Showing papers on "Radio frequency published in 1988"

Automatic over-temperature control apparatus for a therapeutic heating device

Abstract: The use of radio frequency currents to heat and destroy neurological tissues is well known in the field of neurosurgery and typically involves monitoring of the tissue temperature as it is being heated by an in-dwelling electrode. This patent deals with an apparatus and method which enables the operator of such apparatus to be in control of the rise of temperature and the increase in radio frequency power delivered to such electrodes, and yet also to pre-set a temperature and have control circuitry and other means to prevent the electrode temperature to exceed a set temperature point. We refer to this as an over-temperature control for heat lesion generation equipment in the case of neurosurgery. The system is a hybrid between a purely manually controlled radio frequency heating unit and a completely automatically controlled radio frequency unit, the latter being such that it automatically raises the radio frequency power and feedbacks on a set temperature to stabilize the final electrode temperature. The present invention retains the important position of the human operator in establishing the rise of temperature and yet affords the advantage of temperature stabilization at a fixed end point and thereby gives the benefits of a fully automatic control system to the added asset of safety and human control.

Distributed antenna system

Abstract: The present invention provides a distributed antenna system comprising a primary antenna (14A, 16A) and a plurality of secondary antennas (36, 40), a . .fibre.!. .Iadd.fiber .Iaddend.optic network (20, 22) connected between the primary antenna (14A, 16A) and the secondary antennas (36, 40), first means (. .16.!. .Iadd.24.Iaddend., 44) associated with a first one of the antennas (16A, 40) which transmits signals received by that antenna (16A, 40) into the . .fibre.!. .Iadd.fiber .Iaddend.optic network (20, 22), and second means (32, 50) associated with a second one of the antennas (14A, 36) which causes that antenna (14A, 36) to transmit signals received by the second means (32, 50) from the . .fibre.!. .Iadd.fiber .Iaddend.optic network (20, 22). Preferably, the use of a heterodyne circuit is avoided and the light signals travelling within the . .fibre.!. .Iadd.fiber .Iaddend.optic networks (20, 22) are modulated at radio frequency.

A comparison of indoor radio propagation characteristics at 910 MHz and 1.75 GHz

Abstract: The results of temporally and spatially distributed wideband (impulse response) propagation experiments in the 900 MHz and 1.7 GHz radio frequency bands in two different buildings on fixed indoor radio links are reported. Results from the temporal experiments show that, for a specific location in either of the two buildings, the dynamics of indoor channels are slightly less random at 910 MHz than at 1.7 GHz. It is believed that this would result in marginally better performance on a given transmit/receive link in the 900 MHz band. The spatially distributed measurements showed that the structures of average impulse-response envelopes differed for channels in the two buildings. In one building, RMS delay spreads were slightly greater in the 1.7 GHz band for over 90% of transmit/receive link configurations. In the other building, RMS delay spreads were marginally greater in the 900 MHz band for 70% of the configurations. >

Pulsed dual radio frequency CVD process

Abstract: A method of depositing a thin film of silicon oxynitride (Six Oy Nz) onto a semiconductor substrate utilizing dual frequency plasma enhanced chemical vapor deposition (PECVD). Plasma formation is achieved by striking gases in a reaction chamber with a high voltage, low frequency radio wave, and then triggering and applying with the leading or trailing edge of the striking pulse, a second high frequency, low power radio wave. The plasma transfers energy into reactant gases forming a thin film of silicon oxynitride (Six Oy Nz) onto a semiconductor substrate. The high frequency pulses provides more efficient gas ionization and less pattern, and back oxide sensitivity to film deposition rate.

Magnetic field mapping.

Abstract: Homogeneous radiofrequency magnetic fields are necessary for production of high-quality magnetic images and for most forms of magnetic resonance spectroscopy. It is often convenient to map the radiofrequency homogeneity associated with a resonant device by measuring the magnetic image intensity of an aqueous phantom placed within the resonator. The rf field intensity is not related trivially to the magnetic image intensity, and the relationship is different for different image acquisition methods. In this report relationships between rf field intensity and magnetic image intensity are derived and radio-frequency field maps presented for comparison using (1) an rf probe moved about within the resonant volume, (2) spin-echo images, and (3) small tip angle gradient refocused echo images. © 1988 Academic Press, Inc.

