Showing papers on "Radio frequency published in 1972"

Delay Doppler characteristics of multipath propagation at 910 MHz in a suburban mobile radio environment

Abstract: Statistical descriptions of the time delays and Doppler shifts associated with multipath propagation in a suburban mobile radio environment obtained from bandpass impulse response measurements are presented. The measuring equipment which has 0.1 \mu s resolution in time delay and a data output bandwidth of less than 5 kHz is also described. For the first time small scale statistics of the multipath propagation for vehicle travel distances on the order of 30 m along streets are presented in the following forms: 1) average power-delay profiles made up of over 200 individual profiles, 2) cumulative distributions of signal amplitude at fixed delays, and 3) radio frequency Doppler spectra at fixed delays. Delay spreads for typical suburban streets are on the order of 0.25 \mu s. Extreme cases have paths with significant amplitudes at excess delays of 5 to 7 \mu s and the square root of the second central moment delay spreads up to about 2 \mu s. Often the signal at fixed delays has a Rayleigh distributed amplitude but large departures from the Rayleigh distribution also occur. RF Doppler spectra at fixed delays indicate that some of the multipath is from one relatively discrete scattering center while at other delays several scattering centers distributed widely in angle are involved. The observed RF Doppler spectra are consistent with the cumulative amplitude distributions at the same delays.

Radio echo sounding: absorption and scattering by water inclusion and ice lenses

Abstract: The absorption of radio waves propagating through naturally occurring waters varies greatly with the electrical conductivity. Glacier melt water is very transparent and the attenuation by melt water layers is due to reflexion of power, whereas the attenuation of sea-water layers is due to absorption. The attenuation of soaked firn is usually prohibitive if the liquid is brine but it should not be a serious obstacle to radio echo strength if the liquid is rain-water or melt water. However, the magnitude of the scattered power can become greater than that from continuous (bedrock) reflectors if the size of the irregularities in the medium is large (approaching the radio wavelength in ice). Echo power formulae show that ice lenses may have the most serious effect and that low radio frequencies will be necessary to combat this.

Analytical model for a polarizable medium at radio and lower frequencies

Abstract: The Maxwell equations are written and discussed in the frequency domain for a medium exhibiting electrical polarization at radio and lower frequencies, in the range of linearity between current density and electric-field intensity. A complex function of frequency is proposed for the conductivity, which is able to describe all the families of available experimental curves for rock samples in the natural state, showing the effect of polarization. Such a function is a constitutive relation for the polarizable medium in the frequency domain. The concept of ‘abnormal’ dielectric constant for rocks is discussed in the context of the physical mechanisms responsible for the effect of electrical polarization at radio frequencies and below. Such a concept, always possible theoretically, only introduces confusion in the understanding of the basic physical mechanisms involved. As an alternative the extensive use of the concept of a total current complex conductivity is suggested.

Distance measuring apparatus and method utilizing phase comparison of modulated light beams

Abstract: Apparatus and method for accurately measuring and digitally displaying the distance between remotely separated points involves modulating a light beam at a known radio frequency, transmitting the light beam from one of the points to reflect from the remote point and return to the transmitting point, digitally measuring the phase difference between the transmitted and returned beams, and determining from such phase difference the distance between the points. The light beam is modulated in sequence with a plurality of RF signals of different frequency in order to resolve ambiguities associated with phase comparison distance measuring techniques, the primary one of such modulating signals being obtained by mixing a reference radio frequency (RF) signal with a reference intermediate frequency (IF) signal derived by division of that reference RF signal, thus retaining a fixed frequency ratio with the reference RF signal. The return RF signal is also mixed with the reference RF signal to derive a second IF signal for comparison with the reference IF signal in a digital phase comparator which utilizes as the clock signal the reference RF signal. This method of deriving from a single oscillator source the various comparative signals greatly increases the tolerances of the system and reduces the need for expensive oscillators of extreme stability. The remaining modulating signals are likewise derived by mixing various RF signals with the reference IF signal, yet all modulating signals are maintained within a narrow frequency band, thus greatly reducing compensation requirements while improving accuracy, by utilizing as the additional RF signals those having frequency differences with the reference RF signal corresponding to halfwavelengths which are related to the half-wavelength of the primary beam-modulating RF signal by different powers of 10.

