BasicB-007-006-006
What usually happens to radio waves with frequencies below the maximum usable frequency (MUF) when they are sent into the ionosphere?
A
Answer
Interference and suppression
Type
A
They are bent back to the Earth
B
They are changed to a frequency above the MUF
C
They pass through the ionosphere
D
They are completely absorbed by the ionosphere
Answer Notes
The Maximum Usable Frequency (MUF) represents the highest frequency that the ionosphere will successfully refract (bend) back to Earth for a specific path. By definition, if a transmitted frequency is below this maximum limit, the ionosphere is sufficiently ionized to bend the radio wave back down to the surface, enabling skywave communication.
If the frequency is above the MUF, the wave will pass right through the ionosphere into space. Frequencies below the MUF are only completely absorbed if they drop below a different threshold called the Lowest Usable Frequency (LUF), so "completely absorbed" is an incorrect general assumption.
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What is one way to determine if the maximum usable frequency (MUF) is high enough to support 28 MHz propagation between your station and western Europe?
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At what point in the solar cycle does the 20-metre band usually support worldwide propagation during daylight hours?