A comparison of the performance of three HF circuits with computer predictions

During October and November, 1963, and March, 1964, monthly median Maximum Usable Frequencies (MUF) and Lowest Usable Frequencies (LUF) were compared to observed median Maximum Observable Frequencies (MOF) and LUF\´s for three circuits-Hawaii (6443 km), Panama (3944 km), and Spain (7098 km)-transmitting to Cedar Rapids, Iowa. Observed median MOF\´s were determined simply by plotting the percent days of the month for which ionospheric support exists, and observed LUF\´s by the percent days of the month the prescribed sentence intelligibility was equaled or exceeded at discrete frequencies. The observed results were compared with three median MUF predictions methods: the two-control-point method, the "equal hops" method, and the method suggested by Gaspar\´Yantz. The results of the comparisons show that there is not a great deal of difference in error for any of the three methods, although the equal hops method generally exhibits consistently higher errors than the other two. The Gaspar\´Yantz method appears to be slightly superior to the two-control-point method, but the difference in rms error is small. The two-control-point method yields rms errors between monthly median observed MOF\´s and predicted MUF\´s of about 16-17 percent. The Frequency of Maximum Reliability (FMR) is discussed briefly, and the difference in reliability between the FMR and the observed "classical" Frequency of Optimum Traffic (FOT) illustrated.