Bridged loop–gap resonator: A resonant structure for pulsed ESR transparent to high‐frequency radiation

Abstract: A new and inexpensive X‐band resonator structure for pulsed electron‐spin resonance and electron‐nuclear‐double‐resonance applications is introduced The resonator consists of a bridged loop structure and is distinguished by a good reproducibility and reliability It has a high filling factor and an adjustable Q value and is transparent to radio frequency fields with an upper limit >100 MHz The inner diameter of 5 mm allows convenient sample access of standard 4‐mm quartz tubes in the temperature range between 4 and 300 K Numerical computations of the resonant frequencies, the Q values, and the three‐dimensional distributions of the electromagnetic fields are presented They are based on a discretization method for the solution of Maxwell’s equations and include all dielectric elements of the resonator structure The field homogeneity in the sample area and the influence of the dimensions and the thickness of the metallic layers on field intensity, quality factor, and resonant frequency are determined e

Global positioning system receiver with improved radio frequency and digital processing

Abstract: A global positioning system (GPS) receiver having a common radio frequency section and a separate digital signal processing channel for each of a plurality of satellite signals which are simultaneously being received and processed by the receiver in order to calculate the position, velocity or other desired parameters of the receiver. The radio frequency section receives and processes both of the standard satellite signals on different frequency L1 and L2 carriers in order to provide the multi-channel digital section signals from which the relative phase of the carriers from each of the plurality of satellites may be determined. Particular mutually coherent local oscillator and digital clock frequencies are selected in order to minimize the complexity of the receiver without creating any undesired side effects. A high resolution relative phase measurement is made in each digital section by averaging the number of phase shifting pulses over a period of time that are generated by a phase locked loop that is locked onto an L-band carrier frequency, that average incremental phase being added to a base phase measurement obtained simultaneously in each of the digital processing channels.

Multibit decorrelated spur digital radio frequency memory

Abstract: A decorrelated spur digital radio frequency memory (DRFM) system stores incoming radio frequency (RF) signals in a digital memory and at some later time replicates these RF signals at the output. The input RF signal to be stored is mixed with a local oscillator (LO) signal, which is coded with a decorrelation waveform, to produce an intermediate frequency (IF) signal which is next digitized with a multibit analog-to-digital (A/D) converter. This data is stored in a digital memory and is later retrieved from the memory and converted back to an analog IF signal. The IF signal is then mixed with the coded LO to produce a replica of the original RF signal. The code on the LO is the same decorrelation waveform used to produce the input IF signal. The resultant RF output spectrum can be made to be spectrally clean, i.e., containing no spurious harmonic signals arising from the signal's quantization. This invention has the significant benefit of allowing key design options to be selected, in particular such options include the number of bits per sample, the number of channels, and the decorrelation phase resolution to obtain the most appropriate cost, size, instantaneous bandwidth and spur level combination.

Alpha and gamma RF capacitance discharges in N2 at intermediate pressures

Abstract: Measurements have been made on the current and voltage characteristics and the time-resolved and time-averaged visible emission of alpha-( alpha -) and gamma- ( gamma -) type RF capacitative discharges in N2 at frequencies between 10 and 60 MHz over the pressure range 10 to 100 Torr. A time-dependent model is proposed for alpha -type discharges that yields electron energy and density, internal potentials, discharge current and power dissipation given the measured parameters of inter-electrode voltage and separation, gas pressure and RF frequency. The model predicts considerable energy dissipation in the near electrode sheaths and elucidates the increasing stability of alpha discharges for higher input powers as the RF frequency is raised.

Mobile station equipment for a mobile radio telephone system

Abstract: A mobile station equipment for a mobile radio telephone system uses a voltage-controlled, temperature-compensated crystal oscillator (VC-TCXO) as a reference oscillator for local oscillators in frequency converters which convert an RF signal into IF signals. The oscillation frequency of the VC-TCXO is controlled by counting the second IF information and evaluating its difference from a certain reference value. At reception, the local oscillators have their reference frequency stabilized based on the stable frequency information from the base station. The equipment is compact and has reduced power dissipation and lower manufacturing cost.

Balun circuit for radio frequency coils in magnetic resonance systems

Abstract: A balun circuit arrangement for radio frequency (RF) coils in magnetic resonance (MR) systems. The balun circuit arrangement comprises a conductor having a length equal to a quarter wavelength at the tuned resonance frequency of the (RF) coil.

System and method for detecting arcing in dynamoelectric machines

Abstract: System and method for detecting arcing faults in a dynamoelectric machine by monitoring the neutral lead of the machine for a radio frequency voltage produced by arcing, providing a warning signal in response to a change in the radio frequency voltage, and providing a shutdown signal in response to a radio frequency voltage greater than a predetermined level. An RF voltage coupler is capacitively coupled ot the neutrla lead, and a radio frequency monitor connected to the voltage coupler detects peaks in the RF voltage.

