Showing papers on "Frequency band published in 1989"

Slow Bragg solitons in nonlinear periodic structures.

Abstract: We show that a new class of optical solitons is possible in nonlinear periodic structures. These waves can propagate undistorted even though their power spectra lie well within the frequency band gap of the periodic structure and even though their carrier frequency is very close to the Bragg resonance. Analysis shows that these Bragg solitons can exhibit velocities which are orders of magnitude lower than the speed of light in the unperturbed medium.

Speech recognition using noise-adaptive prototypes

Abstract: A probabilistic mixture mode is described for a frame (the short term spectrum) of speech to be used in speech recognition. Each component of the mixture is regarded as a prototype for the labeling phase of a hidden Markov model based speech recognition system. Since the ambient noise during recognition can differ from that present in the training data, the model is designed for convenient updating in changing noise. Based on the observation that the energy in a frequency band is at any fixed time dominated either by signal energy or by noise energy, the energy is modeled as the larger of the separate energies of signal and noise in the band. Statistical algorithms are given for training this as a hidden variables model. The hidden variables are the prototype identities and the separate signal and noise components. Speech recognition experiments that successfully utilize this model are described. >

Near optimal solution to the inverse problem for gravitational-wave bursts.

Abstract: We develop a method for determining the source direction (θ,φ) and the two waveforms h+(t), h×(t) of a gravitational-wave burst using noisy data from three wideband gravitational-wave detectors running in coincidence. The scheme does not rely on any assumptions about the waveforms and in fact it works for gravitational-wave bursts of any kind. To improve the accuracy of the solution for (θ,φ), h+(t), h×(t), we construct a near optimal filter for the noisy data which is deduced from the data themselves. We implement the method numerically using simulated data for detectors that operate, with white Gaussian noise, in the frequency band of 500–2500 Hz. We show that for broadband signals centered around 1 kHz with a conventional signal-to-noise ratio of at least 10 in each detector we are able to locate the source within a solid angle of 1×10^-5 sr. If the signals and the detectors’ band were scaled downwards in frequency by a factor ι, at fixed signal-to-noise ratio, then the solid angle of the source’s error box would increase by a factor ι^2. The simulated data are assumed to be produced by three detectors: one on the east coast of the United States of America, one on the west coast of the United States of America, and the third in Germany or Western Australia. For conventional signal-to-noise ratios significantly lower than 10 the method still converges to the correct combination of the relative time delays but it is unable to distinguish between the two mirror-image directions defined by the relative time delays. The angular spread around these points increases as the signal-to-noise ratio decreases. For conventional signal-to-noise ratios near 1 the method loses its resolution completely.

Eigenfilter design of higher-order digital differentiators

Abstract: An effective approach is proposed for designing higher order differentiators by the eigenfilter method By minimizing a quadratic measure of the error in the frequency band, an eigenvector of an appropriate matrix is computed to get the filter coefficients This method is not only simple and fast, but also optimal in the least-squares sense Comparison to the McClellan-Parks algorithm for minimax equiripple filters shows that both are optimal in the sense of different minimum norms of the error function, but much better performance is obtained with the proposed approach in most of the frequency band, except in the narrowband region near the cutoff edge >

Multiple reuse of an FM band

Abstract: A signal receiving system for receiving messages from each of several unequal amplitude FM carriers occupying the same portion of the frequency band. The signal receiving system receives power division multiplexed signals, each of which being allocated a portion of the total average power of an assigned FM band.

Audio dosage control system

Abstract: Microphones sample the sound output from the speakers of a sound amplification system. The resulting time domain analog signals undergo a Fast Fourier Transform which yields frequency domain signals representative of the intensities of the frequency bands which compose the sound. The intensities or levels of each band are compared to stored permissible level limits for each frequency band. Attenuators respond to signals indicative of band levels being exceeded by respectively attenuating the frequency bands to which they are tuned so the speaker output does not contain frequencies which exceed permissible limits. The time weighted permissible averages for each frequency are also integrated to provide for production of signals representative of the cumulative sound dosage. When total dosage is trending toward exceeding permissible limits for the time during which the listeners are expected to be listening, the cumulative dose signals operate another attenuator to cause the volume emitted by the speaker to drop to a permissible level.

