Search NASA⌕ Search

SEARCH · Search NASA

Results for “Radio Attenuation”

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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Centimeter and millimeter wave attenuation and brightness temperature due to atmospheric oxygen and water vapor

Calculations are presented for atmospheric absorption and radiation emission for several atmospheric conditions and elevation angles. The calculations are for frequencies in the 1 to 340 GHz frequency range. The calculations are compared to those from other models. Agreement is found to within 15% for absorption coefficient (7.5 g/m/cubed water vapor at 290 K) and approximately the same for total zenithal attenuation. The attenuation and gaseous emission noise curves defined by the International Radio Consultative Committee are found to have minor inconsistencies.

Smith, E. K.↗
NASA NTRS2014

Space-Based Reconfigurable Software Defined Radio Test Bed Aboard International Space Station

The National Aeronautical and Space Administration (NASA) recently launched a new software defined radio research test bed to the International Space Station. The test bed, sponsored by the Space Communications and Navigation (SCaN) Office within NASA is referred to as the SCaN Testbed. The SCaN Testbed is a highly capable communications system, composed of three software defined radios, integrated into a flight system, and mounted to the truss of the International Space Station. Software defined radios offer the future promise of in-flight reconfigurability, autonomy, and eventually cognitive operation. The adoption of software defined radios offers space missions a new way to develop and operate space transceivers for communications and navigation. Reconfigurable or software defined radios with communications and navigation functions implemented in software or VHDL (Very High Speed Hardware Description Language) provide the capability to change the functionality of the radio during development or after launch. The ability to change the operating characteristics of a radio through software once deployed to space offers the flexibility to adapt to new science opportunities, recover from anomalies within the science payload or communication system, and potentially reduce development cost and risk by adapting generic space platforms to meet specific mission requirements. The software defined radios on the SCaN Testbed are each compliant to NASA's Space Telecommunications Radio System (STRS) Architecture. The STRS Architecture is an open, non-proprietary architecture that defines interfaces for the connections between radio components. It provides an operating environment to abstract the communication waveform application from the underlying platform specific hardware such as digital-to-analog converters, analog-to-digital converters, oscillators, RF attenuators, automatic gain control circuits, FPGAs, general-purpose processors, etc. and the interconnections among different radio components.

Communications↗
DOE OSTI2022

Design of a 3rd Order Lumped-Element Filtering Attenuator

This paper presents a novel filtering attenuator (filtenuator) concept, which allows for adjustable passband attenuation and filtering characteristics in a single design. The mathematical equations relating the desired passband loss to required resistance values are provided and validated with ideal circuit simulations. A third-order Chebyshev static filtenuator is designed at 1 GHz with multiple values of attenuation using lumped-element components as a proof of concept. Simulated and measured results for a 3 dB filtenuator show good agreement and several attenuation levels are shown to validate the concept. The proposed static filtenuator has advantages of ease of modification, compact size, and low cost, which are necessities in meeting the needs of reducing size, weight, power, and cost (SWaP-C) in future radio frequency transceivers.

Filter, Attenuator, Band-pass Filter (BPF), Lumped↗
NASA NTRS1979

Pulse-width-modulated attenuator for AGC

Automatic-gain-control (AGC) circuit regulates gain of intermediate-frequency and radio-frequency signals over wide dynamic range with high linearity and very low phase shift. Device has potential uses in radio and television receivers, signal distribution systems, and test and measurement instruments.

Macconnell, J. W.↗
DOE OSTI2021

Imaging 192/193m Ir sources using digital autoradiography for nuclear forensic applications [Slides]

This work aims to develop a new methodology for assaying 192/193m Ir-containing materials. SDDs cannot determine activity spatially, thus it is important that the prepared samples are uniformly distributed. Autoradiography is used to image radioactive samples using imaging media by direct exposure. Using this technique, radio-iridium samples will be imaged to determine uniformity and self-attenuation as a function of mass.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
NASA NTRS1982

Modeling the joint statistics of satellite path XPD and attenuation

A new and simple technique for estimating from attenuation statistics alone the joint distribution of attenuation and cross-polarization impairments on a satellite-to-earth radio path is presented. It compares measurements with predictions for the CTS spacecraft 11.7 GHz right-hand circularly polarized downlink during the first six months of 1979.

Gaines, J. M.↗
NASA NTRS1989

Reddening and extinction towards H II regions

The light emitted by the gas in H II regions is attenuated by dust. This extinction can be measured by comparing H alpha, H beta, and radio continuum fluxes, since the intrinsic ratios of the Balmer line and thermal radio continuum emissivities are nearly constant for reasonable conditions in H II regions. In the case of giant extragalactic H II regions, the extinction was found to be considerably greater than expected. The dust between the Earth and the emitting gas may have an optical thickness which varies. The dust may be close enough to the source that scattered light contributes to the flux, or the dust may be actually mixed with the emitting gas. It is difficult to decide which configuration is correct. A rediscussion of this question in light of recent observations, with the Fabry-Perot spectrophotometers, of the large Galactic H II region is presented. The color excesses are compared for stars embedded in these H II regions with those derived (assuming the standard law) from the nebular extinction and reddening.

Caplan, James↗
NASA NTRS1979

A review of the application of nonattenuating frequency radars for estimating rain attenuation and space-diversity performance

Cumulative rain fade statistics are used by space communications engineers to establish transmitter power and receiver sensitivities for systems operating under various geometries, climates, and radio frequencies. Space-diversity performance criteria are also of interest. This work represents a review, in which are examined the many elements involved in the employment of single nonattenuating frequency radars for arriving at the desired information. The elements examined include radar techniques and requirements, phenomenological assumptions, path attenuation formulations and procedures, as well as error budgeting and calibration analysis. Included are the pertinent results of previous investigators who have used radar for rain-attenuation modeling. Suggestions are made for improving present methods.

