Showing papers on "Radio frequency published in 1975"

Theory of the propagation of UHF radio waves in coal mine tunnels

Abstract: The theoretical study of UHF radio communication in coal mines, with particular reference to the rate of loss of signal strength along a tunnel, and from one tunnel to another around a corner is the concern of this paper. Of prime interest are the nature of the propagation mechanism and the prediction of the radio frequency that propagates with the smallest loss. The theoretical results are compared with published measurements. This work was part of an investigation of new ways to reach and extend two-way communications to the key individuals who are highly mobile within the sections and haulageways of coal mines.

Radio frequency detection system and method for passive resonance circuits

Abstract: A system for detecting passive resonant circuits in which bursts of swept radio frequency are transmitted to excite passive resonant circuits. If a circuit is resonant at a particular burst frequency, it is excited, rings and emits a radio frequency signal. Following each transmitted burst, a receiver is turned on to receive energy emitted by a resonant circuit so that if a resonant circuit is excited, its emitted energy is received and the particular resonant circuit identified.

Short-range radio-telemetry for electronic identification, using modulated RF backscatter

Abstract: An electronic identification system which uses modulated backscatter from an RF beam-powered tag is described. A subcarrier is used in the return signal format to allow separation from the background clutter and to allow use of a novel method to avoid RF phase problems.

Light generation by an electrodeless fluorescent lamp

Abstract: An electrodeless discharge lamp has an ionizable medium comprising a particular gas composition at a particular pressure within a sealed envelope. Radio frequency electrical power is applied to an induction coil, the magnetic induction field of which is coupled to the medium. For a particular radio frequency, the magnitude of the induction field is selected to maximize the light emitted by the discharge per watt of radio frequency power coupled thereto. The radio frequency is preferably between 3 megahertz and 300 megahertz. In one embodiment, a mixture of mercury vapor and argon is contained within an envelope having an open cylindrical cavity into which the coil fits; the portion of the interior surface of the envelope defining the cavity has a layer of an electrically insulative, ultraviolet reflective material, and the entire interior surface of the envelope has a phosphor layer; radio frequency power at a frequency of about 4 megahertz is applied to the coil by an oscillator having a tuned circuit including the inductor and the discharge.

RF Spectrum of a Signal after Frequency Multiplication; Measurement and Comparison with a Simple Calculation

Abstract: A novel experimental technique is introduced and used to measure the effect of frequency multiplication on the RF spectrum of an oscillator. This technique makes it possible to produce the RF spectrum at X band?where measurements are relatively straightforward?that would have been produced by frequency multiplication of the 5-MHz source to any frequency from 9.2 GHz to 100 THz (1014 Hz). A simplified theory is developed and shown to reproduce the experimental results for the relative power in the carrier and noise pedestal, and the shape and the width of the carrier and noise pedestal, to within the measurement uncertainty of 2 or 3 dB, from 5 MHz to 10 THz. The calculations are easily made using analytical techniques from the measurement of the spectral density of phase fluctuations of the source, the effective input spectrum density and the bandwidth of the multiplier chain, and the frequency multiplication factor. It is shown that present 5-MHz-crystal-controlled oscillators are useful as a precision source to ~500 GHz. Suggestions for extending their range to ~100 THz are made.

Fiber optic phased array antenna system for RF transmission

Abstract: A system for providing the plural variable phase RF signals required to control the beam pointing angle of a phased array A light energy source (shown as a laser generator) is modulated by an RF signal and fed to a plurality of channels in parallel Each of the said channels corresponds to one radiating element of the phased array and each channel includes as many selectively employed fiber optic delay lines of different lengths as are required to generate the discrete phases required at the corresponding antenna (radiator) element of the array A commutating programmer controls the selection of individual radiating element phases for each successive beam pointing position

Fm rf signal generator using step recovery diode

Abstract: A step recovery diode pulse generator is driven by a fixed frequency oscitor to provide pulses which are modulated in a balanced modulator by means of a voltage controlled oscillator controlled by a variable frequency input. The output of the balanced modulator is attenuated and provides a frequency modulated RF signal output.

Multiple resonance radio frequency microstrip antenna structure

Abstract: A multiple resonance microstrip antenna radiator which includes a plurality of stacked electrically conductive element surfaces disposed above an electrically conductive reference surface with each element surface dimensioned so as to resonate at a different radio frequency. The various element surfaces are spaced one from another and from the reference surface with a dielectric material and an rf feed is attached to at least one of the element surfaces. Non-resonant element surfaces provide inductive capacitive coupling of rf energy to/from a resonant element surface.

