Thesis (MScEng (Electrical and Electronic Engineering))--Stellenbosch University, 2008. / ENGLISH ABSTRACT: This thesis discusses the development of a 5 kVA single phase AC voltage regulator, specifically designed to assist in the reduction of electrification costs in sparsely populated rural areas. The voltage regulator is based on a solid state auto-transformer tap changer, designed to be robust and maintenance free. Electrification cost savings can be realized if the length of the LV network can be extended to reach more households. To accomplish this, a voltage regulator can be installed onto the extended LV feeder at the point where the LV voltage will drop below the minimum valid voltage, thereby boosting the voltage downstream and enabling more customers to be connected. A variety of voltage regulator topologies were investigated to obtain the best topology for the application. The voltage regulator design is discussed in detail with careful attention given to the power loss incurred, surge voltage protection requirements, protection coordination with the existing LV network and the thermal design requirements. An electronic controller based on a digital signal processor together with an appropriate power supply is designed and built. The software to control the voltage regulator is developed, integrated with the hardware and debugged. The complete voltage regulator is evaluated through extensive laboratory testing and field trials are performed to verify the performance of the device. / AFRIKAANSE OPSOMMING: Hierdie tesis bespreek die ontwikkeling van ‘n 5 kVA, enkelfase, wisselstroom spannings reguleerder, spesifiek ontwerp om koste besparings te bewerkstellig in die elektrifisiëring van yl bevolkte landelike gemeenskappe. Die spannings reguleerder se ontwerp is gebaseer op ‘n outo-transformator tap wisselaar met vaste toestand skakelaars, om sodoende robuust en instandhoudings vry te funksioneer. Elektrifisiërings koste besparings is moontlik indien die laag spannings distribusie kabel verleng kan word, om sodoende elektrisiteit aan meer huishoudings te voorsien. Om dit mootlik te maak kan ‘n spannings reguleerder geinstalleer word op die punt waar die kabel spanning onder die minimum toegelate spanning daal. Sodoende word die spanning weer verhoog aan al die huishoudings wat aan die verlengde gedeelte van die kabel verbind is. ‘n Verskeidenheid uiteenlopende spannings reguleerder topologieë is ondersoek om die beste topologie vir die toepassing te identifiseer. Die ontwerp van die spannings reguleerder is baie deeglik bespreek en spesifieke aandag is gegee aan die verliese, spits opwelling spannings beveiliging, sinkronisasie met die huidige laag spannings netwerk se beveiligings meganismes en die termiese ontwerp van die stelsel. ‘n Elektroniese beheerder, gebaseer op ‘n digitale sein verwerker, tesame met ‘n toepaslike kragbron is ontwerp en gebou. Die nodige sagteware om die spannings reguleerder te beheer is ontwikkel, geintegreer met die hardeware en ontfout. Die volledige spannings reguleerder is ontleed deur intensiewe toetse in die laboratorium en toets installasies op laag spannings netwerke, om sodoende die nakoming van die werks verrigting vereistes van die toestel te bevestig.

