This is the first in a multi part set of articles that will help you understand how to work more DX by understand band openings, and band closings. In order to work more DX you will need to understand what bands are open, when they are open or closed, and, if they are open, where they are open to. That said, let’s get started, in this first article, atmospheric, and ionospheric structure will be covered. That will give you the basis for understanding how, and why, DX comes about. What you learn today, will be useful tomorrow, and in understand the rest of this series. Throughout this series of articles, you will see links to other articles, and web pages. These links are to assist you in learning more if you want. You do not need to follow these links to understand what this series of articles is trying to teach.
What is the Ionosphere?
In order to understand propagation one needs to understand how the Ionosphere works, no small undertaking! In order to understand how the ionosphere works, you will need to understand the structure of the Earth’s atmosphere first. The atmosphere is a pool of gaseous components held close to the Earth’s surface by gravity.
The atmosphere is broken down into several layers, each with a soft start, and a soft stop altitude. This means that there is no distinct layering, but that one layer blends into the other. Looking at the image on the left, you will see a set of colored vertical bars. Each bar represents one layer of the Ionosphere. The top and bottom of the vertical bars represent the altitudes where that layer starts and ends. The entire right bar is not to scale, and it fits between the Mesosphere, and the Exosphere. The red curvy line indicates electron density, something we won’t cover for a few installments. The ionospheric shell consists of electrically charged atoms, molecules, and electrons. They can be either positive, or negatively charged. The important thing to remember is they are not neutral, if they are not neutral, then they are ionized. All of this is also within the Earth’s atmosphere, between the Mesosphere, and the Exosphere.
The Ionospheric Shell
The ionospheric shell, (living between the Mesosphere and teh Exosphere), consists of a number of layers just like the atmosphere does. Each layer is named. The names are as follows; D, E, F1, and F2. Not all layers are present at all times. Layers are dynamically created, and destroyed, based on the external stimuli reaching them. Sometimes a layer is thicker, sometimes it is thinner, it all depends on the Sun. Here is a diagram showing the rough day and night layer positions of the ionosphere.
Note that the day and night sides are very different. During the day, the sun is bombarding the ionosphere with X-Rays, Ultraviolet light rays, and in general all sorts of short wavelength, high energy photons. The ionosphere is primarily created when Ultraviolet, (or UV radiation) strikes the upper atmosphere.
Why do we care about all of this? Because the ionosphere is responsible for most, if not all, radio propagation beyond the horizon, and propagation beyond the horizon is called DX, and that’s what we want, more DX!