High-frequency direction finding

The principles underlying high-frequency direction finding are summarised and relevant literature is reviewed. Various forms of direction finder are briefly described. The principal sources of error, including propagation effects, and the statistical problem of combining bearings into a fix are discussed. It is generally accepted that improved accuracy is most likely to be obtained with wide-aperture systems, combined with greater use of information about the ionosphere and the propagation modes involved: this view is supported by the literature reviewed.