No description available.

This report discusses the design, development and the fabrication of a power hybrid. Foldback current limiting which is self reseting is used whereby withstanding indefinitely a short circuit. Thermal design considerations and thermal analysis are described as well as stability analysis. The maximum current capability of this design is four amperes and forty watts can be dissipated in the power transistors over a wide range of temperatures.

The Gallium Arsenide Field Effect transistor (GaAs FET) is experiencing a widespread acceptance in space and terrestrial systems due to its low noise, high gain and frequency characteristics unmatched by bipolar devices. This paper describes a design of a 4 GHz low noise amplifier with GaAs FETs using the scattering parameters method. Special attention is given to overall noise/gain optimization in the band of interest. The Smith Chart is used extensively to match the two-port device with microstrip networks. Analysis and performance of the amplifier are presented.

As 3G handset manufacturers add more and more features such as multimedia applications, color displays, video cameras, web browsing, gaming, WLAN, and MP3 players, the current consumption of a handset is ever increasing. Of the many components, the RF power amplifiers receive the most attention as they draw significant battery current and continue to represent the largest power load on the battery. In order to improve the overall efficiency of a power amplifier, it is important to know the operating uplink transmit power levels of a mobile phone in the WCDMA network. The work in this thesis makes two major contributions. First is the characterization of uplink transmit power in WCDMA networks based on current network data (collected in AT&T's WCDMA network) and realistic usage scenarios. Second is an investigation of the relationship between the battery life and the probability distribution function of the transmit power. Another important finding is that the talk time estimates using field tests, lab testing and theoretical expressions all give results to within 5%. Based on these data, design goals for WCDMA power amplifiers (in order to improve the talk times significantly) are suggested. The output power levels where the PA efficiencies have to be improved in order to significantly increase the battery life of WCDMA handsets are presented. / Master of Science

The effects of internal dimensional variations on the switching and recovery performance of an or/nor gate are investigated. A large scale experimental model is observed for switch pressure and flow rate, return pressure, and output recovery pressure in relation to variations in wall length, control and vent width, wall offsets, and splitter distance. For each dimensional configuration, effects of 1- and 3-nozzle loads are examined over Reynolds numbers (based on power supply nozzle exit width) of 2500 to 4000. The nominal design yields high switch pressures (> 20% of supply) and flow rates, and exaggerated load and Reynolds number dependence. Results of the individual dimensional variations show the control width to display the greatest effect on switching, with attachment wall offset and wall length having less significance. Opposite wall and splitter variations show negligible effects over the range examined. A revised design is obtained by combining the dimensional variations which show desirable performance trends. An analytical model is described which agrees reasonably well with the experimental data with some empirical correlation. / Master of Science

The magnetic amplifier is a device employing saturable reactors as its basic element. The theory or magnetic amplifiers is developed from the standpoint of rectangular hysteresis loops that are simplified in such a manner as to eliminate the problems of nonlinearity. The saturable reactor may be connected in either series or parallel combinations and their operation analyzed on the basis of voltage, current, and flux waveforms. The characteristics or the saturable reactor circuits may be enhanced by the addition of feedback. Feedback is accomplished either by magnetic means using additional windings, or by self-saturation in which rectifiers are used to secure feedback. The result is a device in which a small amount of power can effectively be used to control larger amounts of power. / Master of Science

Small dimensional changes in six parameters were experimentally studied for their effects on the performance of the bistable fluid amplifier. These dimensional parameters were offset, wall length, control width, power nozzle width, wall flat, and power nozzle shape. The investigation was conducted on a ten times actual size model of a typical, commercially available amplifier. Data were taken for operating conditions of 1 nozzle load and blocked outputs over a range of Reynolds numbers (based on the nominal nozzle width) of 2000 to 6000. Evidence in support of the hypothesis of the coexistence of two, different level, overlapping switch points was presented. The hypothesis was used to explain unusual behavior and to fit smooth and regular curves to the experimental data obtained. The center of the investigation was the six tables of data generated and the method used to obtain figures of the specific dimensional characteristics desired by the user. It was found that the overwhelming influence of operating conditions (Reynolds number and output loading) prevented specific discussion of dimension characteristics without having the user's specific needs or operating conditions specified. From a broad or general look at the dimensional characteristics, it was found that wall-length had the most severe characteristics. It was also found that the wider control width promoted a clean and well-behaved switch absent of two coexistent switch points. For reasons unknown, it was found that the shorter power nozzle shapes made the device extremely sensitive to bias. / Master of Science

No description available.

