2,404 research outputs found
The Murchison Widefield Array: the Square Kilometre Array Precursor at low radio frequencies
The Murchison Widefield Array (MWA) is one of three Square Kilometre Array
Precursor telescopes and is located at the Murchison Radio-astronomy
Observatory in the Murchison Shire of the mid-west of Western Australia, a
location chosen for its extremely low levels of radio frequency interference.
The MWA operates at low radio frequencies, 80-300 MHz, with a processed
bandwidth of 30.72 MHz for both linear polarisations, and consists of 128
aperture arrays (known as tiles) distributed over a ~3 km diameter area. Novel
hybrid hardware/software correlation and a real-time imaging and calibration
systems comprise the MWA signal processing backend. In this paper the as-built
MWA is described both at a system and sub-system level, the expected
performance of the array is presented, and the science goals of the instrument
are summarised.Comment: Submitted to PASA. 11 figures, 2 table
The Future of High Frequency Circuit Design
The cut-off wavelengths of integrated silicon transistors have
exceeded the die sizes of the chips being fabricated with them.
Combined with the ability to integrate billions of transistors on
the same die, this size-wavelength cross-over has produced a
unique opportunity for a completely new class of holistic circuit
design combining electromagnetics, device physics, circuits, and
communication system theory in one place. In this paper, we discuss
some of these opportunities and their associated challenges
in greater detail and provide a few of examples of how they can
be used in practice
Distribution automation applications of fiber optics
Motivations for interest and research in distribution automation are discussed. The communication requirements of distribution automation are examined and shown to exceed the capabilities of power line carrier, radio, and telephone systems. A fiber optic based communication system is described that is co-located with the distribution system and that could satisfy the data rate and reliability requirements. A cost comparison shows that it could be constructed at a cost that is similar to that of a power line carrier system. The requirements for fiber optic sensors for distribution automation are discussed. The design of a data link suitable for optically-powered electronic sensing is presented. Empirical results are given. A modeling technique that was used to understand the reflections of guided light from a variety of surfaces is described. An optical position-indicator design is discussed. Systems aspects of distribution automation are discussed, in particular, the lack of interface, communications, and data standards. The economics of distribution automation are examined
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Propagation of Power Line Carrier Signals Through the Distribution Transformer.
In the wake of the governments 1989 Electricity act, privatisation reforms have urged the Electricity Supply Industry to enhance the capabilities of its current communication infrastructure . With this realisation , the possibilities of using the
industries own distribution network as a communication medium has become a serious proposition. Although this may seem an innovative solution , the use of electrical distribution feeders for conveying information is not in fact new. However, recent advances in technology have provided solutions to the outstanding problem of attaining 'usable' data rates in the harsh power line environment. With this in mind, a power line telecommunications network seems a viable option for the electricity distribution companies. Unfortunately, a system which utilises both LV and MV networks remains presently unattainable , due to the unknown characteristics of the distribution transformer. Having highlighted the need to develop a 'through transformer' signalling system , the frequency characteristics of the distribution transformer have become of paramount interest. Although spread spectrum systems are gaining widespread acceptance, the high
process gain required in adverse communication environments mitigates against high data rates. Investigations have demonstrated that an alternative strategy of lower frequency techniques is capable of maintaining a comparable integrity of communications. The following work catalogues the results and draws conclusions from research
devoted to an investigation into the propagation of PLC frequency signals through distribution type transformers. From this analysis the viability of a 'through transformer' architecture may be assessed
Aircraft electromagnetic compatibility
Illustrated are aircraft architecture, electromagnetic interference environments, electromagnetic compatibility protection techniques, program specifications, tasks, and verification and validation procedures. The environment of 400 Hz power, electrical transients, and radio frequency fields are portrayed and related to thresholds of avionics electronics. Five layers of protection for avionics are defined. Recognition is given to some present day electromagnetic compatibility weaknesses and issues which serve to reemphasize the importance of EMC verification of equipment and parts, and their ultimate EMC validation on the aircraft. Proven standards of grounding, bonding, shielding, wiring, and packaging are laid out to help provide a foundation for a comprehensive approach to successful future aircraft design and an understanding of cost effective EMC in an aircraft setting
Definition of Throw-Away Detectors (TADs) and VLF antenna for the AMPS laboratory
A Throw Away Detector (TAD)/subsatellite to be used as an experiment platform for the test flights to map the EMI from the shuttle and during the AMPS science flights is defined. A range of instrument platforms of varying capabilities is examined with emphasis on the EMI test vehicle. The operational support requirements of TAD/subsatellites are determined. The throw away detector is envisioned as a simple instrument package for supporting specific experiments
Index to 1981 NASA Tech Briefs, volume 6, numbers 1-4
Short announcements of new technology derived from the R&D activities of NASA are presented. These briefs emphasize information considered likely to be transferrable across industrial, regional, or disciplinary lines and are issued to encourage commercial application. This index for 1981 Tech Briefs contains abstracts and four indexes: subject, personal author, originating center, and Tech Brief Number. The following areas are covered: electronic components and circuits, electronic systems, physical sciences, materials, life sciences, mechanics, machinery, fabrication technology, and mathematics and information sciences
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