Determine Maximum Usable Frequency

What is a reliable way to determine if the MUF is high enough to support skip propagation between your station and a distant location on frequencies between 14 and 30 MHz?

A. Listen for signals from an international beacon in the frequency range you plan to use
B. Send a series of dots on the band and listen for echoes from your signal
C. Check the strength of TV signals from western Europe
D. Check the strength of signals in the MF AM broadcast band

[G3B04]

If you’ll recall the definition of MUF or Maximum Usable Frequency, its the highest frequency that the bands are supporting long distance communications on. So, lets check the available answers against what we know. So how can we determine maximum usable frequency

Check the strength of TV signals from western Europe? If you’re getting TV signals from western Europe, your receiving equipment is better than mine, for sure. Plus its almost physically impossible (but I’m sure its happened randomly in the past.). So likely not this one.

Check the strength of signals in the MF AM broadcast band? Considering we’re looking for the maximum usable frequency from 14-30 MHz, and the AM broadcast band is way down at roughly 500 kHz to 1.8 MHz….. that won’t really tell us any information about the higher bands.

Send a series of dots on the band and listen for echoes from your signal. This might work, if conditions are right and you can get a long-path return of your own signal. The odds of that are pretty slim, even if the bands are perfect.

That leaves us with A. Listen for signals from an international beacon in the frequency range you plan to use.

This makes the most sense. If you know of stations that are transmitting in that range, you should be able to dial them in, and if you hear them, you can assume that the band is “open” in at least some way. If not, then while hope is not lost, its probably a good bet it won’t work.

So the answer to “how do you determine maximum usable frequency?”, is A. Listen for signals from an international beacon in the frequency range you plan to use.