The motivation for this research is a proposed UHF surface wave communication system in which the waveguides are the stranded, overhead earth wires of Power System transmission lines. Attention is confined largely to an investigation of certain aspects which affect the overall surfaces wave transmission loss, a full-scale system having been set up in the laboratory for experimental purposes. For the prediction of transmission loss the stranded conductor is assumed to be equivalent to a solid conductor of the same diameter but with surface anisotropy in the form of two mutually orthogonal surface impedances the major reactive component of which is attributed to the effects of the helical stranding. This reactance is determined from a consideration of the fields which are assumed to exist within the cavities between the strands, and externally. From a comparison between experimental and theoretical loss characteristics there is sufficient inducement to accept the anisotropic model of the stranded conductor for practical design purposes. Approximate equations are developed to simplify the calculation of transmission loss and the notion of ‘capture cross-section’ is employed for the estimation of the efficiency of conical horn launchers. It is deduced from ‘sensitivity’ relationships that the horn loss is relatively insensitive to small changes in the fictitious surface reactance representing the effects of helical stranding, which tends to justify the assumptions upon which the anisotropic model is based. On the other hand, variations in the helix angle are shown to have a marked effect upon the calculated horn loss. This influences the choice of the stranded conductor used as the waveguide for the experimental verification of the model. The Author’s experimental research is described at length, the principal objective being to establish the anisotropic model as an acceptable theoretical substitute for the stranded conductor. To reduce the horn loss, dielectric sheaths are ted to the waveguide in the vicinity of the horn apertures. The discrepancies which then appear between theory and experiment are attributed both to the scattering of the surface wave by the boundary discontinuities at the ends of the sheaths and to the anomalous behaviour of commercial-grade PVC dielectric. Considering the increase in the transmission efficiency which may be realised by fitting dielectric sheaths to the conductor near the horn apertures it is concluded that a theoretical investigation of the scattering properties of the discontinuities s in order. Thus, the remainder of the Thesis is devoted, to this scattering effect as it may be encountered in the proposed scheme, the theoretical analysis following the lines of earlier documented research. A short-cut method is applied for the determination of certain ‘half-plane’ functions which appear in the expressions for the scattered power. Theoretical results are presented together with a discussion of some experimental measurements and a brief theoretical examination of the effects on the horn loss of varying the thickness of the dielectric sheaths. It is argued that the horn loss may be reduced if the dielectric thickness is graded in steps to a value at the horn apertures consistent with the desired ‘power capture’. The Thesis is concluded with an Addendum which outlines a number of topics suggested by the Author for future research.

The motivation for this research is a proposed UHF surface wave communication system in which the waveguides are the stranded, overhead earth wires of Power System transmission lines. Attention is confined largely to an investigation of certain aspects which affect the overall surfaces wave transmission loss, a full-scale system having been set up in the laboratory for experimental purposes. For the prediction of transmission loss the stranded conductor is assumed to be equivalent to a solid conductor of the same diameter but with surface anisotropy in the form of two mutually orthogonal surface impedances the major reactive component of which is attributed to the effects of the helical stranding. This reactance is determined from a consideration of the fields which are assumed to exist within the cavities between the strands, and externally. From a comparison between experimental and theoretical loss characteristics there is sufficient inducement to accept the anisotropic model of the stranded conductor for practical design purposes. Approximate equations are developed to simplify the calculation of transmission loss and the notion of ‘capture cross-section’ is employed for the estimation of the efficiency of conical horn launchers. It is deduced from ‘sensitivity’ relationships that the horn loss is relatively insensitive to small changes in the fictitious surface reactance representing the effects of helical stranding, which tends to justify the assumptions upon which the anisotropic model is based. On the other hand, variations in the helix angle are shown to have a marked effect upon the calculated horn loss. This influences the choice of the stranded conductor used as the waveguide for the experimental verification of the model. The Author’s experimental research is described at length, the principal objective being to establish the anisotropic model as an acceptable theoretical substitute for the stranded conductor. To reduce the horn loss, dielectric sheaths are ted to the waveguide in the vicinity of the horn apertures. The discrepancies which then appear between theory and experiment are attributed both to the scattering of the surface wave by the boundary discontinuities at the ends of the sheaths and to the anomalous behaviour of commercial-grade PVC dielectric. Considering the increase in the transmission efficiency which may be realised by fitting dielectric sheaths to the conductor near the horn apertures it is concluded that a theoretical investigation of the scattering properties of the discontinuities s in order. Thus, the remainder of the Thesis is devoted, to this scattering effect as it may be encountered in the proposed scheme, the theoretical analysis following the lines of earlier documented research. A short-cut method is applied for the determination of certain ‘half-plane’ functions which appear in the expressions for the scattered power. Theoretical results are presented together with a discussion of some experimental measurements and a brief theoretical examination of the effects on the horn loss of varying the thickness of the dielectric sheaths. It is argued that the horn loss may be reduced if the dielectric thickness is graded in steps to a value at the horn apertures consistent with the desired ‘power capture’. The Thesis is concluded with an Addendum which outlines a number of topics suggested by the Author for future research.

