Showing papers on "Radio frequency published in 1968"

A statistical theory of mobile-radio reception

Abstract: The statistical characteristics of the fields and signals in the reception of radio frequencies by a moving vehicle are deduced from a scattering propagation model. The model assumes that the field incident on the receiver antenna is composed of randomly phased azimuthal plane waves of arbitrary azimuth angles. Amplitude and phase distributions and spatial correlations of fields and signals are deduced, and a simple direct relationship is established between the signal amplitude spectrum and the product of the incident plane waves' angular distribution and the azimuthal antenna gain. The coherence of two mobile-radio signals of different frequencies is shown to depend on the statistical distribution of the relative time delays in the arrival of the component waves, and the coherent bandwidth is shown to be the inverse of the spread in time delays. Wherever possible theoretical predictions are compared with the experimental results. There is sufficient agreement to indicate the validity of the approach. Agreement improves if allowance is made for the nonstationary character of mobile-radio signals.

Frequency shift telemetry system with both radio and wire transmission paths

Abstract: A transmission system using a possibly existing wiring system for transmitting RF signals and covering short distances away from the wiring system through VHF transmission. In hospitals, physiological data are transmitted from a sensor VHF transmitter to a fixed VHF receiver RF transmitter coupled to the wiring system in the building. A RF receiver demodulator monitor is coupled to wiring system at the nurses'' station. The system is particularly designed for noise suppression.

Combustion microwave diagnostic system

Abstract: Systems to resonate the combustion chamber of internal combustion engines at radio frequencies, at all available engine r.p.m. are disclosed. Methods, to employ radio frequency resonances for mechanical and electrical measurements within and near the combustion chamber, at all available engine r.p.m., are also disclosed. The system comprises a tunable source of coherent radio frequency energy and a hybrid transmission line to convey the radio frequency energy into the combustion chamber and also to detect the energy reflected from the combustion chamber. The methods, to perform mechanical and electrical measurements within the combustion chamber are ones that correlate the change in the number and properties of the resonances with the continuously changing properties of the combustion chamber.

Broadband Matching of Resonant Circuits and Circulators

Abstract: In a high-power microwave system (particularly a CW or long-pulse system), it often becomes necessary to protect the transmitter from the damaging effects of RF breakdown in the waveguide. The onset of RF breakdown may be detected by optical detectors or by an increase in the reflected RF signal. Fast switches can be arranged to turn off the transmitter in a time of the order of a microsecond. Under these conditions, it becomes difficult to determine the location of the breakdown. This correspondence describes an experiment to test the feasibility of locating the arc by measuring the time delay required for the sound from the arc to reach a microphone placed at some point in the waveguide.

A high-power, untuned radio-frequency transmitter for pulsed nuclear magnetic resonance spectroscopy

Abstract: A gated radio-frequency transmitter suitable for pulsed nuclear magnetic resonance spectroscopy is described. It has a wide frequency response (3 dB from about 20-50 MHz) and can deliver pulses of greater than 900 v peak to peak into 180 Ω resistive loads with rise and fall times of less than 01 μs. The circuitry described includes a gated radio-frequency mixer-amplifier with two variable phase inputs, and a gated radio-frequency power amplifier. The gating circuits used are d.c. coupled throughout to prevent droop in long pulses and interaction between the pulses.

Nondestructive testing of conductive objects using ultrasonic waves

Abstract: An ultrasonic wave is excited in the surface of the object by direct electromagnetic excitation in the presence of a DC magnetic field having a major component perpendicular to the electric vector of the electromagnetic field at the surface A coil energized with RF may be employed The ultrasonic waves propagate generally perpendicularly to the surface A similar coil and DC magnetic field detect the ultrasonic wave arriving at the object surface after passing through the object, and produce an RF signal varying with flaws or other inhomogeneities in the object Pulsed RF is advantageously employed, and in such case a single coil may be used for both generating the ultrasonic waves and responding to reflections thereof from flaws in the object

Radio frequency properties of a plane grid capacitor immersed in a hot collision-free plasma

Abstract: A pair of plane parallel grids is inserted in a hot plasma, and an oscillatory voltage is applied across them. The electric field excited in the plasma, and the complex admittance of the grid/plasma system, are computed for applied frequencies high enough to justify neglect of ion response. The grids are electrically, but not mechanically, coupled to the plasma, which is assumed to be in a spatially uniform collision free Maxwellian equilibrium state. The field is computed as a function of distance from the grid plates over a range of frequencies covering the plasma frequency, and the complex admittance of the system is computed as a function of frequency at various grid separation distances. The real component of the field and the capacitive component of the admittance are subject to three major effects: cold plasma dielectric behaviour, oscillatory Debye sheaths on the grids, and (above the plasma frequency), longitudinal plasma waves. The imaginary field component and the conductive admittance component are produced by spatial Landau damping. In an accompanying paper (Freeston 1968), the computed admittance is compared with laboratory measurements made in a situation approximating well to the idealized problem considered here.