Radio frequency connector system for portable radios

Abstract: The connector system includes a radio mounted receptacle with an integral transfer switch, and a separate connector and cable for interface with external radio frequency (R.F.) circuits, and provides a method of connecting external R.F. circuits to a portable radio and for simultaneously and automatically transferring the internal radio circuits from an integral radio antenna to the receptacle. The integral transfer switch of the receptacle connector includes a movable conductive plunger retained within a conducting sleeve and adapted to slide in an insulator between a first position at which the head of the plunger engages an inturned end of the sleeve, and a second position in which the plunger engages a flexible contact connected to the radio circuit and moves it away from a contact connected to the selfcontained antenna. A connector connected to a coaxial line, which may be connected to external radio frequency signal source, has an outer conductor adapted to connect to the sleeve and an inner conductor which enters the sleeve and engages the plunger to make electrical connection therewith and move the same to the second position. This disconnects the self-contained antenna from the radio circuit and connects the coaxial line thereto. The sleeve, plunger, and inner and outer conductors provide a matched impedance connection from the external source to the radio circuit. The external connector can be manually connected to the radio mounted receptacle connector or automatically coupled thereto when the portable radio is positioned in a carrying housing.

Nonfrequency-converting microwave radio repeater using a low power consumption amplifier

Abstract: A novel nonfrequency-converting microwave radio repeater for use in multichannel telecommunications is disclosed. A single microwave amplifier provides the requisite gain for two different angle-modulated radio frequency signals. Bandpass filters and circulators permit duplex operation by channeling the received signals through the repeater. The two radio frequency signals are amplified simultaneously in the same amplifier and then separated to be retransmitted at the same frequency in the proper path direction.

Carrier-modulated coherency monitoring system

Abstract: A radio information system is described which uses the exact mathematical tios and the unique periodic angular coherence of the residual RF carrier and the digitally encoded modulation spectral components of the electromagnetic wave as emitted by a source transmitter (or transmitters) to enhance system performance and to provide new instrumentation and measurement capabilities at the receiver apparatus. The digital modulation synchronizing code occupies a wide frequency bandwidth and is encoded for precise repetitive transmission to provide, for example in a satellite navigation system, a means of accurate synchronization and measurement of time and range parameters. Many encoded sequences of either discrete or pseudo-random types may be used as the synchronizing code. However in the description herein the pseudo-random noise (PRN) codes are used for their added advantage in spread spectrum discrimination against intentional interference. The total or composite RF signal typically also includes non-interfering information or message modulation.

A Comparison of Electrically Short Bare and Insulated Probes for Measuring the Local Radio Frequency Electric Field in Biological Systems

Abstract: The problems associated with measuring the local electric field in a medium with spatally inhomogeneous electrical constitutive parameters like biological tissue are discussed. Simple theoretical analyses that describe the operation of electrically short bare and insulated electric field probes in a dissipative medium are presented. The conditions that must be satisfied for each of these probes to have an electric field response that is independent of the electrical constitutive parameters of the surrounding tissue are determined. The results of a systematic experimental study of both types of probes are presented. In the study the probes were immersed in a succession of liquids with dielectric properties similar to those for biological tissues at radio frequencies.

Apparatus for monitoring television receivers

Abstract: Apparatus for monitoring the use of television receivers to obtain information for the rating of television programs. The apparatus makes a comparison between the intercarrier frequency signal (i.e., phase) produced by extracting from an operating television receiver tuned to a channel the visual and aural IF frequencies and the respective intercarrier frequency signals (i.e., phase) produced by successively extracting from transmitting sources of television channels the visual and aural IF frequencies. The intermediate frequency signals of the television receiver are sampled and converted into an intercarrier frequency signal. A voltage controlled tuner is tuned to the radio frequency carriers of the various television channels in a hunting sequence. The output signals of the voltage controlled tuner are intermediate frequency signals, which are converted into intercarrier signals. When the intercarrier frequency emanating from the voltage controlled tuner is phase coherent with the intercarrier frequency signal emanating from the operating television receiver over a prescribed period of time, such as 10 seconds, then an identification is made of the channel to which the operating television receiver is tuned and this information is recorded.

Phase and amplitude scintillations in the 10 to 40 GHz band

Abstract: Simultaneous measurements of phase and amplitude variability were made on a 64 km slant path using five radio frequencies: 9.55, 19.1, 22.2, 25.4, and 33.3 GHz. The three middle frequencies were chosen for their relation to water vapor absorption. The amplitude data show occasional fades in excess of 20 dB superimposed on ubiquitous smaller scintillations of several decibels. The latter generally increased with radio frequency and the fluctuations at the different frequencies were only moderately correlated (e.g., < 0.7). Neither phase nor amplitude variability show effects on the molecular resonance of water vapor.

