Design of a YIG-tuned oscillator

A technique for designing YIG (yttrium-iron garnet) tuned transistor oscillators, tunable over the range of frequencies from 500 to 950 MHZ, is presented. The approach taken differs appreciably from that used in the design of conventional LC-tuned oscillators. One major difference is that the YIG tuning mechanism is electrically controlled. The YIG tuning element is treated as a single unit and is not resolved into an equivalent LC circuit. Instead, a direct method using reflection coefficients measured at network terminals to characterize various design stages is applied. The transistor is also characterized by reflection and transmission coefficients, i.e., S-parameters. Thus the Smith Chart becomes a useful tool and network calculations are greatly simplified by means of signal flow analysis with application of Mason\u27s rule. Because S-parameters are measured when the device is terminated in the characteristic impedance of the measuring system, they are more accurately determined at high frequencies than other parameters requiring open and short circuit terminations for their measurement. Furthermore, the availability of network analyzers, such as the Hewlett-Packard S-Parameter Test Set, simplifies such measurements. As a result, a concise method using S-parameters is most applicable for the design of transistor YIG-tuned oscillators

An investigation into the requirements for an efficient image transmission system over an ATM network

This thesis looks into the problems arising in an image transmission system when transmitting over an A TM network. Two main areas were investigated: (i) an alternative coding technique to reduce the bit rate required; and (ii) concealment of errors due to cell loss, with emphasis on processing in the transform domain of DCT-based images. [Continues.

The Vietnamese Amerasian Resettlement Experience: From Initial Application to the First Six Months in the United States

The Amerasian Homecoming Act of 1987, allowed Vietnamese Amerasian individuals fathered by U.S. military servicemen and born in Vietnam after January 1, 1962 and before January 1, 1976, to enter the United States

Scale Effect of Premixed Methane-Air Combustion in Confined Space Using LES Model

Gas explosion is the most hazardous incident occurring in underground airways. Computational Fluid Dynamics (CFD) techniques are sophisticated in simulating explosions in confined spaces; specifically, when testing large-scale gaseous explosions, such as methane explosions in underground mines. The dimensions of a confined space where explosions could occur vary significantly. Thus, the scale effect on explosion parameters is worth investigating. In this paper, the impact of scaling on explosion overpressures is investigated by employing two scaling factors: The Gas-fill Length Scaling Factor (FLSF) and the Hydraulic Diameter Scaling Factor (HDSF). The combinations of eight FLSFs and five HDSFs will cover a wide range of space dimensions where flammable gas could accumulate. Experiments were also conducted to evaluate the selected numerical models. The Large Eddy Simulation turbulence model was selected because it shows accuracy compared to the widely used Reynolds\u27 averaged models for the scenarios investigated in the experiments. Three major conclusions can be drawn: (1) The overpressure increases with both FLSF and HDSF within the deflagration regime; (2) In an explosion duct with a length to diameter ratio greater than 54, detonation is more likely to be triggered for a stoichiometric methane/air mixture; (3) Overpressure increases as an increment hydraulic diameter of a geometry within deflagration regime. A relative error of 7% is found when predicting blast peak overpressure for the base case compared to the experiment; a good agreement for the wave arrival time is also achieved

Modeling of Geometric Change Influence on Blast-Wave Propagation in Underground Airways Using a 2D-Transient Euler Scheme

The impact of methane explosions on mining operations can never be over-emphasized. The safety of miners could be threatened and local ventilation facilities are likely to be damaged by the flame and overpressure induced by a methane explosion event, making it essential to understand the destructiveness and influence range of a specific explosion. In this paper, the attenuation effect of geometric changes, most commonly bends, obstacles, and branches, present in the way of blast-wave propagation and the capability of the selected numerical model were studied. Although some relevant experimental research has been provided, quantitative analysis is insufficient. This paper investigates the attenuation factors of seven bends, three obstacles, and two T-branch scenarios to ascertain a better insight of this potentially devastating event quantitatively. The results suggest that (1) the numerical model used is capable of predicting four of the seven validated scenarios with a relative error less than 12%; (2) the maximum peak overpressure is obtained when the angle equals 50° for bend cases; and (3) the selected numerical scheme would overestimate the obstacle cases by around 15%