Multi-frequency band phased array antenna using coplanar dipole array with multiple feed ports

Abstract: In a printed circuit embodiment, dielectric boards in a multilayer arrangement have their ends protruding from a ground plane. Sets of printed dipole elements are disposed along the edge of each board. Each set of dipole elements has three feed ports. Bandpass filters are provided for each feed port. Phase shifters are coupled to each of the feed ports through its respective bandpass filter. At the low band, the outer feed ports are shorted by the filters so that the two sections of dipole elements to the left of the center feed port form one lone band dipole arm, and the two sections of dipole elements to the right of the center feed port form the other low band dipole arm. The low band dipole is driven at the center feed port. At the high band, the center feed port becomes an open circuit so that the two sections to the left thereof form one high band dipole, and the two sections to the right thereof form a second high band dipole. The two outer feed ports drive the dipole array at the high band. In an MMIC embodiment, printed circuit stubs are bridged across the outer feed ports. The length of each stub is one wavelength at the low frequency band, and one-and-one-half wavelengths at the high frequency band. At the low frequency, the stubs appear to be short-circuited. At the high frequency band, the terminals of the stubs provide a 180 degree phase difference for a balun.

Sound level control equipment

Abstract: Automatic level control equipment, for example for a coin-operated music system, has a sound level adjusting device, such as a variable resistance device (30) interposed between amplifier inputs (23) and outputs (24) for sound reproducing apparatus, such as loudspeakers. The resistance (30) is adjusted by control circuitry (28) to compensate for changes in the level of background noise picked up by a microphone (22). The control circuitry (28) has microphone monitoring filters (25) and amplifier output monitoring filters (27) operable at different frequency bands so that background noise can be monitored at different frequency bands, depending on the frequency distribution of the sound output of the amplifier. If the amplifier has a sound output in the same frequency band as that being monitored in the background noise, the circuitry can switch to a different monitored frequency band of background noise.

Digital signal magnetic recording/reproducing apparatus using multi-level QAM modulation and maximum likelihood decoding

Abstract: A digital signal magnetic recording/reproducing apparatus converts a digital signal into multi-value digital signals and performs recording/reproducing of a multi-value quadrature amplitude-modulated signal. By using the multi-value quadrature amplitude modulation, it is possible to remove the DC component in the recording signal and improve the utilization efficiency of the recording frequency band. Further, using a system to memorize the frequency characteristic of the magnetic recording/reproducing unit and effect Viterbi decoding regarding the intersymbol interference caused by the frequency as a convolutional coding, it is possible to detect the level without necessitating frequency equalization. Accordingly, there arises no deterioration of the S/N ratio by frequency equalization. Furthermore, by providing an encoder for error control coding by increasing the number of multi-values and a corresponding decoder, the error rate can be improved against the deterioration of the S/N ratio. Further, by bias recording the multi-value quadrature amplitude modulated signal, non-linearity of the electromagnetic conversion system is relaxed, and deterioration of the S/N ratio by distortion is improved.

Up-conversion homodyne receiver for cable television converter with frequency offset to avoid adjacent channel interference

Abstract: A carrier is received containing a plurality of signals within a first frequency band, for example television signals within the cable television band. The signals are upconverted to a second frequency band above the first band wherein a selected one of the upconverted signals will reside at an intermediate frequency within the second band. The selected upconverted signal is input to a homodyne detector operating at or near intermediate frequency. In-phase and quadrature signals output from the homodyne detector are digitally processed to recover a baseband signal.

Radio interference suppression

Abstract: An arrangement for the suppression of radio interference in an electric motor (10) having at least two brushes (11,13,15), the arrangement comprising a high frequency interference suppression circuit and a low frequency interference suppression circuit, the high frequency interference suppression circuit comprising a ferrite bead (24,26) which surrounds a portion of a lead (36,38) connectable to one (11,13) of the brushes, and a capacitor (28,30) which is capable of self resonance in the high frequency band, and the low frequency interference suppression circuit comprising a capacitor (32,34). Also disclosed are an isolating element between the low frequency and high frequency suppression circuits and a separate grounding method for each circuit for reducing the interaction between the high frequency and the low frequency suppression circuits.

