Showing papers on "Frequency band published in 1992"

Signal transmission system

Abstract: At the transmitter side, carrier waves are modulated according to an input signal for producing relevant signal points in a signal space diagram. The input signal is divided into two, first and second, data streams. The signal points are divided into signal point groups to which data of the first data stream are assigned. Also, data of the second data stream are assigned to the signal points of each signal point group. A difference in the transmission error rate between the first and second data streams is developed by shifting the signal points to other positions in the space diagram. At the receiver side, the first and/or second data streams can be reconstructed from a received signal. In TV broadcast service, a TV signal is divided by a transmitter into two, low and high, frequency band components which are designated as a first and a second data stream respectively. Upon receiving the TV signal, a receiver can reproduce only the low frequency band component or both the low and high frequency band components, depending on its capability.

Broadband matched‐field source localization

Abstract: A straightforward algorithm for broadband matched‐field source localizaton is developed and subsequently applied to experimental data. For the two‐receiver case, the algorithm involves correlating modeled and measured cross spectra and summing coherently over frequency. The extension to the multiple‐receiver case is to perform the two‐receiver algorithm on each pair of hydrophones and sum the complex results coherently. The frequency band over which the summation is made may be chosen to maximize the signal‐to‐noise ratio. Using an acoustic propagation model based on ray theory to produce modeled cross spectra, the broadband localization scheme is applied to an experimental dataset in which a pseudorandom noise source was towed past a bottom‐moored vertical array in a deep‐ocean environment. Localization is successful out to the maximum range of 43 km. The effects on the source localization of varying such parameters as the number of phones, bandwidth, and receiver aperture are examined. It is found that ...

Design of quadrature mirror filters with linear phase in the frequency domain

Abstract: The design of quadrature mirror filter (QMF) banks whose analysis and synthesis filters have linear phase is considered. Because the design problem in the frequency domain is a highly nonlinear optimization problem, a linearization technique is proposed. An analytical solution formula is obtained, leading to a very efficient procedure. Computer simulations show that the design technique achieves better results in fewer iterations than conventional approaches when starting at the same preset initial guess. Moreover, the technique produces almost the same good results in six iterations if it starts at a better initial guess compared to the preset initial guess. By incorporating the technique with a weighted least squares, (WLS) algorithm, the design of QMF banks whose overall reconstruction error is minimized in the minimax sense over the entire frequency band is facilitated. Computer simulations for illustration and comparison are provided. >

Transceiver with rapid mode switching capability

Abstract: An RF transceiver achieves a fast switching time between transmit and receive modes by leaving the transmit oscillator (12) on all the time. The transmit chain comprises a wide pulling voltage controlled crystal oscillator (12) that operates at one third the transmit frequency followed by a frequency tripler/filter/amplifier chain that can be quickly switched on and off. By operating the transmit oscillator at one third the transmit frequency, only the third harmonic of the oscillator falls into the sensitive receive frequency band. Further isolation during the receive mode is achieved by gating off the frequency tripler, pulling the frequency of the oscillator out of the receive band, electronically detuning the harmonic filter (16) and switching off the transmitter's power amplifier (18).

Frequency agile sharing technology (FAST) for a personal communications service system

Abstract: A frequency agile sharing technology (FAST) system for controlling frequent usage in a communications system is disclosed. Specifically, a frequency agile sharing technology system of controlling frequency usage and eliminating interference for use with a Personal Communications Service (PCS) System is described. The frequency control system allows PCS systems to coexist in the same frequency band as Private Operational Fixed Microwave Service (POFS) systems without mutual interference. This system also controls frequency usage within a PCS system to eliminate interference from within the PCS system. This interference elimination system combines theoretical radio frequency interference analysis with measurements of actual frequency usage and allows for efficient and coordinated dynamic frequency allocation planning and management. To control frequency assignment and eliminate interference, the system employs several mechanisms including an intersystem interference analysis, an intrasystem interference analysis, a channel use verification (CUV) procedure, and a measured data analysis (MDA). These mechanisms are performed by a centralized controller, channel utilization controller (CUC), comprised of interference analysis/frequency planning computer programs with supporting data bases and data communication links. The system and method described allows for PCS frequency use around existing microwave users and can be readily adapted for use in any area and most efficiently make use of the available communications spectrum in that area. The system protects existing microwave users from interference while providing high quality PCS to subscribers utilizing small, low power and lightweight handsets in the same frequency band.

