Maximum usable frequency

Maximum usable frequency, or MUF for short, is like a limit for how high radio waves can go before they start to disappear. Imagine you are playing catch with a ball, but the higher you throw it, the harder it gets to catch it back. Radio waves are like that ball, they bounce off the earth's atmosphere and can travel further distances, but the higher they go, the more the air gets thinner, and the waves start losing their strength.

So, scientists have found out that there is a certain height, called the ionosphere, that radio waves can bounce off of and travel long distances. This height changes depending on where you are on the earth and what time of day it is, but it is usually around 200 to 300 miles up.

The maximum usable frequency is the highest radio wave frequency that can use this height to bounce off of and travel long distances without disappearing. The MUF depends on many things, such as the strength of the radio wave, the time of day, and the weather conditions.

So, just like playing catch with a ball, if you throw it too high, it might get lost or disappear. The same thing happens with radio waves, and that's why scientists use the concept of maximum usable frequency to make sure that their radio signals can reach other parts of the world without getting lost.