4 Dandaloo Steet, Kariong NSW 2250
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Solar Weather

Central Coast Amateur Radio Club



SOLAR WEATHER – (a laymans introduction).



There are many pages that go into detail about the intricacies of Solar weather but here, ” I’d like to give a basic “normal persons” introduction to it”. To many it may be “over-simplified” – if you say that you don’t need to be reading this page!

First of all, Solar weather affects our operation on the HF (or Short wave) bands. In general, what happens on the sun has little or no effect on communications on VHF and above and only limited effect on the MF and LF bands (at least not as far as the average amateur radio enthusiast is concerned).

There are 4 ways that the sun can deliver energy:

1. light

2. heat

3. Ionisation (charge)

4. winds.

The first two while important for living on earth are not immediately relevant to amateur radio.

As we all have learnt HF propagation travels around the earth by bouncing off the earth’s Ionosphere. That layered Ionospheric gaurd is affected by the last two items in my list.

When looking at space weather one of the first readings we look at is the SFI or solar flux index figure. With no small explosions (sunspots) happening on the sun the SFI sits at around 66. “As we get more and more sunspots the SFI can rise and (in the good times) it is often between 100 and 250 (or more).” There is a cycle between the maximum and minimum number of sunspots that runs over 11 years. We are currently at the bottom and nearing the end of cycle number 24 and cycle number 25 is just beginning.

Why is the SFI important? “Putting this is laymans terms” – when we have a lot of sunspots, they give off electrical ionisation which travel to the earth and charge up the Ionosphere around the earth. When charged up the Ionosphere reflects the signals better, with less loss of signal. So, in short, a high SFI number is a good thing.

Number 4 on my list – Solar Winds are caused when Coronal holes open up in the gasses around the sun and it spits out charged particles. These charged particles are not our friends as they do not improve the Ionosphere, rather they cause the background noise level on the HF bands to rise swamping weaker signals.

We also have a measurement that we watch to see how the Ionosphere is being affected by such winds and this is the “K index” – it can go from zero to 6 – as a general rule 3 and below is OK anything higher will affect your abilty to make contacts as the background noise level will be higher.

Solar weather can change quickly however some things can be forecast for example when a coronal hole opens up and a CME (Coronal Mass Ejection) occurs, it will take 2 – 3 days before those Solar Winds will reach the Earth.

However “bad news” for some with the solar winds raising our background noise level on HF is very good news for photographers as these winds are what cause the beautiful multi-coloured auroras in the skies. Six meter Ops also can use the Auroas to bounce their 50MHz signals off and get contacts further away, so for some amateurs the CME (Coronal mass ejection) from Coronal holes can be a good thing.

These winds also push the space ahead of them along and we often see BETTER HF conditions in the two days that the charged particles are between the Sun and the Earth, so it’s worth getting on the bands before the solar winds hit – once they hit though conditions will be gone.

Here’s a site that tells you the speed of solar winds (as well as other useful information) – anything under 400km/second is no wind.    https://www.spaceweatherlive.com

Depending upon the state of the Ionosphere, the frequencies and hence bands that can be used for longer distance contacts of say over 3000 km will change and we are interested here in a couple of readings made in semi-realtime by ionosond sites around the world.

You will find that there are a number of frequencies that are of importance when looking at ionospheric radio propagation. Relevant frequencies including the Critical Frequency; Lowest Usable Frequency, LUF; Maximum usable frequency, MUF; and the Optimum Working Frequency, OWF. The one we most often look at is MUF, above that frequency you will not normally make long distance contacts on HF.

These frequencies are often mentioned in radio communications propagation predictions based of statistics but you need to remember they are related to a PATH from one point on the earth to another. Hence an MUF frequency given from Colorado in the US (as is often the case) may not be relevant in Australia or Europe.

It should be noted that the Ionesphere is made up of layers that we label D, E, F1 and F2 – I will not be going into detail on these except to say that they can have different effects on different bands and they are different day and night.

So how do you know whether you can make a contact from your location in Woy Woy to let’s say Europe, and which band and time of day will give you the best chance.

Probably the most used planning tool is the website from VOACAP from the US “Voice of America” association. It bases its predictions for the day and path you chose on statistics and some basic values taken at the start of a month and hence is not totally accurate but can be a good guide.

You will find the VOACAP website here: http://www.voacap.com/


A good alternative providing similar information (and easier to use) is this one:  http://www.predtest.uk/area.html


There are many other propagation prediction sites. Some simpler to use, some more complex. But these are ONLY prediction websites, what about some realtime information? If I turn my rig on now – where are the open “paths” from my part of the world?

There are websites that work with near realtime input from Ionosonds to tell you the various frequencies for particular skip distances (the distance your signal should go with one bounce off the ionosphere). One which shows the situation in the UK is http://www.propquest.co.uk/graphs.php



in Australia there is the <http://www.sws.bom.gov.au/Category/HF Systems/Online Tools/Prediction Tools/HF/HF.php> site.



But there is also a “crowd sourcing” method.  Joe Taylor’s WSPR or whisper Network, which shows the paths that low power transmitters are being heard on the various bands – that website is here:  http://wsprnet.org/drupal/wsprnet/map . Note they have an issue with Google Maps licensing at the moment (November 2018) which will hopefully soon be fixed. You can still see however, where many lines are going from one part of the world to another for whichever band you have chosen and this is an indication that you might be able to make contacts along the same path.


So, what does this all tell you (VASTLY SIMPLIFIED)?

In brief,

•With the SFI below 70 you are going to find it difficult to make DX contacts except on FT8 or perhaps high-power CW

•With the K Index over 3 you are only going to hear the stronger signals.

•With an MUF of 10MHz, you are not going to make anything but ground-wave (close) contacts on 20m(14MHz).

•If WSPR.net doesn’t show activity on the path you want to use, the chances are you’re not going to be successful.

The final rule – you will never get a contact if you don’t put out a CQ – despite all these predictions and real time measurements the HF bands can always surprise you with a good contact!!

73 Ed DD5LP.