Inexpensive Solutions for Direction Finding of Bridge-to-Bridge Radio Transmitters Using Phase Difference in Received Signal

This thesis presents two methods for determining the bearing of a source generating a Very High Frequency (VHF) bridge-to-bridge radio transmission. Using principles of interferometry, one can utilize the calculated phase difference between the received signal at multiple antennas to determine the Angle of Arrival of the detected transmission. This translation of phase difference to Angle of Arrival is accomplished using equations based on signal properties and geometry. The theoretical method is shown proving the relationship between Angle of Arrival and phase difference, as well as how a single platform could accomplish this detection and calculation. Theoretical simulation was accomplished using various simulation tools including Mathwork’s Simulink and Tonne Software’s Elsie. Methods are then provided to detect the phase difference using both a series of analog mixers and
filters as well as digitally, using software radio. Analog filters were built and tested to determine the relationship between phase difference and voltage output. Software programs were written for a Software-Defined Radio implementing digital filtering to verify the analog performance. Results and accuracy are shown based on initial testing.