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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Effects of asymmetric passband filtering on the phase of the Costas loop's reconstructed carrier

The reconstructed carrier of a telemetry return signal is used in deriving the Doppler and range information in the radiometric systems. When suppressed carrier BPSK signalling with Costas loop demodulation is used, there are concerns on the amount of shift in the reconstructed carrier phase, when the received signal suffers asymmetric bandpass filtering through the various stages of the receiver. It is concluded that the phase shifts due to asymmetric bandpass filtering on the Costas loop's reconstructed carrier can be slightly worse than those suffered by the residual carrier loop's reconstructed carrier. However, they are well within the error budgets of the radiometric system.

Woo, K. T.↗
NASA NTRS1977

On the false lock behavior of polarity-type Costas loops with Manchester coded input

A modification of a Costas loop is described, and the false lock behavior of this system is studied. The modified Costas loop hard limits the output of the in-phase channel, replaces the analog multiplier with a chopper-type device, and is equipped with single-pole arm filters in the loop. The false lock behavior associated with the use of Manchester coded data is investigated; the results can be applied to the assessment of the false lock margin on the Ku-band uplink to the Space Shuttle Orbiter through the TURSS.

Simon, M. K.↗
NASA NTRS1981

Analysis of tracking performance of the MTDD Costas loop for UQPSK signal

The tracking performance of the breadboard Costas loop for the Multimegabit Telemetry Demodulator/Detector (MTDD) System using an unbalanced quadriphase-shift-keyed (UQPSK) signal is considered. The particular Costas loop is a biphase polarity type with passive arm filters. The loop contains a hard limiter in front of the third multiplier, which is a chopper-type device. The rms phase jitter predictions made have also been verified experimentally.

Park, Y. H.↗
NASA NTRS1981

Two-channel Costas loop tracking performance for UQPSK signals with arbitrary data formats

Previous results on the tracking performance of two-channel Costas-type carrier synchronization loops are generalized and corrected, in order that they may be applied to several mixed-format cases. In particular, the mean-square phase jitter performance of these loops with active arm filters, synchronous or asynchronous symbol clocks, and arbitrary data formats on the two channels is examined. It is demonstrated that for each case, selection of the channel gain ratio, as motivated by the MAP estimation theory, does not guarantee optimum loop tracking performance: in some instances, a conventional single-channel Costas loop would outperform the two-channel version with the MAP choice of gain ratio. It is suggested that the gain ratio be chosen to directly minimize the mean-square phase tracking jitter which is equivalent to minimizing the loop's 'squaring loss'. This can, in some cases, improve the performance measure, although in all cases, the two-channel loop will still outperform the single-channel version.

Simon, M. K.↗
NASA NTRS1981

Tracking performance of the polarity-type costas loop at low SNR for UQPSK signal

Carrier tracking performance of the polarity type costas loop is analyzed for unbalanced quadriphase-shift-keyed (UQPSK) signals at low SNR. Squaring losses for various SNR, IF bandwidth, and data rate ratios are presented. The RMS phase jitter for a particular loop is computed for various I and Q channel power and data rate ratios. Experimental results using a breadboard costas loop are also included.

Park, Y. H.↗
NASA NTRS1989

Costas loop lock detection in the advanced receiver

The advanced receiver currently being developed uses a Costas digital loop to demodulate the subcarrier. Previous analyses of lock detector algorithms for Costas loops have ignored the effects of the inherent correlation between the samples of the phase-error process. Accounting for this correlation is necessary to achieve the desired lock-detection probability for a given false-alarm rate. Both analysis and simulations are used to quantify the effects of phase correlation on lock detection for the square-law and the absolute-value type detectors. Results are obtained which depict the lock-detection probability as a function of loop signal-to-noise ratio for a given false-alarm rate. The mathematical model and computer simulation show that the square-law detector experiences less degradation due to phase jitter than the absolute-value detector and that the degradation in detector signal-to-noise ratio is more pronounced for square-wave than for sine-wave signals.

