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At least 613 records · Page 34

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NASA NTRS1979

Performance of mismatched Viterbi receiver on satellite channels

This paper presents an analysis of a satellite communication system using a Viterbi receiver. Here we have a bandlimited nonlinear channel where both uplink and downlink are taken into account as well as the effect of Intersymbol Interference, phase and time synchronization errors. In order that ISI can be combatted effectively, we use a Viterbi demodulator which is designed for the satellite channel when there is no uplink noise. The Viterbi demodulator for the channels with large memory is too complex to be implemented. To reduce the complexity, a Viterbi demodulator with memory shorter than the true channel memory is used. The objective of this paper is to analyze the performance degradation of this 'Mismatched Viterbi Receiver' due to the uplink noise and memory truncation, and to understand how the time and phase synchronization errors influence the performance.

Divsalar, D.↗

NASA NTRS1980

The performance of suppressed carrier receivers in a pulsed RFI environment

This paper investigates the tracking performance of a Costas loop in the presence of single and multiple in-band pulsed RFI signals and receiver additive noise. It is shown that the loop's tracking performance is very sensitive to the pulse durations of the RFI signals, as well as their repetition rates and peak powers relative to those of the desired signal. The presence of in-band RFI can affect the loop's tracking performance in basically three ways. 1) The loop tracks the composite phase of the RFI instead of the phase of the desired signal when the effective RFI power is greater than that of the signal. 2) When the effective RFI power is not sufficiently large to capture the loop, there still will exist static phase error biases which cause the loop to lock at a phase between that of the desired signal and the composite RFI. 3) There is an increase in the rms phase jitter over the nominal design. These latter two effects degrade the bit error probability performance of the receiver. More significantly, if the nominal loop bandwidth is not designed properly to account for the increase in jitter phenomenon, frequency cycle slipping may result.

Simon, M. K.↗

NASA NTRS1982

Heat-Energy Analysis for Solar Receivers

Heat-energy analysis program (HEAP) solves general heat-transfer problems, with some specific features that are "custom made" for analyzing solar receivers. Can be utilized not only to predict receiver performance under varying solar flux, ambient temperature and local heat-transfer rates but also to detect locations of hotspots and metallurgical difficulties and to predict performance sensitivity of neighboring component parameters.

Lansing, F. L.↗

NASA NTRS1980

Identification and analysis of factors affecting thermal shock resistance of ceramic materials in solar receivers

An analysis was conducted of the possible modes of thermal stress failure of brittle ceramics for potential use in point-focussing solar receivers. The pertinent materials properties which control thermal stress resistance were identified for conditions of steady-state and transient heat flow, convective and radiative heat transfer, thermal buckling and thermal fatigue as well as catastrophic crack propagation. Selection rules for materials with optimum thermal stress resistance for a particular thermal environment were identified. Recommendations for materials for particular components were made. The general requirements for a thermal shock testing program quantitatively meaningful for point-focussing solar receivers were outlined. Recommendations for follow-on theoretical analyses were made.

Hasselman, D. P. H.↗

NASA NTRS1981

Telemetry degradation due to a CW RFI induced carrier tracking error for the block IV receiving system with maximum likelihood convolution decoding

Models to characterize the behavior of the Deep Space Network (DSN) Receiving System in the presence of a radio frequency interference (RFI) are considered. A simple method to evaluate the telemetry degradation due to the presence of a CW RFI near the carrier frequency for the DSN Block 4 Receiving System using the maximum likelihood convolutional decoding assembly is presented. Analytical and experimental results are given.

Sue, M. K.↗

NASA NTRS1981

The development of an 85-kW (thermal) air Brayton receiver

The results of the program from its inception through December 1980 are presented. The design requirements, concept, and significant analysis upon which the receiver is based are described. The fabrication processes that have been utilized in the construction of the prototype receivers at the test station are summarized. The test and evaluation phase at the Parabolic Dish Test Site are described.

