Ionospheric perturbations and their effect on the accuracy of h.f. direction finders

The principles of high frequency direction finding are briefly described and the main sources of error in these systems discussed. The deviations in bearing produced by travelling ionospheric disturbances (t.i.d.s) are considered in detail since these errors are particularly difficult to predict and correct. General background information on the physics of t.i.d. phenomena has been included and attention given to the source mechanism and propagation characteristics of the disturbances. The paper concludes with a review of some possible methods for the correction of t.i.d. induced errors and details are given of some recent investigations of error correction procedures.