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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Radiant source tracker independent of nonconstant irradiance

A tracker of a radiant source is disclosed. The tracker is composed of a sectored matrix of detectors whose output voltages correspond to their respective levels of irradiance. The voltages are each sampled during a variable length period and the resulting samples are shaped into triangular samples by an integration process. They are supplied to a demodulator which provides an output corresponding to the difference of the time-voltage product of appropriate combinations of the samples. This output, after filtering, represents the angle of incidence on the detectors with respect to a central axis. The triangular samples are also supplied to a demodulator whose output is an AGC voltage which is a function of the sum of the time-voltage integrals of the triangular samples.

Campbell, F. D.↗
NASA NTRS1974

Impact of scintillation of transionospheric communications

Analyses of AGC analog data from the Small Astronomy Satellite (SAS) at VHF (136 MHz) have shown amplitude fluctuations in the signals received at several equatorial tracking sites operated by NASA. Coincident digital telemetry data, transmitted from SAS at 1 kbps, has also been analyzed. Errors in data are shown to increase markedly for nighttime satellite passes around the periods of the two equinoxes as compared to the errors observed during other periods. This paper establishes the qualitative and quantitative correlations between the ionospheric scintillation phenomenon and the occurrence of errors. Strong time and geographic cause and effect relationships are established by determining the statistical correlation between scintillation indices and bit error rates.

Blank, H. A.↗
NASA NTRS1974

Shuttle bit rate synchronizer

A shuttle bit rate synchronizer brassboard unit was designed, fabricated, and tested, which meets or exceeds the contractual specifications. The bit rate synchronizer operates at signal-to-noise ratios (in a bit rate bandwidth) down to -5 dB while exhibiting less than 0.6 dB bit error rate degradation. The mean acquisition time was measured to be less than 2 seconds. The synchronizer is designed around a digital data transition tracking loop whose phase and data detectors are integrate-and-dump filters matched to the Manchester encoded bits specified. It meets the reliability (no adjustments or tweaking) and versatility (multiple bit rates) of the shuttle S-band communication system through an implementation which is all digital after the initial stage of analog AGC and A/D conversion.

Huey, D. C.↗
NASA NTRS1975

Reduced backscattering cross section (Sigma degree) data from the Skylab S-193 radar altimeter

Backscattering cross section per unit scattering area data, reduced from measurements made by the Skylab S-193 radar altimeter over the ocean surface are presented. Descriptions of the altimeter are given where applicable to the measurement process. Analytical solutions are obtained for the flat surface impulse response for the case of a nonsymmetrical antenna pattern. Formulations are developed for converting altimeter AGC outputs into values for the backscattering cross section. Reduced data are presented for Missions SL-2, 3 and 4 for all modes of the altimeter where sufficient calibration existed. The problem of interpreting land scatter data is also discussed. Finally, a comprehensive error analysis of the measurement is presented and worst case random and bias errors are estimated.

Brown, G. S.↗
NASA NTRS1975

Skylab altimeter observations over terrain

The author has identified the following significant results. Data obtained by Skylab radar altimeter (S193) over the continental U.S.A. for pass 1 of SL-3 were analyzed to relate radar return signal parameters such as range, power, and waveform to ground track terrain features. The altimeter, which was originally designed for ocean observations, performed predictably well over terrain with moderate to low relief. The maximum return from more complex areas corresponded usually to the lower flatter regions within the seven kilometer diameter footprint. Altimeter measured heights correlated with map topography with an rms deviation of + or - 30 m for terrain topography with large height dispersion (passes 1 and 28) and + or - 5 m for slowly varying terrain (passes 16, 17, and 18). Analysis of the waveform and statistical characteristics of the individual signals indicated that larger signal power was usually related to dominantly specular reflections from patches 100 m or larger. Results established the capability of a spacecraft altimeter system to observe characteristic radar signatures for different types of terrain within the bandwidth restrictions of the AGC and range tracker loops.