Submitted in fulfillment of the academic requirements for the Master’s Degree of Technology: Electrical Engineering – Light Current, Durban University of Technology, 2012. / The development of a transit radio telescope at the hydrogen line frequency of 1420 MHz is described. The telescope antenna uses a 5 m diameter parabolic reflector with an estimated efficiency of 50 % and an F/D ratio of 0.5. The gain of the antenna at 1420 MHz (wavelength of 21.1 cm) is approximately 35 dB with a beamwidth of approximately 3°. The antenna is mounted on a concrete beam at the first floor level, running between two 5 floor tower blocks on the Steve Biko campus of the Durban University of Technology. The majority of the components of the radio telescope antenna and receiver were designed and manufactured at the Durban University of Technology by students of the Departments of Mechanical and Electronic Engineering. The measured sensitivity of the receiver is approximately -94 dBm with a bandwidth of approximately 80 MHz. Radio sources successfully detected by the radio telescope include the Sun, the Moon, Sagittarius A, Centaurus A and Vela X.

Thesis (MSCIng)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: Bi-polar Si transistors optimized for pulse conditions is still the most popular choice as amplification element in the final stages of solid-state radar amplifiers in L and S band. With the radar market being small, the design data for these devices is normally fairly limited and it is up to the designers to thoroughly characterize them for their designs. This is normally done through loadpull experiments. Professional automated load-pull equipment is very expensive especially at the higher power levels. In spite of being automated and under computer control, load-pull exercises still is very time consuming and as such expensive. For small companies that only occasionally need to design such amplifiers it is not economically viable to acquire such equipment and different strategies have to be found to stay competitive. This report investigates such a strategy and its implementation. A procedure to quickly and accurately characterize such devices was developed and two amplifiers were designed and build with this procedure and compared to their traditional counterparts for verification. The results were very promising and with a bit more work, the technique can likely be used to characterize these devices for design work outside of the parameters designated by the manufacturers. / AFRIKAANSE OPSOMMING: Bipolere Silikon transistors wat vir werking onder gepulsde toestande geoptimiseer is, is nog steeds die mees gewilde keuse as versterkingselement in die finale stadiums van vastetoestand radar versterkers in die L en S bande. Met die radar mark wat geredelik klein is, is die ontwerp inligting vir hierdie elemente gewoonlik redelik karig en is dit die taak van die ontwerpers om die elemente te karakteriseer vir hulle ontwerp doeleindes. Dit word normaalweg gedoen deur lastrek eksperimente. Geoutomatiseerde lastrek toerusting is baie duur, veral as dit onder hoë drywingstoestande moet werk. Al is die toerusting geoutomatiseer en onder rekenaar beheer, is lastrek oefeninge nog steeds baie tydrowend en daarom dan ook baie duur. Vir klein maatskappye wat net nou en dan nodig het om sulke versterkers te ontwerp is dit gewoon nie ekonomies regverdigbaar om sulke toerusting aan te skaf nie, en ander strategië moet gevind word om ekonomies kompeterend te bly. Hierdie verslag ondersoek so 'n strategie en die implimentering daarvan. n Prosedure om gepulsde bipolere transistore vinnig en akkuraat te karakteriseer is ontwikkel en twee versterkers is met die prosedure ontwerp en gebou. Die versterkers is geverifieer deur hulle met hulle tradisionele eweknië te vergelyk. Die resultate lyk baie belowend en met n bietjie meer werk kan die metode waarskynlik ook gebruik word om die transistors buite die toepassings gebied, soos deur die vervaardigers aangedui, te gebruik.