Thesis (MEng (Electrical and Electronic Engineering))--University of Stellenbosch, 1995. / 189 leaves single sided printed, preliminary pages and numbered pages 1-126. Includes bibliography, list of appendixes, figures, notation and symbols. Digitized at 300 dpi (OCR), using a Bizhub 250 Scanner. / ENGLISH ABSTRACT: The Sunsat microsatellite is being developed at the University of Stellenbosch. It is equipped with a high resolution earth imager which requires a sophisticated attitude determination and control system. Precise control of the satellite is impossible without high precision attitude sensors. The most accurate attitude sensor presently used by satellites is the star sensor. The aim 'of this thesis is to develop a low cost, high precision star sensor for the Sunsat microsatellite. The development included the selection of electronic and optical hardware followed by the design, construction and testing of the sensor. Software algorithms were developed and programmed to control the imager, extract stars from images and match the observed constellations to a star catalogue. A set of matching observed and reference vectors are passed to the attitude determination and control system which calculates the three axis orientation of the satellite. / AFRIKAANSE OPSOMMING: Die Sunsat mikrosatelliet word tans by die Universiteit van Stellenbosch ontwikkel. Dit is toegerus met 'n hoeresolusie aardwaarnemingskamera en vereis 'n gevorderde orientasiebepaling-en beheerstelsel. Presiese beheer is onmoontlik sonder akkurate sensore. 'n Stersensor is die mees akkurate tipe sensor waarmee satelliete tans toegerus word. Die doelwit van hierdie tesis is die ontwikkeling van 'n hoe resolusie, laekoste stersensor vir die Sunsat mikrosatelliet. Die ontwikkeling behels die seleksie van elektroniese en optiese apparatuur wat gevolg is deur die ontwerp, opbou en toets van die sensor. Programmatuur algoritrnes is ontwerp om die kamera te beheer, sterre in fotos te herken en waargenome konstellasies in die sterkatalogus te vind. 'n Stel waargenome en verwysingsvektore stel die orientasiebepaling-en beheerstelsel in staat om die orientasie van die satelliet te bereken.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The Coal to Liquid facility, Sasol, Secunda operates as a train of processes. Disturbances and capacity restrictions can occur throughout the plant and the throughput fluctuates whenever disturbances occur. When capacity restrictions occur in a subplant and more substances enter the sub-plant than can be processed, the extra substances are flared or dumped and therefore lost. To reduce losses and extra costs and to maximise the throughput of the whole plant, supervisory control is implemented over the whole plant system. Each process in the process train is controlled with regulatory controllers and the overall process is then controlled with a supervisory controller. These two sets of controllers operate in two different layers of control, with the regulatory controllers the faster inner layer. The supervisory control is the outer layer of the two control layers. The supervisory controller takes over the work of the human operator by deciding on the changes in total throughput as well as the set points for each individual process. These set points for each process are then followed with the regulatory controllers. For the regulatory control of the system, different control methods are investigated and compared. The different control methods that are looked at are PI control, Linearised State Feedback control, Fuzzy Logic control and Model Reference Adaptive Control. After an investigation into the various control methods Fuzzy Logic control was chosen for the regulatory as well as the supervisory control levels. Fuzzy Logic control is a rule based control method. Fuzzy variables are everyday terms such as very slow or nearly full. These terms are easy to understand by the operator and multi-variable control is possible with Fuzzy Logic control without an accurate mathematical representation of the system. These facts made Fuzzy Logic control ideal for this implementation. To improve the profit of the Coal to Liquid facility the throughput was maximised. The combination of regulatory and supervisory controllers minimised losses and rejected disturbances. This resulted in a smoother output with maximum profit. / AFRIKAANSE OPSOMMING: Die Steenkool-na-Olie fasiliteit, Sasol, Secunda funksioneer as ’n trein van prosesse. Versteurings en kapasiteit beperkings kan deur die hele aanleg voorkom en die deurset wissel voortdurend wanneer versteurings voorkom. Wanneer kapasiteit beperkings voorkom in ’n aanleg en meer stowwe word in die aanleg ingestuur as wat dit kan verwerk, word die ekstra stowwe gestort en dit gaan verlore. Om verliese en kostes te verminder en om die deurset van die hele aanleg te vergroot, is oorhoofse beheer geïmplementeer oor die hele stelsel. Elke proses in die trein van chemiese prosesse word beheer met regulerende beheerders. Die totale proses word dan beheer met ’n oorhoofse beheerder. Hierdie