Wideband indoor radio propagation measurements at 58 GHz

Abstract: Wideband measurements of indoor radio channels operating in a 2 GHz frequency band centred around 58 GHz were performed using a frequency step sounding technique. The results are presented of cell coverage and RMS delay spreas under both line-of-sight (LOS) and obstructed (OBS) situations.

Accurate characterization of planar printed antennas using finite-difference time-domain method

Abstract: The finite-difference-time-domain method (FD-TD) is used to characterize complex planar printed antennas with various feed structures, which include coaxial probe feed, microstrip line feed, and aperture coupled feed structures. A coaxial probe model is developed by using a three-dimensional FD-TD technique. This model is shown to be an efficient and accurate tool for modeling coaxial line fed structures. A novel use of a dispersive absorbing boundary condition is presented for a printed antenna with a high dielectric constant. All the numerical results obtained by the FD-TD method are compared with experimental results, and the comparison shows excellent agreement over a wide frequency band. >

A 20 GHz microwave sampler

Abstract: A microwave sampler circuit which operates over the frequency band of 1-20 GHz and has a number of novel features is described. These features include a wideband microstrip-to-slot balun and a wideband active isolator the function of which is to reduce the local oscillator to RF leakage from the input port of the sampler. The signal-to-noise ratio over the input bandwidth is greater than 20 dB at an input power level of -32 dBm. This signal-to-noise ratio was measured in an IF bandwidth of 175 MHz and includes the contribution from the IF amplifier. The sampler, which is made on alumina using MIC techniques, has an integrated impulse generator driven with a sinusoidal local oscillator of only 20 dBm over the frequency band of 250-350 MHz. The IF signal is in the 10-175-MHz band. The RF input VSWR is better than 2:1 up to 20 GHz, and the oscillator to RF breakthrough is better than -58 dBm (-78 dBc) when driven with a local oscillator of 20 dBm. This unusually low leakage was achieved by using the active isolator prior to the sampling circuit. >

Quantitative measurement of blood flow at multiple positions using comb excitation and fourier velocity encoding

Abstract: A method of imaging and quantitatively measuring blood velocity distribution within a selected vessel employs Nuclear Magnetic Resonance excitation of a number of regions of a subject to be imaged by an rf excitation pulse applied in a magnetic field gradient. The rf excitation pulse has several frequency bands with the frequencies between the bands having essentially no amplitude. A frequency band causes excitation of a region of the subject. Each frequency band is encoded with a unique phase angle offset so that the signals from each region may be separated. The excited regions are Fourier velocity encoded along a second axis based upon their flow velocities. A re-radiated signal is acquired in the presence of a readout gradient to provide resolution along a selected axis and reconstruct a velocity profile. This method can be combined with cardiac synchronization to measure flow dynamics or it can be applied without synchronization to measure steady flow. The geometry of the measurement is flexible in that the directions of flow sensitivity and geometric resolution are independent.

Method for allocating channels in a microcellular system .

Abstract: In a microcellular system operated in the same frequency band as a cellular system, an interference-free channel is automatically searched and allocated. The microcellular system which shares the frequency band with the cellular system comprises a control unit, a base station and a multi-channel selecting receiver. The multi-channel selecting receiver monitors a use status of cellular channels of the band to detect idling channels and allocates them to its own system. Whenever a communication request is issued, the base station detects a channel not used by its own system from the idling channels and allocates it for communication.