Shapiro, A.↗
NASA NTRS1976

Console test report for shuttle task 501 shuttle carrier aircraft transceiver console (SED 36115353-301)

Performance tests completed on the Space Shuttle Carrier Aircraft (SCA) transceiver console, verifying its design objectives, were described. These tests included: (1) check of power supply voltages for correct output voltage and energization at the proper point in the turn on sequence, (2) check of cooling system (LRU blower, overload sensors and circuitry, and thermocouple probe), (3) check of control circuits logic, including the provisions for remote control and display, (4) check of the LRU connector for presence of correct voltages and absence of incorrect voltages under both energized and deenergized conditions, and (5) check of the AGC and power output monitor circuits.

Lane, J. H.↗
NASA NTRS1976

A bandwidth-compressive modulation system

The phrase 'bandwidth-compressive modulation' means that the compression is achieved not by removing redundancy from the data (data compression), but rather by modulating the carrier phase and amplitude with blocks of data bits. The modulation described here is quadrature amplitude shift keying (QASK), a logical extension of quadrature phase shift keying, (QPSK, or quadriphase). QASK is a cost-effective form of combined phase-and-amplitude modulation. That is, n-bit QASK, like most phase-amplitude forms of modulation, requires considerably less transmitter power than comparably performing n-PSK, while among the class of all n-bit phase-modulation types, n-bit QASK performs nearly optimally but requires the least circuit complexity. A simple, unique microwave transmitter is described which provides high-rate QASK modulation with 4:1 bandwidth compression. A suppressed carrier multiple-loop QASK receiver provides the necessary phase tracking, automatic gain control (AGC), and symbol timing.

Smith, J. G.↗
NASA NTRS1976

Solid State Television Camera (CID)

The design, development and test are described of a charge injection device (CID) camera using a 244x248 element array. A number of video signal processing functions are included which maximize the output video dynamic range while retaining the inherently good resolution response of the CID. Some of the unique features of the camera are: low light level performance, high S/N ratio, antiblooming, geometric distortion, sequential scanning and AGC.

Steele, D. W.↗
NASA NTRS1976

Solid state television camera (CCD-buried channel)

The development of an all solid state television camera, which uses a buried channel charge coupled device (CCD) as the image sensor, was undertaken. A 380 x 488 element CCD array is utilized to ensure compatibility with 525 line transmission and display monitor equipment. Specific camera design approaches selected for study and analysis included (a) optional clocking modes for either fast (1/60 second) or normal (1/30 second) frame readout, (b) techniques for the elimination or suppression of CCD blemish effects, and (c) automatic light control and video gain control (i.e., ALC and AGC) techniques to eliminate or minimize sensor overload due to bright objects in the scene. Preferred approaches were determined and integrated into a deliverable solid state TV camera which addressed the program requirements for a prototype qualifiable to space environment conditions.

Source record↗
NASA NTRS1979

One-third selection for matrix-addressing ferroelectrics

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. Potential application include radio and television receivers, signal distribution systems, and test and measurement instruments.

Tannas, L. E., Jr.↗
NASA NTRS1978

A bandwidth compressive modulation system using multi-amplitude minimum shift keying /MAMSK/

A bandwidth compressive modem making use of multi-amplitude minimum shift keying (MAMSK) has been designed and implemented in a laboratory environment at microwave frequencies. This system achieves a substantial bandwidth reduction over binary PSK and operates within 0.5 dB of theoretical performance. A number of easily implemented microwave transmitters have been designed to generate the required set of 16 signals. The receiver has been designed to work at 1 Mbit/s and contains the necessary phase tracking, AGC, and symbol synchronization loops as well as a lock detector, SNR estimator and provisions for differential decoding. This paper describes this entire system and presents the experimental results.

Weber, W. J., III↗
NASA NTRS1979

Decision-directed automatic gain control

Logic circuitry determines whether gain fluctuation are result of signal-strength changes or of atypical strings of like data symbols. Automatic Gain Control (AGC) system provides tight control that is independent of short-term, average, received signal energy and has negligible degrading effect on probability of error for signal.

Weber, W. J., III↗
NASA NTRS1978

Phase-locked loops and their application

A collection of papers is presented on the characteristics and capabilities of phase-locked loops (PLLs), along with some applications of interest. The discussion covers basic theory (linear and nonlinear); acquisition; threshold; stability; frequency demodulation and detection; tracking; cycle slipping and loss of lock; phase-locked oscillators; operation and performance in the presence of noise; AGC, AFC, and APC circuits and systems; digital PLL; and applications and miscellaneous. With the rapid development of IC technology, PLLs are expected to be used widely in consumer electronics.