Bounded-plasma theory of radio-frequency heating of toroidal machines

Abstract: A systematic study is made of the coupling of RF energy to a plasma column by means of an external set of current sources in the toroidal cavity constituted by the machine. The coil loading due to the absorption of RF power by the plasma and by the wall is discussed inside various frequency domains of interest for RF heating. The plasma is described by hot-fluid theory with effective collision frequencies; the latter are either particularized to describe analytically linear collision-less damping or used as parameters to simulate other loss mechanisms like the non-linear ones. Boundary conditions consistent with the magnetic confinement are taken at the plasma-vacuum interface.Special emphasis is placed on the bounded-plasm a effects in the entire frequency range (from ωωciup to ω>ωLH). In particular, magnetoacoustic resonances may strongly increase the efficiency of RF energy transfer when the physical absorption mechanisms are electron TTMP or ion cyclotron resonance. At higher frequency, resonance modes of the coaxial type are found in which the plasma plays the role of the central conductor of a coaxial toroidal cavity.

Measurements of power absorption by human phantoms immersed in radio-frequency fields.

Abstract: The most common biologic effect of exposure to radio-frequency radiation fields may be described as an acute thermal burden. The extent of the effect depends primarily on the time rate of transfer of the energy to the biologic specimen. I t has been known for some time that the depth of penetration, and the amount of incident energy absorbed, varies as a function of the frequency of the incident radiation.’ As the frequency decreases, the penetration of energy into biologic tissue becomes deeper; however, wavelengths in the kHz and lower MHz region are so long with respect to the aperture of the human subject that energy absorption is negligible. The objective of the present research was to measure the energy absorption of a human phantom when exposed to hf band (10, 20, and 30 MHz) radio-frequency radiation fields.

Frequency and Orientation Effects on Whole Animal Absorption of Electromagnetic Waves

Abstract: Experiments using a parallel plate waveguide as the measurement medium have revealed a strong dependence of RF absorption in rats and biological-phantom prolate spheroidal bodies upon the frequency and polarization of electromagnetic fields. The results correlate well to those of free space irradiation. Strongest power deposition is observed for fields polarized along the long dimension of the bodies for frequencies such that the major length is about one-quarter wavelength of radiation. At resonance, an effective absorption area of 2.5 to 3.5 times the shadow cross section is measured.

Subcarrier modulated optical transceiver

Abstract: A coherent optical modulated sensor for use with missiles and the like wherein a series of pulses of optical energy which are intensity modulated by a radio frequency sub-carrier are transmitted to a preselected target having relative motion thereto and wherein returned pulses from the target are received. Phase coherence is effectively maintained by utilizing a single continuously operating local oscillator for down-converting the received detected pulses to a Doppler frequency signal. Target velocity information may be extracted from the Doppler frequency shift induced on the coherent radio frequency sub-carrier of the return pulses. A first channel, or radio frequency sub-carrier channel is provided for receiving the Doppler signal and generating a threshold signal in response to the magnitude of the Doppler signal being equal to or greater than a predetermined magnitude. A second channel (baseband) detects the average direct current power of the received pulse. The average direct current power is compared to the threshold signal for providing a firing control signal when the magnitude of the threshold signal is greater than the magnitude of the detected average current power. The coherent optical modulated sensor may thus be used for detecting preselected targets while discriminating against pulse returns from aerosols.

Geometric resonances near the lower hybrid frequency

Abstract: Radio frequency waves at extremely low power and near the lower hybrid frequency are coupled inductively to a plasma cylinder. The dominance of geometric resonances is verified. The strength of anomalous damping is observed to be related to the steepness of radial density gradients; a qualitative explanation by means of linear mode conversion is discussed.

Multichannel radio transmitter with means to prevent abnormal wave radiation

Abstract: A multichannel transmitter incorporating a phase-locked loop frequency synthesizer to generate a carrier signal of a selected radio frequency, which carrier is subsequently amplified, modulated, and radiated into space. In order to prevent abnormal radiation which would take place as when the PLL frequency synthesizer is switched from one transmission channel to another, a transmission stopper circuit is connected to the output of the phase comparator or detector of the synthesizer so as to be actuated thereby when the desired phase or frequency lock is not established in the synthesizer. When actuated, the transmission stopper circuit prevents the wave radiation of the transmitter, as by causing nonconduction through a transistor provided therein. The invention is disclosed as adapted for a transceiver.