Low-loss dielectric resonant devices having lattice structures with elongated resonant defects

Abstract: A dielectric resonator comprising a resonant defect structure diposed in a lattice structure formed of a plurality of multi-dimensional periodically arranged dielectric elements confines electromagnetic energy within a frequency band in the photonic band gap. The frequency band of the confined electromagnetic energy is tunable. The unique structure of the dielectric resonator leads to reduced power dissipation losses when used in microwave and millimeter wave components. Accordingly, the dielectric resonator may be used to produce high quality resonant cavities, filters and power generators.

A method to generate different frequency signals in a digital radio telephone

Abstract: A method of generating the different frequency signals required in transmission and reception in a digital radio telephone for operation on at least two different frequency bands. According to the method the mixing frequencies (F1, F2) are selected so that from the frequencies obtained as the mixing results it will always be possible to select the intermediate frequencies (IF1, IF2) required in reception and the transmission frequency (FTX) required in transmission for a radio telephone operating on the desired frequency band.

Combined mobile radio communication system

Abstract: A combined mobile radio communication system comprises a first mobile radio communication system with a first geographic coverage area and with first base and mobile stations and allocated a first set of radio channels within a first frequency band for transmission from the first mobile stations to the first base stations and a second set of radio channels within a second frequency band for transmission from the first base stations to the first mobile stations. Included is also a second mobile radio communication system with a second geographic coverage area, which at least partially coincide with the first geographic coverage area, and with second base and mobile stations and allocated a third set of radio channels within a third frequency band, which at least partially coincides with the first frequency band, but is different from the second frequency band, for transmission both from the second mobile station to the second base stations and vice versa. A detector within the second geographic coverage area detects radio signals within the second frequency band and an estimator estimates the disturbance risk from the second mobile radio communication system at said first base stations with the aid of the signal strengths of the detected radio signals.

Optical communications systems for the subscriber area with optical amplifiers

Abstract: Optical communications system for the subscriber area with optical amplifiers. The system according to the in-vention is used to distribute information signals, particularly telephone signals, from a center to a large number of subscribers and to make possible a bidirectional transmission of telephone and data signals between the center and the subscribers. According to the invention, the network used for this purpose is a multistar fiber-optic network in which fiber-optic amplifiers (10, 11) are present between successive branch points. The information signals to be distributed are transmitted via the fiber-optic network with a first wavelength (.lambda.1) to the sub-scribers, and the subscriber-specific information signals to be transmitted from the center (1) to the subscribers (Ti) are converted by frequency modulation to a different frequency band (FB2) than the distribution signals (by frequency modulation) and transmitted to the subscribers at the same wavelengths as the distribution signals, and the subscriber-specific signals to be transmitted from the subscribers (Ti) to the center (1) are converted by frequency modulation to another frequency band (FB3) and are transmitted optically to the center with a second wavelength (.lambda.2). This optical signal is amplified at suitable points (A) and several alternative embodiments for this amplifi-cation are indicated.

Acoustically coupled antenna utilizing an overmoded configuration

Abstract: An antenna utilizing an overmoded configuration for coupling energy in a predetermined frequency band between an electrical circuit and a propagating medium. The antenna includes a first thin film resonator having a first pair of electrodes and a first thin film piezoelectric element interposed between the first pair of electrodes, with the first thin film resonator coupled to the electrical circuit. A second thin film resonator includes a second pair of electrodes and a second thin film piezoelectric element interposed between the second pair of electrodes, the second thin film resonator being operable for interfacing between the antenna and the propagating medium. A delay element interposed between the first and second thin film resonators has a thickness substantially equal to a multiple of one-half wavelength of a desired frequency in the predetermined frequency band for acoustically coupling energy in the predetermined frequency band between the first and second thin film resonators. Alternatively, the delay element can have a thickness of a multiple of one-half wavelength plus one-quarter wavelength so that the delay element acts as an impedance inverter.

