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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 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Demonstration program for Omega receiver prototype microcomputer data processing

The JOLT (TM) commercial microcomputer, based on the MOS Technology 6502 processor chip, for use in Omega navigation system is evaluated. A computer program was prepared in hand-assembled code to demonstrate receiver operation. The processor provides binary processing with interrupts enabled, a carriage return is given to initialize the teleprinter, and a jump is performed to enter the program loop to wait for an interrupt. The program loop operates continuously testing the interrupt flag. The interrupt routine reads the receiver status word and determines whether the current time-slot is the A slot. If so, the interrupt flag, which is also the data index pointer, is reset to zero. The status word is stored in the status buffer. If the time-slot is not A, the interrupt flag/pointer is incremented by one to index the phase and status to the proper buffer words for later use by the print routine.

Lilley, R. W.↗
NASA NTRS1977

Mini-L Loran-C receiver

A brief description of the Loran-C system is presented with a suggested receiver based on a standard AM-FM integrated circuit chip. Construction details of the Mini-L Loran-C prototype front-end are considered. The Mini-L system was bench tested for approximately 500 hours under a variety of reception conditions. The Mini-L concept combined with a microprocessor system is a promising approach to the development of truly low-cost Loran-C receivers for the marine and airborne user.

Burhans, R. W.↗
NASA NTRS1977

Pioneer Venus wind experiment receiver

The final design of the Pioneer Venus Wind Experiment Receiver and Phase Calibrator is discussed from the block diagram viewpoint. Measured phase data are shown to derive the predicted performance. The STDN receiver implementation is also discussed.

Nishimura, H.↗
NASA NTRS1977

Optimum design and performance of Costas receivers containing soft bandpass limiters

This paper investigates several key questions concerning the mechanization and design of a Costas receiver for reconstruction of a carrier from a suppressed carrier signal. For baseband NRZ encoded data symbols and a soft bandpass limiter preceding the loop, several design issues which are considered herein and which affect acquisition and tracking performance are: (1) The choice of an IF bandwidth. (2) The optimum choice of the Costas arm filter bandwidths as well as the spectral roll-off characteristics. (3) The optimum choice of loop bandwidth to data rate ratio for a given signal-to-noise ratio. (4) The signal suppression factor and the combined limiter-squaring loss. (5) The variations in loop bandwidth and damping with signal level. (6) The choice of the limiter transfer characteristic. (7) Performance degradation due to the presence of a limiter. Various new results in system design are presented and typical numerical results are given and graphically demonstrated in SNR regions of practical interest. The theory is applicable to the design of carrier reconstruction loops required in the implementation of spread spectrum communication receivers.

Lindsey, W. C.↗
NASA NTRS1979

Narrow-bandwidth receiver

Synchronous switching circuit reduces bandwidth and improves sensitivity of communications receiver. With modified receiver, signals 35 db below level can be detected.

Manus, E. A.↗
NASA NTRS1977

A fixed tilt solar collector employing reversible vee-trough reflectors and vacuum tube receivers for solar heating and cooling systems

The usefulness of vee-trough concentrators in improving the efficiency and reducing the cost of collectors assembled from evacuated tube receivers was studied in the vee-trough/vacuum tube collector (VTVTC) project. The VTVTC was analyzed rigorously and various mathematical models were developed to calculate the optical performance of the vee-trough concentrator and the thermal performance of the evacuated tube receiver. A test bed was constructed to verify the mathematical analyses and compare reflectors made out of glass, Alzak and aluminized FEP Teflon. Tests were run at temperatures ranging from 95 to 180 C. Vee-trough collector efficiencies of 35 to 40% were observed at an operating temperature of about 175 C. Test results compared well with the calculated values. Predicted daily useful heat collection and efficiency values are presented for a year's duration of operation temperatures ranging from 65 to 230 C. Estimated collector costs and resulting thermal energy costs are presented. Analytical and experimental results are discussed along with a complete economic evaluation.