Lindsey, W. C.↗
NASA NTRS1980

An initial assessment of the performance achieved by the Seasat-1 radar altimeter

The results of an initial on-orbit engineering assessment of the performance achieved by the radar altimeter system flown on SEASAT-1 are presented. Additionally, the general design characteristics of this system are discussed and illustrations of altimeter data product are provided. The instrument consists of a 13.5 GHz monostatic radar system that tracks in range only using a one meter parabolic antenna pointed at the satellite nadir. Two of its unique features are a linear FM transmitter with 320 MHz bandwidth which yields a 3.125 nanosecond time delay resolution, and microprocessor implemented closed loop range tracking, automatic gain control (AGC), and real time estimation of significant wave height (SWH). Results presented show that the altimeter generally performed in accordance with its orginal performance requirments of measuring altitude to a precision of less the 10 cm RMS, significant wave height to an accuracy of + or - 0.5 m or 10%, whichever is greater, and ocean backscatter coefficient to an accuracy of + or - 1 db, all over an SWH range of 1 to 20 meters.

Townsend, W. F.↗
NASA NTRS1980

An initial assessment of the performance achieved by the Seasat-1 radar altimeter

This paper describes the results of an initial on-orbit engineering assessment of the performance achieved by the radar altimeter system flown on Seasat-1. Additionally, the general design characteristics of this system are discussed and illustrations of altimeter data products are provided. The instrument consists of a 13.5-GHz monostatic radar system that tracks in range only using a 1-m parabolic antenna pointed at the satellite nadir. Two of its unique features are a linear FM transmitter with 320-MHz bandwidth, which yields a 3.125-ns time-delay resolution, and microprocessor-implemented closed-loop range tracking, automatic gain control (AGC), and real-time estimation of significant wave height (SWH). Results presented herein show that the altimeter generally performed in accordance with its original performance requirements of measuring altitude to a precision of less than 10-cm rms, SWH to an accuracy of plus or minus 0.5 m or 10 percent whichever is greater, and ocean backscatter coefficient to an accuracy of plus or minus 1 dB, all over an SWH range of 1 to 20 m.

Townsend, W. F.↗
NASA NTRS1981

Microcomputer processing for Loran-C

Schematic diagrams are presented for the microcomputer processing for Loran-C. Diagrams are included for the following: microcomputer Loran-C loop improvements; Loran-C receiver commutated AGC; and DC-DC power supply.

Lilley, R. W.↗
NASA NTRS1981

Ice sheet altimetry

Generalized surface slopes were computed for the Antarctic and Greenland ice sheets by differencing plotted contour levels and dividing them by the distance between the contours. It was observed that more than 90% of the ice sheets have surface slopes less than 1%. Seasat test mode-1 Seasat altimeter measurements over Greenland were analyzed by comparisons with collinear and intersecting normal mode Seasat altimeter passes. Over the ice sheet, the computed surface elevations from test mode-1 measurements were consistently lower by about 45 m and the AGC levels were down by approximately 6 dB. No test mode-1 data were acquired over Antarctica. It is concluded that analysis of the existing altimeter data base over the two ice sheets is crucial in designing a future improved altimeter tracking capability. It is recommended that additional waveform retracking be performed to characterize ice sheet topography as a function of geographic area and elevation.

Brooks, R. L.↗
NASA NTRS1981

PN lock indicator for dithered PN code tracking loop

In a delay-lock one-delta (+or - 1/2 chip) dithered PN code tracking loop, an indication of lock in the PN code tracking loop is provided by delaying the dithered local PN code by a half chip to produce a +0, -1 dithered PN code that is then multiplied with the received PN-spread IF signal to produce a signal proportional to the correlation of this dithered code offset from the received code. The correlation signal is bandpass filtered, amplified with AGC control, and square-law detected to obtain a dc signal proportional to the degree of correlation. The dc signal is multiplied by the dithering control signal to effectivity substract noise voltage from the lock correlation signal which is then compared with a PN lock status signal.

Carson, L. M.↗