twee tipes beheerders funksioneer in twee lae van beheer met die regulerende beheerders die vinniger binneste laag. Die oorhoofse beheerder vorm die buitenste laag van die twee beheer lae en neem die werk van die menslike operateur oor deur die veranderinge in die totale deurset, sowel as die stelpunte vir elke afsonderlike proses, te bepaal. Hierdie stelpunte vir elke proses word dan met die regulerende beheerders gevolg. Verskillende beheer metodes is ondersoek vir die regulerende beheer van die stelsel. Die verskillende beheer metodes waarna gekyk word, is PI beheer, Geliniariseerde Toestands Terugvoer beheer, Wasige Logiese beheer en Model Verwysing Aanpassende beheer. Na ’n ondersoek na die verskillende beheer metodes is Wasige Logiese beheer gekies vir die regulerende asook die oorhoofse beheer. Wasige Logiese beheer is ’n reël gebasseerde beheer metode. Wasige Logika veranderlikes is alledaagse terme soos baie stadig of byna vol. Hierdie terme is maklik om te verstaan deur die operateur. Meervoudige-veranderlike beheer is moontlik met Wasige Logiese beheer sonder ’n akkurate wiskundige voorstelling van die stelsel. Hierdie feite maak Wasige Logiese beheer ideaal vir hierdie doel. Om die wins van die Steenkool-na-Olie fasiliteit te verbeter, is die deurset gemaksimeer. Die kombinasie van regulerende- en toesighoudende beheerders beperk verliese en verwerp versteurings. Dit lei tot ’n gladder uitset en ’n maksimum wins.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The World Wide Web brought with it an unprecedented level of information overload. Computers are very effective at processing and clustering numerical and binary data, however, the automated conceptual clustering of natural-language data is considerably harder to automate. Most past techniques rely on simple keyword-matching techniques or probabilistic methods to measure semantic relatedness. However, these approaches do not always accurately capture conceptual relatedness as measured by humans. In this thesis we propose and evaluate the use of novel Spreading Activation (SA) techniques for computing semantic relatedness, by modelling the article hyperlink structure of Wikipedia as an associative network structure for knowledge representation. The SA technique is adapted and several problems are addressed for it to function over the Wikipedia hyperlink structure. Inter-concept and inter-document similarity metrics are developed which make use of SA to compute the conceptual similarity between two concepts and between two natural-language documents. We evaluate these approaches over two document similarity datasets and achieve results which compare favourably with the state of the art. Furthermore, document preprocessing techniques are evaluated in terms of the performance gain these techniques can have on the well-known cosine document similarity metric and the Normalised Compression Distance (NCD) metric. Results indicate that a near two-fold increase in accuracy can be achieved for NCD by applying simple preprocessing techniques. Nonetheless, the cosine similarity metric still significantly outperforms NCD. Finally, we show that using our Wikipedia-based method to augment the cosine vector space model provides superior results to either in isolation. Combining the two methods leads to an increased correlation of Pearson p = 0:72 over the Lee (2005) document similarity dataset, which matches the reported result for the state-of-the-art Explicit Semantic Analysis (ESA) technique, while requiring less than 10% of the Wikipedia database as required by ESA. As a use case for document similarity techniques, a purely content-based news-article recommender system is designed and implemented for a large online media company. This system is used to gather additional human-generated relevance ratings which we use to evaluate the performance of three state-of-the-art document similarity metrics for providing content-based document recommendations. / AFRIKAANSE OPSOMMING: Die Wêreldwye-Web het ’n vlak van inligting-oorbelading tot gevolg gehad soos nog nooit tevore. Rekenaars is baie effektief met die verwerking en groepering van numeriese en binêre data, maar die konsepsuele groepering van natuurlike-taal data is aansienlik moeiliker om te outomatiseer. Tradisioneel berus sulke algoritmes op eenvoudige sleutelwoordherkenningstegnieke of waarskynlikheidsmetodes om semantiese verwantskappe te bereken, maar hierdie benaderings modelleer nie konsepsuele verwantskappe, soos gemeet deur die mens, baie akkuraat nie. In hierdie tesis stel ons die gebruik van ’n nuwe aktiverings-verspreidingstrategie (AV) voor waarmee inter-konsep verwantskappe bereken kan word, deur die artikel skakelstruktuur van Wikipedia te modelleer as ’n assosiatiewe netwerk. Die AV tegniek word aangepas om te funksioneer oor die Wikipedia skakelstruktuur, en verskeie probleme wat hiermee gepaard gaan word aangespreek. Inter-konsep en inter-dokument verwantskapsmaatstawwe word ontwikkel wat gebruik maak van AV om die konsepsuele verwantskap tussen twee konsepte en twee