Real‑Time HF Propagation Space Weather

OWF versus MUF

HF propagation prediction is a statistical science.

The maximum usable frequency (MUF) is the highest frequency that, with a probability of 50% of the time, can be used for radio communication between two points at a specified distance (but not necessary in all directions) via refraction by the ionosphere.

The optimum working frequency (OWF) is the highest frequency that, with a probability of 90% of the time, can be used for radio communication between two points at a specified distance (but not necessary in all directions) via refraction by the ionosphere. It can be estimated as: $OW\!F=0.85\,MU\!F$.

Sporadic E_s layer

When a sporadic E_s layer is present, its maximum usable frequency relates to its ordinary critical frequency approximatively as follows:¹

\[MU\!F_{E_s} \approx \frac{f_{o,E_s}}{0.188} \approx 5.319\,f_{o,E_s}\]

$Plot (updated every 15 minutes) of the critical frequency fo,Es of the sporadic Es layer in the vicinity of where your IP address is thought to be located. The maximum useable frequency of a sporadic Es layer, MU\!F_{E_s} is about 5.319 times the depicted critical frequency f_{o,E_s}. Source: NOAA$

References

Emil Pocock, W3EP. Sporadic-E propagation at VHF: A review of progress and prospects. QST. Published online April 1988. https://www.uksmg.org/content/sporade.htm

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