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Current radio direction finding techniques are limited in flexibility and focus on specific applications. Commercial off the shelf systems exist for a wide range of applications from navigation to search and rescue and wildlife tracking. However these systems rely on commercially available VHF receivers and are limited in transmission modulation techniques and frequency ranges. The majority of these systems are expensive which places them outside the reach of most individuals while the current open source designs require specialized skills and knowledge to build. The goal of this work was to design a low cost system capable of determining the approximate location of a non-cooperative VHF transmitter that could easily be implemented on a variety of unmanned systems. One unmanned aerial system was designed, built, and evaluated. Existing open source hardware and software systems were utilized for the development of the pseudo Doppler direction finding system, and work was conducted utilizing recursive Bayesian techniques to estimate the VHF transmitter's location. Results and explanations of system behaviors are presented along with limitations and possible modifications to improve performance and reliability. / Master of Science / Radio direction finding uses specialized radio equipment to determine the direction that a radio signal is coming from. Commercial systems are often expense, and existing hobbyist designs require specialized skills, and both are not flexible in application or frequency. The same is true for commercially available drones, which tend to be expensive or face other limitations. In this work a low cost radio direction finding system that uses easily found open source hardware and software was built and evaluated, along with a low cost unmanned aerial system. Then using the data collected, a computer algorithm was tested that could estimate the transmitting radio’s location. After testing it was determined that all systems did work, but still had room for improvement. Future steps and system modifications are presented that could improve the system’s performance.

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A radio direction finding (DF) system uses a multiple-element antenna array coupled with one or more receivers to estimate the direction-of-arrival (DOA) of a targeted emitter using characteristics of the signal received at each of the antennas in the array. In general, DF systems can be classified both by the number of receivers employed as well as which characteristics of the received signal are used to produce the DOA estimate, such as the signal's amplitude, phase, or time of arrival. This work centers on the development and implementation of a novel single-channel direction finding system based on the differential phase of the target signal received by a uniform circular antenna array with a commutative switch. The algorithm is called the PLL DF Method and differs from older single-channel DF techniques in that it is a digital algorithm intended for implementation on a software-defined radio (SDR) platform with a custom-designed antenna array and RF switching network. It uses a bank of parallel software PLLs to estimate the phase of the signal received at each element of the multi-antenna array. Theses estimated phase values are then fed to a specialized signal processing block that estimates the DOA of the received signal. This thesis presents the details of the initial version of the PLL algorithm which was used to produce a proof-of-concept system with an eight-element circular array. It then discusses various technical challenges uncovered in the initial implementation and presents numerous enhancements to the algorithm to overcome these challenges, such as a modification to the PLL model to offer increased estimator robustness in the presence of a frequency offset between the transmitter and receiver, revisions of the software implementation to reduce the algorithm's processing requirements, and the adaptation of the DF algorithm for use with a 16-element circular array. The performance of the algorithm with these modifications under various conditions are simulated to investigate their impact on the DOA estimation process and the results of their implementation on an SDR are considered. / Master of Science

The objective of this thesis was to evaluate radio receivers that had been previously acquired for other tasks by the Swedish Defence Materiel Administration, for additional service in a radio direction finding (DF) system. The antenna, calibration signal generator and DF algorithm were provided. As the receivers used the VITA 49 frame format, much of the work involved the interpretation of the frame structure and contents. The other main challenges were to put the receivers into the correct internal state, to compensate the analogue phase errors due to cabling, and to correlate the digital frames according to the time stamps. The work was performed partly as a literature study and, during implementation, by using an investigative trial and-error method. Collection of reference signals, for later offline analysis, was made at the Swedish Defence Research Agency. The findings of the evaluation was that the receivers were phase coherent and that the VITA 49 frame format was suitable for DF use. An apparently systematic error of unknown origin rendered the DF results inaccurate, even though the precision of the results was high. The automatic gain control (AGC) of the receivers did not perform according to norm. If the systematic error is compensated for, and the AGC problem is eliminated, the receivers will function as a DF system using the manufacturer's instructions, with the provided antenna. The performance of the receivers in this setting was not a primary concern for the thesis, but was deemed to be acceptable. Suggestions for further development include finding the source of the systematic error, an automatic calibration function, a more thorough performance analysis, and code optimizations using multiple threads.

Diploma thesis describes direction finding principles for passive localization of emitting source. Direction finding system with one rotating antenna was chosen with triangulation calculation of emitter position. Input parameters are position of measurement point and direction of maximum signal receiving level. A suitable digital compass module and GPS receiver module for this measurement was chosen. For this purpose was created a graphic user interface, which allow user to communicate with external devices and control spectrum analyzer. Results of measurements are displayed at map, together with area of possible positions of transmitter. Receiving Yagi antenna is placed on rotator and whole system is placed on roof of car. Whole system was construct and results of measurement are discuss here.

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The Range Limited Antenna (RLA) has the ability to track and pin-point RF devices operating within a certain accepted range. Using two antenna arrays, each made up of several elements, direction-finding algorithms such as MUSIC and Modified Root Pisarenko (MRP) are used to estimate the angles of arrival of incoming signals. Using the estimated angles of arrival, a range estimation algorithm is used to estimate the distance of the emitter from the antenna array. The aim of this thesis is to check the sensitivity of the range estimation and to form a statistical analysis for such conditions. Conditions of error are introduced into the system and several extensive Monte Carlo simulations are run for both MUSIC and MRP. Upon simulating physical errors in the antenna set-up, it is realized that the range estimation algorithm is sensitive to the slightest of phase shift differences, cable loss differences, mixer mismatches, and antenna mismatches. / Master of Science

We have created an eight-element antenna array system for evaluating various Angle of Arrival (AOA) Position Location (PL) algorithms, such as MUltiple SIgnal Classification (MUSIC) and Estimation of Signal Parameters via Rotational Invariance Techniques ESPRIT algorithms. Since using delay of arrival information can improve AOA estimates and classical PL algorithms do not incorporate Delay of Arrival (DOA) information, the performance of these algorithms is not optimal. Recently proposed Joint AOA and DOA Estimation (JADE) algorithms, though more complicated, potentially have higher resolutions in both space and time domains. Our investigation shows that by using bandlimited known signals it is possible to resolve the DOA within a fraction of the sample period using JADE algorithms. Joint AOA and DOA algorithms can provide high resolution DSP-based channel measurement using low bandwidth hardware. / Master of Science