System for transmitting digital data over an electricity power line

Abstract: The invention relates to a communications system suitable for application directly to a national electricity grid and comprising a transmitter for transmitting data over a plurality of transmission frequency bands, a receiver for receiving messages over any one of the frequency bands, means for evaluating the transmission quality of each of the frequency bands, and a way to adapt the system for transmitting and receiving over the frequency band that has optimum transmission quality. The system of the invention may be applied, in particular, to remote reading of electricity meters.

Multiple user digital receiver apparatus and method with combined multiple frequency channels

Abstract: A digital receiver apparatus and method, designed for multiple simultaneous users, digitizes a received analog RF signal and performs multiple frequency translations of the signal so that desired stations are grouped into a common frequency band separate from the remaining stations. This frequency band is then isolated, and the individual selected stations are digitally separated, demodulated and processed to provide multiple simultaneous outputs. The frequency translations are preferably performed initially on a time multiplexed basis. Isolated station separation is performed either by time multiplexing, or by the use of multiple phase or tan locked loops.

Component wave delineation of ECG by filtering in the Fourier domain

Abstract: A complete solution to the fundamental problem of delineation of an ECG signal into its component waves by filtering the discrete Fourier transform of the signal is presented. The set of samples in a component wave is transformed into a complex sequence with a distinct frequency band. The filter characteristics are determined from the time signal itself. Multiplication of the transformed signal with a complex sinusoidal function allows the use of a bank of low-pass filters for the delineation of all component waves. Data from about 300 beats have been analysed and the results are highly satisfactory both qualitatively and quantitatively.

Sound field offset device

Abstract: A sound field offset device having two channels, each of which includes a frequency selection filter for dividing a stereophonic input signal into two frequency bands by a given frequency falling within an audio frequency, at least one digital filter for performing sound field offsetting within a lower frequency band, and at least one loudspeaker assembly for a higher frequency band having a sharp directivity pattern and capable of defining an area to which acoustic power is emitted. This device allows a sound field to be offset in a cost effective and simple manner, by improving the frequency characteristic of a sound field space and by clarifying the sense of locality of acoustic images.

Microwave adaptive transversal filter employing variable photonic delay lines

Abstract: By applying a spatial frequency dependent phase compensation in an optical heterodyning system, a variable rf delay line can be synthesized. The system is able to generate continuously variable phased microwave signals over a prescribed frequency band. A primary application of these variable delay lines is in the area of phased array antenna systems. Because the phototonic delay line synthesizes true time delay, it can be used as part of wide bandwidth system to achieve 100% fractional bandwidth without beam squint. The system lends itself to an optically integrated implementation using a 2-D deformable mirror device to achieve very high packing density which is very useful for an adaptive transversal filter.

Wide-band measurements of MM-wave indoor radio channels

Abstract: The results of wide-band measurements of indoor radio channels operating in a 2 GHz frequency band centered around 58 GHz are presented. The measurements were performed with a frequency step sounding technique. From the resulting frequency domain data base, cell coverage and time delay spread with both line-of-sight and obstruction of the direct path are derived. Eight indoor environments were subjected to propagation experiments. Since these areas are well defined and described the results can be readily related to other environments. >

Spread-spectrum data publishing system

Abstract: A system for publishing data (409) on shared broadcast channels using spread-spectrum techniques, which may comprise a spread-spectrum encoder (405) capable of receiving data and placing it in a spread-spectrum signal format (407) and a transmitter (406) operating on a shared communication channel or frequency band, such as might be allocated to terrestrial point-to-point or broadcast communications. The shared communication channel may comprise a cellular system, in which data (409) may be transmitted (406) using spread-spectrum techniques using the transmitters (406) and repeaters of the cellular system simultaneously with voice and other transmissions associated with the cellular system. A subscriber station may be capable of receiving using a plurality of different communication channels or frequency bands, such as a first receiver capable of cellular reception and a second receiver capable of satellite reception, at least one of which uses spread-spectrum techniques. The subscriber station may also comprise a transmitter using at least one communication channel or frequency band, so that the subscriber station may receive data or other transmissions using one channel and may request further data or other transmissions using a second channel.

