Maximum Usable Frequency

The maximum usable frequency (MUF ) is the highest usable for a short-wave radio communication between two places frequency. Only the jump distance between transmitter and receiver determines a specific frequency. For example, the MUF is referred for a 3000 - km - jump as MUF (3000).

MUF is the highest frequency at which a reflection at the ionosphere is also possible. It allows, in at least 50% of the time of reception, a reliable connection. To operate a reliable wireless connection but this is not enough. Therefore, a frequency of optimum transmission ( FOT ) is defined which is 15 % lower than MUF. FOT provided in 90 % of the time a reliable radio link.

The MUF varies depending on the day and season. Furthermore, the solar activity and the sunspot cycle has a strong influence on the MUF.

The counterpart of the MUF is the LFR, the Lowest Usable Frequency, which is the lower frequency limit for a reliable wireless connection. From these two results, the usable for radio link frequency window. This can be closed when the LUF higher than the MUF is, for example, after an X-ray outburst of the sun ( X -ray event ). Then leaves from the eruption following increase in attenuation in the D layer of the ionosphere, the LUF rise so high, that all rays are able to penetrate the D layer yet, can not be reflected by the overlying F- layer, since their frequency over the MUF is. This is referred to as the short - wave Fade ( out).

The MUF can be determined from the critical frequency of the ionosphere approximately wiefolgt:

= angle with the shaft relative to the horizon, = incidence angle relative to the perpendicular, = distance between the transmitting and the receiving location = virtual height of reflection.

Virtual and real magnitude of the reflection

The relationship between real and virtual reflection height in the ionosphere resulting wiefolgt:

Virtual Height:

Real height:

Jump distance:

Frame values: