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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 19 records
All sourcesNASA NTRSDOE OSTI
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.↗
NASA NTRS1971

Operational manual for MX-290 data-voice PN Mod, MX-291 data-voice PN DEMOD

This operation manual is also the final report of the program to design, assemble, checkout, and deliver to the customer three MX-290 transmitters and two MX-291 companion receivers. These equipments are designed and assembled to provide for maximum flexibility with respect to making changes in electrical circuits which may be required for future applications. A number of test points for monitoring and troubleshooting are provided along with easy access to subunits.

Source record↗
NASA NTRS1968

Pseudonoise (PN) synchronization of data system with derivation of clock frequency from received signal for clocking receiver PN generator

A digital communicating system for automatically synchronizing signals for data detection is described. The systems consists of biphase modulating a subcarrier frequency by the binary data and transmitting a carrier phase modulated by this signal to a receiver, where coherent phase detection is employed to recover the subcarrier. Data detection is achieved by providing, in the receiver, a demodulated reference which is in synchronism with the unmodulated subcarrier in transmitting system. The output of the detector is passed through a matched filter where the signal is integrated over a bit period. As a result, random noise components are averaged out, so that the probability of detecting the correct data transmitted is maximized.

Couvillon, L. A., Jr.↗
NASA NTRS1985

PN velocity beneath Western New Mexico and Eastern Arizona

The experiment involved observing Pn arrivals on an areal array of 7 seismic stations located in the transition zone and along the Jemez lineament. Explosions in coal and copper mines in New Mexico and Arizona were used as energy sources as well as military detonations at White Sands Missile Range, New Mexico, Yuma, Arizona, and the Nevada Test Site. Very preliminary results suggest a Pn velocity of 7.94 km/s (with a fairly large uncertainty) beneath the study area. The Pn delay times, which can be converted to estimates of crustal thickness given knowledge of the velocity structure of the crust increase both to the north and east of Springerville, Arizona. As a constraint on the velocity of Pn, researchers analyzed the reversed refraction line GNOME-HARDHAT which passes through Springerville oriented NW to SE. This analysis resulted in a Pn velocity of 7.9-8.0 km/s for the transition zone. These preliminary results suggest that a normal Pn velocity might persist even though the crust thins (from north to south) by 15 km along the length of the Arizona-New Mexico border. If the upper mantle is currently hot anywhere in western New Mexico or eastern Arizona then the dimensions of the heat source (or sources) might be small compared to the intra-station distances of the seismic arrays used to estimate the velocity of Pn.

Jaksha, L. H.↗
NASA NTRS1987

Detection of interstellar PN - The first phosphorus-bearing species observed in molecular clouds

Phosphorus nitride (PN) has been detected in the interstellar medium. The J = 2-1, 3-2, 5-4, and 6-5 rotational lines of this species have been observed toward Orion-KL, and the J = 2-1 transition in Sgr B2 and W51. The PN line profiles in Orion indicate that the molecule's emission arises from the 'plateau' or 'doughnut' region associated with the outflow from IRc2. The species is thus primarily present in hot, dense gas. Column densities derived for PN toward Orion-KL are (3-4) x 10 to the 13th/sq cm, but may be as high as 10 to the 14th/sq cm, if the species is located in a 10-arcsec region. These column densities imply a fractional abundance for PN in the Orion 'plateau' of (1-4) x 10 to the -10th. Such a large abundance for PN is not predicted by quiescent cloud ion-molecule chemistry and suggests that high-temperature processes are responsible for the synthesis of PN in the KL outflow.

Ziurys, L. M.↗
NASA NTRS1982

Optimum waiting time for acquisition of return link PN signals

The subject of this paper is a model that takes into account the effect that acquisition of a PN signal on the forward link has on the acquisition of a PN signal on the return link. The model is used to determine how long the start of the PN search on the return link should be delayed in order to minimize the combined acquisition time (delay + acquisition time) as a function of desired acquisition probability. It is assumed that the return link a-priori epoch uncertainty information is available. Software has been developed that models the return link PN receiver and incorporates in it the effect of forward link PN acquisition statistics in assessing performance.

Kolata, W.↗
NASA NTRS1991

Radio frequency interference effect on PN code sequence lock detector

The authors find the probabilities of detection and false alarm of the pseudonoise (PN) sequence code lock detector when strong radio frequency interference (RFI) hits the communications link. Both a linear model and a soft-limiter nonlinear model for a transponder receiver are considered. In addition, both continuous wave (CW) RFI and pulse RFI are analyzed, and a discussion is included of how strong CW RFI can knock out the PN code lock detector in a linear or a soft-limiter transponder. As an example, the Space Station Freedom forward S-band PN system is evaluated. It is shown that a soft-limiter transponder can protect the PN code lock detector against a typical pulse RFI, but it can degrade the PN code lock detector performance more than a linear transponder if CW RFI hits the link.

