DX Atlas includes a set of dynamic, interactive ionospheric maps. Each map displays the selected parameter, such as the F2 layer critical frequency, D layer peak electron density, etc. The parameter value under the mouse cursor is displayed on the status bar, and various levels of shadows show how the parameter is distributed across the Globe.

If you had to drive from point A to point B, would you prefer to have the driving instructions or a road atlas? The task looks easier in the first case: you just follow your instructions, and you do not have to read the map. This works fine until you discover that the exit mentioned in the instructions is closed. Now you are helpless! You do not know what other routes exist. If you have a roadmap, however, you can easily find an alternate route. Ionospheric maps are like a road atlas to a DXer, they allow you to find 'alternate routes' even if the 'driving instructions' produced by the propagation prediction programs fail to work.

To use the ionospheric maps, one needs to understand how the ionosphere works. As you probably know, the F layer reflects radio waves, and the D layer is responsible for signal absorption. By checking the F layer's critical frequency along the path, you can tell if the high bands are open, and the D layer density gives you an idea how strong the signal is going to be. There is much more information that can be extracted from the maps. For example, chordal propagation is likely to occur in the areas where the F2 critical frequency (foF2) or height changes quickly along the path, and path bending can occur if there is a significant transverse foF2 gradient.

The more you know about the propagation mechanics, the more useful ionospheric maps are to you. Use your knowledge to interpret the maps, and use the maps (with a good book on propagation) to improve your knowledge. Propagation 101 by Bob Brown, NM7M is an excellent example of such book. You can download it from our Web site: Prop101.zip.

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