Skywave adaptable communication apparatus

Abstract: An adaptive TDMA (time division multiple access) communication system is illustrated which dynamically maintains potentially different frequencies between nodes of the communication system using a process of communicating the quality of received signals between the nodes and storing this information so that an optimum frequency band can be selected whereby whenever signal quality deteriorates, an alternate frequency can be selected to provide continued communications. An embodiment of the system spans both high frequency (HF) and very high frequency (VHF) to establish the communications through atmospheric induced refractions (reflections) beyond line of sight between directly communicating nodes of the system. Further, the system uses frequency hopping both for signal transmission security and for node identification. When a node is traffic idle and also on a periodic maintenance basis, frequency bands other than the traffic frequency are analyzed for potential future use.

Technique for reducing distortion characteristics in fiber-optic links

Abstract: The present invention relates to a technique for suppressing intermodulation products introduced by nonlinearities of a laser in a multi-­carrier Frequency Division Multiplexed (FDM) fiberoptic link. More particularly, for two or more closely spaced FDM channel information signals within a predetermined band of frequencies in an FDM optical transmission system, third-order intermodulation products, which are produced by nonlinearities of a transmitting laser, also fall in-band and provide interference in the channel information signals. Suppression of these in-band intermodulation products is achieved in the present invention by the simultaneous transmission of a strong suppression tone (44) which is disposed outside the band of the FDM channel information signals (40, 41) being transmitted, and at a frequency within the overall response band of the transmitting laser (24) such that the mixing of the channel information signals and the suppression tone will provide minimal, or no, intermodulation products (42, 43) in the frequency band of the the FDM channel information signals.

Edtv recording apparatus

Abstract: Extended definition television (EDTV) signals including a compatible composite wideband signal and a separate helper or extended definition signal are combined, for example, for recording purposes, using frequency multiplexing techniques. The helper signal is applied to a modulator, which produces a suppressed carrier modulated signal, to frequency shift the helper signal to a spectral band above the frequency band occupied by the compatible composite wideband signal. The frequency shifted and wideband signal are then added to form the combined signal.

Theoretical and experimental characterization of nonsymmetrically shielded coplanar waveguides for millimeter-wave circuits

Abstract: A quasi-planar structure, the nonsymmetrically shielded coplanar waveguide (NSCPW), is proposed as a quasi-TEM transmission line with advantageous characteristics for millimeter-wave circuit applications. Advantages in terms of broadband behavior and ease of machining, as well as device mounting and substrate mounting, are pointed out. An experimental method is developed which allows the evaluation of the transmission line spectrum in a very wide frequency band (15:1) with a single transmission measurement. The experimentally evaluated propagation characteristics of the dominant and higher order modes are shown to be in excellent agreement with the theoretical predictions based on the generalized transverse resonance technique. This method is also used for an extensive characterization of the structure in terms of characteristic impedance and useful frequency band. >

The rheology of an anelastic medium studied by means of the observation of the splitting of its eigenfrequencies

Abstract: It is seen how the rheology of anelastic media causes a splitting of each of the free modes of an oscillator into a number of lines spread over a frequency band depending on the type of rheology. The experimental identification of these lines and/or of the width of each multiplet allows the retrieval of the rheological properties of the medium.

Process for the simultaneous detection of several gases in a gaseous mixture, and equipment for using the process

Abstract: Process and interferometric device for detecting and measuring the concentration, in a single operation, of all gases, having almost periodic absorption structures, contained in a gaseous mixture, each of the gases being associated with a characteristic path difference. Luminous flux is analyzed after passage through a cell containing the mixture, using to a multiple-wave interferometer, for example, a Fabry-Perrot interferometer, in which the inside faces of plates therein are highly reflective, and one of which plates is displaceable at a constant speed, it thus being possible to sweep a very wide range of path difference. Analysis of the output signal is performed frequency band by frequency band, by seeking the maximum.

Compatible and spectrum efficient high definition television

Abstract: High definition television (HDTV) signals are broadcast in a manner to be compatible with television receivers that operate to reproduce standard definition images, and the broadcast HDTV signals are contained within an existing frequency band in the electromagnetic spectrum allocated for transmission of the standard definition images. An image to be broadcast is scanned with a high definition camera capable of producing an image frame of N lines of resolution, wherein N is equal to about twice the line resolution of a standard definition image frame. The camera produces N/2 odd line image signals and N/2 even line image signals for each image frame. The odd line signals are modulated on a radio frequency (RF) carrier wave to produce HDTV odd line image signals occupying at most the same frequency band in the electromagnetic spectrum as occupied by standard definition images. The even line signals are modulated on a RF carrier wave signal to produce HDTV even line image signals that occupy at most the same frequency band. The HDTV odd line image signals are radiated from a first transmitting antenna to produce first radiated waves of a first polarization, and the HDTV even line image signals are radiated from a second transmitting antenna to produce second radiated waves of a second polarization mutually orthogonal with the first polarization. Reception of HDTV images is carried out with mutually orthogonally polarized antennas matched to the first and the second radiated waves.