Goldhirsh, J.↗
NASA NTRS1999

EGRET Team Papers to Be Published in the Proceedings of the Fifth Compton Symposium

Papers to be included in this symposium are: Detecting the Attenuation of Blazar Gamma-Ray Emission by Extragalactic Background Light with GLAST; Some Aspects of the Radio Emission of EGRET-Detected Blazars; GeV Outburst in Mrk 501; Spectral Modeling of the EGRET 3EG Gamma Ray Sources Near the Galactic Plane; X-ray and Gamma-ray Observations of the COS-B Field 2CG 075+00; Multiwavelength Studies of the Peculiar Gamma-Ray Source 3EG J1835+5918; EGRET/COMPTER Observations of an Unusual, Steep-Spectrum Gamma-Ray Source; Preliminary Results from a New Analysis Method for EGRET Data; and A Systematic Search for Short-term Variability of EGRET Sources.

Source record↗
NASA NTRS1979

Liquid content of the lower clouds of Venus as determined from Mariner 10 radio occultation

S- and X-band radio occulation data obtained during the Mariner 10 flyby of Venus are analyzed to determine the effects of signal attenuation due to the clouds of Venus. The signal-amplitude data are corrected for errors introduced by spacecraft motion and antenna steering during the occultation, absorption-coefficient profiles are computed, and the liquid content of the Venusian clouds is estimated. Excess attenuation effects are found and ascribed to absorption by small liquid particles, consisting of a water-sulfuric acid mixture containing 75% + or - 25% sulfuric acid, in the clouds. Three absorbing cloud layers at respective heights of 68, 60, and 48 km are suggested by the X-band absorptivity profile, but only the 68- and 48-km layers are clearly indicated by the S-band profile. The relatively slow S-band absorption at 60 km is tentatively attributed to an unknown constituent that is much more absorbing in the X-band than in the S-band. The results are compared with nephelometer measurements performed at 0.9 micron by the Venera 9 and 10 probes.

Kliore, A. J.↗
NASA NTRS1984

Natural radio noise - A mini-review

Natural radio noise in telecommunication systems can be accounted for by the contribution which it makes to antenna noise temperature. Attenuation due to water vapor and oxygen, clouds, and precipitation is accompanied by thermal noise which further degrades the applicable signal-to-noise ratio. Extraterrestrial noise may be of thermal or nonthermal origin and may cover a continuum of frequencies or occur at discrete frequencies. The spectral index n (the exponent giving the variation of noise power density with wavelength) is -2 for a black body and between 0 and -2 for thermal emission in general. The mechanism responsible for much of the extensive nonthermal extraterrestrial noise is synchrotron radiation, characterized by a positive spectral index.

Flock, W. L.↗
NASA NTRS1998

Second Harmonic Hectometric Radio Emission at Jupiter

Galileo has been in orbit around Jupiter since December 1995. The plasma wave instrument on board the spacecraft has occasionally detected a rotationally modulated attenuation band in the hectometric (HOM) emission that most likely is due to scattering of the radiation from density fluctuations along the Io L-shell, as reported earlier. The occurrence of the attenuation band is likely to be dependent on Io activity and the presence of density scattering centers along the Io L-shell as well as the location of the source region. Some of the attenuation bands show clear indications of second harmonic emission. Without polarization measurements, it is difficult to place constraints on the local generation conditions based on the cyclotron maser instability, but the results imply that second harmonic emission could be present in the decametric (DAM) radiation as well. A survey of the data has revealed about 30 examples of second harmonic HOM.

Menietti, J. D.↗
NASA NTRS1998

Second Harmonic Hectometric Radio Emission at Jupiter

Galileo has been in orbit around Jupiter since December 1995. The plasma wave instrument on board the spacecraft has occasionally detected a rotationally modulated attenuation band in the hectometric (HOM) emission that most likely is due to scattering of the radiation from density fluctuations along the Io L-shell, as reported earlier. The occurrence of the attenuation band is likely to be dependent on Io activity and the presence of density scattering centers along the Io-L-shell as well as the location of the source region. Some of the attenuation bands show clear indications of second harmonic emission. Without polarization measurements, it is difficult to place constraints on the local generation conditions based on the cyclotron maser instability, but the results imply that second harmonic emission could be present in the decametric (DAM) radiation as well. A survey of the data has revealed about 30 examples of second harmonic HOM.

Menietti, J. D.↗
NASA NTRS1971

Estimation of microwave absorption in the Jupiter atmosphere

A procedure for estimating the microwave absorption loss of the Jupiter atmosphere is presented. Estimation of microwave absorption by planetary atmospheres involves two different investigative disciplines (1) the determination of an acceptable model of the atmosphere itself and (2) the determination of the microwave attenuation rate applicable to each different volume sample of the atmosphere, and the integration of this loss over the varying radio propagation path for any given entry trajectory to obtain the total loss.

Coombs, W. C.↗
NASA NTRS2005

Modeling and Simulation for Realistic Propagation Environments of Communications Signals at SHF Band

In this article, most of widely accepted radio wave propagation models that have proven to be accurate in practice as well as numerically efficient at SHF band will be reviewed. Weather and terrain data along the signal's paths can be input in order to more accurately simulate the propagation environments under particular weather and terrain conditions. Radio signal degradation and communications impairment severity will be investigated through the realistic radio propagation channel simulator. Three types of simulation approaches in predicting signal's behaviors are classified as: deterministic, stochastic and attenuation map. The performance of the simulation can be evaluated under operating conditions for the test ranges of interest. Demonstration tests of a real-time propagation channel simulator will show the capabilities and limitations of the simulation tool and underlying models.

simulation↗