Multi-layer array antenna

Abstract: A multi-layer array antenna having high frequency band microstrip antennas formed on a surface of a first dielectric substrate, comb-shaped low frequency band microstrip antennas formed on a surface of a second dielectric substrate which is disposed on the first dielectric substrate, and through-holes for supplying microwave power to the comb-shaped low frequency band microstrip antennas through the first and the second dielectric substrates.

Noise reduction system

Abstract: A system for reducing noise in a wideband signal, such as speech, using a first filterbank and running cross-correlator to detect narrowband frequency components in the signal and an analysis-synthesis filterbank to attenuate the wideband signal in which narrowband frequency components are not detected The narrowband frequency components are detected by performing a running cross-correlation of the outputs of two bandpass filters that have center frequencies that straddle the narrowband frequency and differ by 180 degrees relative to each other at the frequency to be detected Relatively low value cross-correlations indicate that a signal is present in a given frequency band and high value cross-correlations indicate only noise is present The wideband signal is processed by an analysis-synthesis filterbank to attenuate bands where narrowband frequency components have not been detected and to pass or amplify bands where narrowband frequency components have been detected

Method and apparatus for transmitting electromagnetic signals into the earth from a capacitor

Abstract: A method and apparatus in which a capacitor is disposed in direct contact with the earth, and a short voltage pulse is applied to the capacitor to transmit a pulse of electromagnetic radiation having a broad frequency band into the earth. In a preferred embodiment, a portion of the electromagnetic radiation that has propagated through the subsurface is detected and processed to image the subsurface. The size, L, of the transmitting capacitor should be sufficiently small to satisfy the relation Re[kL]<1, where k is the wavenumber in the earth formation of each frequency component of radiation transmitted into the earth. In a preferred embodiment, the voltage pulse applied to the transmitting capacitor has frequency components in a broad band from below 1 MHz to above 100 MHz, and the only frequency components of the detected electromagnetic radiation that are processed to image the subsurface have frequency in the range from about 500 KHz to 25 MHz.

Apparatus and method for stabilizing the background magnetic field during mri

Abstract: A pair of serially-connected coils (L1 and L2) detect noise variations in an MRI background magnetic field. Although the coils (L1 and L2) are closely coupled to the primary background magnetic field generator of the MRI system, they are disposed so as to be substantially de-coupled from rapidly changing MRI gradient magnetic fields. The noise detecting loops drive a negative feedback loop including a low pass filter (50), amplifier (52) and controlled current source (54) driving a large correcting loop (L3). The device attenuates background magnetic field noise during MRI data acquisition over a frequency band extending from a few millihertz to more than 100 Hz. It is preferably used with existing field stabilization software that otherwise compensates for fluctuations in an overlapping frequency band which starts at d.c. Thus, when used together, background magnetic field noise may be attenuated (or compensated for in subsequent MRI data processing) over a frequency band that extends from d.c. to more than 100 Hz.

Antenna used for a plurality of frequencies in common

Abstract: An antenna used for a plurality of frequencies in common according to the present invention has two signal feeding systems for an integrated antenna. The antenna is so constructed that the signal feeding systems are perfectly isolated in DC from each other through a capacitor and at the same time in high frequency, only the signal system for the car telephone frequency band, which is a communication with a moving body, is coupled with the whole antenna, while the signal system for the AM/FM radio frequency band is separated from the antenna radiator portion (radiating element) working at the car telephone frequency band. Owing to a great difference in the frequency between the AM/FM radio frequency band and the car telephone frequency band, no disturbance such as mutual interference, etc. is produced and thus it is possible to obtain stable signal systems separated from each other.

