Showing papers on "Frequency band published in 1997"

Ultrasonic system and method for harmonic imaging in three dimensions

Abstract: An ultrasound method and system are provided for producing three dimensional images. During an imaging session, a transducer, in response to a transmit beamformer, transmits ultrasonic energy at a first frequency band into a subject. The subject may be kept free of added ultrasound contrast agent throughout the entire imaging session. A receive beamformer receives ultrasonic echo information associated with the transmitted ultrasonic energy. Information signals associated with a second frequency band, such as a harmonic frequency band, are obtained from the echo information. A three-dimensional reconstruction is formed or a volume quantity is calculated in response to the information signals. The transmission of ultrasonic energy may also include energy focused along an elongated high power region or a line focus.

Iterative least-squares synthesis methods for conformal array antennas with optimized polarization and frequency properties

Abstract: An iterative least-squares synthesis technique is presented for the optimization of the element excitation in conformal array antennas. This method allows the designer to have predefined goals for the shaped radiation pattern over a selected frequency band and for the polarization properties of the array. Linear or circular polarization can be used in the synthesis. Different kinds of synthesis goals can be set, whereby the copolarization or cross-polarization properties of the array are weighted or a narrowband or wideband design is sought. The amplitudes of the element excitations can be fixed. Several synthesis examples are presented for an array on a sphere with circular polarized elements. Broad-band and low cross-polarization designs are included.

Reduced complexity bit allocation to subchannels in a multi-carrier, high speed data transmission system

Abstract: A communications system employing the Discrete Multitone (DMT) line code divides the used frequency band W into a large number of subchannels, each with a bandwidth Δf=W/N. The signal in each subchannel is independently modulated at the symbol rate 1/Δf. Because of noise and the non-ideal characteristics of the transmission channel, the signal-to-noise ratio (SNR) varies for different subchannels across the frequency band. Each subchannel is used to transmit an integer number of bits in a two-dimensional signal constellation, the susceptibility to noise increasing with the size of the constellation assuming that the same signal energy is used. In order to use the transmission channel optimally, subchannels are assigned different numbers of bits depending on their specific SNR values, i.e., a subchannel with a high SNR value is assigned a large number of bits and vice versa. An optimal bit allocation is determined that ensures a certain bit error rate (BER) is obtained for all subchannels. In order to simplify numerical computations, thresholding is employed to make initial bit assignments. Further simplification of the bit loading procedures is obtained by ending bit allocation optimization efforts after a targeted BER is achieved.

Folded quarter-wave patch antenna

Abstract: A folded quarter-wave patch antenna which includes a conductor plate having first and second arms spaced apart. A ground plane is separated from the conductor plate by a dielectric substrate and is approximately parallel to the conductor plate. The ground plane is electrically connected to the first arm at one end. A signal unit is electrically coupled to the first arm. The signal unit transmits and/or receives signals having a selected frequency band. The folded quarter-wave patch antenna can also act as a dual frequency band antenna. In dual frequency band operation, the signal unit provides the antenna with a first signal of a first frequency band and a second signal of a second frequency band.

Arc fault detection apparatus and circuit breaker incorporating same

Abstract: Arcing-faults in an electric power distribution system are detected by a circuit which includes a band-pass filter generating a low frequency bandwidth limited arcing current signal having a bandwidth above the measurable harmonics of the ac current but below the frequency band of power line communications systems, about 3 KHz to 20 KHz and preferably about 6 KHz to 12 KHz. For each cycle of the ac current that this low frequency bandwidth limited arcing current exceeds a threshold, preferably related to the amplitude of the ac current, for a selected duration of the cycle, a fixed pulse is generated. If a time attenuated accumulation of these fixed pulses reaches a selected level representative of a number of closely spaced cycles in which the arcing current has been detected for the selected duration, an arc indicative signal is output. Preferably, the value of the time attenuated accumulation of pulses at which the arc indicative signal is generated is variable so that fewer pulses are needed to generate the output as the amplitude of the ac current increases.

