Abstract
Abstract. Doppler VOR (D-VOR) transmitters are used as navigation aids in aviation. They transmit an omnidirectional phase reference in an amplitude-modulated (AM) sideband and directional phase information on a frequency-modulated (FM) subcarrier. In an airborne D-VOR navigation receiver, a directional information (azimuth angle) related to the position of the aircraft and the location of the transmitter can be derived from the difference of these two phase signals. In this work, the accuracy of AM and FM phase signals is firstly investigated analytically and afterwards verified by measurements. It will be shown that in established procedures, phase inaccuracy is dominated by the AM signal, since the FM signal is about 21 dB less noisy. Subsequently, a novel method is presented that improves the accuracy of the azimuth angle by orders of magnitude in case of D-VOR transmitters. This new method inherently reduces noise of the AM phase and thus yields a significant increase in accuracy. As a result, the remaining FM phase uncertainty becomes dominant for the total uncertainty of the bearing indication. Finally, the application of the new method to real measured signals confirms the theoretical expectations.
Highlights
Within the framework of “WERAN plus” research project (Schrader, 2019), interactions between wind turbines and various radio and navigation services are being investigated
Doppler very high frequency omnidirectional range transmitters (VOR) (D-VOR) transmitters are used as navigation aids in aviation
In an airborne D-VOR navigation receiver, a directional information related to the position of the aircraft and the location of the transmitter can be derived from the difference of these two phase signals
Summary
Within the framework of “WERAN plus” research project (Schrader, 2019), interactions between wind turbines and various radio and navigation services are being investigated. In addition to the airborne SDR, another identical receiving system was set up on the ground near the D-VOR transmitter Since both systems are synchronised by GPS, groundbased and airborne measurements can be performed quasisynchronously. During the analysis of recorded data, a novel technique was developed which yields a significantly improved accuracy for the reference phase in a D-VOR receiver. The improvement with respect to short-term stability is about two orders of magnitude Following this introduction, signals transmitted by a DVOR are described in time and frequency domain in Sect. Afterwards, based on actual measurements, the accuracy of azimuth calculation by traditional and novel techniques is presented
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