Simulation of magnetrons and crossed-field amplifiers

Abstract: Describes a computer program for simulation of the magnetron oscillator and crossed-field amplifiers. Emphasis is placed on accuracy and efficient computation with moderate numbers of electrons and moderately large time steps. Distinctive features are (1) space-charge field evaluation by Buneman's cycle reduction method and separate treatment of electrons near the cathode; (2) circuit field and electronic induction calculation by use of a Ramo (Green's) function, accounting for space-harmonics; (3) calculation of RF network response by means of Green's functions; (4) predictor/corrector evaluation of average RF signals; and (5) use of fifth-degree power series calculation of electron trajectories. The simulation is illustrated in the starting of oscillations from computer noise. >

On-glass antenna

Abstract: An antenna is disclosed which is particularly suitable for use with a cellular mobile phone. The antenna may be mounted on the rear window of a vehicle, and it includes a current fed one-quarter wavelength radiator adapted for mounting on one side of the window. An electrically conductive inner transfer member is mounted on the inside of the window in alignment with the radiator and a pair of spaced field-cancelling conductors are attached to the inside of the window and are spaced from the inner transfer member. The central conductor of an RF coaxial cable is coupled to the inner transfer member and the surrounding ground conductor of the coaxial cable is coupled to the field-cancelling conductors. In one embodiment, the one-quarter wavelength radiator comprises a pair of parallel, spaced radiator elements. RF energy is transferred through the vehicle window and the drilling of a hole for coupling the radiator to the coaxial cable is unnecessary.

Methods and apparatus for detecting certain compounds

Abstract: The detection of compounds containing both nuclei of a kind which exhibit nuclear magnetic resonance (nmr) and nuclei of a kind which exhibit nuclear quadrupole resonance (nqr), for example compounds containing both 1 H and 14 N nuclei, is carried out by subjecting a substance suspected of containing such a compound to a magnetic field and repetitively to three parallel activities A,H and B. Activity A comprises two similar rf pulse sequences PA and PB at the nmr frequency. Activity H is a temporary change in the value of the magnetic field, which may be a reduction to zero. Activity B is the application of additional rf signals. Activity H and/or activity B are different during each of the respective pulse sequences PA and PB. The activity B rf signals are at one or more frequencies selected so that in combination with the activity H in at least one of the pulse sequences the subsequent nmr signal is modified if such a compound is present. The difference in magnitude of the nmr signals obtained following the two types of rf pulse sequence is then measured.

Low temperature plasma generator with minimal RF emissions

Abstract: A low temperature plasma generator having reduced radio frequency (RF) emissions, and a method for reducing the RF emissions of a plasma generator. A low temperature plasma generator (100) includes a pair of electrodes (150 and 160) that are energized by an RF power supply (138) through a balanced impedance matching network (200). The impedance matching network includes a balun transformer (158), matched variable inductors (222 and 230), a fixed capacitor (240) in parallel with a variable capacitor (244) and a fixed capacitor (242) in parallel with a variable capacitor (246). The RF potential on electrodes (150 and 160) varies sinusoidally between opposite positive and negative values with respect to ground potential, such that the net potential on the two electrodes with respect to ground is always substantially equaol to zero, thus eliminating a glow discharge current and radiation emissions that otherwise are produced by similar prior art low temperature plasma generators.

Quasi-optical integrated antenna and receiver front end

Abstract: A quasioptical receiver front end applicable to both microwave and millimeter-wave receiver arrays is presented. Two planar microwave integrated circuit (MIC) quasioptical receiver circuit designs that integrate a coupled slot antenna, a Schottky-diode balanced mixer, and a local oscillator on the same substrate are described. The even-mode/odd-mode characteristics of the coupled slotlines are used to achieve intrinsic RF/LO and RF/IF isolation. To demonstrate circuit feasibility, X-band scaled models of the circuit unit using a Gunn-diode oscillator on an Epsilam-10 substrate, and MESFET local oscillator on a R/T Duroid substrate were built and tested. Results of these tests are included. >

Near obstacle detection system

Abstract: In a radar system, an RF signal is transmitted at a frequency modulated by a sawtooth signal. The transmitted RF signal is mixed with the transmitted signal reflected from an object. The resulting IF signal is analyzed into a Fourier series having a DC coefficient and harmonic frequency coefficients. The range to the object is determined from the harmonic frequency coefficients in multiples of the range resolution determined by the RF bandwidth of the system when the DC coefficient is less than each of the harmonic frequency coefficients. The range to the object is determined to be within 1/2 the range resolution determined by the RF bandwidth when the DC coefficient is greater than each of the harmonic frequency coefficients.