Greevan, M.↗

NASA NTRS1981

Organic Rankine cycle receiver development

The selected receiver concept is a direct-heated, once-through, monotube boiler operated at supercritical pressure. The cavity is formed by a cylindrical copper shell and backwall, with stainless steel tubing brazed to the outside surface. This core is surrounded by lightweight refractory insulation, load-bearing struts, and an outer case. The aperture plate is made of copper to provide long life by conduction and reradiation of heat away from the aperture lip. The receiver thermal efficiency is estimated to be 97 percent at rated conditions (energy transferred to toluene divided by energy incident on aperture opening). Development of the core manufacturing and corrosion protection methods is complete.

Haskins, H. J.↗

NASA NTRS1981

The effects of receiver tracking phase error on the performance of the concatenated Reed-Solomon/Viterbi channel coding system

Analytical and experimental results are presented of the effects of receiver tracking phase error, caused by weak signal conditions on either the uplink or the downlink or both, on the performance of the concatenated Reed-Solomon (RS) Viterbi channel coding system. The test results were obtained under an emulated S band uplink and X band downlink, two way space communication channel in the telecommunication development laboratory of JPL with data rates ranging from 4 kHz to 20 kHz. It is shown that, with ideal interleaving, the concatenated RS/Viterbi coding system is capable of yielding large coding gains at very low bit error probabilities over the Viterbi decoded convolutional only coding system. Results on the effects of receiver tracking phase errors on the performance of the concatenated coding system with antenna array combining are included.

Liu, K. Y.↗

NASA NTRS1980

Universal delta modulation receivers using the bit slice approach

The architecture of programmable processors is described, with particular reference to the design of a programmable delta-modulation decoder capable of receiving DM encoders employing different schemes. A switching receiver implementation, allowing communication between different DM algorithms, is designed and shown.

Apelewicz, T.↗

NASA NTRS1981

Design studies for a technology assessment receiver for global positioning system

The operational conditions of a radio receiver - microprocessor for the global positioning system are studied. Navigation fundamentals and orbit characterization are reviewed. The global positioning system is described with emphasis upon signal structure and satellite positioning. Ranging and receiver processing techniques are discussed.

Painter, J. H.↗

NASA NTRS1981

A prototype interface unit for microprocessor based Loran-C receiver

An inexpensive data/command entry and CRT display system capable of alphanumeric and graphics moe operation and designed to operate in place of a separate ASCII terminal, is documented. The software to interface this unit to the 6502-based Loran C receiver is also described. The system simplifies receiver operations to a level typical of current avionics systems.

Novacki, S. M., III↗

NASA NTRS1982

Ultrasonic input-output for transmitting and receiving longitudinal transducers coupled to same face of isotropic elastic plate

The quantitative understanding of ultrasonic nondestructive evaluation parameters such as the stress wave factor were studied. Ultrasonic input/output characteristics for an isotropic elastic plate with transmitting and receiving longitudinal transducers coupled to the same face were analyzed. The asymptotic normal stress is calculated for an isotropic elastic half space subjected to a uniform harmonic normal stress applied to a circular region at the surface. The radiated stress waves are traced within the plate by considering wave reflections at the top and bottom faces. The output voltage amplitude of the receiving transducer is estimated by considering only longitudinal waves. Agreement is found between the output voltage wave packet amplitudes and times of arrival due to multiple reflections of the longitudinal waves.

Williams, J. H., Jr.↗

NASA NTRS1982

Global positioning system timing receivers in the DSN

The system (GPS) is a worldwide navigation system using a constellation of Earth satellites with onboard clocks. The GPS is also usable to transfer time and frequency. Preliminary tests with the breadboard receiver at NBS produced precision in time and frequency transfer between the United States Naval Observatory (USNO) and NBS. JPL's plans to install receivers in the DSN to demonstrate their ability to transfer time and frequency within the DSN and between the DSN and outside agencies are discussed.

