This thesis describes the development of an ionospheric map for the South African region using the current available resources. The International Reference Ionosphere (IRI) model, the South African Bottomside Ionospheric Model (SABIM), and measurements from ionosondes in the South African Ionosonde Network, were incorporated into the map. An accurate ionospheric map depicting the foF2 and hmF2 parameters as well as electron density profiles at any location within South Africa is a useful tool for, amongst others, High Frequency (HF) communicators and space weather centers. A major product of the work is software, written in MATLAB, which produces spatial and temporal representations of the South African ionosphere. The map was validated and demonstrated for practical application, since a significant aim of the project was to make the map as applicable as possible. It is hoped that the map will find immense application in HF radio communication industries, research industries, aviation industries, and other industries that make use of Earth-Space systems. A potential user of the map is GrinTek Ewation (GEW) who is currently evaluating it for their purposes

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This thesis examines the practices and techniques involved with particular electronic instruments and proposes an archaeological approach to reconsider the ways in which noise can communicate various details of instrument design and practice to the listener. I present two case studies concerning electronic music practice using repurposed devices - stepped filters - and by combining a detailed material analysis of the instruments with interviews, video and other evidence, I document the practices involved with their use. By rebuilding these instruments, and designing and building other devices, I test my hypotheses through my own practice, and by doing so I refine my results and extend my composition, performance practice and technical design skills to include valuable lessons learned through this research. The portfolio engages with the three archaeological levels (Listening Situation, Reproduction Stage, Production Environment) and the three areas of the production continuum (Composition, Performance Practice, Technical Design) and through sound installations, crafted media, recorded performances, and the documentation of devices designed for these pieces, it supports the thesis through experimentation and incorporation of results through reflective practice.

This master’s thesis describes RF power amplifier design. The designed amplifier has been built. The first three chapters outline basics about radio frequency amplifiers. The basic theory needed for amplifier implementation is also described there. In the fourth chapter the power amplifier is designed. The design is based on the theoretical knowledge. Complete amplifier contains RF preamplifier, power amplifier and filters. The OrCAD PSpice, Ansoft Designer SV and EAGLE programs have been used for the design and verification of some sections of circuits. Measurement results of the built amplifier are in the fifth chapter. This thesis contains also the draft for laboratory exercise.

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by Wong Chun Kau, Jolly. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1992. / Includes bibliographical references (leaves 84-88). / ABSTRACT --- p.1 / ACKNOWLEDGEMENT --- p.3 / Chapter 1. --- INTRODUCTION --- p.7 / Chapter 1.1 --- Land Mobile Radio (LMR) Communications / Chapter 1.2 --- Paramilitary Communications Security / Chapter 1.3 --- Voice Scrambling Methods / Chapter 1.4 --- Digital Voice Encryption / Chapter 1.5 --- Digital Secure LMR / Chapter 2. --- DESIGN GOALS --- p.20 / Chapter 2.1 --- System Concept and Configuration / Chapter 2.2 --- Operational Requirements / Chapter 2.2.1 --- Operating conditions / Chapter 2.2.2 --- Intelligibility and speech quality / Chapter 2.2.3 --- Field coverage and transmission delay / Chapter 2.2.4 --- Reliability and maintenance / Chapter 2.3 --- Functional Requirements / Chapter 2.3.1 --- Major system features / Chapter 2.3.2 --- Cryptographic features / Chapter 2.3.3 --- Phone patch facility / Chapter 2.3.4 --- Mobile data capability / Chapter 2.4 --- Bandwidth Requirements / Chapter 2.5 --- Bit Error Rate Requirements / Chapter 3. --- VOICE CODERS --- p.38 / Chapter 3.1 --- Digital Speech Coding Methods / Chapter 3.1.1 --- Waveform coding / Chapter 3.1.2 --- Linear predictive coding / Chapter 3.1.3 --- Sub-band coding / Chapter 3.1.4 --- Vocoders / Chapter 3.2 --- Performance Evaluation / Chapter 4. --- CRYPTOGRAPHIC CONCERNS --- p.52 / Chapter 4.1 --- Basic Concepts and Cryptoanalysis / Chapter 4.2 --- Digital Encryption Techniques / Chapter 4.3 --- Crypto Synchronization / Chapter 4.3.1 --- Auto synchronization / Chapter 4.3.2 --- Initial synchronization / Chapter 4.3.3 --- Continuous synchronization / Chapter 4.3.4 --- Hybrid synchronization / Chapter 5. --- DIGITAL MODULATION --- p.63 / Chapter 5.1 --- Narrowband Channel Requirements / Chapter 5.2 --- Narrowband Digital FM / Chapter 5.3 --- Performance Evaluation / Chapter 6. --- SYSTEM IMPLEMENTATION --- p.71 / Chapter 6.1 --- Potential EMC Problems / Chapter 6.2 --- Frequency Planning / Chapter 6.3 --- Key Management / Chapter 6.4 --- Potential Electromagnetic Compatibility (EMC) Problems / Chapter 7. --- CONCLUSION --- p.80 / LIST OF ILLUSTRATIONS --- p.81 / REFERENCES --- p.82 / APPENDICES --- p.89 / Chapter I. --- Path Propagation Loss(L) Vs Distance (d) / Chapter II. --- Speech Quality Assessment Tests performed / by Special Duties Unit (SDU)

In this paper we will deal involving short-wave radio station and its control by the sequencer. Mostly it will be a time delay of the PA and the antenna switching relay in the transmitter (TX) to receiver (RX) side. Time delays will be controlled programmatically using ATmega 16 microprocessor, which will form part of the main control sequencer. The delay will set the total time of keying in messages, when we take into account the loss due to delayed first symbol. Keying will be done from several sources, among the main sources will be ordered from keying the radio, telegraph keys, and PC. The transmission signal is used amplitude modulation (SSB) in the CB zone.