rf augmentation in CO2 closed‐cycle dc electric‐discharge convection lasers

Abstract: dc electrical power deposition in CO2 closed‐cycle electric‐discharge convection lasers (EDCL) can be increased to levels characteristic of open‐cycle performance by the application of rf (13.7‐MHz) auxiliary power. Experiments have been conducted with the radio frequency capacitively coupled into the discharge zone transverse to the dc field through the top and bottom walls of a rectangular laser channel. The effect of rf power on the dc power level and on the small‐signal gain coefficient is described.

Multiple address direct coupled communication and control current carrier system

Abstract: A multi-address two-way communication system with a control channel. A master position is inter-connected with a plurality of remote positions only over the AC power lines serviced by the same AC power distribution network. The master position contains a source of RF signals, an RF signal modulator and circuitry for energizing the RF signal source and the RF signal modulator to provide a very large number of unique signal combinations. Each remote position contains a decoder circuit which identifies and responds to a signal combination unique to it. A multiplicity of AC power lines in an AC power distribution network are coupled together by frequency selective coupling devices to permit signalling and communication between positions in separated AC power lines in a large building.

Integrated circuit device having monolithic rf shields

Abstract: A monolithic, multiple integrated circuit device for use in the radio frequency (RF) stages in a television receiver in which monolithic RF shields are provided to isolate the multiple circuits on the same integrated circuit chip.

Radio frequency electrically excited flowing gas laser

Abstract: Apparatus for producing laser action in a flowing gas by electromagnetic energy at radio frequencies wherein the discharge circuit is capacitively ballasted by providing capacitive impedance between the electrode and the gas.

Automatic frequency control system for driving a linear accelerator

Abstract: An automatic frequency control system is described for maintaining the drive frequency applied to a linear accelerator to produce maximum particle output from the accelerator. The particle output amplitude is measured and the frequency of the radio frequency source powering the linear accelerator is adjusted to maximize particle output amplitude.

Passive ranging technique

Abstract: A system for passively determining range to a threat emitter from a single tactical vehicle based upon the change in the difference of phase of a radio frequency carrier between two physically spaced antennas.

Sensitivity of Radio Frequency Measurements in the Presence of Oscillator Noise

Abstract: The inherent sensitivity of an rf measuring system and the effect of the system transmission characteristics on the detectability of the rf source noise are examined. The results are applied to resonant reflection and transmission systems and to a nonresonant transmission system. The conventional reflection cavity paramagnetic resonance system is discussed in detail, and the conclusion is that this configuration will be source noise limited at power levels above 1 mW. Unconventional configurations, such as a dual mode induction cavity or a dual cavity transmission system, would have to be used to achieve higher sensitivity.

Circuit for instant restart of high pressure discharge lamp

Abstract: In the running condition, a high pressure lamp is connected in series with an inductive reactor across the line (240 volts), and a power factor correcting capacitor is connected across the line. To assure instant starting whether the lamp is hot or cold, an igniter is energized which injects kilovolt radio frequency pulses in series with the reactor open circuit voltage across the lamp, and the reactor open circuit voltage is boosted a predetermined factor up to 3 X line voltage by temporarily connecting the power factor correcting capacitor to a tap in the inductive reactor.