natuurlike-taal dokumente te bereken. Ons evalueer hierdie benadering oor twee dokument-verwantskap datastelle en die resultate vergelyk goed met die van ander toonaangewende metodes. Verder word teks-voorverwerkingstegnieke ondersoek in terme van die moontlike verbetering wat dit tot gevolg kan hê op die werksverrigting van die bekende kosinus vektorruimtemaatstaf en die genormaliseerde kompressie-afstandmaatstaf (GKA). Resultate dui daarop dat GKA se akkuraatheid byna verdubbel kan word deur gebruik te maak van eenvoudige voorverwerkingstegnieke, maar dat die kosinus vektorruimtemaatstaf steeds aansienlike beter resultate lewer. Laastens wys ons dat die Wikipedia-gebasseerde metode gebruik kan word om die vektorruimtemaatstaf aan te vul tot ’n gekombineerde maatstaf wat beter resultate lewer as enige van die twee metodes afsonderlik. Deur die twee metodes te kombineer lei tot ’n verhoogde korrelasie van Pearson p = 0:72 oor die Lee dokument-verwantskap datastel. Dit is gelyk aan die gerapporteerde resultaat vir Explicit Semantic Analysis (ESA), die huidige beste Wikipedia-gebasseerde tegniek. Ons benadering benodig egter minder as 10% van die Wikipedia databasis wat benodig word vir ESA. As ’n toetstoepassing vir dokument-verwantskaptegnieke ontwerp en implementeer ons ’n stelsel vir ’n aanlyn media-maatskappy wat nuusartikels aanbeveel vir gebruikers, slegs op grond van die artikels se inhoud. Joernaliste wat die stelsel gebruik ken ’n punt toe aan elke aanbeveling en ons gebruik hierdie data om die akkuraatheid van drie toonaangewende maatstawwe vir dokument-verwantskap te evalueer in die konteks van inhoud-gebasseerde nuus-artikel aanbevelings.

Dissertation (PhD)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: Though not so prominent as the wide band, high speed, mainstream development of data communication networks, cost and particular bandwidth limitations, still ensure extensive and continuing use of low-speed, half-duplex data link equipment. Most of these applications are radio based and aimed towards telemetry systems serving a wide range of utilities. Experience has shown that systems engineering for this type of installation, is seldom undertaken to a satisfactory analytical level. Investigation of published analyses of CSMA protocols in general, has indicated scope of extension of theoretical work to include system parameters for the type of protocol investigated in this dissertation. This dissertation describes the mathematical modeling of such a strategy by utilising a significantly modified, finite source, transition state-matrix approach derived from queueing theory. The contribution of the dissertation is to include system overhead parameters, such as backoff strategy, channel noise, equipment rise times, propagation- and retry delays, into the abovementioned model. The latter provides a relatively straightforward and readily applicable method for system analysis and performance prediction. A further contribution is the presentation of a software emulation with which different strategies could be simulated, allowing for adjustment of all design parameters. The simulation is intended for parallel and confimatory use with the theoretical model. A dual set of tools, theoretical and emulation based, is thus contributed to assist with the system design, performance prediction and protocol selection process. / AFRIKAANSE OPSOMMING: Alhoewel nie so prominent soos die wyeband, hoëspoed, hoofstroom ontwikkeling van datakommunikasie netwerke nie, verseker koste en spesifieke bandwydte beperkings nog die uitgebreide en voortdurende gebruik van laespoed half-dupleks data verbindingstoerusting. Meeste van die toepassings is radio gebaseer en gerig op telemetriestelsels wat deur 'n wye verskeidenheid diensverskaffers benut word. Stelselontwerp vir hierdie tipe installasies word selde op analitiese vlak benader. Ondersoek van gepubliseerde analises van kontensieprotokolle in die algemeen, het ruimte aangetoon vir die uitbreiding van bestaande teoretiese werk om stelselveranderlikes soos van toepassing op die tipe protokol in hierdie proefskrif ondersoek, in te sluit. Hierdie proefskrif beskryf die wiskundige modelering van sodanige strategie, deur gebruik te maak van 'n beduidend veranderde eindige bron, oorgangs-toestandmatriks benadering, afgelei van touteorie. Die bydrae van hierdie proefskrif is die insluiting van oorhoofse stelselveranderlikes, soos herhaal strategie, kanaalruis, toerusting stygtye, herhaal- en voortplantingsvertragings, in bogenoemde model. Laasgenoemde verskaf 'n relatief eenvoudige en maklik toepasbare metode vir stelselanalise en werkverrigtingvoorspelling. 'n Verder bydrae is die daarstelling van 'n sagteware simulasie waarmee verskillende strategieë nageboots kan word. Verstelling van alle ontwerpparameters word ondersteun. Die simulasie is bedoel vir parallelle en bevestigende gebruik tesame met die teoretiese model. 'n Dubbele, teoreties- en simulasie gebaseerde benadering, word dus aangebied vir gebruik by stelselontwerp, gedragsvoorspelling en optimale protokolseleksie.

