Measurements of the direction of arrival of an oblique chirp sounder signal

The performance of high frequency direction finding systems is known to be related to the mode content of the incoming signal and to the frequency of operation. Furthermore, signals propagating via the high latitude ionosphere are known to be particularly disturbed with, for example, the signal often arriving at the receiver over paths well displaced from the great circle. Observations at Alert, located high in the Canadian Arctic, have indicated that large off great circle bearings on fixed frequency signals are associated with definable features on oblique ionograms taken over the paths of interest. In order to further investigate these phenomena, a system has been developed which can measure the bearings of signals radiated by the worldwide network of BR chirpsounder transmitters across the full range of propagating frequencies. Preliminary tests of the system were undertaken in Ottawa during August 1991 and at Cheltenham during January 1992 with further requirements at Alert during April 1992. Results of a preliminary nature from January 1992 test are presented