Dual band architectures for mobile stations

Abstract: A dual band user terminal (10) includes a controller (18) for outputting a BAND signal for specifying operation in one of a first frequency band or a second, higher frequency band; a single frequency synthesizer (46) that is responsive to the BAND signal for outputting an RF signal in one of two frequency bands; and an RF transceiver (11) comprising a dual band receiver that receives RF signals in the first frequency band and in the second, higher frequency band, and a dual band transmitter that transmits RF signals in the same frequency bands. The dual band receiver includes a first receiver chain that operates in the first frequency band as a single conversion receiver having a downconversion mixer that is preceded by a first filter and that is followed by second filter, and a second receiver chain that operates in the second frequency band as a dual conversion superheterodyne receiver having a first downconversion mixer preceded by a first filter and followed by a second filter coupled to a second downconversion mixer followed by a third filter. The downconversion mixer of the single conversion receiver is also the second downconversion mixer of the dual conversion superheterodyne receiver, and the second filter of the single conversion receiver is also the third filter of the dual conversion superheterodyne receiver.

Method for categorization of multiple providers in a wireless communications service environment

Abstract: A communication device locates a preferable wireless service provider in a multi-service provider environment using a frequency band search schedule. Initially, the communications device registers with a less preferred service provider in a first frequency band. While remaining registered with the less preferred service provider, the device examines several frequency bands in the order specified by the frequency band search schedule. A frequency band is examined by dividing the frequency band into many sub-bands, and by locating the strongest signal above a threshold within the sub-band being examined. The examination continues until a second frequency band having a more preferred service provider is located. The communication device then registers with the more preferred service provider. The category of service provider may be identified and displayed on the communication device.

Radio transmission method for digital multimedia data signals between subscriber stations in a local network

Abstract: In the radio transmission method according to the invention, which operates with a mixed frequency and time division multiplex method FDMA/TDMA, in which a relatively broad frequency band is divided according to the FDMA method into a plurality of carrier frequency ranges, namely the so-called main channels, and a plurality of time slots, namely the so-called sub-channels, distributed in a frame structure, are formed on each carrier frequency level according to the TDMA method, a grouping, that is to say a so-called cluster, of subscriber stations is assigned a limited number of main channels. A main channel signal is divided into one or more sub-channel signals which are associated with a cluster and which are transmitted using the TDMA method. Each transmitter of an activated subscriber station transmits a detectable check signal, so that, on the basis of detection of a check signal in the respective receiver, other, newly activated subscriber stations can determine the presence of transmit signals which are present within a specific, spatially limited range, namely their own respective transmission range. The method according to the invention can be used for transmitting information between terminals in indoor networks in a wireless manner without a central station.

Method for generating frequencies in a direct conversion transceiver of a dual band radio communication system, a direct conversion transceiver of a dual band radio communication system and the use of this method and apparatus in a mobile station

Abstract: The invention relates to a method for generating frequencies in a direct conversion transceiver of a radio communication system operating in two different frequency bands. In this method a first frequency band comprises a first transmission frequency band and a first reception frequency band, and a second frequency band comprises a second transmission frequency band and a second reception frequency band. The frequencies are Generated by using one frequency synthesizer (12) and a reference oscillator (14), which generates an essentially constant mixing frequency (L04).

Fast frequency sweep technique for the efficient analysis of dielectric waveguides

Abstract: This paper describes a new approach to spectral response computations of an arbitrary two-dimensional (2-D) waveguide. This technique is based on the tangential-vector finite-element method (TVFEM) in conjunction with the asymptotic waveform evaluation (AWE) technique. The former is used to obtain modes characteristics for a central frequency, whereas the latter employs an efficient algorithm to compute frequency moments for each mode. These moments are then matched via Pade approximation to a reduced-order rational polynomial, which can be used to interpolate each mode over a frequency band with a high degree of accuracy. Furthermore, the moments computations and subsequent interpolation for a given set of frequency points can be done much more rapidly than just simple simulations for each frequency point.

Broadband low-noise low-intermodulation receiver

Abstract: An RF receiver apparatus that is suitable for implementation as a monolithic IC core with minimum external components is disclosed. The receiver apparatus features low noise figure, low intermodulation and almost fixed input impedance over a broad frequency band covering cable TV, broadcast TV, direct broadcast satellite TV. Other outstanding features includes 40 dB dynamic gain controllable range and minimum electromagnetic radiation due to fully differential signal design. Above all, due to the highly integrated design of the invention, it is suitable for miniaturized tuner appliation.

A down-conversion optical link with RF gain

Abstract: A down-conversion optical link with a radio frequency (RF) conversion gain of 33 dB was demonstrated at 450 MHz. The gain was increased to 17 dB using photodetector impedance matching. Limitations due to each link element are examined and down-conversion gain up to the millimeter-wave (mm-wave) frequency band is predicted.

