Showing papers on "Radio frequency published in 1973"

Fourier synthesized excitation of nuclear magnetic resonance with application to homonuclear decoupling and solvent line suppression

Abstract: A method is described for exciting a nuclear magnetic resonance spectrum with a radio frequency source having any desired frequency spectrum. The frequency spectrum of the source is first specified and then Fourier synthesized to define a function which is used to modulate a radio frequency carrier. The NMR spectrum is obtained by Fourier transforming the response of the spin system to this excitation. The technique is applied to the problem of suppressing a strong solvent line while simultaneously observing all other resonance lines in a spectrum and to homonuclear decoupling while observing a complete spectrum.

Electron beam electrical power transmission system

Abstract: Electrical power is transmitted from a transmitting location to a remote receiving location by means of an electron beam injected into an evacuated magnetically shielded pipe extending between the transmitting location and the receiving location. The beam is magnetically focused within the evacuated pipe. Electrical power to be transmitted is put into the beam in the form of kinetic energy by accelerating the beam to a high kinetic energy. The kinetic energy is extracted from the beam at the receiving location and converted into potential electrical energy for application to the load. In one embodiment, the kinetic energy is extracted from the beam by collecting the beam current at a potential substantially equal to the potential of the source of the electrons, i.e. cathode potential, and causing the collected beam current to flow through the load to develop the depressed collector potential. In another embodiment, radio frequency accelerator means are utilized for r.f. current density modulating and accelerating the beam. The radio frequency current modulation on the beam is extracted at the receiving end by means of radio frequency circuits coupled to the beam. The extracted radio frequency energy is rectified for application to the load. In another embodiment, AC power at conventional AC power frequencies, as of 60 Hertz, is extracted from the beam by sequentially directing the beam into a plurality of depressed collectors coupled to respective primary windings of power transformers for deriving AC output power for application to a load.

Interstellar Radio Communication and the Frequency Selection Problem

Abstract: THE largest microwave radio telescope on Earth, at the Arecibo Observatory of the National Astronomy and Ionosphere Center, will soon have the capability of communicating with an identical radio telescope, if such exists, anywhere in the Galaxy. But such communication assumes some previous agreement between the transmitting and receiving civilizations, or mutual discovery of the chosen radio frequency, bandpass, information rate and each other's location.

On the equivalent parabola technique to predict the performance characteristics of a Cassegrainian system with an offset feed

Abstract: The so-called equivalent parabola technique has been used extensively in the design of Cassegrainian systems. Hannan substantiated the validity of the technique by showing the excellent agreement between his measured data on a Cassegrainian system and the calculated results obtained using the equivalent parabola technique. However, his demonstration was restricted to an on-axis feed Cassegrainian. This paper derives an analytical expression involving only a 2-dimensional vector integral for the secondary vector field from the Cassegrain system with an offset feed by integrating over the surface currents on both the main dish and subdish with the \phi integrations performed in closed form, and proceeds to compare its results with those obtained from the equivalent parabola technique, for different f/D of the main dish, eccentricities of the subdish, illumination patterns, and lateral displacements of the primary radiator. The agreement in general is good for Cassegrainians with an on-axis feed. For Cassegrainians with an offset feed, the error in using the equivalent parabola technique remains negligible for a beam scan of as much as four beamwidths.

Multiple-channel information translation system and method

Abstract: A multiple-channel information translation system includes a Bragg light-sound interaction cell interposed in the path of a spatially coherent input light beam. Carrier generating means generates a plural number greater than two of electrical carriers each having a different RF frequency. The carriers are respectively amplitude modulated by information-bearing input signals to produce a like plural number of amplitude-modulated carrier signals used to drive the Bragg cell. The cell Bragg-diffracts the input beam into a corresponding plural number of primary output light beams respectively amplitude-modulated in accordance with the input signals. The carrier generating means causes the frequencies, or frequencies and relative phase, of the carriers to be such that random, signal-related spurious amplitude modulation of the primary output light beams which might otherwise result from cross-channel interference effects in the cell is suppressed. In one disclosed embodiment the carrier frequencies are selected such that the frequency differences between each carrier frequency and all others are equally spaced in the frequency domain. In a second disclosed embodiment the carriers are phase-locked in order to effect the said suppression of spurious amplitude modulation of the primary output beams.

Dual radio frequency measurement of dielectric constant and resistivity of borehole media

Abstract: An illustrative embodiment of the invention discloses methods and apparatus for measuring the resistivity and dielectric constant of earth formations in the vicinity of a well borehole. Radio frequency electromagnetic fields are generated in the borehole at a pair of frequencies of approximately 16 and 30 megahertz. The amplitude of the total field voltage induced in a single receiver coil located a longitudinally spaced distance away is detected at each of the two frequencies and either recorded directly or used to derive from predetermined relationships the resistivity and dielectric characteristics of the earth formation materials.