Thesis (MScIng)--University of Stellenbosch, 2008. / ENGLISH ABSTRACT: The Applications of Superconductors in Cellular Network Base Stations R. Du Toit Department of Electronic Engineering University of Stellenbosch Private Bag X1, 7602 Matieland, South Africa Thesis: MScEng (E&E) March 2008 Wireless communications have increasingly become part of our world. The growth of radio frequency (RF) wireless communications has led to an increasing demand for frequency spectrum licenses, increased system capacity and larger user bandwidths. These demands lead to frequent improvements on the physical and higher layers of wireless communication protocols. Changes in the physical layer are frequently followed by the need for replacement of dedicated hardware components. The need therefore exists for a more general and programmable physical layer. A more general and programmable radio architecture implies increased radio front-end performance without losing programmability. The contribution of this thesis is the analysis of how superconductor electronics (SCE) using Rapid Single Flux Quantum (RSFQ) logic may advance wireless radio front-ends by providing a general-purpose programmable radio architecture. Superconductor analogue to digital converters (ADCs) are employed as high performance, programmable digitization structures. Once a received signal is digitized, SCE can be used to rapidly do recursive operations such as synchronization and multi-path delay estimation. These operations are based on correlation, and for evaluation of such operations with SCE the popular CDMA multiplexing method is studied along with the WCDMA protocol used in the 3G UMTS standard. Two delta-type oversampling superconductor ADC modulator designs are presented and evaluated along with a hybrid decimation filter design, using both the benefits of SCE and room temperature electronics. A fast RSFQ correlator design is also presented and evaluated for use in a multi-path estimation structure. A rapid multi-path delay estimation architecture based on fast RSFQ circular data buffers and correlators is presented. The architecture uses the fast speeds of RSFQ logic to obtain accurate path delay estimates in a rapidly changing wireless environment. It is concluded that RSFQ-based wireless receiver components offer promising new options for data conversion, correlation and multi-path delay estimation implementations. / AFRIKAANSE OPSOMMING: The Applications of Superconductors in Cellular Network Base Stations R. Du Toit Department of Electronic Engineering University of Stellenbosch Private Bag X1, 7602 Matieland, South Africa Thesis: MScEng (E&E) March 2008 Draadlose kommunikasie word al hoe meer deel van ons wêreld. Groei in radiofrekwensietipe kommunikasie het gelei tot ’n toenemende aanvraag na frekwensiespektrum lisensies, vergrote stelselkapasiteit en groter gebruikerbandwydtes. Hierdie aanvrae lei tot gereelde en spoedige verbeteringe op die fisiese en hoër lae van huidige draadlose kommunikasieprotokol. Veranderinge in die fisiese laag vereis gewoonlik dat toegewyde hardewarde komponente vervang word. Die behoefte bestaan dus vir ’n meer algemene, programmeerbare fisiese laag. Dit vereis dus ’n verbetering in die radio-ontvanger se komponente naaste aan die antenna sonder om programmeerbaarheid te verloor. Die bydrae van hierdie tesis is hoofsaaklik die analise van hoe supergeleierelektronika wat van Rapid Single