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Propagation Part I

Posted by on July 3, 2022


The Ionosphere


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.

Atmospheric layering

Atmospheric/Ionospheric layering

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.

Want to know more?

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.

Ionospheric Layers

Day and night Ionospheric layering

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!

Want to know more?Why call it the ionosphere?


The sun provides the high energy events for ionization to take place.

Well– it’s close to a sphere in shape, (it surrounds the almost round Earth), and things get ionized in it, so you have a sphere of ionization, or an ionosphere!  But what does ionized really mean, and why do we care about it?  When an atom loses, or gains a charge unit, (the atom, or molecule becomes more, or less, negative, or more, or less positive), it becomes ionized, that is to say the atom has an charge of some type, positive, or negative, but not zero, or neutral.  When a radio wave hits an ionized cloud of atoms or molecules, or even a loose cloud of electrons, that radio wave can be bent.  That bending is called refraction.  Refraction is what causes all DX.

Want to know more?Refraction
Sky Wave

Signals being refracted by ionosphere.

Your signal is refracted over the horizon hopefully to places far away.  UV light, X-Rays, and other shortwave, high energy events, can, and do dislodge electrons from neutral gas atoms, or molecules, when absorbed.  This can create a large number of ionized particles, forming an ionized cloud, which can refract radio waves.  So your DX is intimately connected to the count of ionized particles in the ionosphere.  For the most part, more ionization is better, less ionization is worse for where DX is concerned.  Ionization, and hence your DX, is also intimately connected to the current state of the Sun.  So as the Sun excites the upper atmosphere, ionized clouds are formed and dissapate depending on the levels of high energy radiation the sun is providing, or not providing.  So your DX is tied very directly to the current state of the atmosphere, and hence to the state of the Sun.  What have we learned in this session?

Want to know more?Conclusion

DX is tied very directly to the state of the ionosphere, which in turn is tied to the higher energy output items the Sun produces.  That output from the Sun then modulates the ionization state of the ionosphere, (higher, or lower), and hence how well, (or if at all), our signals are refracted across the planet.  The higher the energy being deposited into the upper atmosphere, the better DX is.

Next Month

Next month we will look at the Sun, and what actions it can take to affect the ionosphere, and hence your DX.

Graphic Credits:
All graphics were created by either NASA, NASA visualization studio,
or Wikipedia.  All graphics are used with permission, or via Creative Commons licensing.


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