RF channel expansion in a trunked radio communications system

Abstract: In a trunked radio frequency communications system, an arrangement dynamically "expands" or extends the frequency allocation table stored within the "personality" defining non-volatile storage device of transceivers to include additional RF channels. A channel configuration control message specifying a logical channel field and an FCC channel number defining an RF channel frequency is periodically transmitted over the active RF digital control channel. Transceivers correctly receiving this channel configuration message extend their stored frequency allocation tables to add the additional channel entry specified by the message. The transceivers reference these additional records in response to call messages and are thus capable of operating on the new channels. Channel configuration messages are periodically repeated at time intervals long enough to ensure the messages have no real adverse impact on control channel loading but short enough to cause transceivers to almost immediately update stored channel information. Errors are prevented from occurring by transmitting the channel configuration message in both slots of an outbound control channel message and requiring receipt of a non-zero site identification control message before processing any channel configuration message.

Multi-dimensional selective nmr excitation with a single rf pulse

Abstract: A single rotating NMR π pulse provides simultaneous spatially-selective inversion or spin-echo refocussing of nuclear spins in two orthogonal dimensions. The two-dimensional spatially-selective pulse utilizes a single RF pulse, with either a square or an amplitude-modulated or a frequency-modulated envelope, and applied in the presence of an amplitude-modulated magnetic field gradient which reorients through the desired dimensions in which selection is desired while the RF pulse is present. These rotating, or "p", pulses are useful for reduction of aliasing signal artifacts in restricted field-of-view high-resolution NMR imaging and, when combined with one-dimensional-localized chemical shift spectroscopy techniques (such as those employing surface detection coils) is especially useful for the production of three-dimensionally localized NMR spectra. Substantial suppression of undesirable residual excited signals, arising from outside the desired two-dimensional spatially selected region, can be obtained by simulated annealing optimization of both the RF and magnetic field gradient amplitude portions of the p pulse and/or by use of surface coil detection. The location of the selected volume is varied by frequency modulation of the RF signal pulse, or by variation of the ratio of currents in the halves of the magnetic field gradient coils.

An electrically self-oscillating, rf-excited gas laser

Abstract: An electrically self-oscillating radio frequency-excited gas laser. The discharge section of the laser resonates at a de­ sired radio frequency as a result of incorporating the discharge section into the feedback loop of a power oscillator circuit. This laser structure facilitates initial plasma breakdown and adapts its frequency depending upon whether the gas in the discharge section has broken down. When the laser plasma tube is integrated with the oscillator, the laser is also somewhat smaller compared to gas lasers having conventional crystal-controlled amplifier chains.

HDVC converter station tests in the 0.1 to 5 MHz frequency

Abstract: Radiofrequency (RF) quantities in and around an HVDC converter station were measured in the 0.1 to 5 MHz frequency range to provide baseline data for the formulation of a means to predict the RF performance of such stations. Special records were taken at selected points and traverses in the station. The RF voltages of buses were measured and ground-level electric field strength and magnetic flux density measurements were conducted. To obtain the maximum amount of information about a converter pole when it is considered as an RF source, swept frequency (broadband) measurements were selected as the prime records for the analysis of pole performance. The principal source of the RF noise is the firing valve. Additional impedance versus frequency measurements of station components were also performed for undertaking RF modeling of the converter station. >

Long time constant eddy current compensation

Abstract: Magnetic coils (12) create a generally uniform magnetic field through an examination region (10). A radio frequency transmitter applied RF pulses to an RF antenna (26). A gradient field controller (30) generates gradient excitation current pulse profiles which pass through an eddy current calibration circuit (50) to gradient coils (38). A radio frequency receiver (92) receives magnetic resonance signals from the examination region, which signals are Fourier transformed (94) into an image representation (96). The eddy current calibration circuit (50) modifies the current pulse profiles in order to compensate for eddy currents, i.e. to remove the effect of eddy currents such that the resultant gradient magnetic field has a selected profile. An automatic calibration circuit (60) adjusts the decay constant or center frequency of a band pass filter (56) and the gain of an amplifier (58). A sine wave generator (62) applies a sine wave voltage to the gradient coils as a search coil monitors (64) the resultant magnetic field and a current probe (70) monitors the current flowing through the gradient coil. The magnetic field and current are phase sensitively detected (66, 72) to determine the relative amplitude and phase of each. The relative amplitude and phase are compared as the frequency of the sine wave signal is swept. The time constant or center frequency of the band pass circuit is set to the frequency (78) at which the field phase lags the current phase by a maximum and the gain is set in accordance with a fractional fall-off (f) in the relative amplitude.

