T.P. Cheatham. / "April 24, 1947." / Includes bibliographical references. / Army Signal Corps Contract No. W-36-039 sc-32037

published_or_final_version / abstract / toc / Electrical and Electronic Engineering / Master / Master of Philosophy

published_or_final_version / Electrical Engineering / Doctoral / Doctor of Philosophy

Thesis (MScEng)--Stellenbosch University, 2004. / ENGLISH ABSTRACT: The aim of this thesis was to investigate the use of behavioral level models in receiver simulations using the capabilities of Agilent's Advanced Design System. Behavioral level modeling has become increasingly attractive because it offers faster and easier results for system level simulations. The work in this thesis focused strongly on nonlinear measurements to characterize the various nonlinear phenomena that are present in amplifiers and mixers. Measurement automation software was developed to automate the process. An error correction technique was also developed to increase the accuracy of spectrum analyzer measurements. The measured data was used to implement the behavioral level amplifier and mixer models in ADS. The accuracy of the models was compared to measured data and the different available models were compared. Finally the models were combined to realize different receivers and were used to do typical receiver tests. These test include gain and gain compression, two-tone intermodulation and spurious responses. The results are compared to measured data to test the accuracy and usefulness of the models and simulation techniques. / AFRIKAANSE OPSOMMING: Die doel van hierdie tesis was om stelsel-vlak gedrags-modelle te ondersoek soos hulle in Agilent se Advanced Design System (ADS) aangebied word. Die modellering van die stelselvlak-gedrag van komponente en stelsels is aantreklik aangesien dit 'n hoë vlak beskrywing van komplekse kommunikasie stelsels moontlik maak. Akkurate stelsel-vlak simulasies sal lei tot vinnige ontwikkeling en evaluasie van nuwe sisteme. Die resultate wat verkry word is egter afhanklik van die beskikbaarheid van akkurate stelsel-vlak gedragsmodelle Die tesis het baie sterk op metings staat gemaak om die nie-liniêre gedrag van versterkers en mengers te karakteriseer. Meet sagteware is ontwikkel om die verskillende metings te automatiseer. Fout korreksie vir spetrum-analiseerder-metings is ook ontwikkel. Die gemete data is gebruik om die nie-liniêre gedrags-modelle in ADS te implementer. Die modelle is in simulasies gebruik en die akuraatheid van die simulasies is teen gemete data getoets. Die finale deel van die tesis gebruik die modelle om tipiese ontvanger karakteristieke te voorspel. Die volgende toetse is gedoen: aanwins en kompressie, twee-toon intermodulasie en hoer orde meng produkte. Die resultate van die toetse is met gemete data vergelyk om die akuraatehied en bruikbaarheid van die verskillende modelle te vergelyk.

No description available.

An extensive radio wave propagation measurement campaign was conducted at 1.3 GHz and 4.0 GHz inside four buildings, including a sports arena, a modern closed-plan office building, and two dissimilar, open-plan factories. Measurements were recorded at 57 locations using base station antenna heights of 1.7 meters and 4.0 meters. Results were obtained for mean and maximum excess delay, rms delay spread, time delay jitter, differential delay jitter, and path loss through analyses of impulse response estimates, which were obtained via repetitive 5 ns probing pulses. The effects of frequency, antenna height, topography (line-of-sight or obstructed direct path), and building environment on delay spread and path loss are quantified. Results indicate that, on average, the frequencies and antenna heights used in this study have minimal impact on rms delay spread and path loss. However, topography and building environment significantly affect these parameters. RMS delay spread values as high as 230 ns were observed in open plan factories. Computed path loss power law exponents are 1.84 and 2.35 for line-of-sight and obstructed topographies, respectively. A second campaign was conducted to determine the effects of antenna directivity and polarization on propagation parameters. On average, line-of-sight indoor channels offer 8 dB of cross-polarization discrimination, whereas obstructed environments offer less than 3 dB. Directional antennas provide a significant reduction in rms delay spread over omni-directional antennas. In line-of-sight environments, circular polarization provides an additional delay spread reduction. / Master of Science

The radio interface greatly affects performance of wireless communication systems. Hard-wired communication links use transmission lines to connect communication terminals. The propagation characteristics of radio frequency signals on these transmission lines are well known. In wireless communication systems, however, the transmission line with a known impulse response is replaced by a radio channel with an impulse response that is constantly changing as the users roam throughout the coverage area. The varying impulse response is due to the multiple path propagation of the signals from the transmitter to the receiver. The design of emerging small cellular (commonly known as microcellular) wireless systems is limited by the multipath propagation characteristics of the channel. Once these propagation conditions are understood, systems may be designed more efficiently in terms of cell layout, interference reduction, and system performance. This thesis presents a technique for automated propagation prediction in outdoor microcellular radio channels using ray tracing. The basic method is to integrate site-specific environmental data with a geometrical optics model to trace the propagation of energy from the transmitter to the receiver. Software written in C++ is used to automatically trace rays that are reflected, transmitted, scattered, or diffracted as they propagate through the channel. The automated software uses AutoCAD® to maintain the site-specific building data incorporated into the model. Details of the building database, propagation model, and software implementation are included in this thesis. The accuracy of the model and its software implementation is tested against wide band measurements taken on the Virginia Tech campus. Results, included here, indicate that the received signal can be accurately predicted in both line-of-sight and obstructed microcell topographies. / Master of Science

This study investigates whether quality management has developed to such an extent that retailers, service repair organisations and consumers are satisfied with product and repair service quality provided by South African manufacturing companies. To investigate these aspects, the colour television industry has been selected because it contains various manufacturing companies of varying sizes and characters, employing different quality policies and performances. It offers relatively standardised products and services, which facilitates intercompany comparisons and employs a simple flow type assembly line process that is representative of other mass production industries. The hypotheses are tested by interviewing four selected populations by means of carefully constructed questionnaires, namely a retail population, a repair service population, a consumer population and a manufacturing population. The empirical results are statistically evaluated in terms of the various manufacturers ability to provide satisfactory product and repair service quality. Consumers and repair service organisations are selected because they represent a broad spectrum of the population with varying, but important opinions on product and repair service quality. Retailers selling colour television receivers are also selected as they play an important role in the management of quality and vary from small independent retailers to large chain stores and discounters. The results obtained from this study show that: • there is a need from the retailers, service repair organisations and consumers for the South African manufacturers to improve the quality of colour television receivers • there is a need by the consumers and the retailers for the manufacturers to improve their repair service quality • there is a need to improve the quality control procedures employed by the colour television manufacturers. / Business Management / D. Com. (Business Management)

Thesis (D.Sc.)--University of the Witwatersrand, Faculty of Science, 1959.

Typescript (photocopy). / Digitized by Kansas Correctional Industries / Department: Electrical and Computer Engineering.