Global modes constituting the solar magnetic cycle. I - Search for dispersion relations

Abstract: The spherical-harmonic-Fourier analysis of the Sun's magnetic field inferred from the Greenwich sunspot data is refined and extended to include the full length (1874–1976) of the data on the magnetic tape provided by H. Balthasar. Perspective plots and grey level diagrams of the SHF power spectra for the odd and the even degree axisymmetric modes are presented. Comparing these with spectra obtained from two simulated data sets with random redistribution within the wings in the butterfly diagrams, we conclude that there is no clear evidence for the existence of any relation between the harmonic degree and the temporal frequency of the power concentrations of the inferred field. Apart from the power ‘ridge’ in the narrow frequency band at ∼ 1/21.4 y−1, and low ridges at odd multiples of this frequency, there are no other spectral features. This strongly suggests that the solar magnetic cycle consists of some global oscillations of the Sun ‘forced’ at a frequency ∼ 1/21.4 y−1 and, perhaps, weak resonances at its odd harmonics. The band width of the forcing frequency seems to be much less than 1/107 y−1. In case the global oscillations are torsional MHD, the significance of their parity and power peak is pointed out.

A minimal cost function method for optimizing the age‐Depth relation of deep‐sea sediment cores

Abstract: The question of an optimal age-depth relation for deep-sea sediment cores has been raised frequently. The data from such cores (e.g., δ18O values) are used to test the astronomical theory of ice ages as established by Milankovitch in 1938. In this work, we use a minimal cost function approach to find simultaneously an optimal age-depth relation and a linear model that optimally links solar insolation or other model input with global ice volume. Thus a general tool for the calibration of deep-sea cores to arbitrary tuning targets is presented. In this inverse modeling type approach, an objective function is minimized that penalizes: (1) the deviation of the data from the theoretical linear model (whose transfer function can be computed analytically for a given age-depth relation) and (2) the violation of a set of plausible assumptions about the model, the data and the obtained correction of a first guess age-depth function. These assumptions have been suggested before but are now quantified and incorporated explicitly into the objective function as penalty terms. We formulate an optimization problem that is solved numerically by conjugate gradient type methods. Using this direct approach, we obtain high coherences in the Milankovitch frequency bands (over 90%). Not only the data time series but also the the derived correction to a first guess linear age-depth function (and therefore the sedimentation rate) itself contains significant energy in a broad frequency band around 100 kyr. The use of a sedimentation rate which varies continuously on ice age time scales results in a shift of energy from 100 kyr in the original data spectrum to 41, 23, and 19 kyr in the spectrum of the corrected data. However, a large proportion of the data variance remains unexplained, particularly in the 100 kyr frequency band, where there is no significant input by orbital forcing. The presented method is applied to a real sediment core and to the SPECMAP stack, and results are compared with those obtained in earlier investigations.

Signal synchronized digital frequency discriminator

Abstract: A digital frequency discriminator processes input pulses including first and second time separated input pulses to determine if the frequency of any two sequential pulses lie within a predetermined frequency band with upper and lower frequency limits and that they are received for at least a predetermined period of time. A delay timer is coupled to sense the input pulse stream and operates in a pulse sensing standby mode prior to receipt of the first input pulse. Upon receipt of the first input pulse, the delay timer switches into a time-limited active mode to define a fixed duration delay interval having a duration equal to the period of the upper frequency limit of the frequency band. The delay timer switches back into the pulse sensing standby mode upon completion of the delay interval. A gate timer is coupled to the output of the delay timer and switches from a standby mode into a time-limited active mode upon completion of the delay interval to define a fixed duration bandwidth interval. A monitoring circuit includes a first input coupled to monitor the input pulse stream and a second input coupled to monitor the output of the gate timer. The monitoring circuit generates a frequency coincidence signal when the second input pulse is received during the bandwidth interval to indicate that the frequency of the input pulse lies within the predetermined frequency band. A recognition circuit is coupled to monitor the output of the coincidence detector to ensure that the coincidence signal is received for at least a predetermined period of time.