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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Encoding and decoding of color information using two-dimensional spatial filtering.

Spatial frequency encoding is described as it applies to both photographic and television systems. In each case, color separations amplitude modulate spatial frequency carriers. The photographic system separates the carriers in the two-dimensional Fourier transform plane using coherent optics; the television system employs a two-dimensional electrical filter to perform the same separation. These filters are synthesized so that the two-dimensional bandwidths of the television camera are used efficiently. Nonlinear processing techniques are also described to minimize crosstalk between channels.

Schaefer, L. F.↗
NASA NTRS1977

Low-cost pressure-data encoder

Electronic encoding altimeter has pulsed output with pulse width proportional to altitude and converts pressure-proportional input voltage to digital signal that may then be routed to monitoring or display equipment.

Kolbly, R. B.↗
NASA NTRS1976

Digital plus analog output encoder

The disclosed encoder is adapted to produce both digital and analog output signals corresponding to the angular position of a rotary shaft, or the position of any other movable member. The digital signals comprise a series of binary signals constituting a multidigit code word which defines the angular position of the shaft with a degree of resolution which depends upon the number of digits in the code word. The basic binary signals are produced by photocells actuated by a series of binary tracks on a code disc or member. The analog signals are in the form of a series of ramp signals which are related in length to the least significant bit of the digital code word. The analog signals are derived from sine and cosine tracks on the code disc.

Hafle, R. S.↗
NASA NTRS1977

Electronic shaft-angle encoder

Contactless encoder is used at higher angular velocities and for objects lacking integral supporting shaft.

Powell, J. A.↗
NASA NTRS1977

Twin-capacitive shaft angle encoder with analog output signal

A precision capacitive shaft encoder providing a dc signal corresponding to the angular position of a shaft is described. Two variable capacitances are coupled in tandem by a rotatable shaft. Each capacitor has a capacitance that varies linearly with a change in the angular position of the shaft. The sum of the two capacitances is always constant for any angular position of the shaft. Each capacitance is alternately coupled to a reference dc voltage and a discharge circuit. The capacitances are electrically coupled in series and the charge periodically acquired at the junction of the capacitance is a function of the position of the shaft. An error-compensating voltage is imposed on the junction when the capacitances are coupled to the reference voltages. The junction is coupled to sample-and-hold apparatus provided with a error-correcting circuit.

Hruby, R. J.↗
NASA NTRS1976

Performance of convolutionally encoded noncoherent MFSK modem in fading channels

The performance of a convolutionally encoded noncoherent multiple-frequency shift-keyed (MFSK) modem utilizing Viterbi maximum-likelihood decoding and operating on a fading channel is described. Both the lognormal and classical Rician fading channels are considered for both slow and time-varying channel conditions. Primary interest is in the resulting bit error rate as a function of the ratio between the energy per transmitted information bit and noise spectral density, parameterized by both the fading channel and code parameters. Fairly general upper bounds on bit error probability are provided and compared with simulation results in the two extremes of zero and infinite channel memory. The efficacy of simple block interleaving in combatting channel memory effects are thoroughly explored. Both quantized and unquantized receiver outputs are considered.

Modestino, J. W.↗
NASA NTRS1979

Efficient digital encoding scheme

Modified NRZ (non-return-to-zero) code immunizes record and playback systems against dc drift and bit slippage. In order to maximize bit packing density improved code called J-NRZ gives 100 percent NRZ efficiently and solves DC drift problem by adding check bits in specified format when long string is encountered. Remainder of data stream is encoded in NRZ format.

Obrien, D. E., III↗
NASA NTRS1977

Performance of DPSK with convolutional encoding on time-varying fading channels

The bit error probability performance of a differentially-coherent phase-shift keyed (DPSK) modem with convolutional encoding and Viterbi decoding on time-varying fading channels is examined. Both the Rician and the lognormal channels are considered. Bit error probability upper bounds on fully-interleaved (zero-memory) fading channels are derived and substantiated by computer simulation. It is shown that the resulting coded system performance is a relatively insensitive function of the choice of channel model provided that the channel parameters are related according to the correspondence developed as part of this paper. Finally, a comparison of DPSK with a number of other modulation strategies is provided.

Mui, S. Y.↗
NASA NTRS1979

Binary-to-Manchester encoders

Two circuit system converts 16-bit-word binary encoded data to 24-bit Manchester II code to allow easy interface of flight simulators with aircraft communications equipment.

St. Cyr, R. H., III↗
NASA NTRS1979

Improved reader for magnetically-encoded ID cards

Hybrid demodulator in electronic card reader for magnetically encoded identification cards, accommodates variations in insertion speeds, yet is simpler and less expensive than equivalent all-digital circuits.

Wu, T. T.↗
NASA NTRS1978

Voice encoding for the Space Shuttle using adaptive delta modulation

The paper describes the SONG and modified ABATE adaptive delta modulation algorithms for voice encoding. Waveforms of the response of the delta modulators to channel errors are given, and performance data which show the relationship between channel errors and word intelligibility are provided. An analytic derivation yielding a comparison between PCM and adaptive delta modulation with respect to channel errors is given. The Space Shuttle is employing the modified-ABATE device because it can tolerate a high error rate and operates at a relatively low sampling rate.

Schilling, D. L.↗
NASA NTRS1979

The effect of interference on delta modulation encoded video signals

An adaptive delta modulator which encodes composite color video signals was shown to provide a good response when operating at 16 Mb/s and near-commercial quality at 23Mb/s. The ADM was relatively immune to channel errors. The system design is discussed and circuit diagrams are included.

Schilling, D. L.↗
NASA NTRS1982

Spatial, High-Accuracy, Positioning-Encoding Sensor (SHAPES) for large space system control applications

The Spatial, High-Accuracy, Position-Encoding Sensor is a controls sensor suitable for the determination of the static shape and vibrational motion of large space structures and similar systems and for the determination of position and velocity in rendezvous and docking. It uses a combination of electro-optical techniques to measure the three-dimensional coordinates distributed over the structure at reading rates high compared to the rates at which the coordinates are changing. The technical approach is that of measuring the distance to and the direction of points on the structure from a single sensor head. Many points can be measured simultaneously from a single head without significantly increasing the complexity of the system.

Mclauchlan, J. M.↗