Tech Briefs

Automated Announcements of Approaching Emergency Vehicles

Pedestrians would be given advance warning.Street intersections that are equipped with traffic lights would also be equipped with means for generating audible announcements of approaching emergency vehicles, according to a proposal. The means to generate the announcements would be implemented in the intersection-based subsystems of emergency traffic-light-preemption systems like those described in the two immediately preceding articles and in “Systems Would Preempt Traffic Lights for Emergency Vehicles” (), NASA Tech Briefs, Vol. 28, No. 10 (October 2004), page 36.

Posted in: Briefs, TSP, Electronics & Computers

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Digital Front End for Wide-Band VLBI Science Receiver

An upgrade to the very long baseline interferometry (VLBI) science receiver (VSR) — a radio receiver used in NASA’s Deep Space Network (DSN) — is currently being implemented. The current VSR samples standard DSN intermediate frequency (IF) signals at 256 MHz and after digital down-conversion records data from up to four 16-MHz baseband channels. Currently, IF signals are limited to the 265-to-375-MHz range, and recording rates are limited to less than 80 Mbps. The new digital front end, denoted the Wideband VSR, provides improvements to enable the receiver to process wider bandwidth signals and accommodate more data channels for recording. The Wideband VSR utilizes state-of-the-art commercial analog-to-digital converter and field-programmable gate array (FPGA) integrated circuits, and fiber-optic connections in a custom architecture. It accepts IF signals from 100 to 600 MHz, sampling the signal at 1.28 GHz. The sample data are sent to a digital processing module, using a fiber-optic link for isolation. The digital processing module includes boards designed around an Advanced Telecom Computing Architecture (ATCA) industry-standard backplane. Digital signal processing implemented in FPGAs down-convert the data signals in up to 16 baseband channels with programmable bandwidths from 1 kHz to 16 MHz. Baseband samples are transmitted to a computer via multiple Ethernet connections allowing recording to disk at rates of up to 1 Gbps.

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Full-Duplex Digital Communication on a Single Laser Beam

The laser beam would be transmitted with one modulation and retroreflected with another modulation.A proposed free-space optical communication system would operate in a full-duplex mode, using a single constant-power laser beam for transmission and reception of binary signals at both ends of the free-space optical path. The system was conceived for two-way data communication between a ground station and a spacecraft in a low orbit around the Earth. It has been estimated that in this application, a data rate of 10 kb/s could be achieved at a ground-station- to-spacecraft distance of 320 km, using a laser power of only 100 mW. The basic system concept is also applicable to terrestrial free-space optical communications.

Posted in: Briefs, Electronics & Computers

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Pointing Reference Scheme for Free-Space Optical Communications Systems

A technique is proposed for referencing infrared transmit lasers with silicon detectors.A scheme is proposed for referencing the propagation direction of the transmit laser signal in pointing a free-space optical communications terminal. This recently developed scheme enables the use of low cost, commercial silicon-based sensors for tracking the direction of the transmit laser, regardless of the transmit wavelength. Compared with previous methods, the scheme offers some advantages of less mechanical and optical complexity and avoids expensive and exotic sensor technologies.

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Microwave Oscillators Based on Nonlinear WGM Resonators

Optical signals are phase-modulated with spectrally pure microwave signals.Optical oscillators that exploit resonantly enhanced four-wave mixing in nonlinear whispering- gallery- mode (WGM) resonators are under investigation for potential utility as low-power, ultra-miniature sources of stable, spectrally pure microwave signals. There are numerous potential uses for such oscillators in radar systems, communication systems, and scientific instrumentation.

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Stabilizing Microwave Frequency of a Photonic Oscillator

Microwave frequency is stabilized by stabilizing optical frequency to an atomic transition. A scheme for stabilizing the frequency of a microwave signal is proposed that exploits the operational characteristics of a coupled optoelectronic oscillator (COEO) and related optoelectronic equipment. An essential element in the scheme is a fiber mode-locked laser (MLL), the optical frequency of which is locked to an atomic transition. In this scheme, the optical frequency stability of the mode-locked laser is transferred to that of the microwave in the same device. Relative to prior schemes for using wideband optical frequency comb to stabilize microwave signals, this scheme is impler and lends itself more readily to implementation in relatively compact, rugged equipment. The anticipated development of small, low-power, lightweight, highly stable microwave oscillators based on this scheme would afford great benefits in communication, navigation, metrology, and fundamental sciences.

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Covering a Crucible With Metal Containing Channels

Metal is deposited on a sacrificial pattern that defines the channels. In a procedure that partly resembles the lost-wax casting process, a crucible made of a brittle material (ceramic, quartz, or glass) is covered with a layer of metal containing channels. The metal cover and the channels can serve any or all of several purposes, depending upon the application: Typically, the metal would serve at least partly to reinforce the crucible. The channels could be used as passages for narrow objects that could include thermocouples and heat-transfer strips. Alternatively or in addition, channels could be used as flow paths for liquid or gaseous coolants and could be positioned and oriented for position or direction-selective cooling. In some cases, the channels could be filled with known gases and sealed so that failure of the crucibles could be indicated by instruments that detect the gases.

Posted in: Briefs, TSP, Manufacturing & Prototyping

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