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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.

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At least 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

RFI in hybrid loops - Simulation and experimental results.

A digital simulation of an imperfect second-order hybrid phase-locked loop (HPLL) operating in radio frequency interference (RFI) is described. Its performance is characterized in terms of phase error variance and phase error probability density function (PDF). Monte-Carlo simulation is used to show that the HPLL can be superior to the conventional phase-locked loops in RFI backgrounds when minimum phase error variance is the goodness criterion. Similar experimentally obtained data are given in support of the simulation data.

Ziemer, R. E.↗
NASA NTRS1973

Adaptive ground implemented phased array

Tests were conducted to determine the feasibility of using an adaptive ground implemented phased array (AGIPA) to overcome the limitations of the radio frequency interference limited low data Tracking and Data Relay Satellite VHF return link. A feasibility demonstration model of a single user channel AFIPA system was designed, developed, fabricated, and evaluated. By scaling the frequency and aperture geometry from VHF to S-band, the system performance was more easily demonstrated in the controlled environment of an anechoic chamber. The testing procedure employs an AGIPA in which received signals from each element of the array are processed on the ground to form an adaptive, independent, computer controlled beam for each user.

Smith, J. M.↗
NASA NTRS1973

RFI analysis applied to the TDRSS system

The effect of radio frequency interference (RFI) on the proposed Tracking and Data Relay Satellite System (TDRSS) was assessed. The method of assessing RFI was to create a discrete emitter listing containing all the required parameters of transmitters in the applicable VHF and UHF frequency bands. The transmitter and spacecraft receiver characteristics were used to calculate the RFI contribution due to each emitter. The individual contributions were summed to obtain the total impact in the operational bandwidth. Using an as yet incomplete emitter base, it is concluded that the 136- to 137-MHz band should be used by TDRSS rather than the whole 136- to 138-MHz band because of the higher interference levels in the 137- to 138 MHz band. Even when restricting the link to 136 to 137 MHz, the existing link design is marginal, and it is recommended that interference reduction units, such as the adaptive digital filter, be incorporated in the TDRSS ground station.

Jenny, J. A.↗
NASA NTRS1974

EMC test plan for shipboard in-harbor and at-sea measurements for L-band terminal

This test plan is to provide a procedure for the measurement of on-board radio frequency interference resulting from the operation of on-board radars (S-Band and X-Band). Field intensity measurements in the range of 1 to 10 GHz will be made using calibrated test instrumentation to determine possible adverse effects to the operation of the future installation of a Maritime L-Band Shipboard Satellite Communications Terminal, for use with the ATS-F and MARISAT Communications Satellites. A measurement will be made of power line conducted interference to determine the degree of power line isolation that may be required. There is also consideration of interference to the radars by the proposed L-Band terminals and observations will be made of the radar displays while L-Band transmitter operation is simulated. These tests will be made aboard the American Alliance container ship, United States Lines.

Source record↗
NASA NTRS1974

TDRSS multimode transponder program. Phase 2: Equipment development

This report contains a complete description of the TDRS Multimode Transponder and its associated ground support equipment. The transponder will demonstrate candidate modulation techniques to provide the required information for the design of an eventual VHF/UHF transponder suitable for installation in a user satellite, capable of operating as part of a Tracking and Data Relay Satellite (TDRS) systems. Use of geosynchronous TDRS which can serve both low data rate users at VHF and high data rate users at other frequencies has been considered. The effects of radio frequency interference from the earth and of multipath propagation due to reflections from the earth are expected to pose problems for the TDRS system at VHF. Investigations have suggested several modulation techniques that offer promise to overcome these problems.

Cnossen, R. S.↗
NASA NTRS1974

Feasibility Study of a Satellite Solar Power Station

A feasibility study of a satellite solar power station (SSPS) was conducted to: (1) explore how an SSPS could be flown and controlled in orbit; (2) determine the techniques needed to avoid radio frequency interference (RFI); and (3) determine the key environmental, technological, and economic issues involved. Structural and dynamic analyses of the SSPS structure were performed, and deflections and internal member loads were determined. Desirable material characteristics were assessed and technology developments identified. Flight control performance of the SSPS baseline design was evaluated and parametric sizing studies were performed. The study of RFI avoidance techniques covered (1) optimization of the microwave transmission system; (2) device design and expected RFI; and (3) SSPS RFI effects. The identification of key issues involved (1) microwave generation, transmissions, and rectification and solar energy conversion; (2) environmental-ecological impact and biological effects; and (3) economic issues, i.e., costs and benefits associated with the SSPS. The feasibility of the SSPS based on the parameters of the study was established.

Glaser, P. E.↗
NASA NTRS1975

Test plan and preliminary report of airborne electromagentic environment survey over USA urban areas 0.4 to 18.0 GHz

An airborne electromagnetic environment survey is described of five urban areas where terrestrially-generated radio-frequency interference was measured over the frequency range from 0.4 to 18.0 GHz. A chartered Cessna 402 aircraft contained necessary measurement test equipment, including the receiving antennas mounted beneath the fuselage. Urban areas including Washington, D.C.; Baltimore, MD; Philadelphia, PA; New York, NY; Chicago, ILL; and Palestine, TX were surveyed. A flight test plan and preliminary test results for the 0.4 to 1.4 GHz frequency range, are included; a final test report describes more detailed results.

Taylor, R. E.↗
NASA NTRS1974

Shuttle station, and satellite communications program

A parametric approach is developed to analyze and evaluate the performance of any link or links of a satellite relay system. The approach factors into the calculations the constraints of coherent radio frequency interference, multipath, and equipment design. The report is divided into three sections dealing with Spread Spectrum Techniques (Section 1), Power Budget Calculations (Section 2), and Required Capabilities and Design Factors for Tracking and Data Relay Systems TDRS (Section 3).