Measurement of integrated tuning elements for SIS mixes with a Fourier transform spectrometer

Abstract: Planar lithographed quasioptical mixers can profit from the use of integrated tuning elements to improve the coupling between the antenna and the SIS mixer junctions. We have used a Fourier transform spectrometer with an Hg-arc lamp source as an RF sweeper to measure the frequency response of such integrated tuning elements. The SIS junction connected to the tuning element served as the direct detector for the spectrometer. This relatively quick, easy experiment can give enough information over a broad range of millimeter and submillimeter wavelengths to test both design concepts and success in fabrication. One type of tuning element, an inductive wire connected in parallel with a series array of 5 SIS junctions across the terminals of a bow-tie antenna, shows a resonant response peak at 100 GHz with a 30% bandwidth. This result is in excellent agreement with theoretical calculations based on a simple L-C circuit. It also agrees very well with the RF frequency dependence of the mixer gain measured using the same structure. The other type of tuning element, an open-circuited stub connected in parallel with a single SIS junction across the terminals of a bow-tie antenna, exhibits multiple resonances at 110, 220, and 336 GHz, with bandwidths of 9–15 GHz. This result is in good agreement with theoretical calculations based on an open-circuited stub with small loss and small dispersion. The position and the bandwidth of the resonance at 110 GHz also agrees with the RF frequency dependence of the mixer gain measured using similar structures.

Calculation of EM power deposition for operator exposure to RF induction heaters

Abstract: Calculations are presented for electromagnetic power deposition (specific absorption rates, or SARs) in an anatomically realistic model of the human torso for spatially varying leakage magnetic fields due to a 450 kHz RF induction heater. A previously described impedance method that neglects the effects of the operator's body on the source, because of weak coupling, is used for the calculations. SARs on the order of a few mu W/Kg are found for magnetic fields on the order of 1.8 A/m at the central plane of the model. This implies that fairly low SARs result from leakage magnetic fields on the order of 1-20 A/m that are typical of RF induction heaters. >

Radio control transmitter which suppresses harmonic radiation

Abstract: A radio control transmitter which suppressed harmonics includes an oscillator which is coded by code selecting switches and in which undesired harmonics are reduced from the output of the transmitter by adding inductors into the emitter, the collector or the base of the radio frequency oscillator.

RF power amplifier protection

Abstract: An RF power amplifier is operated by supplying an RF signal to the amplifier for amplification and thereby providing an output RF signal to the amplifier's output circuit which has an impedance matching output network connected in series with a load. A detector serves to detect any reflected power in the output circuit. The RF power amplifier is turned off when the detected RF power exceeds a reference level. The amplifier is protected by discontinuing the supply of the RF signal to the amplifier while it is turned off and, instead, a frequency signal is supplied to the RF amplifier having a frequency that corresponds with that of any current flowing in the output circuit.

RF power supply for supplying a regulated power amplified unmodulated drive signal to an RF modulator

Abstract: An RF power supply serves to supply a regulated power amplified RF drive signal to an RF transmitter. The supply includes an RF oscillator for providing an RF input signal. A DC voltage source provides a DC voltage V. A plurality of power amplifiers are provided with each receiving the input RF signal and each having an input for receiving a DC voltage signal, and each serving to amplify the input RF signal by an amount dependent upon the magnitude of the DC voltage signal supplied to its input and thereby provide an amplified RF signal. The amplified RF signals are combined to provide an RF drive signal. The DC voltage V is directly supplied to the input of at least a first one of the power amplifiers. A regulating means serves to regulate the magnitude of the RF drive signal with the regulating means including circuitry for applying a fractional portion of the DC voltage V to the input of at least a second one of the power amplifiers with the fractional portion varying as a function of any variation in the magnitude of the DC drive signal with respect to a desired magnitude thereof.

Radio with broad band automatic gain control circuit

Abstract: The disclosure relates to a radio which prevents the level of a signal transmitted from a desired broadcasting station from being suppressed by the operation of a broad band automatic gain control circuit in the presence of an interference signal. The radio comprises a first detector for detecting the intensity of the electric field of a received signal; a second detector for detecting whether or not the broad band automatic gain control is operating; and a device for changing the tuning condition of a radio frequency tuning circuit in a small extend in response to the signals outputted from the first and second detectors.