The motivation for this research is a proposed UHF surface wave communication system in which the waveguides are the stranded, overhead earth wires of Power System transmission lines. Attention is confined largely to an investigation of certain aspects which affect the overall surfaces wave transmission loss, a full-scale system having been set up in the laboratory for experimental purposes. For the prediction of transmission loss the stranded conductor is assumed to be equivalent to a solid conductor of the same diameter but with surface anisotropy in the form of two mutually orthogonal surface impedances the major reactive component of which is attributed to the effects of the helical stranding. This reactance is determined from a consideration of the fields which are assumed to exist within the cavities between the strands, and externally. From a comparison between experimental and theoretical loss characteristics there is sufficient inducement to accept the anisotropic model of the stranded conductor for practical design purposes. Approximate equations are developed to simplify the calculation of transmission loss and the notion of ‘capture cross-section’ is employed for the estimation of the efficiency of conical horn launchers. It is deduced from ‘sensitivity’ relationships that the horn loss is relatively insensitive to small changes in the fictitious surface reactance representing the effects of helical stranding, which tends to justify the assumptions upon which the anisotropic model is based. On the other hand, variations in the helix angle are shown to have a marked effect upon the calculated horn loss. This influences the choice of the stranded conductor used as the waveguide for the experimental verification of the model. The Author’s experimental research is described at length, the principal objective being to establish the anisotropic model as an acceptable theoretical substitute for the stranded conductor. To reduce the horn loss, dielectric sheaths are ted to the waveguide in the vicinity of the horn apertures. The discrepancies which then appear between theory and experiment are attributed both to the scattering of the surface wave by the boundary discontinuities at the ends of the sheaths and to the anomalous behaviour of commercial-grade PVC dielectric. Considering the increase in the transmission efficiency which may be realised by fitting dielectric sheaths to the conductor near the horn apertures it is concluded that a theoretical investigation of the scattering properties of the discontinuities s in order. Thus, the remainder of the Thesis is devoted, to this scattering effect as it may be encountered in the proposed scheme, the theoretical analysis following the lines of earlier documented research. A short-cut method is applied for the determination of certain ‘half-plane’ functions which appear in the expressions for the scattered power. Theoretical results are presented together with a discussion of some experimental measurements and a brief theoretical examination of the effects on the horn loss of varying the thickness of the dielectric sheaths. It is argued that the horn loss may be reduced if the dielectric thickness is graded in steps to a value at the horn apertures consistent with the desired ‘power capture’. The Thesis is concluded with an Addendum which outlines a number of topics suggested by the Author for future research.