Radar target simulator

Abstract: Apparatus is disclosed which simulates the operation of a plurality of radar transmitters so as to permit an evaluation of electronic countermeasure equipment The system generates sequences of pulsed radio frequency signals whose carrier frequency, modulation, amplitude and power lever are controllable to realistically reflect the signal conditions which may be encountered by an aircraft when a multiplicity of radar emitters are operating simultaneously in its vicinity

Scanning control circuit for use in signal seeking radio receiver

Abstract: For use in a signal-seeking radio receiver for automatically and sequentially tuning to a plurality of predetermined radio frequencies, the receiver including means for reproducing the intelligence in radio frequency signals received at said predetermined frequencies, the combination comprising local oscillator means for generating a plurality of different local oscillator signals and a switching circuit for automatically and sequentially activating predetermined portions of the local oscillator means thereby sequentially and repetitively to generate the aforementioned plurality of local oscillator signals individually and in a predetermined sequence. A pulse generator is provided for sequencing the switch means at a first predetermined stepping rate thereby to tune the receiver to receive radio frequency signals for a first predetermined time period at each of said frequencies in sequence. The receiver further includes means for holding said receiver tuned to individual ones of said predetermined radio frequencies in response to reception of a radio frequency signal thereat after a predetermined delay period shorter than said first predetermined period. The switching circuit further includes means for increasing the stepping rate of the pulse generator in synchronism with tuning of said receiver to selected ones of said radio frequencies to thereby reduce said first predetermined period to a period less than said delay period, whereby the receiver cannot ''''lock'''' onto the selected frequencies.

Digitally controlled attenuator

Abstract: A digitally controlled attenuator adapted for use with radio frequency signals is disclosed. The digitally controlled attenuator includes a radio frequency bus having connected thereto, at proper points therealong, a number of coupling and switching networks, each one thereof including a different attenuating shunt element of a ladder network. Each switching element, in turn, is responsive to a different digital control signal. The coupling and switching networks are connected to the radio frequency bus such that the signals passing through the shunt elements selected by any digital control signal are in proper relative phase relationship at various nodes of the ladder network. Unwanted radio frequency signals, leaking through a switching element which has been placed in its ''''off'''' condition, are cancelled by radio frequency signals having a relative 180* phase shift from the radio frequency signals being attenuated.

Radio frequency antenna system

Abstract: Tactical radio navigation systems provide distance measuring information to an interrogating aircraft in response to pairs of interrogation pulses received at a beacon transponder, the system also provides bearing and identification information. The transponder receives pairs of interrogation pulses which are decoded into a single pulse for operation of a reply transmitter. Bearing, distance and identification determining signals are generated by the reply transmitter and its antennas. A single antenna functions to both receive the interrogation pulses and radiate the position determining signals. To provide the required bearing information, the antenna radiates pulses from a central antenna array that is stationary with respect to a support housing. These pulses are modulated at a 15 Hz frequency by parasitic elements rotating around the stationary central array. Further modulation of the transmitted pulses at a 135 Hz frequency, superimposed on the 15 Hz frequency, is provided by additional parasitic elements also rotating about the central antenna array. Both the low band frequency parasitic elements and the high band frequency parasitic elements have a configuration to provide improved radiation from the antenna above the horizontal. Also to improve the antenna radiation pattern, the 135 Hz parasitic elements are positioned on a rotating drum of a dielectric material, such as fiberglass. To still further improve the amount of radiation energy above the horizontal reference, radio frequency chokes are coupled to the central antenna array in the feed line from the signal transmitter.

Computer controlled rf noise and modulation analyzer

Abstract: A computer controlled test set capable of measuring FM and AM noise of an RF signal as well as the index of modulation, RF power level and the linearity of a ramped FM signal output from a microwave signal oscillator included in a unit under test.

Drying of wool slivers

Abstract: Textile fibers, for example wool slivers, are dried by passing them through a series of co-axial loop electrodes energized at a radio frequency preferably above 10 MHz to effect dielectric heating, successive electrodes along the path being at opposite polarity. The material is carried on an aportioned endless belt of resin-bonded glass fibre material. Simultaneously a stream of hot air is directed over or through the fibre material. Sensing means at the fibre outlet sense the moisture content and control the radio frequency power. A fibre break detection at the film entry switches off the radio frequency power in the event of a fibre break and also reduces the speed of traverse so that the material in the apparatus is dried by the hot air.