Mileant, A.↗
NASA NTRS1992

The behavior of a Costas loop in the presence of space telemetry signals

When the Costas loop is operated in the presence of a residual carrier space telemetry signal, the loop reconstructs its carrier reference from an input signal whose carrier component is not completely suppressed. The telemetry signal investigated in this work is generated by phase shift-keying the data onto a subcarrier and then phase modulating onto the sinusoidal carrier. The telemetry modulation index, telemetry bit rate, subcarrier waveform, and subcarrier frequency are shown to be the key system parameters that contribute to the performance degradation of a Costas loop. Furthermore, the effect of Doppler shift on the loop is also investigated in this work.

Nguyen, Tien M.↗
NASA NTRS1994

(abstract) GPS Monitoring of Crustal Deformation and the Earthquake Cycle in Costa Rica

This paper will discuss the objectives, approach, and anticipated results of a study of earthquakes in Costa Rica. GPS measurements will be taken and field surveys will be made. Assessments of seismic strain accumulation and post-seismic deformation will be made in an effort to understand the effect these processes have on regional tectonic models.

tectonics↗
DOE OSTI2021

Taxonomic and Functional Diversity of Aquatic Macroinvertebrate Assemblages and Water Quality in Rivers of the Dry Tropics of Costa Rica

One of Costa Rica’s driest areas is the province of Guanacaste, in the Pacific Northwest, with almost no rain during the dry season from November to April. Due to this marked seasonality, the area is covered by dry tropical deciduous forest, considered the most threatened and least known tropical ecosystem in this area. This study analyzes and characterizes the assemblages of aquatic macroinvertebrates in water bodies within the Tempisque basin. Biological water quality was measured using the BMWP′-CR index. Macroinvertebrate assemblages were analyzed using abundance, richness, and functional feeding group approaches (FFG). Partial least square (PLS) analyses were performed, and the relationships between environmental factors and macroinvertebrate assemblages are also discussed. Macroinvertebrate assemblages were dominated numerically by mayflies, caddisflies, flies, and beetles. The BWMP′-CR index showed varying biological water quality, ranging from “very bad” to “excellent,” depending on rainfall and site management. Results suggest that tropical Mesoamerican rivers contradict the “river continuum concept” because predators and scrapers displace shredders in numbers. On the other hand, the study area shows a notable high richness of the Coleoptera genera. The class Rhynchocoela (Nemertea) is reported for the first time in Central America. The results indicate that the dry forest river ecosystem shows staggering biodiversity despite the surrounding agricultural land use, probably because of their older origin concerning tropical rain forests in Central America.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Modeling land surface processes over a mountainous rainforest in Costa Rica using CLM4.5 and CLM5

This study compares the performance of the Community Land Models (CLM4.5 and CLM5) against tower and ground measurements from a tropical montane rainforest in Costa Rica. The study site receives over 4000 mm of mean annual precipitation and has high daily levels of relative humidity. The measurement tower is equipped with eddy-covariance and vertical profile systems able to measure various micrometeorological variables, particularly in wet and complex terrain. In this work, results from point-scale simulations for both CLM4.5 and its updated version (CLM5) are compared to observed canopy flux and micrometeorological data. Both models failed to capture the effects of frequent rainfall events and mountainous topography on the variables of interest (temperatures, leaf wetness, and fluxes). Overall, CLM5 alleviates some errors in CLM4.5, but CLM5 still cannot precisely simulate a number of canopy processes for this forest. Soil, air, and canopy temperatures, as well as leaf wetness, remain too sensitive to incoming solar radiation rates despite updates to the model. As a result, daytime vapor flux and carbon flux are overestimated, and modeled temperature differences between day and night are higher than those observed. Slope effects appear in the measured average diurnal variations of surface albedo and carbon flux, but CLM5 cannot simulate these features. This study suggests that both CLMs still require further improvements concerning energy partitioning processes, such as leaf wetness process, photosynthesis model, and aerodynamic resistance model for wet and mountainous regions.

58 GEOSCIENCES↗
NASA NTRS1977

Optimum performance of suppressed carrier receivers with Costas loop tracking

The performance of suppressed carrier receivers with Costas loop tracking is optimized by proper choice of loop arm filter bandwidth. In particular, it is shown that for a variety of passive arm filter types, there exists, for a given data rate and data signal-to-noise ratio, an optimum filter bandwidth in the sense of minimizing the loop's squaring loss. For the linear theory case, this is equivalent to minimizing the loop's tracking jitter. When symbol synchronization is known, it is shown that by replacing the passive arm filters with active filters, i.e., integrate-and-dump circuits, one can achieve an improvement in carrier-to-noise ratio of as much as 4 to 6 dB depending on the passive arm filter type used for comparison and the value of data signal-to-noise ratio.