Whole document restricted, see Access Instructions file below for details of how to access the print copy. / Correct coagulant dosage is necessary for the efficient operation of conventional drinking water treatment plants, yet no accurate or automated way of determining this exists. Streaming current (SC) is a measurement of charge on particles in water and is useful in feedback control of coagulant dosage. Analysis of the movement of change within a SC sensor can provide some explanation of its slow response, while signal processing utilising Fourier analysis improves the instrument's bandwidth. Presently inaccurate manual jar tests are the only way determine the SC required for best coagulation. An online automated jar tester is presented to improve on this. It uses an automatic sampling system that takes a sample from the process stream. An optimisation algorithm makes repeated step adjustments to the SC set point and gradually moves it in the direction of improving jar test results. The system was evaluated on both a small-scale model and a full-scale plant. Noise in the test measurements means the optimal set point cannot be located accurately enough, but the results indicate that this is possible. Greater accuracy would allow optimisation of turbidity and costs for multiple chemicals. A representative neural network model can be made of the dynamic relationship between coagulant dosage and streaming current in a scale model, with an alkali dosed to simulate a disturbance. In a rapid mixer, the measured response is significantly slower than the true response. Several common types of linear controller are designed and their performance at set point tracking and disturbance rejection is compared on this system. Model predictive control with a Kalman filter performs best in these tests, while the self-tuning regulator has benefits when the rate of set point change is slower. A non-linear feed-forward radial basis function network that adapts to the system's steady-state inverse can effectively augment a linear controller for this system. Adaptation rules based on vector eligibility are derived from dynamic back-propagation and extended to the general dynamic non-linear case. This can result in a useful and efficient feed-forward neural controller for dosing systems that can be represented by a Wiener model.

This thesis describes research undertaken as an initial step in the development of a nationwide land mobile coverage area prediction model for New Zealand. The most suitable approach is shown to be a computer-based method which includes corrections for both environmental and terrain features. Extensive field trials performed in Auckland at 76 and 465MHz to develop a propagation data base are described. Measurements have been made in a variety of environments over unobstructed, obstructed and mixed land-sea paths. An analysis of these measurements indicates that, subject to the availability of suitable topographic and environmental data bases and with the exception of two special cases, a plane earth based prediction method is suitable for incorporation in a nationwide land mobile coverage area prediction model for New Zealand. Recommendations are made for the implementation and further development of this model.

A new method for the synthesis of broadband impedance transformers having predictable passband frequency response is presented. The technique is based on the use of non-commensurate (i.e. unequal element length) transmission line networks. Through the use of approximations and computer optimization studies non-commensurate circuits are shown to be advantageous in distributed circuit design. The new method derives a non-commensurate circuit from a conventional commensurate prototype in such a way that the transmission matrix of pairs of elements in both circuits is made equal at one frequency. The transformation used ensures that the frequency response of the derived circuit closely matches that of the prototype circuit. Limitations on section characteristic impedances imposed either by constructional constraints or other practical realizability considerations are more easily met using the new design technique than when using conventional commensurate networks alone, Moreover, wide harmonically related passbands are largely avoided. The method finds greatest application where there are circuit length (or size) restrictions which must be met. Where such restrictions do not apply, conventional commensurate techniques are usually sufficiently flexible. The non-commensurate technique can however still provide benefits of even greater flexibility or better stop-band attenuation. The method presented is only an approximate equivalence and so an analysis of the technique is presented. The analysis establishes the degree of approximation. The use and application of the non-commensurate design technique are supported by an experimental investigation.

