MUF diving, a further look at getting from A to B
Last month we looked at the height and strength of the
ionosphere. In that the Critical frequency FoF2 and the height either
real or virtual (hmF2 or h’F2) are important for determining what
frequencies get what distance. The MUF vs Range table at the bottom of
the ionogram lists this.
For example Figure 1 lists MUF data for Dourbes in Belgium, again, I circle in
red the important bits
The critical frequency of 5.7MHz means we will get a skip
zone at 7MHz and we can talk to stations 3000km away on 14MHZ but 18MHz is a
bit iffy since the maximum usable frequency is 18.17MHz.
That’s really a repeat of what we said last month, but it is
important you understand it before looking at how things work planet wide.
This month I will show you world wide maps that are drawn by
using the FoF2 and h’F2 downloaded from ionosondes all over the planet. You
should take these with a pinch of salt because the global network of ionosondes
is not always reliable, the server has been down 3 or 4 days this month already
for instance. (by mid March)
I found a useful calculator at https://www.hfunderground.com/propagation/#skipzone
It is about halfway down the page if the bookmark doesn’t get you straight to
it. It should look like figure 2
As you see at the moment the calculation refers to, you cannot talk to anyone within 256 miles of you on 40m. If you live in the UK or near Europe.
We did not talk too much about how the ionosphere changes
with time, both over a few tens of minutes as waves and “clouds”
travel along the layers and over the course of day, or season, or year/decade.
All have patterns that affect us.
One thing at a time. Over the day some of the ionosondes can give us a useful graph, https://www.propquest.co.uk/graphs.php can give us the graph below (I switched off the MUF and E layer data for this plot – click the symbols on the bottom line)
Figure 3 Plot of how FoF2 varies over
the day
If the MUF factor is 3.19 (see the fat red oval in Figure 1)
then DX is possible at 7.85 * 3.19 = 24.88MHz. even at 7pm you can use 15m and
maybe, maybe! Even 12m…
Of course, we have only been using the ionosonde at Dourbes for the above, we should really use a station at the midpoint of our path. We need a map of where they are. Globally a lot of the data is brought onto a couple of servers. KC2G keeps a live list of ionosondes at https://prop.kc2g.com/stations/ and I just counted 48 “live” stations. He quotes the sources as the NOAA National Centers for Environmental Information (https://www.ngdc.noaa.gov/stp/IONO/rt-iono/ )and the Lowell Global Ionospheric Radio observatory. (https://giro.uml.edu/ ). Figure 4 below is from Lowell’s website.
But the NOAA site only takes data from the stations listed on Figure 5
The reason I am highlighting this as I am about to show you a worldwide MUF map. IF THE NUMBER OF STATIONS SUPPLYING DATA WAS HIGHER, THE MAP WOULD BE MORE ACCURATE. Again, you need a pinch of salt. Don’t believe everything the web (or anyone) tells you.
“Trust in God, for all others verify”
So, now a few screenshots from the web site of KC2G, please explore the site –
it only has half a dozen pages, one is a dynamic list of ionosondes updated
every 5 to 20 minutes, one is an explanation of the site and one is a MUF map,
shown in figure 6.It does not reproduce very well as the colours are quite
pale, for best results click https://prop.kc2g.com/ (the MUF tab)
So, geographically, at the time the map was plotted, we can work the Americas using highish frequencies but not East Europe or Asia.
But do take note that the number of stations that have
contributed data to allow the graph to be plotted is quite small only 15 or so,
and they are highly clustered (the yellow and green numbered circles in Figure
6). The software is clever enough to
interpolate as best it can but it cannot be accurate without sufficient
accurate data. Be careful.
A further source of a map that attempts to show similar data
comes from Australia, unfortunately they just plot critical frequency, but if
you remember to multiply by the MUF ratio (roughly 3 ) you can see how well
communication might work. The actual MUF ratio does depend on the height of the
ionosphere and the intensity and thickness of all the layers but the map is
still useful nonetheless. The Australian Space Weather Forecasting Centre has
links for “GLOBAL HF” down the left hand side of its home page and the
“IONOSPHERIC MAP” link produces figure 7 on the next page.
Be careful to click the 0° option under the “MAP CENTRE
AT LONGITUDE” text.
At lease the map is highly coloured and easier to read then
the faint colors(sic) of KC2G
And that is that, we have talked about the height and
intensity of the F2 layer and how it creates a path for a single bounce radio
contact. We can see how the conditions vary over the day.
We have not looked at multi-bounce communications, although
it is just an extension of what we have covered here.
We have not looked at greyline communications and other
weird communication paths due to strange going’s on in the ionosphere
We have not talked about the effect of magnetic fields,
these are recorded as the A and K indices
We have not looked at solar storms and the several ways they
can affect things.
All these just change the ionosphere, its intensity, height
and profile of the various layers. I think understanding FoF2 and h’F2 is a
good start!