Multiple receiver selection system

Abstract: The invention provides apparatus for selecting from a plurality of receiving stations, each station simultaneously receiving radio frequency signals containing identical information, the signal with the best signal-noise ratio. At each receiving station a control signal is generated, the frequency of which is determined by the signal-noise ratio of the radio signal received by that station. These signals are fed from the respective receiving stations to a central control which monitors the incoming control signals and selects the signal with the best signal-noise ratio.

Computer simulation of instability and noise in high-power avalanche devices

Abstract: The operation of avalanche transit-time devices at or near their output saturation point is often accompanied by instabilities and a deterioration of the spectral purity of the output signal. This can be attributed to a number of nonlinear effects that give rise to additional static or dynamic negative resistance. Depending on the external RF and bias circuit conditions, spurious oscillations, discontinuities, and quasi-random modulation of the carrier due to non-linear signal interaction can result. Prior to the onset of instabilities, low-frequency avalanche-noise components are selectively amplified, up-converted, and appear as noise sidebands of the output signal. These effects and their dependence on external circuit conditions are examined with the aid of a computer, simulation program. The features of this particular program are high computational speeds flexibility in the assumption of input data, and the inclusion of random noise in the simulation. The results of the computations are compared with analytical expressions and experiment. It is shown that the basic excess noise contribution at high signal levels stems from the "buildup" noise of the avalanche and increases approximately inversely proportional to the conduction current minimum. Instabilities are due to negative resistance components induced either by parametric signal interaction or rectification effects of the diode. Under high-power operation the spectrum of negative induced resistance extends from dc to the transit-time signal frequency. Strong parametric oscillations occur at subharmonic frequencies of the output signal while the period of dc block oscillations is primarily determined by the growth rate of the RF signal and the time constants of the external circuit elements. Under unfavorable bias and RF circuit conditions the initiation of lower frequency instabilities can lead to very high peaks of the current-density that are believed to be the cause of the frequently observed "anomalous" burnout of high-power diodes. The deterioration of the noise performance and stability at low temperatures results from the combined effect of the temperature dependence of effective reverse saturation currents and breakdown field. An example of a simple TRAPATT oscillator simulation is given and it is shown that the AM and FM noise spectra depend strongly on the magnitude of the minority saturation currents.

Marine object detector

Abstract: A system is disclosed for detecting and locating the occurrence of anomal to radio frequency electromagnetic transmission in conductive liquids. Applications are described for use in swimmer detection and for process monitoring.

Scanning radio receiver

Abstract: A signal-seeking receiver automatically scans a plurality of channels of respective predetermined radio frequencies lying in a multiplicity of frequency bands. The channels are tuned in successively by successively coupling respective tuning crystals into the tuning circuit of a signal generator which produces the beating signals for heterodyning. Scanning is stopped upon receiving a signal. For higher bands the frequency of a basic oscillator is multiplied by cascaded frequency-multiplying circuits. Automatic frequency control is provided, for channels in the highest band, with gating means for disabling the frequency control in the absence of a received signal. For bypassing selected channels during scanning, the clock driving the scanner is speeded up when the channels to be bypassed would otherwise be tuned in.

Radio-frequency pulse generation system and method

Abstract: This disclosure is concerned with radio-frequency pulse generation, as for Loran type navigation transmissions and the like, wherein the transmitted pulse is generated by causing a pair of opposite poled half-cycle pulse generators to impulseexcite a tuned coupling network and antenna (or other load), the transfer function characteristics of which are adjusted to yield the desired pulse shape, with the complete cycle resulting from the pair of pulse generator half-cycles controlling, for example, the first two half cycles of the leading edge of the antenna pulse current, and the network and antenna characteristics controlling the remaining half cycles.

Dual radio frequency method for determining dielectric and conductivity properties of earth formations using normalized measurements

Abstract: A representative embodiment of the present invention discloses methods for determining the conductivity and dielectric characteristics of earth formations in the vicinity of a well borehole. Prior to entry into the borehole, radio frequency electromagnetic fields are generated in a homogeneous medium (such as air) at a pair of frequencies of approximately 16 and 30 megahertz. The amplitude of the total field measured in a single receiver coil located at a longitudinally spaced distance is detected at each frequency and used to define a normalization unity amplitude. Measurements of the total field amplitudes taken in the borehole at the pair of frequencies are then normalized to the unity amplitude homogeneous medium signal. The borehole total field normalized signals may be recorded directly as a function of depth or used with predetermined relationships to derive signals representative of the conductivity and dielectric properties of the formations.