Three phase AC drives controlling cage induction motors have become widely accepted in industry, but one extant problem with this technology is that of increased acoustic noise emitted from the driven motor. This Thesis addresses the problem of the acoustic noise emitted from motors driven from voltage sourced PWM inverters and proposes a technique - Spread Spectrum Switching - for minimizing its effects. In the course of the work many other issues associated with real-time microprocessor-based PWM have also been advanced: • efficient microprocessor based PWM waveform generation, • harmonic analysis of generalized PWM waveforms, • compensation for the effects of power switch timing delays, and • compensation for the finite resolution of timers. The Thesis uses a variety of computational and analytical methods, backed by experimental observations, to quantify the improvement gained in each of these areas. Spread spectrum switching is a technique for eliminating the characteristically tonal structure of the acoustic noise emitted from a PWM inverter driven motor. Similar to the concept of spread spectrum communications, spread spectrum switching involves pseudo-randomly varying the instantaneous PWM switching frequency so that the energy of any PWM switching harmonics is dispersed over a wide bandwidth. This energy dispersion effectively eliminates any tonal components from the resultant motor acoustic noise while leaving the overall sound level largely unchanged; spread spectrum switching provides a significant qualitative yet minimal quantitative noise reduction. The PWM generation paradigm used in this Thesis is the recently reported Space Vector Modulation. A novel algorithm for microprocessor based space vector PWM generation is proposed, providing a basis for fast, efficient generation, even when overmodulating - a situation where many algorithms operate significantly more slowly. Furthermore, it is shown that the space vector method inherently generates a near optimum - in terms of motor harmonic loss - PWM waveform. However, when physically realized on a practical inverter such ideal PWM waveform s are corrupted by timing errors associated with both the inverter's power switches, predominantly the lockout time, and the finite resolution of hardware timers. Resolution corrected modulation is proposed for overcoming the problem of finite timer resolution and involves the use of integral feedback to account for any errors between ideal and physically realizable PWM switching times. This technique effectively provides 4 to 5 bits of added resolution to a given timer, allowing accurate waveform generation at low sinewave amplitudes and high switching frequencies using readily available, often microprocessor based, timers. Lockout times cause inverter output voltage errors, with consequent current zero crossing distortion, and a strategy for alleviating this problem is proposed and implemented in both a triangulation and space vector modulator. Two harmonic analysis techniques are proposed for analyzing PWM waveforms. The first technique is suitable for the analysis of regularly sampled PWM waveforms and has been used here to obtain closed form expressions for the harmonics of both space vector and asymmetrical triangulation PWM. These expressions show that PWM harmonics occur as a series of "combs" centered on multiples of the switching frequency. A second technique - the Directional Rotational Transform - is proposed for numerical analysis of general PWM waveforms. This technique uses an equivalent space vector representation of the PWM waveform, yielding the magnitude, phase and sequence (positive or negative) of the harmonics, and is useful in situations where each of the three phase waveforms is different, as in these cases Fourier Transform analysis of a single phase or line voltage only approximates the harmonics actually seen by the motor. The spectra generated using both these techniques compare favourably with those measured experimentally and, for synchronous PWM, those evaluated from Fourier Transforms. The culmination of modulation techniques presented in this Thesis yields a microprocessor based AC inverter drive featuring low acoustic noise emission at but a few kiloHertz switching rates and accurate PWM waveform generation using a single chip, low cost, micro-controller.

Studies of the families of variable length self-synchronising T-Codes are presented. The studies use Monte Carlo computer simulations to analyse the synchronising properties of the T-Codes and the relationships between these and their coding efficiency. Software and hardware implementations of the algorithms which are used to support these simulations are documented, and one of the encoding/decoding techniques presented is shown to be capable of operating at very high speed while being simple to implement. This technique is also shown to be applicable to the encoding and decoding of any variable length, exhaustive, instantaneous code. From the results of the simulations it is shown that some T-Codes consistently outperform others in the family with respect to their synchronising properties, and that the best of these codes have an average synchronisation delay of approximately 1.5 codewords. More importantly, it is shown that the T-Codes with the best synchronising performance are also the most efficient when encoding symbols from a specified information source, and that the coding efficiency of these codes is only nominally less than that of an optimal Huffman code generated for the source. A theoretical analysis of the synchronising properties is presented, and this is used to explain the relationships which exist between the average synchronisation delay and coding efficiency. These results are used to demonstrate that it is possible to choose a T-Code which has both the desirable properties of unrivalled synchronising performance and optimal coding efficiency, and guide-lines are given for choosing such a T-Code for a specified information source. This combination of a fast and simple encoding/decoding technique with codes which have unrivalled synchronising performance without sacrificing coding efficiency is offered as a solution to many of the problems normally associated with variable length coding techniques.