Resistorless radio frequency hybrid signal splitter

Abstract: A radio frequency signal splitter is described wherein a hybrid coil utilizes a ferrite core whose RF resistance is selected bearing predetermined ratios to the characteristic impedances of the RF input and RF output lines. Several embodiments are described.

Integrated frequency-selective amplifiers for radio frequencies

Abstract: The design approach for integrated selective amplifiers described here is based on a feedback configuration with a positive real zero in the loop transmission function. The basic circuit consists of two unity gain amplifiers and a transconductance block with RC imbedding. Temperature- insensitive performance, with Q values up to at least 150, at center frequencies in the RF range, is obtained for circuits fabricated with conventional diffusion and thin-film deposition techniques. Design equations are given and experimental data are reported for a 650-kHz amplifier with a Q of 50/spl plusmn/5 percent over the temperature range -10 to +110/spl deg/C.

Electronic image rejection apparatus

Abstract: Disclosed is electronic image rejection apparatus which provides relatively uniform image rejection performance over a band of input frequencies and a range of operating temperatures without supplemental frequency or temperature compensation. The apparatus accepts an L.O. signal and an input RF signal containing both desired and image frequency components, and processes the signals in two parallel signal conversion channels to develop a resultant output IF signal which contains substantially only frequency components corresponding to the desired components of the input RF signal. In the parallel channels conversion of the input RF signal to IF takes place together with the introduction of equal but opposite phase shifts. The phase-shifted IF signal in each channel is then further phase shifted an amount equal in magnitude to that introduced in the RF to IF conversion process, and the resulting two IF signals then combined to develop the aforementioned resultant output IF signal. Other embodiments are covered.

CW Transmission Spectrometer for Direct Detection of Nuclear Acoustic Resonance Utilizing Magnetic Field or Frequency Modulation

Abstract: A continuous wave transmission spectrometer operating in the radio frequency range has been developed for direct detection of nuclear acoustic resonance (NAR) in solids. The inherent flexibility of a spectrometer of this type makes possible studies over a wider range of frequencies and ultrasonic powers than is attainable by the more conventional marginal oscillator acoustic spectrometer. With the transmission spectrometer one can observe both absorption and dispersion of acoustic waves, while with the marginal oscillator one is limited to NAR absorption only. An additional feature is the ease of operation of the transmission spectrometer as compared to the marginal oscillator technique. Both magnetic field and frequency modulation have been used with the transmission spectrometer. Certain advantages of frequency modulation, especially with respect to investigations in bulk conductors, are cited.

Performance of Phase-Coherent Receivers Preceded by Bandpass Limiters

Abstract: In phase-coherent communication systems, where bandpass limiters precede the radio frequency (RF) carrier tracking loop, it is of interest to understand how the noisy RF carrier reference effects system performance. This paper characterizes a model probability distribution for the RF phase error and uses this to predict the performance of phase-shifted keyed and differentially coherent systems. The theory developed is directly applicable to the Mariner- and Pioneer-type communication systems. For these systems two physical situations are considered: 1) system performance when the phase error is constant over the duration of one bit, and 2) system performance when the phase error is allowed to vary over the duration of one bit.

Apparatus for maintaining field frequency control in a gyromagnetic instrument

Abstract: An apparatus for automatically controlling the field/frequency ratio of a gyromagnetic resonance instrument during sample exchanging by automatically switching from the resonance parameters of an internal reference control within the unknown sample to the resonance parameter of an auxiliary control sample positioned within a space vacated by the unknown during exchange wherein the audio frequency, radio frequency or magnetic field are changed to compensate for deviations in the resonance parameter of the reference and control samples.

Phase-lock circuit for a 100 MHz nuclear magnetic resonance spectrometer.