Selcuk, M. K.↗
NASA NTRS1977

An algorithm for the automatic synchronization of Omega receivers

The Omega navigation system and the requirement for receiver synchronization are discussed. A description of the synchronization algorithm is provided. The numerical simulation and its associated assumptions were examined and results of the simulation are presented. The suggested form of the synchronization algorithm and the suggested receiver design values were surveyed. A Fortran of the synchronization algorithm used in the simulation was also included.

Stonestreet, W. M.↗
NASA NTRS1978

The 1.06 optical receiver

High performance 1.06 micron m avalanche photodetectors (APDs), fabricated in the GaAlSb system, have high quantum efficiency (90 percent), high speed (risetime less than 60 ps) and low leakage currents (less than 50 na). The dark current represents more than an order of magnitude reduction compared to previously reported results. The high speed avalanche gain of these devices is between 20 and 50. The area uniformity is better than + or - 10 percent. GaAlAs APDs at 0.53 micron m have even faster speed, lower dark currents, and high speed gains of 100 to 200. Optical rangefinders based on measured APD performance parameters have far superior performance when compared to even ideal photomultiplier tubes in either a one color or two color rangefinder system. For a one color system, f factor of two lower time jitter can be achieved with identical transmitted power. The superiority of the APD based two color receiver is significant and exists in the entire range of desired time jitters (less than 100 ps) and received power levels.

Tomasetta, L. R.↗
NASA NTRS1978

Error probability performance of unbalanced QPSK receivers

A simple technique for calculating the error probability performance and associated noisy reference loss of practical unbalanced QPSK receivers is presented. The approach is based on expanding the error probability conditioned on the loop phase error in a power series in the loop phase error and then, keeping only the first few terms of this series, averaging this conditional error probability over the probability density function of the loop phase error. Doing so results in an expression for the average error probability which is in the form of a leading term representing the ideal (perfect synchronization references) performance plus a term proportional to the mean-squared crosstalk. Thus, the additional error probability due to noisy synchronization references occurs as an additive term proportional to the mean-squared phase jitter directly associated with the receiver's tracking loop. Similar arguments are advanced to give closed-form results for the noisy reference loss itself.

Simon, M. K.↗
NASA NTRS1979

Internal noise of a phase-locked receiver with a loop-controlled synthesizer

A local oscillator design that uses a digitally programmed frequency synthesizer instead of an analog VCO was proposed. The integral of the synthesizer input, the digital phase, is a convenient measure of integrated Doppler. The internal noise of such a receiver was examined. At high carrier margin, the local oscillator phase noise equals that of the Block IV receiver, about 2 deg rms at S-band, whereas the digital phase noise is about 0.5 deg rms.

Greenhall, C. A.↗
NASA NTRS1979

Multi-Mission Receiver (MMR)

An introduction to the Multi-Mission Receiver (MMR) is presented. The MMR contains occultation receiver channels (OCC) and very long baseline interferometry channels. The design considerations, performance and implementation of the OCC channels are discussed.

Donnelly, H.↗
NASA NTRS1978

Effects of pointing errors on receiver performance for parabolic dish solar concentrators

The effects of dynamic (moving) pointing errors on the performance of solar thermal receivers is investigated. Only point focusing types of solar collectors are considered. The key element in the study is the analytical derivation of the intercept factor that relates pointing errors to captured energy at the receiver. A detailed example using typical parameter values is modeled on the digital computer and demonstrates the theory and the dynamic nature of the problem.

Hughes, R. O.↗
NASA NTRS1978

Calculation of the relative influence of cloud layers on received ultraviolet and integrated solar radiation

Discrete ordinate radiative transfer calculations are used to examine the relative influence of cloud layers on the received ultraviolet flux and the received solar energy for a plane parallel atmosphere. The wavelength dependence for the cloud influence on the integrated solar radiation is primarily a function of the interaction of the cloud layer with the surrounding atmosphere and the underlying surface. It is found that for uv wavelengths greater than 300 nm, the ratio of uv to solar energy flux transmission through the atmosphere is insensitive to changes of cloud height, cloud scattering parameters and surface albedo (for realistic values), but is dependent on cloud thickness. For wavelengths approaching and less than 300 nm, absorption by tropospheric ozone results in sensitivity to cloud height and surface albedo.