Flux Quantum (RSFQ) logika gebruik maak, huidige draadlose sellulêre basisstasies se fisiese laag kan verbeter deur ’n meer algemene en programmeerbare radio-argitektuur op te lewer. Supergeleier analoog-na-syfer omsetters (ADCs) word bestudeer as moontlike programmeerbare versyferingstrukture wat steeds hoë werkverrigting lewer. Wanneer ’n ontvangde sein in digitale vorm omgesit is, kan supergeleierelektronika gebruik word om vinnig rekursiewe operasies uit te voer. Voorbeelde van sulke operasies is sinkronisasie en die waardebepaling van die vertraging van verskillende paaie wat ’n sein volg na die ontvanger. Hierdie spesifieke operasies se werking is gebaseer op korrelasie, en vir die evaluasie van sulke operasies met supergeleierelektronika is die gewilde wyeband-CDMA (WCDMA) protokol wat gebruik word in die 3G UMTS-standaard. Twee supergeleier-delta-tipe oorversyferings-ADC-moduleerderontwerpe word voorgelê en evaluasie word daarop gedoen saam met ’n hibriede desimasiefilterontwerp wat gebruik maak van beide die voordele van supergeleierelektronika en kamertemperatuurelektronika. ’n Vinnige RSFQ-korreleerder word ook voorgelê en evaluasie word daarop gedoen vir gebruik binne ’n multi-padvertraging-waardebepalerstruktuur. Hierdie struktuur wat gebaseer is op RSFQ sirkulêre buffers en korreleerders, word voorgelê. Die waardebepaler maak gebruik van die spoed van RSFQ-logika om akkurate multi-padvertragingswaardes te bepaal in ’n vinnig veranderende draadlose omgewing. Die gevolgtrekking word gemaak dat RSFQ-gebaseerde draadlose ontvangerkomponente groot voordele in versyfering-, korreleerder- en multi-padvertragingsbepaler-toepassings bied.

Thesis (MScIng)--Stellenbosch University, 2008. / ENGLISH ABSTRACT: Modern communication systems demand efficient, linear power amplifiers. The amplifiers are often operated in the backed-off power levels at which linear amplifiers such as class B amplifier are particularly inefficient. The Doherty amplifier provides an improvement as it increases efficiency at backed of power levels. Doherty amplifiers consists of two amplifiers, a carrier amplifier and a peaking amplifier, of which the output is combined in a novel way. Implementation of the Doherty amplifier with transistors is not ideal. One of the main problems is the insufficient current production of the peaking amplifier at peak envelope power (PEP) if it is implemented as a class C amplifier. A suggested solution to this problem is a bias adaption system that controls the peaking amplifier gate voltage dynamically depending on the input power levels. The design and evaluation of such a adaptive Doherty amplifier is the main goal of this thesis. A classical Doherty amplifier with and an uneven Doherty amplifier with unequal power division between the carrier and peaking amplifiers are also evaluated and compared with the adaptive Doherty amplifier. The amplifiers are designed using a 10 W LDMOS FET device, the MRF282. The adaptive Doherty amplifier and the uneven Doherty amplifier show significant improvements in efficiency and output power over the even Doherty amplifier. At PEP the adaptive Doherty delivers 42.4 dBm at 39.75 % power added efficiency (PAE), the uneven Doherty amplifier 41.9 dBm at 40.75 % PAE and the even Doherty amplifier 40.8 dBm at 38.6 % PAE. At 3dB backed-off input power the adaptive Doherty amplifier has an efficiency of 34.3%, compared to 34.9 5% for the uneven