Computer Optimization of E-Plane Resonance Isolators

Abstract: A method has been developed to optimize the geometry of the structure and the permittivity of the dielectric material used in E-plane isolators, for an arbitrary ferrite material. The structure is first computer analyzed, using an exact analytical approach. The minimum isolation and the maximum forward attenuation per unit length are calculated within a specified frequency band. The objective function, defined as the ratio minimum isolation per maximum forward losses, is then maximized. Several optimization procedures are compared and tested; the optimum gradient method was found to be well suited to this problem. Various optimized results are presented.

Two-Cavity Ring-Type Channel-Dropping Filters for a Millimeter-Wave Guided Wave Communication System (Correspondence)

Abstract: Newly developed two-cavity ring-type filters for a millmeter-wave communication system are described They are used in a five-channel transmit and receive multiplexer which operates in the 50-GHz frequency band The pulse response and interchannel crosstalk characteristics for 250-Mbit PCM-AM or PCM-PSK transmission were calculated and compared with experimental results

Frequency interference reduction in cable television systems

Abstract: A cable television system includes: A. HEAD END MEANS FOR RECEIVING MULTIPLE CHANNEL PROGRAMMING WITH STANDARD 1.5 MHz spread between adjacent channel picture and sound carriers, and for shifting said bands to provide greater than 1.5 MHz spread therebetween on the distribution cable, B. A CONVERTER HAVING AN INPUT FROM THE CABLE AND AN OUTPUT OPERATIVELY CONNECTIBLE WITH THE TELEVISION RECEIVER, THE FREQUENCY SPREAD BETWEEN ADJACENT CHANNEL PICTURE AND SOUND CARRIERS AT SAID INPUT BEING SUBSTANTIALLY GREATER THAN 1.5 MHz, and C. THE CONVERTER INCLUDING CIRCUIT MEANS FOR SELECTING A DESIRED CHANNEL ON THE CABLE AND CONVERTING THE FREQUENCIES ASSOCIATED WITH THAT CHANNEL TO A PREDETERMINED OUTPUT FREQUENCY BAND.

Earphone with frequency correction

Abstract: Each earphone of a stereo headset comprises an electroacoustic transducer with an audio-frequency signal applied to its input. The electroacoustic transducer is provided with an electric filter connected in series in the current path of the audiofrequency signal and the filter has frequency characteristics which, added to the frequency characteristic of transducer radiation, compensate for frequency attenuation of the high and low end thereof and provide a linear overall radiation characteristic within the assigned frequency band.

Object detection system using electro magnetic waves

Abstract: Objects such as personnel and vehicles are detected when they enter a sensing field produced by an antenna which is excited by oscillators operating in the VHF frequency band by producing cyclic variations in the frequency and in the amplitude of the oscillators exciting signal, which variations are in approximately quadrature phase relationship. The system responds to the correlation between the amplitude and the phase variation so as to produce an alarm indication of both the presence of an intruding object and its direction of movement, either toward or away from sensing the antenna.

Method for recording a pal color television signal

Abstract: In the recording of a PAL color television signal wherein the modulated chrominance subcarrier frequency is shifted by 25 Hz with respect to a frequency having a quarter-line frequency offset with respect to the horizontal sweep frequency and is recorded in this form in a frequency band outside that of the luminance signal, the chrominance subcarrier is so shifted that in its recorded form it retains the 25 Hz shift and quarter-line frequency offset.

Frequency band shifter

Abstract: A frequency band shifter for shifting a selected frequency band in a complex waveform, which frequency band is translated with its relative frequency, phase and amplitude relationships maintained to a reproduced lower frequency and, if desired, to a smaller frequency band for analysis, which translation is processed by manual or digital control with a master local oscillator control clock that provides protection against drift in frequency and phase throughout the system.

Two-port network for signal transmission circuit

Abstract: A dummy transmission line having an attenuation characteristic proportional to square root f over the frequency band of interest is constructed from two uniformly distributed RC networks. The characteristic impedances of both networks are identical and the length of the second network is determined by the lowest frequency of interest in using the networks.

A Wide Band Correlator

Abstract: A wide band correlator based on an orthogonal expansion of the correlation function to be analyzed is described. The resultant correlation function is displayed on an oscilloscope screen in ``live'' time. A frequency band from some kilohertz to 1 MHz can be dealt with only by changing the time constant of analyzing orthogonal filters. Some discussions about truncation error of orthogonal expansions and a treatment for the case of periodic functions are described.

Interference Effects of Pseudo-Random Frequency-Hopping Signals

Abstract: When a pseudo-random frequency-hopping signal is intercepted by a conventional receiver operating within the same frequency band, the interfering signal has the form of a pulse-amplitude modulated signal. Each pulse amplitude is dependent upon the hopping frequency and the selectivity characteristic of the victim receiver. The probability density function for the interfering pulse amplitude prior to demodulation is determined when the probability density function for the hopping frequency is uniform and the victim-receiver characteristic is 1) ideal flat bandpass, 2) single tuned, and 3) Gaussian shaped. It is shown that the average interfering pulse amplitude and interference power decrease as the frequency-hopping bandwidth increases with respect to the victim-receiver bandwidth. Fast Fourier transform computer techniques are used to obtain the probability density function of the interference amplitude in a Gaussian receiver when several (from 2 to 10) pseudo-random frequency-hopping systems are simultaneously using the same frequency band. The probability that the interference exceeds a prescribed threshold value is computed from the derived probability density functions. This probability may be used in signal-to-interference ratio calculations, to describe the capture effect, or to compute the expected number of clicks produced in an FM discriminator.