The motivation for this research is a proposed UHF surface wave communication system in which the waveguides are the stranded, overhead earth wires of Power System transmission lines. Attention is confined largely to an investigation of certain aspects which affect the overall surfaces wave transmission loss, a full-scale system having been set up in the laboratory for experimental purposes. For the prediction of transmission loss the stranded conductor is assumed to be equivalent to a solid conductor of the same diameter but with surface anisotropy in the form of two mutually orthogonal surface impedances the major reactive component of which is attributed to the effects of the helical stranding. This reactance is determined from a consideration of the fields which are assumed to exist within the cavities between the strands, and externally. From a comparison between experimental and theoretical loss characteristics there is sufficient inducement to accept the anisotropic model of the stranded conductor for practical design purposes. Approximate equations are developed to simplify the calculation of transmission loss and the notion of ‘capture cross-section’ is employed for the estimation of the efficiency of conical horn launchers. It is deduced from ‘sensitivity’ relationships that the horn loss is relatively insensitive to small changes in the fictitious surface reactance representing the effects of helical stranding, which tends to justify the assumptions upon which the anisotropic model is based. On the other hand, variations in the helix angle are shown to have a marked effect upon the calculated horn loss. This influences the choice of the stranded conductor used as the waveguide for the experimental verification of the model. The Author’s experimental research is described at length, the principal objective being to establish the anisotropic model as an acceptable theoretical substitute for the stranded conductor. To reduce the horn loss, dielectric sheaths are ted to the waveguide in the vicinity of the horn apertures. The discrepancies which then appear between theory and experiment are attributed both to the scattering of the surface wave by the boundary discontinuities at the ends of the sheaths and to the anomalous behaviour of commercial-grade PVC dielectric. Considering the increase in the transmission efficiency which may be realised by fitting dielectric sheaths to the conductor near the horn apertures it is concluded that a theoretical investigation of the scattering properties of the discontinuities s in order. Thus, the remainder of the Thesis is devoted, to this scattering effect as it may be encountered in the proposed scheme, the theoretical analysis following the lines of earlier documented research. A short-cut method is applied for the determination of certain ‘half-plane’ functions which appear in the expressions for the scattered power. Theoretical results are presented together with a discussion of some experimental measurements and a brief theoretical examination of the effects on the horn loss of varying the thickness of the dielectric sheaths. It is argued that the horn loss may be reduced if the dielectric thickness is graded in steps to a value at the horn apertures consistent with the desired ‘power capture’. The Thesis is concluded with an Addendum which outlines a number of topics suggested by the Author for future research.

Outage probability calculations are presented for the analogue land mobile radio situation where in order to obtain satisfactory radio reception both a sufficient CNR and CIR need to be achieved simultaneously. Such calculations can be used in the design and analysis of mobile radio systems and may be particularly useful for investigating the effects of cochannel interference in cellular systems. The outage probability expressions are derived using previously reported statistical descriptions of mobile radio propagation. Attention is generally focussed on situations where signals suffer Rayleigh fading and/or lognormal shadowing. However calculations for Nakagami-m, Rice and Weibull fading are also considered. The rapid growth in cellular mobile radio systems has stimulated the development of outage probability calculations for multiple interferer situations. Previously, while single interferer situations had been treated exactly, multiple interferers had been treated by approximate methods. In this thesis exact multiple interferer outage probability expressions are presented for the Rayleigh fading and the joint 'fading and shadowing' (Suzuki) situations. Similar expressions, but for more limited cases, are also presented for lognormal and Nakagami-m statistics. Using results from these expressions the accuracies of several approximate outage probability methods are assessed. The exact outage probability expressions for multiple Suzuki interferer situations are closely related to those for multiple Rayleigh interferer situations. Indeed, the exact analytic expressions for Rayleigh statistics form an integral part of the corresponding outage probability expressions for Suzuki statistics. These latter expressions can be readily evaluated using Gauss-Hermite numerical integration. In order to demonstrate the use of such calculations for mobile radio system analysis several theoretical examples are presented. Outage probability calculations for multiple interferer systems which employ diversity reception as a means of improving communications reliability are considered. Similarly, the extension of outage probability concepts to digital systems is briefly outlined.