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## CF vs MUF | Difference between CF and MUF

This page defines CF (Critical Frequency) and MUF (Maximum Usable Frequency) and mentions difference between Critical Frequency (CF) and Maximum Usable Frequency (MUF). The formula for CF and MUF are also mentioned.

The layers above earth are troposphere, stratosphere and ionosphere. Ionosphere ranges approximately between 90 to 250 Km above the Earth.

Both critical frequency and maximum usable frequency are related with the ionosphere layer. ### CF | Critical Frequency Formula

Radio frequency waves propagate between transmitter and receiver using antennas. The radio frequency at or below, the wave gets reflected from ionosphere and above this frequency waves penetrate through ionospheric layer. This is frequency is known as critical frequency. Equation-1: CF Formula

The formula or equation of critical frequency is mentioned above. Critical frequency depends on atmosphere and angle of fire from transmitting antenna. Hence critical frequency value changes as per time of the day. In the equation, Nmax is maximum electron density or ionization density.

### MUF | Maximum Usable Frequency Formula

Though critical frequency represents highest frequency which is reflected back from the layer at vertical incidence; it is not highest frequency which is reflected from the layer.

The highest frequency which can be reflected depends on angle of incidence and on distance between transmitter and receiver antennas. As mentioned in the MUF formula, it depends on critical frequency and angle of incidence. MUF (Maximum Usable Frequency) is the maximum frequency which can be reflected for given distance of transmission.

MUF is usually 3 to 4 times of critical frequency.