The significance of real time frequency selection

In HF automatic link establishment there are three approaches to frequency selection. One is to simply operate from a table based upon predictions of propagation. The second approach is to periodically update the table, either by monitoring other traffic or establishing periods for network sounding or both. The third approach is to test all of the frequencies prior to placing the call and selecting the best one. The authors present performance predictions for a `typical´ link where the selection of frequencies is based upon the third approach. This is compared with the performance based upon the first approach