Spinhirne, J. D.↗
NASA NTRS1978

False lock performance of Shuttle Costas loop receivers

The false (sideband) lock problem in Shuttle Costas loop receivers, in the presence of noise, is assessed. False lock margin is defined depending on symbol signal-to-noise ratio rather than in the absence of noise. Closed-form results are given for the case where the arm filters of the Costas loop are one-pole Butterworth filters as used in the Shuttle receivers. However, the approach taken is also general enough to cover filters of arbitrary characteristics. As part of the development of the false lock margin, it is shown that the false lock phenomenon of the squaring loop is identical to that of the Costas loop.

Woo, K. T.↗
NASA NTRS1979

Analysis, development and testing of a fixed tilt solar collector employing reversible Vee-Trough reflectors and vacuum tube receivers

The Vee-Trough/Vacuum Tube Collector (VTVTC) aimed to improve the efficiency and reduce the cost of collectors assembled from evacuated tube receivers. The VTVTC was analyzed rigorously and a mathematical model was developed to calculate the optical performance of the vee-trough concentrator and the thermal performance of the evacuated tube receiver. A test bed was constructed to verify the mathematical analyses and compare reflectors made out of glass, Alzak and aluminized GEB Teflon. Tests were run at temperatures ranging from 95 to 180 C during the months of April, May, June, July and August 1977. Vee-trough collector efficiencies of 35-40 per cent were observed at an operating temperature of about 175 C. Test results compared well with the calculated values. Test data covering a complete day are presented for selected dates throughout the test season. Predicted daily useful heat collection and efficiency values are presented for a year's duration at operation temperatures ranging from 65 to 230 C. Estimated collector costs and resulting thermal energy costs are presented. Analytical and experimental results are discussed along with an economic evaluation.

Selcuk, M. K.↗
NASA NTRS1980

Microprocessor control for phase-lock receiver

Subsystem facilities flexible data acquisition by combining hardware and software processing. Device controls complex signal acquisition sequence and assists in precise phase locking to received signal. Key features include software system and code-generator initialization routines, executive routine, utility subroutines, control sequence routines for each receiver acquisition state, control-command decoding routine, and look-up tables for code-generator configuration versus code-set number. Steps can be added to extend input signal dynamic range.

Carson, L. M.↗
NASA NTRS1979

Design study of a low cost civil aviation GPS receiver system

A low cost Navstar receiver system for civil aviation applications was defined. User objectives and constraints were established. Alternative navigation processing design trades were evaluated. Receiver hardware was synthesized by comparing technology projections with various candidate system designs. A control display unit design was recommended as the result of field test experience with Phase I GPS sets and a review of special human factors for general aviation users. Areas requiring technology development to ensure a low cost Navstar Set in the 1985 timeframe were identified.

Cnossen, R.↗
NASA NTRS1980

Radio frequency arraying method for receivers

A method and apparatus for increasing the signal to noise ratio of a receiving facility for coherent frequency reception by arraying receiving systems using separate antennas for each, or one antenna for all systems are presented. One system is operated with a carrier tracking loop to provide a first local oscillator frequency for the first and all other systems arrayed, with individual tracking loops in all other systems operated at IF for tracking out any phase differences due to separate group delays using an adjustable phase shifter for a second reference to compensate for different group delays in the antenna and low noise amplifier of each of the other systems. The second IF output of all systems is summed into the first system. This technique may also be used when two systems are arrayed to an antenna designed for circular or linear polarization diversity reception to effectively provide the same signal to noise ratio for both polarized signal transmission channels that would result from matched polarization. An arrangement adapted to high rate telemetry reception is disclosed. With additional components, the same arrangement is adapted to provide low rate telemetry reception as well.

Brockman, M. H.↗