Solar activity and HF/VHF propagation page


                                       Information about radio propagation on HF and VHF for Hams and SWL.

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          Understanding HF Propagation VE2XIP PDF document.(694 kbyte)
          Understanding solar indices by Ian P., G3YWX PDF document.(538 kbyte)
          Fundamentals of Ionospheric Propagation.

At 18 minutes past the hour, radio stations WWV and WWVH broadcast the latest solar flux number, the average planetary A-Index and the latest mid latitude K-Index. In addition, they broadcast a descriptive account of the condition of the geomagnetic field and a  forecast for the next three hours. You should keep in mind that the A-Index is a description of what happened yesterday. Strictly speaking, the K-Index is valid only for mid latitudes.     3 day forecast.     Predicted Sunspot Numbers and Radio Flux for next 27 days.     Predicted Sunspot Numbers and Radio Flux for next 27 days.     Solar activity forecast for next 27 days..     Last 30 days daily solar data.     Predicted Sunspot Numbers and Radio Flux for next years.     Recent Solar Indices of Observed Monthly Mean Values.
    VOACAP Online, propagation predictions.
    Propagation forecast.

        Pass solar cycles.


                                   Click here to see the most recent image of the far side of the sun at




                                                                 Solar X-Rays

                                                          Geomagnetic Field
   VHF Aurora      Status

144 MHz E-Skip  



                                                                                                K index.



                                                                                Current solar images.




                                         Solar wind velocity.                                                     Solar wind density.


  Putting it all together

* Higher solar flux levels are generally good for HF
* High K and A indices are generally bad – result in absorption and breakdown of the F region.
* Solar Flux / K index / Solar wind speed and Bz will give you a real-time indication of what bands you should concentrate on.
* Bz going south(-) and an increased solar wind speed (450km/s+) are generally bad news for HF.
* If your signals follow a polar path that cuts through the auroral zone(s) and the K index is high you will have problems.
* Spring/Autumn/Winter are better than Summer as the ionosphere is cooler, denser and MUF is higher during the day. Ionic  composition is different in Winter too. But night time MUFs are higher in summer.
* The opposite is true in the southern hemisphere.
* Spring/Autumn good for trans-equatorial contacts.
* As the sun gets higher D layer absorption grows, but the MUF rises, so follow the MUF up during the day and down at night.
* The center of the visible solar disk is the region that has maximum effect on Earth.
* Check the higher bands for openings for several hours following a solar flare, or a ten-flare event, due to the enhanced E/F layer ionization, possibly temporarily raising the MUF.
* If you’re in a QSO when a major flare causes an HF blackout, it seldom lasts more than an hour. If you’re working a contest, this hint could be useful. Take a break, but don’t QRT!
* X-rays do provide extra ionization to the E/F layers for improved reflectivity and a higher MUF. Exploit the benefits of a solar flare.
* The most damaging effects of a solar flare is actually the arrival of the shockwave 2-3 days later, triggering a geomagnetic storm.
* Often our magnetic field gets very quiet following a strong geomagnetic storm for 12–24 hours. This is an excellent time to work 40–160M due to very low noise levels.
* Use the current K-Index from WWV or the internet to determine the current geomagnetic conditions. The A-Index is actually yesterday’s geomagnetic condition, and does not represent present conditions.
* As soon as the solar storm ceases, HF noise levels become quiet with an elevated MUF, lasting until sundown. Night time conditions on 80-40M can be excellent. The daytime MUF the next day may be elevated as well.
* when the geomagnetic storm subsides. Night time noise levels on 40-80M can be very low.
* The x-rays from flares (class M5.0 or larger) can be intense enough to have a considerable impact on ionospheric radio communications. In some cases, the absorption can be strong enough to completely blackout all radio communications between points more than 3,000 to 4,000 km up to frequencies as high as 10 MHz for a period of between 15 to 30 minutes. Minor absorption can maintain weaker than normal signal strengths for an additional 20 to 30 minutes. These types of major flares are much less frequent than minor M-class flares.





                                                               Grey line map - One (click here)
                                                               Grey line map - Two (click here)
                                                               Grey line map - Three (click here)
The grey line is a band around the Earth that separates the daylight from darkness.  Radio propagation along the grey line is very efficient.  One major reason for this is that the D layer, which absorbs HF signals, disappears rapidly on the sunset side of the grey line, and it has not yet built upon the sunrise side.  Ham radio operators and shortwave listeners can optimize long distance communications to various areas of the world by monitoring this area as it moves around the globe.  This map shows the current position of the grey line terminator.

                                                                                Near real time MUF map.

The following map shows Maximum Usable Frequencies (MUFs) for 3000 kilometer radio signal paths.  More importantly, the current sunspot number (SSN) and Planetary A-index are updated every 30 minutes on the bottom of this image.  Additionally, the grey line position, auroral ovals, and sun position are provided.


                                                                                      Near real time MUF map.



If the radio wave reaches the ionosphere following a vertical o near vertical path (NVIS),
reflection will occur in the F2 layer only if the frequency of operation is below a threshold
known as F2 layer critical or cut frequency (foF2), which can be measured using ionosondes.
The following experimental maps are built using data from ionosondes located in Australia, Japan, South Africa, Italy, Argentina and the United States. Systems/Global HF/Ionospheric Map/West/fof2_maps.png



The Total Electron Content (TEC) gives an idea about the ionization grade of
the ionosphere. Its unit of measurement is the TECU (1 TECU = 10E+16 electrons
per square meter). The zones with the highest TEC are affected by the occurence
of different ionization phenomena, such as photoionization, absorption, etc. Electron Content/Regional Maps/World_tec.gif


Solar Cycle Progression ...

Predicted Sunspot Number And Radio Flux ...



Tropospheric Propagation Forecast
Worldwide refractive index forecasts
        Click here ( ) Professional-grade high-frequency (3-30 MHz) propagation predictions
        Click here ( )  VHF/UHF qso real time maps.
        Click here ( ) to see  DX Sherlock 2.0 - QSO real time maps
        Click here ( ) to see  D-Region Absorption Prediction



                                                                                         Cycle 21, 22, 23 and 24.



                                                                                                Solar Cycle radio flux progression.



Solar Cycle Progression ...
Predicted Sunspot Number And Radio Flux ...


          Click to see 400 year of sunspot observation.

          Click to get an  Azimutal map.


                                                                             Also you most to see.

HF propagation: The basics by Dennis J., W1LJ/DL  PDF document ( 976 kbyte)
Introduction to HF propagation by IPS Radio and space services  PDF document (1.28 mbyte)
Solar activity and HF propagation  PDF document (987 kbyte)
Transequatorial propagation  PDF document (181 kbyte)  ARRL propagation bulletin.  Propagation real time.   VHF/UHF qso real time maps.   Make more miles on VHF.   K9LA propagation tutorial.
   NCDXF beacons. 28 Mhz beacon list.    Worldwide list of HF beacons by G3USF.   Worldwide list of 50 mhz beacons by G3USF.   Propagation software, V2.70 (479 kbytes)   Propagation software. (1.0 mbyte)   Propagation software. (two programs 2.7 mbyte)

          e-mail: CO8TW e-mail address

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