Vibration control using a tunable vibration neutralizer

Abstract: The harmonic vibration of a machine at one position can be controlled using a vibration neutralizer whose natural frequency is the same as the excitation frequency. However, a conventional vibration neutralizer is only effective over a narrow frequency band and is unable to track changes in excitation frequency. A way of overcoming this problem is to use a tunable vibration neutralizer which, due its variable stiffness capability, can be tuned to operate at different frequencies. With this system, however, there is an inevitable delay between a change in the excitation frequency and the re-tuning of the neutralizer. This delay is dependent upon the control system, and the way it affects the vibration of the machine depends upon certain design parameters. This paper discusses the behaviour of a machine fitted with a tunable vibration neutralizer during the adaptation process when the system is in a transient state. It is shown that if a neutralizer cannot respond quickly enough to a frequency trans...

Fault detection in a frequency duplexed system

Abstract: A frequency band, or test band, located between the uplink and downlink frequency bands of a distributed, frequency duplexed network is used in a novel way to isolate block-level faults within the network. A test signal having frequencies within the test signal band is generated and fed into a downlink path of a branch of the communication network. When the test signal encounters a remote station having duplexing means, the test signal leaks through the duplexing means into an uplink path of the remote station. This occurs because the real filters of the duplexing means do not work perfectly, frequencies outside of the uplink and downlink bands, especially those in the test signal band, will leak through its components. The amount of attenuation of the test signal in leaking through the communication station indicates the operability status of the components therein. By monitoring the power level of the test signal in the uplink and downlink paths of the branch, faults can be quickly isolated.

A diversity scheme for a phase-coherent frequency-hopping spread-spectrum system

Abstract: Frequency diversity for a phase-coherent frequency-hopping spread-spectrum system is proposed. The frequency band of the communicator is partitioned into L disjoint subbands on which L replicas of the communicator signal are simultaneously transmitted; each signal replica hops independently in its subband. Therefore, both phase continuity and coherent optimal combining of the received replicas are possible. Optimum diversity is thus at least 6 dB better than the conventional noncoherent FH-SS system. We show that a smart jammer should be present in all subbands. We also give a sufficient condition that forces the jammer to spread its interference signal on the whole communicator frequency band.

Dual band transceiver

Abstract: A dual band transceiver for operating in a first lower frequency band such as the band allocated to cellular systems, and in a second higher frequency band such as the band allocated to personal communication services (PCS) systems (as shown in Figs. 2-4). In a representative embodiment, the dual band transceiver (108 and 118) comprises a main voltage controlled oscillator (VCO) (134) for generating a local oscillator (LO) signal; an offset VCO (136) for generating an offset frequency (OF) signal; a first mixer (132) for combining the LO signal with the OF signal to produce a first transmit signal; a modulator (130) for modulating the first transmit signal with a data signal to produce a first data modulated transmit signal; and a second mixer (154) for combining the first data modulated transmit signal with the LO signal to produce a second data modulated signal. The main VCO (134) and the offset VCO (136) can be programmed such that the first data modulated transmit signal is in the first band and the second data modulated transmit signal is in the second band.

Mobile radio transmitter with normal and talk-around frequency bands

Abstract: A transmitter circuit for use in a mobile radio using both a normal frequency transmission band and a talk-around frequency transmission band is disclosed. The transmitter employs a local oscillator in the modulation circuit that operates at only a single frequency band characteristic. At the output of the modulation circuit, one of two transmission paths is selected by an RF switch. In the normal transmission path, the input signal is output in the normal frequency band. Alternatively, in the talk-around transmission path, the input signal is modulated to the talk-around frequency band and then output. The present circuitry eliminates the requirements for local oscillators having dual operational characteristics.

High efficiency linear power amplifier of plural frequency bands and high efficiency power amplifier

Abstract: The invention presents a high efficiency linear power amplifier of plural frequency bands reduced in the number of parts and elements, simplified in the circuit construction, and saved in the circuit space, and in FIG. 1, signals entering from a common input terminal 1 in frequency bands A and B are matched in both frequency bands A and B in a wide band matching network 2, amplified in a pre-amplifier 3, put into a common terminal 4a of a switch circuit 4, and the signal in frequency band A is put into a changeover terminal 4b, matched in a matching network 5 and amplified in a post-amplifier 6, and its output is matched in a post-matching network 7 and sent out into an output terminal 8, while, similarly, the signal in frequency band B is put into other changeover terminal 4c of the switch circuit 4, matched in a matching network 9, amplified in a post-amplifier 10, and its output is matched in a post-matching network 11 and is sent out into an outputs terminal 12. The invention also presents a power amplifier capable of maintaining a similar high efficiency characteristic if the output power is lowered from the output power of maximum efficiency, and in FIG. 10, first and second power amplifiers 113, 114 are disposed in parallel, and a necessary number of power amplifiers are connected depending on a required output power by switch circuits 115 to 118, and the power source is turned on only in the connected power amplifiers, while the other power amplifiers are turned off, and therefore by the lowering portion of the output power, the current consumption decreases in proportion, so that the equivalent high efficiency operation same as in the case maximum efficiency is realized.