Doherty amplifier and 29.75 % for the even Doherty amplifier. / AFRIKAANSE OPSOMMING: Moderne kommunikasie stelsels vereis effektiewe, linieêre drywing versterkers. Die versterkers word dikwels in laer drywings vlakke bedryf waar linieêre versterkers soos ’n klas B versterker besondere lae effektiwiteit het. Die Doherty versterker bied ’n uitweg omdat dit verbeterde effektiwiteit by lae drywings vlakke bied. ’n Doherty versterker bestaan uit twee versterkers, die hoof versterker en die aanvullende versterker, waarvan die uittrees met ’n spesiale kombinasie netwerk bymekaar gevoeg word. Die implementasie van Doherty versterkers met transistors is nie ideaal nie. Een van die hoof probleme is die onvoldoende stroom wat deur die aanvullings versterker gebied word by piek omhulsel drywing (POD). ’n Oplossing vir die probleem is om ’n aanpassings sisteem te gebruik wat die aanvullende versterker se hekspanning dinamies beheer afhangende van die intree drywings vlakke. Die ontwerp en evaluasie van so ’n aanpassings Doherty versterker is die hoof doel van hierdie tesis. ’n Klassieke Doherty versterke met gelyke drywings verdeling en ’n ongelyke Doherty versterker wat gebruik maak van ongelyke drywings verdeling tussen die hoof-en aanvullende versterkers is ook gevalueer en vergelyk met die aanpassings Doherty versterker. Die versterkers was ontwerp met ’n 10 W LDMOS FET, die MRF282. Die aanpassings Doherty versterker en die ongelyke Doherty versterker het aanmerklike verbeteringe in effektiwiteit en uittree drywing gebring in vergelyking met die ewe Doherty versterker. By POD het die aanpassings versterker 42.4 dBm teen 39.75 % drywing toegevoegde effektiwiteit (DTE) gelewer, die ongelyke Doherty versterker 41.9 dBm teen 40.75 % DTE, en die ewe Doherty versterker 40.8 dBm teen 38.6 DTE. By ’n intree drywingsvlak 3 dB laer as POD het die aanpassings Doherty versterker ’n effektiwiteit van 34.3 % getoon, in vergelyking met die onewe Doherty versterker se 34.9 % en die ewe Doherty versterker se 29.75 % DTE.

Thesis (MScIng)--University of Stellenbosch, 2008. / ENGLISH ABSTRACT: This thesis describes the design, modelling and implementation of a prototype request- processing software system, which can be used as the basis for a request processing frame- work for systems with limited request processing resources. Due to design constraints, the request-processor system described here consists of multiple processes. It is problematic to prove that a multiple process design satis es the conditions of a set of prede ned requirements. One way to verify that such a multiple process design works as intended, is to use modelchecking tools. The system was veri ed for correctness and translated into a working prototype soft- ware system. / AFRIKAANSE OPSOMMING: Hierdie tesis beskryf die ontwerp, modellering en implementering van 'n prototipe versoek- verwerking-sagtewarestelsel. Die stelsel kan gebruik word om 'n versoekverwerkings- raamwerk te ontwerp vir stelsels met beperkte versoekverwerkingshulpbronne. Die ver- soekverwerkingsstelsel bestaan uit veelvoudige prosesse. Die veelvoudige proses-ontwerp was die direkte gevolg van stelselbeperkings. Dit is problematies om te bewys dat 'n multi-proses-ontwerp korrek funksioneer. Mod- elchecking-sagteware kan gebruik word om te veri eer of 'n stelsel korrek funksioneer. Die korrektheid van die stelsel is geveri eer voordat die nale prototipe ge¨implementeer is.