Television receiver response indicating apparatus

Abstract: The overall response of a television receiver is displayed on the face of the cathode ray tube of the receiver involved by test apparatus which requires electrical connection only to the antenna terminals of the television receiver and the mounting of a small light sensor unit onto the face of the cathode ray tube. The test apparatus generates an amplitude modulated signal having a video carrier frequency corresponding to that of a selected television channel. The amplitude modulated video carrier frequency signal includes an envelope containing synchronizing pulses for operating the sweep circuits of the television receiver in a normal manner and which clamps the automatic gain control circuits of the receiver to a desired level and a video signal to produce a given brightness reference background on the tube face which is preferably gray or black. Periodically, the main video carrier is interrupted for the generation of a constant amplitude test carrier frequency signal. This test carrier frequency signal progressively varies in frequency during successive fields, so the test carrier frequencies will scan through the entire band of frequencies for the channel involved. The points in time at which the main video carrier is periodically interrupted is controlled so that the beam trace or traces produce a rectangle of light resulting from the video signal detected from the test carrier frequency. This rectangle of light appears opposite the light sensor unit. The brightness of the rectangle of light during each field is a measure of the overall response of the radio frequency and intermediate frequency tuned circuits in the receiver at the test carrier frequency involved. The light sensor output from each field is stored and then utilized to modulate the video carrier to produce a response curve on a curve display area of the cathode ray tube.

Beacon tracking receiver

Abstract: A radio frequency receiver is responsive to signals radiated by a remote transmitter. The receiver includes at least one pair of antennas separated by approximately one-half wavelength at the transmitter frequency. The phases of the signals detected by the antennas are compared for the purpose of determining the relative direction to the transmitter.

Method of making an antenna array using printed circuit techniques

Abstract: Radio frequency array antenna structures and methods for fabricating such structures are disclosed wherein a plurality of radio frequency circuits forming the radiating face of an array antenna and a corporate feed are formed on one or more relatively flexible dielectric sheets and then bonded to a suitable core material to form a complete array structure which is light weight, inexpensive and structurally sound.

Dual quadrature polarization radar system

Abstract: A radar system provides a measurement of the co-linear and cross-polarization characteristics of a radar target. Vertically and horizontally polarized RF signals are selectively transmitted to a target and the co-linear and cross-polarized RF returns from the target are detected with each return being coupled to an output switch which is selectively operated to provide an output RF signal for providing either the co-linear or cross-polarized RF return. RF null circuits are provided for nulling internal system RF reflections for both co-linear and cross-polarized returns when either polarized signal is transmitted.

Monocycle pulse generator

Abstract: The radio frequency source for a low power, lightweight radar is provided by operating a transistor in the avalanche mode. An open delay line is in the collector circuit and a shorted delay line in shunt with the output line is part of the emitter load. The resulting device can be employed as a low power, nanosecond, monocycle pulse generator with low range, or time domain, sidelobes.

Method and apparatus for colinear acousto-optic RF spectrum analysis

Abstract: There is disclosed a method and apparatus for radio frequency signal spectrum analysis wherein an acoustic wave having frequency components representative of those which exist in the radio frequency signal to be analyzed is derived from the signal and transmitted through an optically anisotropic crystal simultaneously and colinearly with a beam of polarized wide-band white light. The acoustic wave produces changes in the index of refraction of the crystalline material which result in diffraction of the plane of polarization of those frequency components of the light beam which bear a unique predetermined relationship to the frequency components present in the acoustic wave. The output of the crystal is then passed through a polarization analyzer to transmit only those frequency components which have been polarization diffracted. The light output of the polarization analyzer is applied to a grating or other means for dispersing the light output so that its various frequency components are deflected by varying amounts indicative of the frequency. The rays deflected from the grating or other dispersing means are then displayed in any suitable manner to provide a visually readable spectrum analysis of the original signal.

Co-channel multiple signal broadcasting system

Abstract: Interference in the overlapping of at least two transmission transmitters areas of a co-channel multiple signal broadcasting system is suppressed by an asymmetrical radio frequency carrier deviation in one given direction of one of the two transmitters and an asymmetrical radio frequency carrier deviation in a direction opposite to the one given direction of the other of the two transmitters. The oppositely directed asymmetrical carrier deviations create a ± 2.5 kHz rms carrier frequency offset from the nominal carrier frequency in a manner which is compatible with present FCC regulations.

Portable heat sealer

Abstract: A portable dielectric Radio Frequency generator adapted with wheels and a flexible output cable through which a suitable range of Radio Frequency currents pass. A levelable press applies Radio Frequency voltage to a plastic load and is adapted with a set of various shaped quick mounting electrodes and control circuitry. When the generator is moved to a work site, the press is stored in a holding device facilitating ease of transportation. The press provides suitable compressive forces on the electrode system selected by utilizing a spring compressed by a hand operated cam.

Radio frequency transformer

Abstract: An improved radio-frequency transformer, particularly useful in conductive-body antenna systems, is provided in which telescoping of two or more portions of the primary of the transformer results in increased compactness, high effeciency and decreased cost.