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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 NTRS1995

Pulse Code Modulation (PCM) encoder handbook for Aydin Vector MMP-900 series system

This handbook explicates the hardware and software properties of a time division multiplex system. This system is used to sample analog and digital data. The data is then merged with frame synchronization information to produce a serial pulse coded modulation (PCM) bit stream. Information in this handbook is required by users to design congruous interface and attest effective utilization of this encoder system. Aydin Vector provides all of the components for these systems to Goddard Space Flight Center/Wallops Flight Facility.

Raphael, David↗
NASA NTRS1990

Local oscillator induced degradation of medium-term stability in passive atomic frequency standards

As the performance of passive atomic frequency standards improves, a new limitation is encountered due to frequency fluctuations in an ancillary local oscillator (L.O.). The effect is due to time variation in the gain of the feedback which compensates L.O. frequency fluctuations. The high performance promised by new microwave and optical trapped ion standards may be severely compromised by this effect. Researchers present an analysis of this performance limitation for the case of sequentially interrogated standards. The time dependence of the sensitivity of the interrogation process to L.O. frequency fluctuations is evaluated for single-pulse and double-pulse Ramsey RF interrogation and for amplitude modulated pulses. The effect of these various time dependencies on performance of the standard is calculated for an L.O. with frequency fluctuations showing a typical 1/f spectral density. A limiting 1/sq. root gamma dependent deviation of frequency fluctuations is calculated as a function of pulse lengths, dead time, and pulse overlap. Researchers also present conceptual and hardware-oriented solutions to this problem which achieve a much more nearly constant sensitivity to L.O. fluctuations. Solutions involve use of double-pulse interrogation; alternate interrogation of multiple traps so that the dead time of one trap can be covered by operation of the other; and the use of double-pulse interrogation for two traps, so that during the time of the RF pulses, the increasing sensitivity of one trap tends to compensate for the decreasing sensitivity of the other. A solution making use of amplified-modulated pulses is also presented which shows nominally zero time variation.

Dick, G. John↗
NASA NTRS1987

Radar Time-Base and Pseudonoise Generator

Long pulses effectively compressed by pseudonoise technique. Computer-controlled, polynomial-driven time-base and pseudonoise generator enables radar system to achieve range resolution of about 80 m with radar pulses of 1-s duration. Normally, unmodulated 1-s pulse has relatively coarse range resolution of several thousand kilometers. Radar system effectively compresses modulated pulse into one of 100-ns pseudonoise-modulating pulses. Intended primarily for use with interplanetary radar, time-base/pseudonoise concept proves useful in test instruments or in time-base correction for video recording.

Brokl, S. S.↗
NASA NTRS1974

Engineering information on an Analog Signal to Discrete Time Interval Converter (ASDT-IC)

An electronic control system for nondissipative dc power converters is presented which improves (1) the routinely attainable static output voltage accuracy to the order of + or - 1% for ambient temperatures from -55 to 100 C and (2) the dynamic stability by utilizing approximately one tenth of the feedback gain needed otherwise. Performance is due to a functional philosophy of deterministic pulse modulation based on pulse area control and to an autocompensated signal processing principle. The system can be implemented with commercially available unselected components.

Schwarz, F. C.↗
NASA NTRS1976

Development and evaluation of a set of group delay standards

A set of cable assemblies serving as group delay standards having nominal delays of 15, 30, and 60 nsec are described. Various types of measurements were performed on the cable standards, including impedance, microwave phase shift, RF pulse burst delay, modulation pulsed delay, and envelope phase shift measurements. The results of these tests are given, and various sources of error are discussed, in particular, dispersion and internal reflections.

Otoshi, T. Y.↗
NASA NTRS1983

Using SAW Resonators in RF Oscillators

Surface-acoustic-wave (SAW) resonators used as frequency-determining elements in radio-frequency oscillators circuits. Oscillators are frequencymodulated, phase-modulated, or pulse-modulated. SAW resonators are especially applicable to low-power subminiature applications, such as biotelemetry and wind-tunnel instrumentation, where they advantageously replace crystals. Resonators are smaller than crystals and very thin--advantage where small package size is important.

Westbrook, R. M.↗
NASA NTRS1973

ASDTIC control and standardized interface circuits applied to buck, parallel and buck-boost dc to dc power converters

Versatile standardized pulse modulation nondissipatively regulated control signal processing circuits were applied to three most commonly used dc to dc power converter configurations: (1) the series switching buck-regulator, (2) the pulse modulated parallel inverter, and (3) the buck-boost converter. The unique control concept and the commonality of control functions for all switching regulators have resulted in improved static and dynamic performance and control circuit standardization. New power-circuit technology was also applied to enhance reliability and to achieve optimum weight and efficiency.

Schoenfeld, A. D.↗
NASA NTRS1989

Pulse-Population Modulation For Induction Machines

Low-frequency synthesizer developed to provide low-frequency waveform by synthesis from high-frequency power system. Waveform assembled by allowing conduction of discrete half cycles of high-frequency carrier. Frequency of synthesized wave controlled by pulse pattern. By controlling relationship between slip and stator frequencies, one operates induction motor either as motor or generator. Such bidirectional energy transducer used as starter/generator for engine, or as servo-mechanism for control of acceleration and deceleration. Other advantages include operation under controlled voltage-to-frequency ratios to maintain high-efficiency and high power factor, and no reflection of low-frequency noise into 20-kHz distribution bus.

Hansen, Irving G.↗
NASA NTRS1973

Temperature control system with a pulse width modulated bridge

A temperature control system, which includes a modified wheatstone bridge with a resistive-capacitive (RC) circuit in one leg of the bridge, is disclosed. The RC circuit includes a resistor which provides an effective resistance as a function of its absolute resistance and the on-time to off-time ratio of pulses supplied to a switch connected across it. A sawtooth voltage is produced across the RC circuit. The voltage is compared with the voltage across a temperature sensor with heat being applied during each pulse period portion when the sawtooth voltage exceeds the voltage across the temperature sensor.

Heyser, R. C.↗
NASA NTRS1968

Portable Pulse Code Modulation /PCM/

Small, programmable, high speed PCM subsystem, supports the variety of signals inherent in sophisticated equipment. A signal generated by a transducer is first conditioned to the proper signal range, then sampled by an external multiplexer or by the subsystem directly and then converted and transmitted to a receiving station.

Bradanini, P. A.↗
NASA NTRS1969

Pulse-code-modulation baseline correction for low signal-to-noise ratios

Time-shared integrate-hold-dump circuits separate the dc level due to the signal /bit information/ from the dc signal due to the baseline error. The system detects the baseline error, filters it, and then algebraically adds enough voltage to a servo loop to reduce the error to zero.

Stephens, T. J.↗
NASA NTRS1971

Pulse width-pulse rate modulator

Attitude control system designed for rockets regulates duty cycle of pneumatic valves so less fuel is required. Operation time of each valve is directly proportional to error signal and the dead band about a null is controlled by independently adjustable threshold circuits.

Cooke, W. A.↗
NASA NTRS1972

Pulse-width-modulated device for precision temperature control

Temperature controller is described which reduces difference between temperature oscillations about control point. Standard temperature-sensitive resistor element is utilized which is highly stable and reproducible. Temperature sensing circuitry is conventional dc bridge with power supplied by battery or highly regulated supply source.

Heyser, R. C.↗