Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “MHZ RANGE”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS2002

LISA phase measurement technique

The LISA mission will form the equivalent of a Michelson interferometric beat signal from the 1064nm laser beams traversing the inter-spacecraft arms. The design gravitational wave sensitivity requires measurement of round trip path differences for each detector to be about 10 pddHz over a frequency range from 10^10-4 to 10^-1 Hz. Thus LISA'S phasemeter must measure the beat signal phase to 10^-5 cycle/square root of Hz at 1mHz. Doppler shifts between spacecraft in their orbits are expected to range from 1 to 15 MHz. Phase measurement using the digital phase-locked loop approach incorporated in a modified TurboRogue GPS receiver has been investigated in this study. It is found that only resolution in the range of 10^-4 to 10^-3 cycle/square root of Hz at 1 mHz is achievable with this hardware. Abrupt fluctuations in the phase measurement at the millicycle level are responsible for the limitation.

phasemeter↗
NASA NTRS1972

Coupled nuclear spin relaxation and internal rotations in magnesium fluosilicate hexahydrate.

Both proton and fluorine nuclear spin-lattice relaxations have been studied by the 180- to 90-deg pulse method in magnesium fluosilicate hexahydrate at 25 and 13 MHz over the temperature range from 170 to 350 K. Observed nonexponential behavior of the nuclear magnetic relaxation is explained by internal rotations of the doubly charged negative fluosilicate ions and doubly charged positive magnesium hexahydrate ions.

Utton, D. B.↗
NASA NTRS1973

A search for periodic structure in solar 2 cm microwave radiation

A power spectral analysis of 285 hr of 2 cm microwave intensity data showed no statistically significant ( 96% confidence) periodicities in the frequency range 1 to 15 mHz. No correlation was found between 2 cm periodicities and solar activity in H alpha, X-ray, and several microwave frequencies. A small shift of power toward higher frequencies in the power spectrum of the 2 cm data was found to be correlated with solar H alpha and X-ray activity. Using the statistical properties of power spectra, an expression for the ratio of the minimum detectable peak-to-peak to ambient temperature at chromospheric heights may be derived. Applied to a model for oscillation bursts in quiescent supergranules, and using the most significant results of experiments to detect the microwave periodicities, this expression yields an upper limit of approximately .0015.

Sentman, D. D.↗
NASA NTRS1974

Radio frequency studies in the NASA Lewis Bumay Torus

The fluctuations in potential of the plasma in the NASA Lewis Bumpy Torus were observed using capacitive probes over frequencies from 1 kHz to 25 MHz and a wide range of operating conditions. The spectra were found to differ greatly above and below a background gas pressure of 3.0.000034 torr deuterium. Above this pressure the spectrum was dominated by the ion spoke frequency and a spectral index was defined. Below this pressure the spectrum below 200 kHz was lower in lower in amplitude by a factor of ten and no spectral index could be defined. At these lower pressures, fluctuations that appeared to be ion spokes were observed, but had a dependence of frequency on operating conditions which was previously unreported.

Gerdin, G. A.↗
NASA NTRS1973

The log-periodic array at the Clark Lake Radio Observatory

A log-periodic array, 3 km in length, is operating at Clark Lake Radio Observatory. It makes one-dimensional sweeps of the solar brightness distribution in the frequency range 20 to 65 MHz once per sec. The phasing of the array and the receiving system are described, as well as how the dynamic spectra are analyzed for the positions of solar radio sources. Simultaneous measurements at many frequencies enable the observer to remove the effects of ionospheric refraction and to obtain fundamental positions to an accuracy of about one arc min at decametric wavelengths. Fundamental positions are given for Cassiopeia A.

Erickson, W. C.↗
NASA NTRS1974

Radio frequency studies in the NASA Lewis Bumpy Torus

The fluctuations in potential of the plasma in the NASA Lewis Bumpy Torus are observed using capacitive probes over frequencies from 1 kHz to 25 MHz and a wide range of operating conditions. The spectra are found to differ greatly above and below a background gas pressure of .000034 torr deuterium. Above this pressure, the spectrum is dominated by the ion spoke frequency and a spectral index may be defined. Below this pressure, the spectrum below 200 kHz is lower in amplitude by a factor of ten and no spectral index can be defined. At these lower pressures, fluctuations appearing to be ion spokes are observed, but have a dependence of frequency on operating conditions which is previously unreported.