Digitally controlled wave analyzer

Abstract: APPARATUS FOR MEASURING NOISE SPECUTRA, BOTH AM (AMPLITUDE MODULATION) AND FM (FREQUENCY MODULATION), OF RF SIGNALS OVER A PREDETERMINED FREQUENCY RANGE BY SWEEPING A VARIABLE FREQUENCY SQUARE WAVE OSCILLATOR BY MEANS OF AN ANALOG RAMP SIGNAL GENERATED BY A DIGITAL SWEEPING CIRCUIT WHICH PRODUCES A SEQUENCE OF SQUARE WAVE PULSES WHOSE PULSE WIDTH INCREMENTALLY INCREASES BY THE SAME AMOUNT OVER A PREDETERMINED TIME PERIOD. THE VARIABLE FREQUENCY OSCILLATOR IS DRIVEN AND AUTOMATIC FREQUENCY CONTROLLED FROM A DIGITAL CLOCK OSCILLATOR WHICH IS ALSO FED TO A MIXER. THE MIXER IS DIRECTLY COUPLED TO A FIRST MIXER WHICH HAS INPUTS COMPRISING THE NOISE SIGNAL INPUT AND THE VARIABLE FREQUENCY OSCILLATOR SIGNAL APPLIED THERETO. THE FIRST AND SECOND MIXER CONFIGURATION PROVIDES A FREQUENCY WINDOW THROUGH WHICH THE DESIRED NOISE WAVEFORM CAN BE DETECTED AND MEASURED. THE SYSTEM SWEEPS A PREDETERMINED FREQUENCY BAND AND WHEN A NOISE SIGNAL OF PREDETERMINED AMPLITUDE IS DETECTED, THE SWEEP CIRCUIT IS AUTOMATICALLY STOPPED, THEREBY LOCKING ONTO AN INPUT SIGNAL OF EXCESSIVE NOISE LEVEL.

Measurement of Spectrum Levels for Shallow Explosive Sources

Abstract: The measurement of transmission loss in the ocean using explosive sources requires knowledge of the spectrum level of the energy released in a given frequency band as it would be measured as in a boundary‐free medium. For the case of shallow charges the measurement of these spectrum levels is often complicated by the fact that the refracted and surface‐reflected arrivals, each containing an initial impulse followed by a series of bubble pulses, cannot be separated by the usual technique of receiver gating. In recent measurements of the spectrum level of 1.8‐lb charges detonated at 60 ft, this difficulty has been obviated by separation of the two arrivals in the frequency domain rather than in the time domain. This was done by smoothing the spectrum of the recorded waveform to reduce the wide variation caused by oscillations of the gas bubble and then adjusting the smoothed spectrum by the amounts necessary to account for the Lloyd's Mirror interaction. The results obtained in this way agree well with values for deeper explosions reported by Christian [E. A. Christian, J. Acoust. Soc. Amer. 42, 905–907 (1967)] at the upper end of the spectrum where the levels are nearly depth independent. [Work supported by the U. S. Navy Electronic Systems Command.]

System for determining whether a signal lies within a selected frequency band

Abstract: Disclosed is a system for receiving and detecting propagated mechanical-wave analog signals in which the analog signals are converted to a digital signal wherein pulse spacing is proportional to the corresponding instantaneous frequency of the detected mechanical wave signals. A digital processor compares the pulse-spacing of successive pulses of the incoming digital signal with selected pulse-spacing limits corresponding to the frequency limits of the selected bandwidth, and an output signal is generated indicating the receipt of analog signals within the selected frequency band whenever all of the successive pulses during a sampling interval lie within the selected pulse-spacing limits. Generation of an output signal is inhibited when any pair of successive pulses has a pulse spacing outside of the pulse-spacing limits during the sampling interval.

Two Innovations for Improving Harbor Resonators

Abstract: The results of an experimental study on two aspects of resonator behavior for harbor entrances are presented. The first aspect involves a battery of three resonators tuned to cover a wide frequency band. It is found that the efficacy of the battery is improved by increasing the distance along the main entrance channel between the individual resonators. An approximate method is presented for estimating the frequency of the most resonant peaks in the response of a battery to a flat incident wave spectrum. The method is a based on previous results. The second aspect investigated is that of nonuniform depths in the resonator configuration. If the still water depth in the resonator is reduced, the length of the resonator for resonance is considerably reduced. This will allow savings in capital expenditure on breakwaters incorporating rectangular resonators, and on excavating the resonators. However, the efficiency of the resonator is also impaired.

Signal spectrum generator

Abstract: This invention consists of a plurality of dividers connected in series, the outputs of which are added and provide (by Fourier series expansion of square waves) a spectrum of the harmonics of the fundamental frequency. At this comb of spectral lines is of precisely known frequencies and amplitudes, an entire frequency band of interest of a data system may be calibrated in a single operation.

Solution of full-wave equation with mode coupling in an inhomogeneous anisotropic plasma

Abstract: The solution of the full wave equation with mode coupling in a horizontally stratified layer of an anisotropic medium is derived with the matrix notation. It is shown that the analytical method used here is satisfied for the fundamental propaga­ tion problems in the lower frequency band, i. e. VLF and ELF.