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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Response of a Fabry-Perot cavity to phase modulated light

A solution to the lock-in detection method, which is valid for arbitrary values of the modulation frequency, is described. The theory for determining frequency modulation of a single frequency laser is presented. The theoretical predictions for the optimum modulation index are compared to experimental solutions for the quasi-static regime. Signal line shapes for first, second, and third harmonic generations are derived and examined. It is noted that there is good correlation between experimental and quasi-static theory data for the relation between small modulation frequency and resonance linewidth.

Hils, Dieter↗
NASA NTRS1972

Miniature biotelemeter gives multichannel wideband biomedical data

A miniature biotelemeter was developed for sensing and transmitting multiple channels of biomedical data over a radio link. The design of this miniature, 10-channel, wideband (5 kHz/channel), pulse amplitude modulation/ frequency modulation biotelemeter takes advantage of modern device technology (e.g., integrated circuit operational amplifiers, complementary symmetry/metal oxide semiconductor logic, and solid state switches) and hybrid packaging techniques. The telemeter is being used to monitor 10 channels of neuron firings from specific regions of the brain in rats implanted with chronic electrodes. Design, fabrication, and testing of an engineering model biotelemeter are described.

Carraway, J. B.↗
NASA NTRS1979

Determining the response of an FM receiver

Frequency response to frequency-modulation (FM) receiver is measured with aid of phase-modulation (PM) transmitter by applying correction to output power level. As modulating frequency is increased, output level obtained in response to PM input is reduced by 6 db per octane.

Perry, J. C.↗
NASA NTRS2007

Recent Results of a New Microwave SQUID Multiplexer

We are developing a proof-of-concept microwave SQUID multiplexer containing four SQUIDs coupled to GHz frequency resonant circuits and fed with a single microwave readout line. The resonators are half-wave coplanar waveguide sections and are similar to the structures used for the microwave kinetic inductance detectors developed in our group. Optimal values for the interdigital gap capacitors were determined to maximize the sensitivity of the transmitted and reflected microwave signal with respect to changes in the dynamic resistance of the SQUID. The dc current-bias line for the SQUID has an in-line inductive high frequency filter to minimize coupling between the bias line and resonator. A high frequency modulation scheme is proposed to eliminate the need for individual flux biasing of the SQUIDs, which extends the dynamic range of the readout. In this scheme a common modulation signal is imposed on each SQUID and the received signal is demodulated at one and two times the modulation frequency to maintain sensitivity at any flux state. We present the recent results of the microwave SQUID multiplexer system operating at a readout frequency range of 10 - 11GHz.

superconducting quantum interference device (SQUID↗
NASA NTRS2012

Covert laser remote sensing and vibrometry

Designs of single-beam laser vibrometry systems and methods. For example, a method for detecting vibrations of a target based on optical sensing is provided to include operating a laser to produce a laser probe beam at a laser frequency and modulated at a modulation frequency onto a target; collecting light at or near the laser to collect light from the target while the target is being illuminated by the laser probe beam through an optical receiver aperture; using a narrow-band optical filter centered at the laser frequency to filter light collected from the optical receiver aperture to transmit light at the laser frequency while blocking light at other frequencies; using an optical detector to convert filtered light from the narrow-band optical filter to produce a receiver electrical signal; using a lock-in amplifier to detect and amplify the receiver electrical signal at the modulation frequency while rejecting signal components at other frequencies to produce an amplified receiver electrical signal; processing the amplified receiver electrical signal to extract information on vibrations of the target carried by reflected laser probe beam in the collected light; and controlling optical power of the laser probe beam at the target to follow optical power of background illumination at the target.