Gerdin, G. A.↗
NASA NTRS1978

A national voice network with satellite and small transceivers

A geostationary satellite utilizing a large multiple-beam UHF antenna is shown to be potentially capable of providing tens of thousands of voice channels for hundreds of thousands of mobile ground terminals using hand-held or vehicular-mounted transceivers with whip antennas. Inclusion of on-board network switching facilities permits full interconnection between any terminal pair within the continental United States (CONUS). Configuration tradeoff studies at selected frequencies from 150 to 1500 MHz, with antenna diameters ranging from 20 to 200 m, and CONUS-coverage multiple beams down to 0.3 deg beamwidth, establish that monthly system user costs in the range of $90 to $150, including leased and maintained ground equipment, are feasible.

Reilly, N. B.↗
NASA NTRS1979

Solar radio spectrum extended to 10 km wavelength

Solar radio spectra for quiet times and radio bursts in the wavelength range from 1 mm to 10 km are presented. Solar nonthermal emission in the range of 100 m to 10 km was monitored by means of long wire antennas connected to multi-channel radiometers in the frequency range 25 kHz to 10 MHz on board the IMP-6 and RAE-1 satellites. Flux densities for very intense type III bursts with intensities ranging from 10 to the -18th to 10 to the -14th W/sq m per Hz with maxima at 330 to 1500 m are shown, and a power-law wavelength distribution function of maximum burst intensities is derived. Intensities of a large type III noise storm are shown to increase with increasing wavelength to a peak near 500 m. The flux densities of both types of burst emission are observed to greatly exceed quiet sun intensities at long wavelengths.

Weber, R. R.↗
NASA NTRS1980

The position and polarization of Type III solar bursts

The position and polarization of Type III solar bursts in the range of 24-220 MHz are studied, with emphasis on the bursts continuing to frequencies lower than 24 MHz. Consideration is given to the statistics of burst polarization, the relation between polarization and source position, and brightness temperature, flux densities, and source sizes.

Dulk, G. A.↗
NASA NTRS1983

Review of specific antenna configurations: An estimate of cost and performance versus frequency for a simple (10 Lambda)-2 clear-air radar antenna array

The building of operational clear air radar wind profilers is discussed. The choice of operating frequency and antenna configuration for these profilers is examined. The cost and performance of a (10 lambda) 2 antenna array versus operating frequency over the range 30 to 400 MHz is compared. To simplify the comparison the array beam will be fixed and the array will be uniformly fed. Yagi and coaxial collinear (COCO) cable antennas are compared, although other configurations may be competitive. It is assumed that the array is driven by a typical 50 kW peak power, 1 kW average, power transmitter located at the array edge when calculating feedline power handling requirements and when system performance is compared. For this comparison an array aperture of (10 lambda) 2 was chosen since a one way beam width of 5 deg or less is desirable to limit beam spreading effects.

Ecklund, W. L.↗
NASA NTRS1984

Three-dimensional ray tracing of the Jovian magnetosphere in the low-frequency range

Three-dimensional ray tracing of the Jovian DAM emission has been performed utilizing the O-4 magnetic field model (Acuna and Ness, 1979) and a realistic plasma model. Minimal assumptions about the emission mechanism have been made that include radiation in the right-hand extraordinary mode, propagating nearly perpendicular to the field line at source points located just above the RX cutoff frequency along Io flux tubes. Ray tracing has been performed in the frequency range from 2-35 MHz from successive Io flux tubes separated by ten degrees of central meridian longitude for a full circumference of northern hemisphere sources. The results show unusual complexity in model arc spectra that is displayed in a constant Io phase format with many similarities to the Voyager PRA data. The results suggest much of the variation in observed DAM spectral features is a result of propagation effects rather than emission process differences.

Menietti, J. D.↗
NASA NTRS1985

On the production mechanism of radio-pulses from large extensive air showers

None of the theories put forward so far to explain the radio emission from cosmic ray showers, has been successful in giving a satisfactory explanation for all the experimental data obtained from various laboratories over the globe. It is apprehended that emission mechanism at low and high frequencies may be quite different. This calls for new theoretical look into the phenomenon. Theoretical as well as the experimental results indicate that the frequency spectrum is rather flat in the frequency range (40 to 60 MHz. Above 80 MHz, the radio emission can be explained with the help of geomagnetic mechanism. But at very low frequency ( 10 MHz), mechanisms other than geomagnetic are involved.