Development of mobile communication system for RACS

Abstract: The development of a road/automobile communication system is discussed. An inductive radio system and a microwave system are potential candidates. The inductive radio system has four lanes*4 m of communication range with a bit error rate characteristic of 5*10/sup -5/ to 5*10/sup -6/ and a maximum data volume of 460 kb attainable at a beacon when an automobile is traveling at 100 km/h. The microwave system using the 2.5 GHz frequency band has five lanes*60 m of communication range and a maximum data volume of 400 kb with a transmission data rate of 512 kbps. By deploying the phase shift keying/reverse amplitude modulation method, the system was able to determine the position of automobiles very accurately and to detect their direction of motion. The microwave system has very high potential for future applications and will be implemented in Japan. >

Satellite communication system with variable coding rate

Abstract: A satellite communication system with a variable coding rate maintains all the channels connectable at all times without resorting to an extra frequency band associated with one carrier wave on a satellite transponder and otherwise required to accommodate the simultaneous occurrence of multiple call requests which is rare. The system selectively changes the coding rate of data to implement the transmission of massive data without the need for an increase in the frequency band on a satellite transponder, contributing a great deal to the efficient use of frequency bands available with a satellite transponder

A noise elimination method

Abstract: The invention relates to a method for the elimination of noise in an information channel. The frequency band of the channel (1) is first divided (CH1-CH4) into sub-bands (B1-­B4), whereafter the useful value of the signal of each sub-­band (B) is determined by comparing the signal level (S) to a reference level (Ref), in which case a constant signal of substantially the same level as the reference level (Ref) is suppressed (P1-P4), whereas a varying signal, defined as a useful signal, is summated, unsuppressed, with the useful signals of the other sub-bands (B1-B4). The frequency band of the channel is divided into sub-bands (CH1-CH4) by means of an all-pass filter construction. The method can be im­plemented using an analog or a digital filter construction.

Operation and theory of a driven single-mode electron cyclotron maser.

Abstract: A study is made of the operation of the electron cyclotron resonance maser (ECRM), when subjected to an external rf signal. The signal is introduced both via direct injection through a coupling hole in the oscillator and by modulating the electron beam in separate cavities, upstream of the oscillator. Experiments using both one and two ``prebunching'' cavities are reported. It is experimentally found that the gyromonotron, a specific embodiment of the ECRM, can be phase locked by premodulating the electron beam at drive power levels more than two orders of magnitude below that predicted by Adler's widely applicable theory for single-cavity oscillators. A perturbation theory is used to predict the phase-locking frequency band for a gyromonotron with any number of prebunching cavities. The predictions of this theory agree with the experimental results for two- and three-cavity phase locking. An investigation is made into the general amplitude and frequency response of the ECRM to an applied external signal. Experimentally, three distinct regions of qualitatively different ECRM behavior are noted: soft excitation, which is free, self-excited oscillation; hard excitation, where the oscillation requires an external impulse for startup; and amplifier, in which the output power level and frequency are linearly related to the drive in the small-signal regime.

Circuit for detecting a video mode

Abstract: The detection of whether an input FM signal, such as a reproduced signal, which includes particular frequency components representing predetermined information, was recorded in a first or second mode, with the modes having different frequency bands. A first output signal is produced when a particular frequency component in one of the frequency bands is detected and a second output signal is produced when a different frequency component, approximately equal to the difference between twice a predetermined frequency included in the other of the frequency bands and the particular frequency in the one frequency band, is detected. A mode identifying signal indicative of the frequency band occupied by the FM signal is produced in response to the first and second output signals.