Maleki, Lutfollah↗
NASA NTRS1991

The measurement system of pulse modulated carrier frequency stability and timing jitter

The definition of pulse modulated carrier frequency stability and timing jitter as well as the configuration and synchronous acquisition measurement method of its measurement system. Frequency stability of the pulse modulated carrier is measured with a discrimination technique. The pulse modulated carrier under testing is mixed with a reference frequency synthesizer. A delay line is used to convert the frequency fluctuation mixed IF signal to the voltage fluctuation. The system has the capability to make the phase noise measurement of two port devices on a pulsed carrier using a phase bridge. The noise voltage mentioned above is applied to the data acquisition and processing unit by PC to realize stability measurement. The data acquisition is in the form of pulse synchronization so that the measurement system accuracy is increased. The pulse width is more than 0.3 microseconds. The phase fluctuation variance, sigma, is less than 0.017. The time interval measuring system with high resolution is used to make interpulse timing and pulse width jitters automatic measurement. The pulse width is less than 0.2 ns. The resolution is 0.1 ns. The system is successfully applied to radar measurement.

Li Cheng-Fu↗
NASA NTRS1975

Communications and navigation

The use of a computer simulation to quantitatively measure the distortion on a standard video test signal which experiences frequency modulation, filtering, and frequency demodulation is discussed. The process is applied to frequency modulated television systems for use with the ATS-F spacecraft. A block diagram of the system is presented. The characteristics of a millimeter wave space communication system are analyzed. The application of the Omega position location equipment (OPLE) for a global rescue net is reported. The development of a high speed photodetector for the neodynium yag laser system is discussed and the characteristics of the system are explained. The effects of gas pressure on waveguide laser tunability are examined.

Source record↗
NASA NTRS1991

Visual sensitivity to spatially sampled modulation in human observers

Thresholds were measured for detecting spatial luminance modulation in regular lattices of visually discrete dots. Thresholds for modulation of a lattice are generally higher than the corresponding threshold for modulation of a continuous field, and the size of the threshold elevation, which depends on the spacing of the lattice elements, can be as large as a one log unit. The largest threshold elevations are seen when the sample spacing is 12 min arc or greater. Theories based on response compression cannot explain the further observation that the threshold elevations due to spatial sampling are also dependent on modulation frequency: the greatest elevations occur with higher modulation frequencies. The idea that this is due to masking of the modulation frequency by the spatial frequencies in the sampling lattice is considered.

Mulligan, Jeffrey B.↗
NASA NTRS1972

Spectral analysis program. Volume 1: User's guide

The spectral analysis program (SAP) was developed to provide the Manned Spacecraft Center with the capability of computing the power spectrum of a phase or frequency modulated high frequency carrier wave. Previous power spectrum computational techniques were restricted to relatively simple modulating signals because of excessive computational time, even on a high speed digital computer. The present technique uses the recently developed extended fast Fourier transform and represents a generalized approach for simple and complex modulating signals. The present technique is especially convenient for implementation of a variety of low-pass filters for the modulating signal and bandpass filters for the modulated signal.

Hayden, W. L.↗
NASA NTRS1989

Data-Processing System For Test Airplane

Real-time display of data on performance supports decisions regarding maneuvers. Data from sensors aboard airplane transmitted to control station on ground for immediate processing and display. Data-acquisition subsystem aboard airplane uses both pulse code modulation and frequency modulation for transmission of sensor data on operation of engine, performance of airplane, and conditions in atmosphere. No data recorded on aircraft.

Ray, R. J.↗
NASA NTRS1983

Dynamic-pressure measurements using an electronically scanned pressure module

Frequency response was measured for different lengths and diameters of tubing between a sinusoidal pressure source and a pressure sensing module from an electronically scanned pressure measuring system. Measurements were made for straight runs of both steel and vinyl tubing. For steel tubing, measured results are compared with results calculated by using equations developed by Tijdeman and Bergh. Measurements were also made with a bend in the vinyl tubing at the module. In addition, measurements were made with two coils placed in the tubing near the middle of the run.

Chapin, W. G.↗
NASA NTRS1972

Gaussian and click noise in an FM/FM multiplex receiver.

