Radiopropagation forecast for ham radio - Solar activity

What is radiopropagation forecast?

Radiopropagation forecast is the cosmic and ionospheric condition that contributes to how far and how well a radio signal travels around the world. This is largely dependent on the sun.

The ionosphere and the propagation conditions for radio waves are influenced by sunspots, solar winds, solar surface eruptions, flares and geomagnetic conditions.

In our article on the Significance of Sunspots for Amateur Radio we explain the physical background: Which conditions influence the radiopropagation forecast and why?

What are the metrics that describe the radiopropagation forecast?

The radiopropagation forecast is described with numerous measured values. The most relevant are these four: R, F, A and K. These mentrics are unitless.


R ranges from 10 to 150.

High R-value results in more favorable conditions on higher bands and is a factor in good radiopropagation forecast.

Very high R value: risk of failure and interference, especially shortwave.


F ranges between 50 and 200. 

A high F-value creates more favorable conditions on higher bands. Factor for good radiopropagation forecast.

Very high F-value: risk of failure and interference, especially shortwave.


A is a value between 10 and 30.

Low mass entry means hardly any interference. Factor for good radiopropagation forecast.

Very high A value: spontaneously better propagation conditions on lower bands.


K is a value between 0 and 9. 

Low K value: quiet magnetosphere. Factor for good radiopropagation forecast.

High K value indicates a turbulent earth magnetic field.

Where can i find the data (measured values) for the current radiopropagation forecast?

There are many sources to get current radiopropagation forecast data. Here is a big overview.


R - Sunspot relative number

A high "R" value is roughly good for us radio amateurs. At the maximum of the solar activity this number increases, at higher values good to very good band openings are to be expected much more often, which usually also last much longer than at low R-values. High R-values are generally a sign for an active sun - which with other effects can also cause "bad radiopropagation forecast" up to total failure. In any case, a high R value represents more interesting times.


F - The solar flux

Like the R-value, a high F-value stands for "better radiopropagation forecast", especially on the higher bands. However, in extreme cases, a high solar flux together with large magnetic unrest of the ionosphere (K-value) can cause interference.


A – Entry of Mass

If the solar wind is at a low level it is usually quieter on the bands, there is little interference. Coronal holes and mass ejections cause a sudden increase of the A-value, which can lead to disturbances (noise up to total failure). If at the same time the magnetic field of the solar wind turns to the south (in the quiet state it mostly points to the north), then strong auroral phenomena can occur at the magnetic poles of the earth.


K - State of the magnetic field

This value describes the change of the earth's magnetic field over time. So a low value describes small changes - no matter on which level! So the K-value describes roughly the radiopropagation forecast. Low values indicate that the current situation can still continue. Higher values show that a change has begun. This can also be a change for the better. In this case it is necessary to watch carefully the other values and the signals on shortwave, for example international beacons. With an unsettled magnetic field, the radiopropagation forecast can change quickly.

What professional radiopropagation forecasts are there?

  1. DARC - A daily radio weather report is published on the site (German Association of Amateur Radio). Click here for the latest radiopropagation forecast. DL1VDL publishes the radio weather report every Wednesday, which is broadcast over the DARC's Deutschlandrundspruch and can be seen on their website every Thursday Wednesday.
  2. Tropospheric Propagation Forecast  
  3. The Space Weather Services of the Australian government with forecasts and information about radiopropagation forecasts in Europe, North America, Australia and New Zealand. There are radio weather maps and the possibility to calculate a propagation forecast between two locations. 

Studies and scientific publications on the subject of radiopropagation forecast

  1. Here you can find the publications of the German Max Planck Institute for Solar System Research  
  2. A 2014 Science Information Service article "The Clocks of the Sun"  

Further information on the radiopropagation forecast

  1. Very handy: The radiopropagation forecast encyclopedia, sorted alphabetically. 
  2. Jens Mielich, Leibniz Institute for Atmospheric Physics explains ionogram interpretations in this pdf.