Abstract: In heteronuclear double resonance experiments the observing and irradiating radio frequencies are fed into the same nuclear magnetic resonance probe. In many cases a stable relationship between the two radio frequencies is essential. A system meeting this requirement is described whereby the observing frequency of a 100 MHz spectrometer is phase-locked to a harmonic of the 100 kHz reference of a frequency synthesizer, the synthesizer being the source of irradiation. The locking system has a hold-in range of 350 Hz.

Multipacting breakdown in coaxial transmission lines

Abstract: Multipacting breakdown data have been obtained in 50-Ω rigid coaxial transmission lines for frequencies above 150 MHz. The data show very good scaling correspondence with those obtained previously at frequencies below 150 MHz.

The effects of polarization rotation and phase delay with frequency on ionospherically propagated signals

Abstract: When a CW skywave signal is received on a linearly polarized antenna, polarization (Faraday) rotation produces a variation of received signal strength with radio frequency. The resulting dependence of received signal amplitude on radio frequency may impose a bandwidth limitation on pulsed signals where waveform preservation is important. A measure of this limitation, termed polarization bandwidth, is defined to correspond to the bandwidth in which the plane of polarization rotates 90\deg . Computer ray-tracing calculations were performed using a single Chapman-layer ionospheric model to determine the 1-hop polarization bandwidth as a function of geomagnetic azimuth and radio frequency. The polarization bandwidth was found to decrease with increasing radio frequency and with increasingly close alignment of the propagation path with the longitudinal component of the earth's magnetic field. Assuming a critical frequency of 9 MHz and a path length of 2000 km, the polarization bandwidth increased from a minimum of 140 kHz at 10.5 MHz and from a minimum of 70 kHz at 17.5 MHz, as the propagation direction varied from geomagnetic north to east. A model for the 1-hop ionospheric signal channel is proposed whose parameters are the rate of change of polarization rotation with frequency and the phase versus frequency characteristic of the path. These two parameters are shown to be readily determined from FM-CW or equivalent oblique-path sounding records. Using this model, predictions are made of the effects of polarization rotation with frequency, and also of ionospheric dispersion or phase distortion, on the envelope shape of short-pulse signals (of from 1.5 to 50 \mu s duration). A pronounced waveshape distortion due to the effects of polarization rotation on the pulse envelope was observed when the signal bandwidth appreciably exceeded the "polarization bandwidth" for the path.

Cell for Dielectric Measurements in the High Radio Frequency Region

Abstract: The design and construction of a dielectric cell and adaptor suitable for use with the Boonton RX meter are presented. The geometry of the cell can be varied easily to accommodate a wide range of permittivity. Data illustrating the cell performance are included for several known liquids.

High Energy Electrons and Emission of the Omnidirectional Synchrotron Radiation in Radio-Frequency and X-Ray Regions

Abstract: High energy electrons and emission of galactic, omnidirectional synchrotron radiation in radio frequency and X rays regions

Variable time compression, expansion, and reversal of rf signals by laser‐acoustic techniques

Abstract: Continuously variable time compression, expansion, and inversion, with the corresponding changes in frequency, of rf signals in the range of 10 to 100 MHz, are described. By using a simple optical heterodyning technique and high‐speed scanning of a laser beam, an rf signal, ``stored'' as an acoustic signal in a quartz bar, can be processed or ``read out'' in a variety of ways. Although present equipment has limited the amount of processing and frequency range of the signals that can be handled, it is felt that input signal frequencies are restricted only by the acoustic properties of the delay medium and the output frequencies will be limited by the response of the photodetector.

Automatic radio frequency pulse measurement system

Abstract: The microwave pulse signal measurement system described herein automatically derives the Fourier power spectrum of a microwave pulse train from a unit under test and simultaneously measures the frequency at which the microwave pulses have their maximum power. The input microwave pulses are mixed with local signals generated in a microwave synthesizer which is controlled by a programmer to change the frequencies of the local signals in discrete steps. The intermediate frequency burst obtained from the mixer upon occurrence of each microwave pulse is sampled and translated into digital information. A Fourier transform computer obtains from this digital information, output information as to the power density of different frequency components across the spectrum of the microwave pulse. This digital information can be displayed on an oscilloscope or a plotter to provide a visual presentation of the power spectrum of the microwave pulse. The computer outputs are also translated into digital outputs corresponding to the Fourier component having maximum power. These digital outputs may be subtracted from digital outputs obtained from the synthesizer which represent the frequency of the local signals to produce a number directly indicating the frequency at which the microwave pulse has its maximum power.