Ham Radio General Class Practice Test

What usually happens to radio waves with frequencies below the Maximum Usable Frequency (MUF) and above the Lowest Usable Frequency (LUF) when they are sent into the ionosphere?

1. They are bent back to the Earth

2. They pass through the ionosphere

3. They are amplified by interaction with the ionosphere

4. They are bent and trapped in the ionosphere to circle the Earth

The correct answer is: They are bent back to the Earth

When radio waves are transmitted into the ionosphere at frequencies below the Maximum Usable Frequency (MUF) and above the Lowest Usable Frequency (LUF), these waves typically exhibit a phenomenon known as refraction. At frequencies below the MUF, incoming radio waves are bent back toward the Earth due to ionospheric layers' varying electron densities. This bending allows for effective communication over long distances, as the waves can traverse vast areas by reflecting off the ionosphere and returning to the ground. In contrast, radio frequencies that exceed the MUF may pass through the ionosphere without significant reflection, limiting their range to line-of-sight communication, while frequencies below the LUF are absorbed and do not propagate effectively. The bending of radio waves below the MUF is crucial for long-distance communication, as it enables signals to reach areas that would otherwise be unreachable.