O conhecimento sobre o perfil de uso dos meios de comunicação utilizados pelo serviço de controle de tráfego aéreo pode subsidiar o dimensionamento de redes de telecomunicação destinadas ao transporte de sinais de voz entre órgãos de controle de tráfego aéreo e estações remotas de VHF. O dimensionamento correto dessas redes destina-se a relacionar a capacidade dos circuitos com a probabilidade de sucesso das comunicações entre controlador de tráfego aéreo e aeronaves, fator fundamental para a manutenção da segurança operacional das atividades de controle de tráfego aéreo. O conhecimento sobre esse perfil de uso, por sua vez, foi alcançado através de estudos estatísticos realizados sobre uma massa de dados relacionada à utilização do chamado Serviço Móvel Aeronáutico, que é o recurso utilizado por controladores de tráfego aéreo e pilotos em aeronaves controladas para a troca de mensagens de voz, através do qual as instruções de controle de tráfego aéreo são passadas. Essa massa de dados estudada foi resultado da aplicação de uma metodologia que processou centenas de horas de gravação do Serviço Móvel Aeronáutico prestado pelo CINDACTA II, entre os dias 14 de dezembro de 2014 e 03 de janeiro de 2015, a qual foi organizada em função da taxa de ocupação do meio de comunicação e analisada no sentido de identificar as dinâmicas de distribuição do uso do Serviço Móvel Aeronáutico. Como resultado, obteve-se que parte das dinâmicas que regem a ocupação desse serviço pode ser representada por curvas de distribuição conhecidas, como weibull e lognormal, associadas a modelos de transição. / The knowledge about the usage of the communications resorces used by the air traffic service provider can be usefull to design the networks needed to transport voice signal between the air traffic provider and remote radio station. The accurate design of those networks, in the other hand, should offer an association between the network instant capacity and the rate of communication sucess in any controller's tries to communicate with the aircrafts. This rate of communication sucess is a parameter that indicates how safe is the air traffic activity, in term of communication between the air traffic controller and the aircrafts, and it must be monitoring to guarante the operational safety. So, the knowledge of interesting was achieved analysing data related to the use of Aeronautical Mobile Service, which is the resource used by air traffic controller and aircraft to exchange voice mensagens of air traffic service. Those data were the results of a methodology that processed hundred of hours of records of the Aeronautical Mobile Service provided by the CINDACTA II, between 14/12/2014 and 03/01/2015, which were sorted by the percent of engagement time and analysed to identify any distribution function that could represent the way the Aeronautical Mobile Service is used. As a result, this study indentified that this usage can be depicted by some typical probability density function, like Weibull and Lognormal, combined with transitional chain.

The ionosphere is an important factor in high frequency (HF) radio propagation providing an opportunity to study ionospheric variability as well as the space weather conditions under which HF communication can take place. This thesis presents the validation of HF propagation conditions for the Ionospheric Communication Enhanced Profile Analysis and Circuit (ICEPAC) and Advanced Stand Alone Prediction System (ASAPS) models over Africa by comparing predictions with the measured data obtained from the International Beacon Project (IBP). Since these models were not developed using information on the African region, a more accurate HF propagation prediction tool is required. Two IBP transmitter stations are considered, Ruaraka, Kenya (1.24°S, 36.88°E) and Pretoria, South Africa (25.45°S, 28.10°E) with one beacon receiver station located in Hermanus, South Africa (34.27°S, 19.l2°E). The potential of these models in terms of HF propagation conditions is illustrated. An attempt to draw conclusions for future improvement of the models is also presented. Results show a low prediction accuracy for both ICEPAC and ASAPS models, although ICEPAC provided more accurate predictions for daily HF propagation conditions. This thesis suggests that the development of a new HF propagation prediction tool for the African region or the modification of one of the existing models to accommodate the African region, taking into account the importance of the African ionospheric region, should be considered as an option to ensure more accurate HF Propagation predictions over this region.

The role of the South African National Defence Force (SANDF) has changed considerably in the last decade. The emphasis has moved from protecting the country's borders to peacekeeping duties in Central Africa and even further North. Communications between the peacekeeping missions and the military bases back in South Africa is vital to ensure the success of these missions. Currently use is made of satellite as well as High Frequency (HF) communications. There are drawbacks associated with these technologies (high cost and low data rates/interference respectively). Successful long distance ionospheric propagation in the low Very High Frequency (VHF) range will complement the existing infrastructure and enhance the success rate of these missions. This thesis presents a feasibility study to determine under what ionospheric conditions such low VHF communications will be possible. The International Reference Ionosphere (IRI) was used to generate ionospheric data for the reflection point(s) of the signal. The peak height of the ionospheric F2 layer (hmF2) was used to calculate the required antenna elevation angle. Once the elevation angle is known it is possible to calculate the required F2 layer critical frequency (foF2). The required foF2 value was calculated by assuming a Maximum Useable Frequency (MUF) of 20% higher than the planned operational frequency. It was determined that single hop propagation is possible during the daytime if the smoothed sunspot number (SSN) exceeds 15. The most challenging requirement for successful single hop propagation is the need of an antenna height of 23 m. For rapid deployment and semi-mobile operations within a jungle environment it may prove to be a formidable obstacle.