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Reading Your Ionogram – Keeping It Simple

reading your ionogram

Here are the basics for reading your ionogram. You can discover real time propagation conditions almost anywhere in the world.

Start by finding the latest ionogram from the nearest ionosonde station to your QTH. You can find data from these networks by clicking on NOAA or Digisonde. Shown above, I have downloaded a late morning ionogram from Boulder, Colorado south of my Calgary location. On it, I have marked some items of particular interest in blue lettering.

First, check out the reflections coming back from the E, F1 and F2 layers at 115, 210 and 298 kilometers altitude, respectively. The ionosonde is transmitting a frequency sweep from 1 to 9 MHz. You can see the reflections as a series of red dots from the ordinary wave. You can also see that these dots spread out, curving upwards and then disappearing.

Where the dots disappear is your critical frequency, the highest frequency that reflects vertical signal echoes from each layer. At the very top of your ionogram you can see echo reflections from multiple hops up and down. A lot of ghost reflections tells you that your D layer is not absorbing or blocking signals very much.

The MUF, or maximum useful frequency is found by multiplying the critical frequency by an M-Factor. Reading your ionogram above, you can see a critical frequency foF2 of 7.163 MHz, multiplied by an M-Factor M(3000) of 3.32. The resulting MUF is almost 24 MHz for the highest F2 layer.

This is a fairly good ionospheric performance for northern latitudes on a winter’s day. Remember, the higher and stronger the F layer, the farther your signals will bounce around the planet at low angle take-off.

Reading Your Ionogram – What is the M-Factor?

Not black magic. The M-Factor is basically spherical geometry, with some adjustments for total electron content in the ionosphere. If you do some reading, you will find out that technicians have selected 3,000 kilometers as a standard one-hop distance. M(D=3000) is the factor showing the oblique reflection rather than the straight up and down shown by an ionogram.

In reading your ionogram there is lots more information, but these are the important points. As I say, the latest ionograms can be downloaded every fifteen minutes from a network of monitoring stations across Earth.

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