Communications system including synchronization information for timing upstream transmission of data and ability to vary slot duration

Abstract: A computer network for high-speed data communication, has a data transmission cable with a root and at least one leaf node wherein the upstream transmission is synchronized by information received on a downstream channel. Each client station receives data on a first frequency band, and transmits data on a second frequency band according to synchronization signals received on the first frequency band. The client station's transmission packets may include requests for reserved slots on the second frequency band for subsequent transmissions, and the SCS has a scheduler operable to determine a start time for requested reserved slots, and transmits the start time for the requested reserved slots. The client stations are operable to wait to continue transmission after waiting for the start time.

Inspection lamp with thin-film dichroic filter

Abstract: An inspection lamp for detection of a fluorescent material which absorbs electromagnetic energy in a specific excitation frequency band and which emits electromagnetic energy in a specific fluorescent emission frequency band within the visible light spectrum. The lamp includes a bulb housing, a light source within the bulb housing, and a dichroic filter. The dichroic filter is adapted to transmit electromagnetic radiation in the excitation frequency band of the fluorescent material and reflect electromagnetic radiation in the fluorescent emission frequency band of the material.

Voice analysis-synthesis method using noise having diffusion which varies with frequency band to modify predicted phases of transmitted pitch data blocks

Abstract: A high efficiency encoding method for encoding data on frequency axis obtained by dividing an input audio signal on block-by-block basis and converting the signal onto the frequency axis, wherein V bands are searched for a band BVH with the highest center frequency if it is decided that there are one or more shift points of voiced (V)/unvoiced (UV) decision data of all bands on the frequency axis, and wherein the number of V bands NV up to the band BVH is found, so as to decide whether proportion of the V bands is equal to or higher than a predetermined threshold Nth, thereby deciding one V/UV boundary point. Thus, it is possible to replace the V/UV decision data for each band by information on one demarcation in all bands, thereby to reduce data volume and to reduce bit rate. Also, by using two-stage hierarchical vector quantization in quantizing the data on the frequency axis, operation volume for codebook search and memory capacity of the codebook are reduced.

Procedure for the elimination of interference in a radar unit of the fmcw type

Abstract: This invention concerns a procedure for the elimination of interferences, such as pulses and linear chirps, in a radar unit of the FMCW type. According to the procedure, the useable signal in the form of a beat signal, is subjected to time-frequency division of the type STFT for division of the signal into narrow-band frequency bands. Interference is detected and eliminated in each frequency band, after which the time signal freed from interference and its Discrete Fourier Transform, DFT, are calculated from the time-frequency division in narrow-band frequency bands.

Signal generation using periodic single and multi-bit sigma-delta modulated streams

Abstract: This paper describes a new method to generate analog signals with high precision at very low hardware complexity. This method consists in reproducing periodically a recorded portion of the bitstream output of a sigma-delta modulate. This technique utilizes less hardware than conventional frequency synthesis methods and does not require a multi-bit DAC. However when a multi-bit DAC is already available, the technique can be used to increase the quality of the signal in the frequency band of interest using existing hardware. The paper demonstrates how this method can be used to generate signals for Built-in Self-Test and standard Analog and Mixed-Signal Test. Experimental results illustrating the design simplicity and low overhead are given.

Technique for simultaneous communications of analog frequency-modulated and digitally modulated signals using precanceling scheme

Abstract: In a system for simulcasting a digitally modulated signal and an analog FM signal over the same FM frequency band, the composite signal is received and applied to a conventional FM receiver, and a digital receiver in accordance with the invention. An extended Kalman filter is employed in the digital receiver to estimate the analog FM signal based on a version of the recovered FM signal from the FM receiver, and a discrete version of the composite signal whose spectrum has been translated and is at an intermediate carrier frequency. The estimated FM signal, which is in a discrete form, is subtracted from the discrete version of the composite signal. The resulting signal, which is an estimated version of the digitally modulated signal, is demodulated to recover the digital data as transmitted.