Intensity modulated optical carrier communication system

Abstract: A low-cost, reliable optical communications system and method, a feature of which is the use of an optical carrier beam which is intensity modulated at radio frequencies above one MHz and below the microwave range to produce a radio frequency subcarrier on the optical carrier. The radio frequency subcarrier is angle modulated, either in frequency or phase, for signal transmission. The frequency or phase modulation at radio frequencies insures high immunity to adverse atmospheric conditions, such as rain, snow, fog and turbulence. Other features include the maintenance of the subcarrier operating point by reversing the polarity of the voltage on the electro-optic crystal without changing the absolute magnitude of the voltage and the manner of locking the transmitter onto the receiver.

R-F switching circuit

Abstract: An insulated gate field effect transistor (IGFET) is used selectively to connect a source of radio frequency (e.g., VHF) signal to means for utilizing the radio frequency signal. First and second gate potentials are selectably applied to the IGFET to render its channel conductive and non-conductive, respectively. The first potential is applied from a source impedance appreciably higher than the reactance of the gate-to-channel capacitance of the IGFET for radio frequency signal. This prevents a distributed RC transmission line effect in the IGFET introducing reflections back to the source of radio frequency signals when the IGFET channel is conductive. The second potential is applied from a source impedance appreciably lower than the reactance of the gate-to-source and gate-to-drain capacitances of the IGFET for radio frequency signal, to reduce feedthrough of radio frequency signal when the channel is non-conductive.

Electron beam electrical power transmission system

Abstract: Electrical power is transmitted from a transmitting location to a remote receiving location by means of an electron beam injected into an evacuated magnetically shielded pipe extending between the transmitting location and the receiving location. The beam is magnetically focused within the evacuated pipe. Electrical power to be transmitted is put into the beam in the form of kinetic energy by accelerating the beam to a high kinetic energy. The kinetic energy is extracted from the beam at the receiving location and converted into potential electrical energy for application to the load. In one embodiment, the kinetic energy is extracted from the beam by collecting the beam current at a potential substantially equal to the potential of the source of the electrons, i.e. cathode potential, and causing the collected beam current to flow through the load to develop the depressed collector potential. In another embodiment, radio frequency accelerator means are utilized for r.f. current density modulating and accelerating the beam. The radio frequency current modulation on the beam is extracted at the receiving end by means of a radio frequency circuits coupled to the beam. The extracted radio frequency energy is rectified for application to the load. In another embodiment, AC power at conventional AC power frequencies, as of 60 Hertz, is extracted from the beam by sequentially directing the beam into a plurality of depressed collectors coupled to respective primary windings of power transformers for deriving AC output power for application to a load.

Magnetic resonance spectrometer employing stochastic resonance by a pseudorandom binary sequence and time-share modulation

Abstract: A magnetic resonance spectrometer employing a pseudorandom binary sequence to simultaneously excite magnetic resonance of a plurality of resonance lines in the spectrum of a sample under analysis, the driving radio frequency field being applied to the sample in a train of pulses in each binary sequence, the timing or phase of the pulses being changed in a stochastic manner in the sequence, the composite noise excited resonance signal being detected in a receiver and sampled in a multitude of time displaced intervals in correlation with the binary sequence and stored in an accumulative manner in the associated channels of a memory of subsequent processing, read-out and display, the receiver being activated during the time intervals between the application of the radio frequency pulses to the sample.

Method and apparatus for measuring physical and/or chemical properties of materials

Abstract: A method and apparatus for measuring physical and/or chemical properties of materials such as dielectric constants, solid content, or the like without establishing any physical contact with the materal. The method and the apparatus rely upon the generation of electromagnetic waves, presumably radio frequency waves in a fringing field which is directed toward the surface of the material to be tested. The electromagnetic waves are coupled through this material and a sensor in an oscillator circuit and this oscillator circuit generates an oscillating frequency proportional to the property of the material.

Method and apparatus for detecting nuclear magnetic resonance

Abstract: Apparatus for detecting nuclear magnetic resonance in which the sample is subjected to a high magnetic field in one direction to polarize the nuclear spins, then an alternating radio frequency magnetic field is applied to the sample and varied from a frequency below the resonant frequency of interest of the sample to a frequency above the resonant frequency, or vice versa, at a rate which provides adiabatic fast passage. A detector detects the change in the magnetization parallel to the direction of the magnetic field during said adiabatic fast passage. The method of detecting nuclear magnetic resonance which comprises polarizing the sample, changing the steady state value of the longitudinal magnetization and detecting the change in the steady state value of the longitudinal magnetization.