An approximation function for frequency constrained structural optimization

Abstract: The purpose is to examine a function for approximating natural frequency constraints during structural optimization. The nonlinearity of frequencies has posed a barrier to constructing approximations for frequency constraints of high enough quality to facilitate efficient solutions. A new function to represent frequency constraints, called the Rayleigh Quotient Approximation (RQA), is presented. Its ability to represent the actual frequency constraint results in stable convergence with effectively no move limits. The objective of the optimization problem is to minimize structural weight subject to some minimum (or maximum) allowable frequency and perhaps subject to other constraints such as stress, displacement, and gage size, as well. A reason for constraining natural frequencies during design might be to avoid potential resonant frequencies due to machinery or actuators on the structure. Another reason might be to satisy requirements of an aircraft or spacecraft's control law. Whatever the structure supports may be sensitive to a frequency band that must be avoided. Any of these situations or others may require the designer to insure the satisfaction of frequency constraints. A further motivation for considering accurate approximations of natural frequencies is that they are fundamental to dynamic response constraints.

Apparatus and method for determining the permittivity of samples of material over a wide frequency band

Abstract: Measurements of the permittivity of samples over a very wide frequency range and a wide temperature range have previously involved such problems as changing parts of the measuring equipment in different regions of the frequency range, substituting one of the components of a bridge used as part of the equipment to obtain bridge balance, and limited permittivity resolution. The present invention employs a capacitance bridge formed by a sample (C₁,R₁) held between electrodes, a series capacitor C₂ and a detector comprising a high input impedance amplifier 11 and correlators 25. The bridge is balanced by applying voltages of known relative amplitude and phase constructed from outputs having relative phases of 0°, 90° and 180° of two phase-locked oscillators 13 and 14. The voltages are constructed using phase shifters 17, 20, attenuators 19, 21 and summer-driver circuits 12, 22. At low frequencies the applied voltages are obtained from a waveform synthesizer 15. In order to allow for any inaccuracies in the amplitude and phase of the applied voltages, a reference bridge is provided which comprises two capacitors 26, 27 connected in series and a detector which includes a high input impedance amplifier 28, connected between the junction of the capacitors and a common terminal.

A 2-18 GHz low-noise/high-gain amplifier module

Abstract: The effectiveness of the two-tier matrix amplifier as a very-low-noise device with very high associated gains across multioctave frequency bands is theoretically and experimentally demonstrated. Experimental modules whose topology is based on a computer-optimized design exhibit an average noise figure of F=3.5 dB with an associated average gain of G=17.8 dB across the 2-18 GHz frequency band. These state-of-the-art results were achieved with GaAs MESFETs whose minimum noise figure is F=2.2 dB at 18 GHz and whose gate dimensions are 0.25*200 mu m. The design considerations and the test results are discussed in detail. >

Circuit for driving an inductive load

Abstract: A switching transistor for driving an inductive load is switched on and off by a switching signal of a PWM signal or a signal equivalent to the PWM Signal. A frequency band of impulse noise components of the switching signal is above a frequency band used in an apparatus including the inductive load.

Sub-band transmission system

Abstract: The frequency band (FB) of a digital audio signal (TS) is divided into sub-bands (SB1 to SB7) by quadrature mirror filters (QMF) in a coding device (CE), coders (CO) being provided in the individual processing branches for the purpose of data reduction. In the signal branch of the sub-band (SBH, SB7), in which the highest frequency range 12-24 kHz of the audio signal (TS) is transmitted, a first filter (F1) for 12-15 kHz band limiting and a first clock rate converter (TC1) for reducing the data rate are arranged. In a decoding device at the receiving end, a band-limited audio signal (TSB) is assembled in further quadrature mirror filters (QMF) from the sub-band signals transmitted in the sub-bands (SB1 to SB7).

Rigorous Field Theory Design of Compact and Lightweight Broadband Diplexers for Satellite Communication Systems

Abstract: A new design of compact, lightweight, broad-band and low-insertion-loss diplexers for satellite conununication systems is introduced utilizing E-plane corrugated and below-cutoff waveguide filters in the septate waveguide sections of E-plane furcated power dividers with asymmetrical transformer heights. The rigorous optimization technique comprises the complete component, including all discontinuities as well as the higher order mode interaction between them. Results are given for a computer optimized design exmnple for a minimum input port return loss of about 22 dB over the transmit (3.7 - 4.3 GHz) and receive (5.83 - 6.5 GHz) frequency band. The theory is verified at a R- 48 waveguide diplexer example which was milled from a solid block.