Clements, P. A.↗

NASA NTRS1981

Steam Rankine Solar Receiver, phase 2

A steam rankine solar receiver (SRSR) based on a tubular concept was designed and developed. The SRSR is an insulated, cylindrical coiled tube boiler which is mounted at the focal plane of a fully tracking parabolic solar reflector. The concentrated solar energy received at the focal plane is then transformed to thermal energy through steam generation. The steam is used in a small Rankine cycle heat engine to drive a generator for the production of electrical energy. The SRSR was designed to have a dual mode capability, performing as a once through boiler with and without reheat. This was achieved by means of two coils which constitute the boiler. The boiler core size of the SRSR is 17.0 inches in diameter and 21.5 inches long. The tube size is 7/16 inch I.D. by 0.070 inch wall for the primary, and 3/4 inch I.D. by 0.125 inch wall for the reheat section. The materials used were corrosion resistant steel (CRES) type 321 and type 347 stainless steel. The core is insulated with 6 inches of cerablanket insulation wrapped around the outer wall. The aperture end and the reflector back plate at the closed end section are made of silicon carbide. The SRSR accepts 85 kwth and has a design life of 10,000 hrs when producing steam at 1400 F and 2550 psig.

Deanda, L. E.↗

NASA NTRS1980

A Conceptual Design Study of a High Temperature Solar Thermal Receiver

A conceptual design was made for a solar thermal receiver capable of operation in the 1095 to 1650 C (2000 to 3000 F) temperature range. This receiver is designed for use with a two-axis paraboloidal concentrator in the 25 to 150 kW sub t power range, and is intended for industrial process heat, Brayton engines, or chemical/fuels reactions. Three concepts were analyzed parametrically. One was selected for conceptual design. Its key feature is a helical coiled tube of sintered silicon nitride which serves as the heat exchanger between the incident solar radiation and the working fluid. A mechanical design of this concept was prepared, and both thermal and stress analysis performed. The analysis showed good performance, low potential cost in mass production, and adaptability to both Brayton cycle engines and chemical/fuels production.

Robertson, C. S.↗

NASA NTRS1982

A Loran-C prototype navigation receiver for general aviation

The design, fabrication and evaluation of a prototype Loran-C receiver is described. Hardware, and microcomputer programming for addition of area navigation capability are reported. The receiver is an envelope processor, offering simplicity of RF processor circuitry.

Lilley, R. W.↗

NASA NTRS1981

Use of ceramics in point-focus solar receivers

One of the research and development efforts in the Solar Thermal Energy Systems Project at the Jet Propulsion Laboratory has been focused on application of ceramic components for advanced point-focus solar receivers. The impetus for this effort is a need for high efficiency, low cost solar receivers which operate in a temperature regime where use of metal components is impractical. The current status of the work on evaluation of ceramic components at JPL and elsewhere is outlined and areas where lack of knowledge is currently slowing application of ceramics are discussed. Future developments of ceramic processing technology and reliability assurance methodology should open up applications for the point-focus solar concentrator system in fuels and chemicals production, in thermochemical energy transport and storage, in detoxification of hazardous materials and in high temperature process heat as well as for electric power generation.

Smoak, R. H.↗

NASA NTRS1982

Sound broadcasting satellite systems for individual reception by mobile receivers

In this paper, the feasibility of a multi-channel sound broadcasting satellite system for operation in a band between 0.5 and 2.0 GHz is investigated. Considered are sound broadcasting satellite systems that provide conventional FM sound broadcasting for individual receivers in a wide geographical area. Comparative weight estimation of sound broadcasting satellites is carried out for various sizes of coverage area and spacecraft antenna, and for different carrier frequencies in the band from 0.5 to 2.0 GHz. It is concluded that relatively light (1200 to about 1500 lbs) spacecraft are feasible, even with low-cost portable or mobile receiving systems.

Park, Y. H.↗