Some Problems of hf Communication at Low Latitudes & Possible Solutions

Abstract

The experience gained in advising a large number of communication organizations on hf propagation parameters has been used to' identify the major problems of hf communication at low latitudes. The specific problems are due to (i) a very sudden increase in <i>f</i>_oF2 during sunrise hours, (ii) a large amount of geophysical noise in the F region electron density that is apparently unrelated to' any specific solar or magnetic event, and (iii) anomalous latitudinal shift in the peak of the geomagnetic anomaly. A statistical analysis of data over half a solar cycle shows that it is impossible to' take care of the geophysical noise in long term predictions. This shows the need to introduce in our hf communication circuits certain amount of flexibility in changing the terminal parameters at a relatively short notice. The study also' shows that better understanding of the ionosphere and its variations is absolutely essential in conserving power as well as radio' spectrum, especially for point-to-point communications.