Aspects of HF radio propagation

<p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">radio systems. From the point of view Working Group 2 of the COST 296 Action, interest lies with effects associated</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">with propagation via the ionosphere of signals within the HF band. Several aspects are covered in this paper:</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">a) The directions of arrival and times of flight of signals received over a path oriented along the trough have</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">been examined and several types of propagation effects identified. Of particular note, combining the HF observations</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">with satellite measurements has identified the presence of irregularities within the floor of the trough that</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">result in propagation displaced from the great circle direction. An understanding of the propagation effects that</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">result in deviations of the signal path from the great circle direction are of particular relevance to the operation</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">of HF radiolocation systems.</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">b) Inclusion of the results from the above mentioned measurements into a propagation model of the northerly</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">ionosphere (<em>i.e. </em>those regions of the ionosphere located poleward of, and including, the mid-latitude trough)</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">and the use of this model to predict the coverage expected from transmitters where the signals impinge on the</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">northerly ionosphere.</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">c) Development of inversion techniques enabling backscatter ionograms obtained by an HF radar to be used</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">to estimate the ionospheric electron density profile. This development facilitates the operation of over the horizon</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">HF radars by enhancing the frequency management aspects of the systems.</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">d) Various propagation prediction techniques have been tested against measurements made over the trough</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">path mentioned above, and also over a long-range path between Cyprus and the UK.</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">e) The effect of changes in the levels of ionospheric disturbances on the operational availability at various</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">data throughput rates has been examined for the trough path mentioned earlier.</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">The topics covered in this paper are necessarily brief, and the reader is referred to full papers referenced</p> <br /&gt