Calculate the maximum usable frequency (MUF) from the critical frequency and incidence angle with the secant law, or solve for critical frequency or angle.
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Maximum Usable Frequency Formula
The following formula is used to calculate the maximum usable frequency (MUF) for a given critical frequency and incidence angle.
Variables:
- MUF is the maximum usable frequency
- fc is the critical frequency
- (theta) is the angle from the normal at the ionospheric layer: 0ยฐ for vertical incidence and less than 90ยฐ. The calculator also accepts radians; this is not the antenna elevation angle.
To calculate the maximum usable frequency, divide the critical frequency by the cosine of the incidence angle.
What is Maximum Usable Frequency?
The maximum usable frequency (MUF) is the highest frequency at which a radio wave can be transmitted between two points via reflection from the ionosphere. It is an important parameter in the field of radio communications, particularly for long-distance communication. The MUF depends on the critical frequency of the ionosphere and the angle at which the radio wave is transmitted. The secant-law calculator is an ideal estimate. Actual usable frequencies vary with path, time and ionospheric conditions; the estimate does not ensure reliable signal transmission.
How to Calculate Maximum Usable Frequency?
The following steps outline how to calculate the Maximum Usable Frequency (MUF).
- First, determine the critical frequency (fc).
- Next, determine the incidence angle from the normal at the layer, in degrees or radians, from 0ยฐ up to but excluding 90ยฐ.
- Next, calculate the cosine of the incidence angle.
- Finally, calculate the Maximum Usable Frequency (MUF) using the formula MUF = fc / (cos(theta)).
- After inserting the values and calculating the result, check your answer with the calculator above.
Example Problem :
Use the following variables as an example problem to test your knowledge.
Critical Frequency (fc) = 5 MHz
Incidence Angle ((theta)) = 45 degrees from the layer normal. The estimate is MUF = 5/cos(45ยฐ) โ 7.0711 MHz.