An FM/FM system is one in which the signal information frequency modulates a subcarrier, which, in turn, frequency modulates a main carrier for transmission. The detection process then involves two frequency demodulators in sequence. Using Rice's click model for both FM demodulators, we obtain the average click rate and an approximate output spectrum that include the effect of the impulses generated by the carrier demodulator on the subcarrier demodulation at and below threshold. We then focus on the threshold behavior of these systems and the proportioning of their modulation parameters so as to provide certain desired characteristics. We find that due to the filtering action of the second demodulator, the number of output clicks from carrier generated spikes can be orders of magnitude smaller, yet their contribution to the output noise can be much greater than that produced by the first demodulation.

Stochel, N. H.↗
NASA NTRS1993

A three channel telemetry system

A three channel telemetry system intended for biomedical applications is described. The transmitter is implemented in a single chip using a 2 micron BiCMOS processes. The operation of the system and the test results from the latest chip are discussed. One channel is always dedicated to temperature measurement while the other two channels are generic. The generic channels carry information from transducers that are interfaced to the system through on-chip general purpose operational amplifiers. The generic channels have different bandwidths: one from dc to 250 Hz and the other from dc to 1300 Hz. Each generic channel modulates a current controlled oscillator to produce a frequency modulated signal. The two frequency modulated signals are summed and used to amplitude modulate the temperature signal which acts as a carrier. A near-field inductive link telemeters the combined signals over a short distance. The chip operates on a supply voltage anywhere from 2.5 to 3.6 Volts and draws less than 1 mA when transmitting a signal. The chip can be incorporated into ingestible, implantable and other configurations. The device can free the patient from tethered data collection systems and reduces the possibility of infection from subcutaneous leads. Data telemetry can increase patient comfort leading to a greater acceptance of monitoring.

Lesho, Jeffery C.↗
NASA NTRS2001

Obliquity Modulation of the Incoming Solar Radiation

Based on a basic principle of orbital resonance, we have identified a huge deficit of solar radiation induced by the combined amplitude and frequency modulation of the Earth's obliquity as possibly the causal mechanism for ice age glaciation. Including this modulation effect on solar radiation, we have performed model simulations of climate change for the past 2 million years. Simulation results show that: (1) For the past 1 million years, temperature fluctuation cycles were dominated by a 100-Kyr period due to amplitude-frequency resonance effect of the obliquity; (2) From 2 to 1 million years ago, the amplitude-frequency interactions. of the obliquity were so weak that they were not able to stimulate a resonance effect on solar radiation; (3) Amplitude and frequency modulation analysis on solar radiation provides a series of resonance in the incoming solar radiation which may shift the glaciation cycles from 41-Kyr to 100-Kyr about 0.9 million years ago. These results are in good agreement with the marine and continental paleoclimate records. Thus, the proposed climate response to the combined amplitude and frequency modulation of the Earth's obliquity may be the key to understanding the glaciation puzzles in paleoclimatology.

Liu, Han-Shou↗
NASA NTRS1988

Models of QPOs in luminous low-mass X-ray binaries

Models of quasi-periodic oscillations (QPOs) in luminous X-ray sources and observational studies relevant to these models are reviewed. QPOs are found to belong to two or three distinct types defined by the spectral state of the source and the properties of the QPOs themselves. Models can be classified according to whether the magnetic field of the neutron star is or is not important and whether the QPOs are produced by luminosity oscillations or beaming. The weakness of the red noise component of the normal branch power spectrum and the discovery that the phase of horizontal branch oscillations and normal branch oscillations at higher energies lags that at lower energies are discussed. The implications of these observations for QPO models are presented. Several QPO models are assessed, including the boundary layer hot spot model, beat-frequency modulated accretion model, the beat-frequency modulated dissipation model, nonradial g-mode model, reflecting clumps model, and the oscillating obscuration model.

Lamb, F. K.↗