Kwon, Hyuck M.↗
NASA NTRS1981

Comparison between variable and fixed dwell-time PN acquisition algorithms

Pseudo noise (PN) spread spectrum systems require a very accurate alignment between the PN code epochs at the transmitter and receiver. This synchronism is typically established through a two-step algorithm, including a coarse synchronization procedure and a fine synchronization procedure. A standard approach for the coarse synchronization is a sequential search over all code phases. The measurement of the power in the filtered signal is used to either accept or reject the code phase under test as the phase of the received PN code. This acquisition strategy, called a single dwell-time system, has been analyzed by Holmes and Chen (1977). A synopsis of the field of sequential analysis as it applies to the PN acquisition problem is provided. From this, the implementation of the variable dwell time algorithm as a sequential probability ratio test is developed. The performance of this algorithm is compared to the optimum detection algorithm and to the fixed dwell-time system.

Braun, W. R.↗
NASA NTRS2020

Sample Transponder Implementations for PN DDOR

The design philosophy and recommended standards for PN DDOR transponders are proposed in RFM 20-04. The referenced document illustrates how to pick a chip rate, roll-off factor, and other PN parameters for a PN DDOR transmitter. The document also proposes various recommendations for these parameters. This document expands upon RFM 20-04 and presents two PN DDOR transmitters that were designed and tested at JPL. First the IRIS cubesat radio is presented with an 8 MHz spread spectrum DDOR signal. Next the Univeral Space Transponder (UST) transmitter is presented with a 32 MHz spread spectrum DDOR signal. These transmitter designs show that the proposed recommendations are reasonably implemented with current technology.

Volk, Christopher P↗
NASA NTRS2020

Proposed Recommendation for DDOR PN Spread Spectrum Systems

Currently, instrumental phase dispersion is a large error term in the Delta-Differential One-way Ranging (DDOR) error budget. This error arises from the spectral difference between the narrowband spacecraft signal and the broadband quasar signal. This error term can be reduced in modern transponders by implementing a pseudo-noise (PN) spread spectrum DOR signal instead of the classic sinusoidal DOR signal. To standardize PN DDOR cross-support, this paper proposes the definitions and specifications required to support a PN DDOR system. The motivation for PN DDOR is first presented. Then, informational background is presented on code selection, pulse shaping, and code parameters. Finally, Appendix A presents a new proposed Recommendation 2.5.7B for Spread Spectrum DDOR, to be included in CCSDS 401.

Volk, Christopher P↗
NASA NTRS1974

The effects of notch filters on the correlation properties of a PN signal

With wideband pseudo-noise (PN) communications systems, it is sometimes desirable to supplement the inherent interference rejection capabilities by adding notch filters to attenuate relatively narrowband interference. This correspondence presents an investigation of the effects of notch filters on the performance of PN correlation receivers. A theoretical analysis of the correlation drop due to filter distortion has been conducted and confirmed by experimentation. Additional measurements and analysis have established the trade-off between correlation drop and interference suppression as a function of interference bandwidth. A typical result is that by incurring a penalty of a 1-dB drop in correlation peak, interfering signals having bandwidths of 2 to 3% of the PN chip rate can be attenuated by 25 dB.

Sussman, S. M.↗
NASA NTRS1977

PN ranging/telemetry transmission

System can transmit range-indicating pseudonoise (PN) codes and simultaneously transmit auxiliary information as binary data at a rate at least on order of pseudonoise chipping rate. PN code is modulated by data stream with relatively low bit rate. Data stream with high bit rate can be transmitted in same frequency band as PN ranging code.

Deerkoski, L. F.↗
NASA NTRS1996

Fast Risetime Reverse Bias Pulse Failures in SiC PN Junction Diodes

SiC-based high temperature power devices are being developed for aerospace systems which will require high reliability. One behavior crucial to power device reliability. To date, it has necessarily been assumed to date is that the breakdown behavior of SiC pn junctions will be similar to highly reliable silicon-based pn junctions. Challenging this assumption, we report the observation of anomalous unreliable reverse breakdown behavior in moderately doped (2-3 x 10(exp 17) cm(exp -3)) small-area 4H- and 6H-SiC pn junction diodes at temperatures ranging from 298 K (25 C) to 873 K (600 C). We propose a mechanism in which carrier emission from un-ionized dopants and deep level defects leads to this unstable behavior. The fundamental instability mechanism is applicable to all wide bandgap semiconductors whose dopants are significantly un-ionized at typical device operating temperatures.

Neudeck, Philip G.↗
NASA NTRS2008

Combined GMSK Communications and PN Ranging

A document discusses a method by which GMSK (Gaussian minimum shift keying) modulation and a pseudonoise (PN) ranging signal may be combined. By isolating the in-phase and quadrature components after carrier lock, and extracting their low-pass and band-pass filtered components, there is enough information available to both demodulate data and track the PN signal. The proposed combined GMSK communications and PN ranging is one potential approach to address emerging requirements for simultaneous high data rate communications from and tracking of vehicles in deep space or at the Moon.

Orr, Richard↗
NASA NTRS1969

On the auto and cross correlation of PN sequences

The autocorrelation and crosscorrelation properties of pseudorandom (PN) sequences are analyzed by using some important properties of PN sequences. These properties make this discussion understandable without the need of linear algebraic approach. The analysis is followed by some experimental results.

Morakis, J. C.↗