Thesis (MScEng)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: Active noise reduction (ANR) is a method of cancelling acoustic noise in a defined enclosure. Two methods exist to implement ANR, they are the analog feedback method and the digital feedforward method. Commercial ANR systems employing feedback methods have been around since the 1980's. Feedforward methods have however only become practically implemental with the age of fast real time digital signal processing. In current systems, feedback ANR is used to attenuate broadband noise whilst feedforward methods are used to attenuate narrow band or tonal noise [2]. This thesis investigates feedforward ANR to cancel broadband acoustic noise in aircraft headsets. Different adaptive filters, optimal configuration of adaptive filters and practical limitations to broadband attenuation for headsets are addressed. Results from this thesis show that at least 10dS noise energy attenuation is attainable over a bandwidth of 2.5kHz. A number of areas for further research are also identified. / AFRIKAANSE OPSOMMING: Aktiewe geraas beheer (AGS) is 'n metode om akoestiese geraas te kanselleer in 'n gedefinieerde omgewing. Twee metodes bestaan om AGS te implementeer. Hulle is die analoog terugvoer en digitale vorentoevoer metode. Kommersiële AGS wat die terugvoer metode gebruik is al in gebruik van die 1980's. Vorentoevoer metodes is egter eers sedert vinnige intydse digitale sein prosessering moontlik. In huidige stelsels word terugvoer AGS gebruik vir die attenuasie van wyeband geraas terwyl vorentoevoer metodes gebruik word om nouband of enkel toon geraas te kanselleer [2]. Die tesis ondersoek vorentoevoer AGS om wyeband akoestiese geraas te kanselleer in vliegtuig kopstukke. Verskillende aanpasbare filters, optimale opstelling van aanpasbare filters en praktiese beperkings tot wyeband attenuasie vir kopstukke word ondersoek. Resultate van die tesis wys dat ten minste 10dS geraas energie attenuasie behaal kan word oor 'n bandwydte van 2.5kHz. 'n Aantal areas vir verder navorsing is ook geïdentifiseer.

Thesis (MScEng)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: The aim of this thesis is to investigate a design of a microcontroller based embedded system that will be used to minimise cable harness on the SUNSAT micro-satellite. The system is called CAN node. The CAN node(s) implements CAN (Controller Area Network) serial bus architecture protocol. The protocol is implemented on the two nodes to transport data from the TCMD tot he 0 ther trays 0 f SUNSAT. CAN node( s) design proj ect focuses on the TCMD tray, because it is the central point for data communication in SUNSAT and it acts as the eyes and hands of the satellite's operator. As a result most of the communication cables are located at this tray. The two nodes are called TX-node and RX-nodes. The TX-node is used to collect data from the TCMD tray and transmits them serially to RX-node. The RX-nodes receives the TCMD data from TX-node and transmits these data to their respective nodes. In application RX-nodes need to be ten, but only one is used for testing purpose. The design had its shortcomings, of which they are discussed in this thesis. The recommendations of an ideal system are also given to elaborate how the system should behave in the real situation. Despite its shortcomings, the CAN node(s) project has successfully proven that cable harness on the TCMD tray of SUNSAT can be minimised by using CAN technology. / AFRIKAANSE OPSOMMING: Die doel van hierdie tesis is om die ontwerp van 'n mikro-beheerder gebaseerde stelsel wat die SUNSA T mikro-satelliet kabel harnas sal verklein, te ondersoek. Die stelsel word die CAN nodus genoem. Die CAN nodus implementeer die CAN (Controller Area Network) bus argitektuur protokol. Die protokol is op twee nodusse geïmplementeer om data vanaf die TCMD na ander laaie van SUNSAT te voer. Die CAN nodus ontwerp fokus op die TCMD laai, want dit is die sentrale punt vir data kommunikasie in SUNSA T en dit tree soos die oog en hande van die satelliet operateur op. As 'n gevolg, is die meeste van die kommunikasie kabels in hierdie laai. Die twee nodusse is genoem TXnodus en RX-nodus. TX-nodus word gebruik om die data van die TCMD af te kollekteer en dan versprei hulle tot hulle onderskeie nodusse. In die toepaslik moet daar tien RX-nodusse wees, maar net een is gebruik terwille van die toets. Die ontwerp het sy eie tekortkomings, wat in hierdie tesis bespreek word. Die rekommendasie van 'n ideale stelsel is ook gemaak om te bewys hoe die stelsel dit in 'n ware situasie moet gedra. Ongeag die tekortkomings daarvan, het die CAN-nodus projek suksesvol bewys dat die kabel harnas in die TCMD laai van SUNSAT kan verminder word deur die gebruik van die CAN tegnologie.