Method for optimal selection among multiple providers in a wireless communications service environment

Abstract: A communication device locates a preferable wireless service provider in a multi-service provider environment using a frequency band search schedule. Initially, the communications device registers with a less preferred service provider in a first frequency band. While remaining registered with the less preferred service provider, the device examines several frequency bands in the order specified by the frequency band search schedule. A frequency band is examined by dividing the frequency band into many sub-bands, and by locating the strongest signal above a threshold within the sub-band being examined. The examination continues until a second frequency band having a more preferred service provider is located. The communication device then registers with the more preferred service provider. The order of search of the frequency spectrum may be based upon registration history of the communication device.

Multi-frequency antenna device and multi-frequency array antenna device using multi-frequency sharing antenna

Abstract: PROBLEM TO BE SOLVED: To provide a device which radiates large power and which can be miniaturized in height/width directions by providing plural logarithm period dipole parts excited from two parallel lines transmitting radio waves from a micro strip line in accordance with respective necessary frequency bands and reflecting the radiated radio wave of the logarithm period dipole part so as to radiate the radio wave. SOLUTION: An input signal is inputted to the micro strip line 12 from a feeder circuit through a connector. The input signal is transmitted through the micro strip line 12 and it is transmitted through a balun 13. Then, it is naturally converted into a signal transmitted through the two parallel lines 14. The converted signal is transmitted through the two parallel lines 14 but a metallic reflection board 17 and the two parallel lines 14 are insulated at a position where they cross the metallic reflection board 17 by a hole provided on the metallic reflection board 17. The signal is transmitted and it is excited in the first necessary frequency band at first and it is not resonated and is not excited in the second necessary frequency band.

Method and apparatus for mitigating intermodulation effects in multiple-signal transmission systems

Abstract: Method and apparatus for mitigating intermodulation distortion effects in frequency division multiple access (FDMA) communications systems. In one embodiment, an effective transmit power level is determined for each communication signal to be transmitted, and signals are allocated to frequency channels such that a smooth tapering or transmit power levels across contiguous frequency channels is achieved. Such smooth power tapering across frequency channels minimizes the possibility that two high power signals will generate an intermodulation distortion product sufficient to disrupt transmission of an immediately adjacent low power signal. In another exemplary embodiment, communication signals are allocated such that high power signals are positioned near a frequency band center, while low power signals are positioned near frequency band edges. As a result, intermodulation distortion between frequency bands in a multiple-band communication system is also minimized.

Spread spectrum communication system

Abstract: The present invention defines a combined channel or a composite channel which is to be transformed into a plurality of element channels. The composite channel may be either shared by a plurality of communication stations on time division multiplex basis, or used by a single communication station. In a transmit side, serial data information which is called a composite channel is transformed (2) to parallel form associated with a plurality of element channels, each of which is spread by using a single common PN code (5). The spread element channels are frequency converted to radio frequency so that the center carrier frequency is offset from that of adjacent element channel by an integer multiple of information transmission rate of each element channel, and frequency band occupied by spread element channels overlap with one another. The element channels thus spread and frequency converted are combined (13) on frequency axis, and transmitted to a receive side. Thus, all the element channels are synchronized with one another because of the use of a single common PN code, and receive level of signal of each element channel is uniform, irrespective of the number of communication stations, and therefore, high quality communication with no interference is obtained in relatively narrow frequency band.

A direct digital synthesizer with an on-chip D/A-converter

Abstract: A Direct Digital Synthesizer (DDS) with an on-chip D/A-converter is designed and processed in 0.8 µm BiCMOS. The digital parts of the chip are implemented with CMOS design to reduce power consumption. The 10-bit D/A-converter is designed with BiCMOS technology in order to operate at a clock rate of 150 MHz. At the 150 MHz clock frequency, the Spurious Free Dynamic Range (SFDR) is 60 dBc at low synthesized frequencies, decreasing to 52 dBc at high synthesized frequencies in the output frequency band (0 to 60 MHz). The DDS covers the output frequency band in steps of 0.0349 Hz with the frequency switching speed of 140 ns. The chip has a complexity of 19,100 transistors with a die/core area of 12.2/3.9 mm2. The power dissipation is 0.6W at 150MHz @ 5V. The maximum operating clock frequency of the chip is 170 MHz.