Radio frequency transmitting apparatus having slotted metallic radio frequency windows

Abstract: A slot antenna or radome having increased bandwidth capability may be made of a metallic sheet which is curved in the case of a radome, or flat in the case of the side of a waveguide, the sheet has a plurality of slots with edges which are beveled toward each other from the outer surface of the sheet, such that the metallic walls of the window are thin and approach the skin depth for the highest frequency of radio frequency waves which are to be transmitted. With longer wavelengths the electromagnetic field penetrates through the thin edge so that the window is effectively larger, thereby providing improved transmittance over a broad bandwidth.

Temperature stabilized spectral source

Abstract: A temperature stabilized spectral source comprising an electrodeless discharge lamp energized in a radio frequency field, the temperature of the lamp being controlled by disposing the lamp in air or other gas of controlled temperature. The exciting field is typically in the microwave frequency range.

A Tunable NMR Spectrometer for the vhf‐uhf Range

Abstract: A nuclear magnetic resonance detection system for the vhf‐uhf frequency range is described in detail. It consists of a radio frequency bridge built around a coaxial hybrid T. The sample is contained in a tunable L‐C resonator coupled with an adjustable impedance transformer to a 50 Ω airline. The system is thus fully tunable over wide ranges of frequency from a remote location. For example, using a two‐turn copper ribbon coil, the range 270–710 MHz is covered: The system may be set to any desired point in this range within a few minutes. The system was used with standard lock‐in detection to obtain the absorption derivative ∂χ″/∂H. An absolute noise measurement was made at a radio frequency of 300 MHz and an audio detection frequency of 200 Hz. This showed that the root mean square noise at the lock‐in output was between four and seven times the value corresponding to the rf Johnson noise at the bridge. The system was used to observe a proton resonance in a Bitter type solenoid at 125 kG.

Depilatory method and means

Abstract: A method by which to accelerate electrolytic destruction of hair. The method involves application to the hair papilla associated with the hair, of current having a unidirectional current component and a radio frequency current component. The unidirectional current produces ions which kill electrochemically. The radio frequency current accomplishes heating less than enough to result in radio frequency burning of the papilla but enough to accelerate the electrochemical processes. An apparatus furnishes unidirectional currents modulated at a radio frequency rate through an impedance changing circuit which constitutes a constant voltage source to the radio frequency generator and which constitutes a high impedance, constant current source to the body thereby to offer protection both to the subject and to the radio frequency generator.

Blocking capacitor for a thin-film rf transmission line

Abstract: A blocking capacitor is formed in the center conductor of a thin-film RF transmission line which is situated over a metal conductor and insulated from the center conductor and outer conductors of the transmission line. The distributed capacitor so formed couples RF signals over a broad frequency range while blocking DC and very low frequency signals on the transmission line.

Electrostatic shield allowing substantially complete electromagnetic propagation from a transmitter

Abstract: A nickel mesh shield comprised of small closed loops surrounds a transmitter and radiating loop to provide an electrostatic shield for the transmitter. The mesh shield provides substantially no electromagnetic radiation attenuation of the radio frequency transmitted by the transmitter.

Millimeter wave imaging system using direct carrier injection

Abstract: Disclosed is a millimeter wave imaging system which includes means for illuminating a remote target with RF energy and means for receiving and processing the RF energy which is reflected from the target. The processing means includes a diode array upon which the received energy is focussed and which is directly driven by an X-Y addressing system. The diodes in the array are digitally scanned directly to thereby directly inject carriers sequentially into the diodes in the panel. These diodes alternately pass and absorb the incoming RF energy at high image conversion rates, thereby imparting maximum resolution to the imaging system and enabling real time operation. Simultaneously, heat and power dissipation is minimized.