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International Telemetering Conference Proceedings / October 20-23, 2003 / Riviera Hotel and Convention Center, Las Vegas, Nevada / In a study sponsored by the Air Force Flight Test Center at Edwards AFB, California, Toyon Research Corporation, Goleta, California, demonstrated that shaped pattern antennas could be used to mitigate interference caused by telemetry signals on GPS systems. Using a technique for fixed reception pattern antenna (FRPA) design, Toyon built and tested a GPS antenna that minimizes reception of telemetry signals from a known location.

The aim of this thesis was to develop a model of a receiver which could be quickly used to analyze radiated interference levels from data captured at the output of the antenna equipment used to measure radiated energy. Active circuits were mainly used in developing this model for the ease with which the design and simulations could be carried out in OrCAD. The guiding document for the thesis work has been CISPR 16-1-1 (International Special Committee on Radio Interference part 16-1-1) which specifies the characteristics and performance of equipment for the measurement of radiated interference. The testing of this receiver model was carried out as far as possible based on the test setups recommended in CISPR, and all results have been compared with the standards laid down for the model. Using the results, it will be shown that a CISPR EMI receiver can be modeled as a simple EMI receiver consisting of filtering, mixing and detecting circuits built according to specifications.

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This dissertation describes methods of mitigating radio frequency interference (RFI) in the frequency range 10-100 MHz, developing and evaluating coherent methods with which RFI is subtracted from the afflicted data, nominally resulting in no distortion of the underlying signals. This approach is of interest in weak signal applications such as radio astronomy, where the signal of interest may have interference-to-noise ratio much less than one, and so can be easily distorted by other methods. Environmental noise in this band is strong and non-white, so a realistic noise model is developed, with which we characterize the performance of signal parameter estimation, a key component of the proposed algorithms. Two classes of methods are considered: "generic" parameter estimation/subtraction (PE/S) and a modulation-specific form known as demodulation-remodulation ("demod--remod") PE/S. It is demonstrated for RFI in the form of narrowband FM and Broadcast FM that generic PE/S has the problem of severely distorting underlying signals of interest and demod-remod PE/S is less prone to this problem. Demod-remod PE/S is also applied and evaluated for RFI in the form of Digital TV signals. In both cases, we compare the performance of the demod-remod PE/S with that of a traditional adaptive canceling method employing a reference antenna, and propose a hybrid method to further improve performance. A new metric for "toxicity" is defined and employed to determine the degree to which RFI mitigation damages the underlying signal of interest. / Ph. D.

International Telemetering Conference Proceedings / October 18-21, 2004 / Town & Country Resort, San Diego, California / Modern spectrally efficient telemetry transmitters are beginning to find their way on a variety of airborne test platforms. Many of these platforms also include Global Positioning System (GPS)-based Time-Space-Position-Information (TSPI) instrumentation systems. Due to space and other limitations, many of these platforms have demanding antenna placement limitations requiring closely spaced antennas. This paper describes steps taken to identify and mitigate potential interference to GPS-based TSPI instrumentation systems by these new technology transmitters. Equipment characterization was accomplished to determine interference potential of the proposed new transmitters and susceptibility of several GPS TSPI receivers. Several filtering techniques were identified as possible solutions to the anticipated interference problems. Telemetry (TM)/GPS system mockups and laboratory tests of the same were accomplished. Open-air testing was then accomplished to validate laboratory results. Finally, on aircraft tests were accomplished prior to performing any aircraft system modifications. Results of these test efforts are presented for others to consider when planning similar modifications to other platforms.

In this thesis, multidimensional signal processing techniques to mitigate disturbances in synthetic aperture systems such as radio telescopes are investigated. Here, two computationally efficient three-dimensional (3D) spatio-temporal (ST) finite impulse response (FIR) cone filter bank structures are proposed. Furthermore, a strategy is proposed to design 3D ST FIR frustum filter banks, having double-frustum-shaped passbands oriented along the temporal axis, derived from appropriate 3D ST FIR cone filter banks. Both types of cone and frustum filter banks are almost alias free and provide near-perfect reconstruction. In the proposed cone and frustum filter banks, both temporal and spatial filtering operations can be carried out at a significantly lower rate compared to previously reported 3D ST FIR cone filter banks implying lower power consumption. Furthermore, the proposed cone and frustum filter banks require a significantly lower computational complexity than previously reported 3D ST FIR cone and frustum filter banks. Importantly, this is achieved without deteriorating the improvement in signal-to-interference-plus-noise ratio. A theoretical analysis of brightness distribution (BD) errors caused by parameter perturbations and mismatches among the transfer functions of receivers employed in synthetic aperture systems is presented. First, the BD errors caused by perturbations in the transfer functions of low noise amplifiers (LNAs) and anti-aliasing filters (AAFs) are considered, and the characteristics of the additive BD error and its effects on synthesized BDs are thoroughly analyzed. Second, the conditions that should be satisfied by the transfer functions of digital beamformers to eliminate the BD errors caused by their phase responses are examined. The sufficient condition to eliminate the BD errors is that the transfer functions are matched, and, interestingly, the phase responses are not necessary to be linear. Furthermore, the BD errors caused by typical tolerances of passive L and C elements used to implement the AAFs and those caused by the random variations of gain from LNA to LNA are quantified through numerical simulations. The simulations indicate that substantial BD errors are observed at frequencies that are close to the passband edge of the AAFs. / Graduate

A methodology for the measurement of the radio frequency environment close to the radio noise floor is presented for urban, suburban and rural areas within New Zealand for the purposes of characterisation and trend monitoring by radio spectrum managers. Flux density measurements in bands within a range of frequencies from 80 MHz to 8 GHz have been made in urban, suburban and rural areas of New Zealand during 2007 and 2008. An analysis of the band occupancy is presented in summary form. These summaries are intended as a starting point for radio spectrum usage and can be used as a reference for any future measurements. A description of the computer directories and charts resulting from these measurements, using 20 MHz bandwidths have also been included. All the results for the work have been collated in a set of computer directories named “NZRFI Directories 2007 2008”, which are intended as a reference for use in the determination of local activity in particular frequency ranges. A disc with the full range measurement spectral density charts and channel occupancy charts accompanies this work. Also included on the disc are sets of 20 MHz band charts for some urban, suburban and rural location measurements.