Velocity modulation microwave tube employing a harmonic prebuncher for improved efficiency

Abstract: The velocity modulation microwave tube includes an electron gun for projecting a stream of electrons over an elongated beam path to a collector structure. An input circuit and an output circuit are disposed at the upstream and downstream ends, respectively, of the beam for applying microwave energy to be amplified to the tube and for extracting the amplified microwave energy from the beam. A penultimate resonator circuit, tuned for a mode of resonance at a frequency near the passband of the tube, is provided just upstream of the output circuit for bunching the current density of the beam passing into the output circuit. A harmonic floating resonator structure is disclosed along the beam path intermediate the input circuit and the penultimate resonator. The harmonic resonator is tuned for a mode of resonance approximately at a frequency corresponding to a harmonic higher than the first of the center frequency of the passband of the tube. The harmonic resonator serves as a prebuncher to bunching the electrons of the beam prior to their entering the final stage of bunching performed by the penultimate floating resonator. The combined action of the harmonic prebuncher resonator and the penultimate final buncher resonator is to substantially increase the radio frequency conversion efficiency of the tube.

A Magnetically Tunable Microstrip IMPATT Oscillator (Short Papers)

Abstract: Magnetically tunable resonators have been constructed in microstrip on a ferrite substrate. A large tuning range is obtained with an external magnetic field applied in the direction of the RF propagation, 17 MHz/Oe for magnetic fields from 0 to 30 Oe. A variable frequency microstrip oscillator which uses this effect is described; measurements made on an X-band IMPATT oscillator illustrate a tuning range from 9.4 to 10.5 GHz with an output power of 330 mW /spl plusmn/ 0.5 dB.

Physical Sciences: Fine Structure of the Jupiter Radio Bursts

Abstract: SHORT pulses with a time scale of milliseconds and fractions of a millisecond have been observed in the radio emissions of Jupiter at wave frequencies near 20 MHz since 1956 (refs. 1 and 2). Little is known about these “S” bursts, however, although it has been established3 that their occurrence depends strongly on the orbital position of the satellite Io. Further, Gordon and Warwick4 were able to show from a small set of observations that the bursts may have a relatively narrow radio frequency bandwith (<50 kHz) and that their centre frequency may change rapidly with time at the rate 25–35 MHz s−1, at least near 26 MHz.

Dark Current and Electron Energy Spread in a Magnetron

Abstract: The circulating electrons in a high power CW magnetron have been investigated with probes in the vane tips. The rf signal shows that the sub-threshold or dark current results from a bunching of the electrons. The probe voltage-current characteristic provides a measure of the electron energy spread.

Rf hazard detector

Abstract: A hand-held tester for determining whether an object that is being irradiated with radio frequency energy is at a dangerously high induced radio frequency voltage level. The tester has a high impedance probe, and when this probe is brought in contact with such an object, the radio frequency flow, which takes place through it and the tester, develops a signal which is compared to a reference voltage. When this voltage is exceeded by a predetermined amount, a warning light source is operated.

Vibration-RF Control of Superconducting-Helix Resonators for Heavy-Ion Acceleration

Abstract: An electronic system for the control of the effects of RF frequency oscillations caused by mechanical vibrations in a superconducting helix are described. A combination of frequency modulation and amplitude modulation is used to lock the phase of a self-excited accelerating structure to that of a controlling master oscillator. The system has been used successfully during beam acceleration with a superconducting helix.

The audio frequency size effect seen in the modulation of the radio frequency size effect

Abstract: The modulation field used in the radio frequency size effect is screened by induced audio frequency currents. The incomplete penetration of the modulation field can be clearly seen in the phase lag of the Gantmakher resonance signal behind the signal due to surface bound states. A comparison of the phase lag as a function of modulation frequency with a simple theory leads to an estimate of the bulk electron mean free path. The influence of modulation field screening on measurements of the phonon limited mean free path and other applications are discussed.

Electron beam electrical power transmission system

Abstract: Electrical power is transmitted from a transmitting location to a remote receiving location by means of an electron beam injected into an evacuated magnetically shielded pipe extending between the transmitting location and the receiving location. The beam is magnetically focused within the evacuated pipe. Electrical power to be transmitted is put into the beam in the form of kinetic energy by accelerating the beam to a high kinetic energy. The kinetic energy is extracted from the beam at the receiving location and converted into potential electrical energy for application to the load. In one embodiment, the kinetic energy is extracted from the beam by collecting the beam current at a potential substantially equal to the potential of the source of the electrons, i.e. cathode potential, and causing the collected beam current to flow through the load to develop the depressed collector potential. In another embodiment, radio frequency accelerator means are utilized for r.f. current density modulating and accelerating the beam. The radio frequency current modulation on the beam is extracted at the receiving end by means of radio frequency circuits coupled to the beam. The extracted radio frequency energy is rectified for application to the load. In another embodiment, AC power at conventional AC power frequencies, as of 60 Hertz, is extracted from the beam by sequentially directing the beam into a plurality of depressed collectors coupled to respective primary windings of power transformers for deriving AC output power for application to a load.