Simon, M. K.↗
NASA NTRS1978

A Costas loop with tangent error signal for use in Navstar GPS avionics

This paper describes an augmented Costas loop for use in low-cost avionics for the Navstar Global Positioning System. A standard loop has been augmented with supplementing feed-back to give a tracking error voltage proportional to the tangent of the phase error, rather than to the sine. The augmented loop yields increased performance in the presence of input phase acceleration and jerk, as caused by maneuvers of the GPS user vehicle. Many Monte Carlo simulation results are given.

Painter, J. H.↗
NASA NTRS1979

Evaluation of Costas Loops for demodulation of a spread spectrum signal for Space Shuttle up-link communications

The Space Shuttle Communication System utilizes a Costas Loop for carrier reconstruction to demodulate the Spread Spectrum signals. This design includes the increasingly popular hard limited in-phase channel which allows use of a switching type multiplier preceding the loop filter. This paper presents the development and performance of this type demodulator and includes supporting measured data.

Killen, H. B.↗
NASA NTRS1979

Data pattern sensitivity in tracking performance of an AC coupled Costas loop with hard-limited in-phase channel

This paper is concerned with data pattern sensitivity in carrier tracking performance of an AC coupled Costas loop with a suppressed BPSK signal. The signal amplitude suppression factor is derived as a function of data 'asymmetry ratio' - the ratio of '1's to the total number of bits in a period of a periodic signal. For an asymmetric pattern, the effect of AC coupling is noticeable whereas there is almost no effect for symmetric square wave. The tracking performance with an asymmetric pattern is worse than that with a symmetric pattern. However, it is also shown that as expected, the tracking performance of a DC coupled loop with an asymmetric pattern is better than that with a symmetric pattern.

Park, Y. H.↗
NASA NTRS1981

Experimental results on tracking performance of the MTDD Costas loop with UQPSK signal

The carrier tracking performance of the breadboard Costas Loop of the Multimegabit Telemetry Demodulator Detector System was tested with unbalanced quadriphase shift keying (UQPSK) signals. An S-band UQPSK modulator was built for the tests. The experimental results are very close to the theoretical rms phase error calculations. The test and analysis show that the rms phase error for UQPSK signals is less than 5 deg at the design point if the I-to-Q channel power ratio is larger than 6 dB.

Park, Y. H.↗
NASA NTRS1980

International Symposium on Remote Sensing of Environment, 14th, San Jose, Costa Rica, April 23-30, 1980, Proceedings. Volumes 1, 2 & 3

Papers are presented on remote sensing applications in resource monitoring and management, data classification and modeling procedures, and the use of remote sensing techniques in developing nations. The subjects of land use/land cover, soil mapping, crop identification, mapping of geological resources, renewable resource analysis, and oceanographic applications are discussed. Papers from Argentina, Bolivia, Brazil, Costa Rica, the Syrian Arab Republic, the People's Republic of China, the Phillipines, Italy, Upper Volta and the United States are included.

Source record↗
NASA NTRS1980

Costas loop tracking performance in the presence of antenna switching transients

The present paper examines the impact of phase, amplitude and Doppler transients on the tracking performance of a Costas loop, both in the presence and absence of noise; the loop's lock maintenance capability is also examined. Specific considerations involve analyzing second order loop transient behavior in the absence of noise and the presence of the three transients noted above; here, the operational differential equations are formulated and numerically solved. In the context of noise presence, a first order loop is treated in conjunction with amplitude and phase transients; toward this end the time dependent version of the Fokker-Planck partial differential equation is developed and numerically solved. Selected performance curves describe second order loop behavior in the presence of transients, whose values are of varying severity. First order loop behavior in the presence of noise is characterized by the illustration of suitably defined time dependent 'truncated probability density functions' and associated loss of lock probabilities.

Weinberg, A.↗