Datta, P.↗
NASA NTRS1986

Input-output characterization of an ultrasonic testing system by digital signal analysis

Ultrasonic test system input-output characteristics were investigated by directly coupling the transmitting and receiving transducers face to face without a test specimen. Some of the fundamentals of digital signal processing were summarized. Input and output signals were digitized by using a digital oscilloscope, and the digitized data were processed in a microcomputer by using digital signal-processing techniques. The continuous-time test system was modeled as a discrete-time, linear, shift-invariant system. In estimating the unit-sample response and frequency response of the discrete-time system, it was necessary to use digital filtering to remove low-amplitude noise, which interfered with deconvolution calculations. A digital bandpass filter constructed with the assistance of a Blackman window and a rectangular time window were used. Approximations of the impulse response and the frequency response of the continuous-time test system were obtained by linearly interpolating the defining points of the unit-sample response and the frequency response of the discrete-time system. The test system behaved as a linear-phase bandpass filter in the frequency range 0.6 to 2.3 MHz. These frequencies were selected in accordance with the criterion that they were 6 dB below the maximum peak of the amplitude of the frequency response. The output of the system to various inputs was predicted and the results were compared with the corresponding measurements on the system.

Williams, J. H., Jr.↗
NASA NTRS1986

HISCAT: A proposed new scatter facility in Northern Scandinavia

It is proposed that a new versatile ionospheric and atmospheric scatter radar be constructed in northern Scandavia through a multinational collaborative effort. The new facility tentatively named HISCAT (High frequency, High power, High latitude, Heating and Ionospheric Scatter facility), should be used for scientific investigations of: the physics of the neutral (middle) atmosphere; fundamental plasma phenomena, natural or artificially induced in the ionosphere; electrodynamic conditions at high altitudes above the auroral region and in the polar cap ionosphere; plasma waves in the solar atmosphere. The system should thus be able to operate as a mesosphere-stratosphere-troposphere (MST) radar, a so-called ionospheric modification facility, incoherent-scatter radar, coherent-scatter radar, and solar radar. Basically, the new facility should be a device that can operate simultaneously on several frequencies in the frequency range 5 to 50 MHz not covered by other instruments. It should comprise: powerful transmitters, capable of delivering a total average power of several megawatts; an advanced phased antenna array of high gain forming one or two steerable and well collimated beams; and an advanced data collection and analysis system.

Bostrom, R.↗
NASA NTRS1987

Ray tracing of Jovian low frequency radiation

The radio emission from Jupiter in the decametric range (2 to 40 MHz) has been studied for three decades. It is known that this emission is correlated with particular longitude regions on the planet and with the position of the satellite Io. The Planetary Radio Astronomy experiment on the Voyager 1 and 2 spacecraft observed this emission, obtaining valuable new information. The objectives of this study are as follows: (1) calculate raypaths for decametric wavelength radiation in Jupiter's magnetosphere; (2) compare the model-dependent raypaths with the Voyager observations; and (3) deduce characteristics of the source regions and the influence of propagation effects.

Six, N. Frank↗
NASA NTRS1990

An electronically tuned, stable 8415 MHz dielectric resonator FET oscillator for space applications

A voltage-controlled 8415-MHz FET oscillator stabilized by a dielectric resonator is described. The oscillator provides over 3.2-MHz linear electronic tuning range with a flat power output equal to +1.8 dBm (27 C, nominal), a single-sideband noise-to-carrier ratio of -68 dBc/Hz at 1 kHz off carrier, and a frequency-temperature coefficient of 0.54 parts per million/C over a -24 C to 75 C range. The oscillator withstood 150 Krads (Si) of gamma radiation with no significant performance degradation. The overall performance of the FET oscillator is far superior in many ways to that of an equivalent bipolar oscillator for space applications. For space applications, the FET dielectric resonator oscillator (DRO) is preferred over bipolar DRO because of its lower DC power consumption, better thermal frequency stability, linear electronic tunability, and higher RF output power capability.

Mysoor, Narayan R.↗
NASA NTRS1992

Observations of high-frequency and high-wavenumber solar oscillations

Doppler shift measurements of the Na D1 absorption line reveal solar oscillations in a new regime of frequency and wavenumber. Oscillations of vertical velocities in the temperature minimum and low chromosphere of the sun are observed with frequencies ranging up to 9.5 mHz. The fundamental modes appear with wavenumbers up to 5.33/Mm (equivalent spherical harmonic degree 3710). No evidence for chromospheric modes of 3-minute period is reported.

Fernandes, D. N.↗