Lawsine, L.↗
NASA NTRS1975

Advanced communications experiments for Spacelab

The Spacelab design and mission capabilities appear to provide a practical vehicle for meeting communication experiment needs. Results of recent discussions and numerous contractual activities have conclusively corroborated the potential useful role that a manned laboratory in space can afford to the communications community. Some examples of the experiments that appear presently as strong candidates for early flights on the Spacelab missions of the 1980s are discussed. Particular attention is given to radio frequency interference, bandwidth compressive modulation, laser experimentation, and use of large deployable communications antenna. It can be expected that the Spacelab will reduce the time, risk, and cost for conducting some communications experiments and developing the related space technology.

Ehrlich, E.↗
NASA NTRS1976

Multispectral and stereo imaging on Mars

Relevant aspects of the design and function of the two-window Viking Landing Camera system are described, with particular reference to some results of its operation on Mars during the Viking mission. A major feature of the system is that the optical tunnel between the lens and the photosensor array contains a multiaperture baffle designed to reduce veiling glare and to attenuate radio frequency interference from the lander antennas. The principle of operation of the contour mode is described. The accuracy is limited by the stereo base, resolution of camera picture elements, and geometric calibration. To help determine the desirability as well as the safety of possible sample sites, use is made of both radiometric and photogrammetric information for each picture element to combine high-resolution pictures with low-resolution color pictures of the same area. Explanatory photographs supplement the text.

Levinthal, E. C.↗
NASA NTRS1976

Space-to-earth power transmission system

A preliminary analysis was conducted to establish the requirements of a space-to-earth microwave power transmission system. The need for accurate phase control on the transmitter was established and methods for assessing the impact of power density and thermal constraints on system performance were demonstrated. Potential radio frequency interference was considered. The sensitivity of transmission system scale to variations in power source, transportation and orbital fabrication and assembly costs was also determined.

Stevens, G. H.↗
NASA NTRS1976

Reduction and analysis of data collected during the electromagnetic tornado experiment

Techniques for data processing and analysis are described to support tornado detection by analysis of radio frequency interference in various frequency bands, and sea state determination from short pulse radar measurements. Activities include: strip chart recording of tornado data; the development and implementation of computer programs for digitalization and analysis of the data; data reduction techniques for short pulse radar data, and the simulation of radar returns from the sea surface by computer models.

Davisson, L. D.↗
NASA NTRS1977

An improved digital algorithm for fast amplitude approximations of quadrature pairs

A computationally fast algorithm for approximating the amplitude (A) of a quadrature pair (I,Q) has been discovered. The piecewise linear formula, the unbiased estimate of A=X+1/8y when X or = 3Y and 7/8X + 1/2Y when X or = 3Y applies where X is congruent to the maximum absolute value of (I,Q) and Y is congruent to the minimum absolute value of (I,Q). This algorithm has been proven to be far more accurate then currently used approximations. An immediate application is the wideband digital spectrum analyzer under development for monitoring radio frequency interference at Deep Space Network stations.

Levitt, B. K.↗
NASA NTRS1977

Ionosphere/microwave beam interaction study

A solar power satellite microwave power density of 20mw sq cm was confirmed as the level where nonlinear interactions may occur in the ionosphere, particularly at 100 km altitude. Radio wave heating at this altitude, produced at the Arecibo Observatory, yielded negative results for radio wave heating of an underdense ionosphere. Overdense heating produced striations in the ionosphere which may cause severe radio frequency interference problems under certain conditions. The effects of thermal self-focusing are shown to be limited severely geographically. The aspect sensitivity of field-aligned striations makes interference-free regions above magnetic latitude about 60 deg. A test program is proposed to simulate the interaction of the SPS beam with the ionosphere, to measure the effects of the interaction on the ionosphere and on communication and navigation systems, and to interpret the results.

Duncan, L. M.↗
NASA NTRS1977

Tornado detection data reduction and analysis

Data processing and analysis was provided in support of tornado detection by analysis of radio frequency interference in various frequency bands. Sea state determination data from short pulse radar measurements were also processed and analyzed. A backscatter simulation was implemented to predict radar performance as a function of wind velocity. Computer programs were developed for the various data processing and analysis goals of the effort.

Davisson, L. D.↗
NASA NTRS1978

Automatic radio-transmission monitor

System continuously monitors radio transmissions stored in memory. If spectrum deviates beyond present limits, alarm is tripped and spectrum is transferred to long-term storage for later analysis. Monitor can be useful in ensuring proper power level and spectral quality and in finding cause of failure. It might also be used to monitor radio-frequency interference or power levels of citizen's-band transmitters.

Bernstein, A. J.↗
NASA NTRS1977

An asymptotic analysis of a general class of signal detection algorithms

For applications to the problem of radio frequency interference identification, or in the search for extraterrestrial intelligence, it is important to have a basic understanding of signal detection algorithms. A general technique for assessing the asymptotic sensitivity of a broad class of signal detection algorithms is given. In these algorithms, the decision is based on the value of X sub 1 + X sub 2...+ X sub n where the X sub 1's are obtained by sampling and preliminary processing of a physical process.

Mceliece, R. J.↗
NASA NTRS1978

An algorithm for generating an m-ary summation tree

An algorithm is presented for generating an m-ary summation tree. The algorithm is completely general and may be applied to any length input string. For an N length sequence summed in groups of m sub l at each level l a maximum of 3L - 2 storage is required. A special case of the general m-ary tree where all m sub l are equal is used to smooth data in a radio frequency interference experiment. The maximum storage required when m l sub l = m for all l reduces to the closed form 3 log m N - 2.

Sievers, M.↗