Frequencies of Optimum Transmission (FOT) are predicted to be usable on most days at what percentage of MUF?

Frequencies of Optimum Transmission (FOT) are predicted to be usable on most days at what percentage of MUF?

• A. 50 percent
• B. 65 percent
• C. 85 percent
• D. 100 percent

Answer: (C)

Frequencies of Optimum Transmission are the frequencies predicted to be usable on most days, expressed as a percentage of the Maximum Usable Frequency. The idea is to choose a frequency below the MUF that will reliably work despite day-to-day ionospheric variability. Using 85 percent of MUF provides a practical balance: it’s high enough to support good propagation on many days, yet below the MUF enough to tolerate fluctuations and prediction errors. If you used 100 percent, you’d risk outages when conditions dip; using much lower percentages, like 50 or 65 percent, would waste usable capacity and unnecessarily limit range. So the correct choice is 85 percent.

Frequencies of Optimum Transmission are the frequencies predicted to be usable on most days, expressed as a percentage of the Maximum Usable Frequency. The idea is to choose a frequency below the MUF that will reliably work despite day-to-day ionospheric variability. Using 85 percent of MUF provides a practical balance: it’s high enough to support good propagation on many days, yet below the MUF enough to tolerate fluctuations and prediction errors. If you used 100 percent, you’d risk outages when conditions dip; using much lower percentages, like 50 or 65 percent, would waste usable capacity and unnecessarily limit range. So the correct choice is 85 percent.