Winter 2006 Issue

Predicting Propagation
on 6 and 2 Meters,
with Extensions to 70 cm

What causes sporadic-E? Can it be predicted? Answers to these questions have eluded us for decades—until now. In this article ZL3NE weighs into the debate by giving us his well-researched answers.

By Bob Gyde, ZL3NE/1

It is general knowledge that the F2-layer absorbs most of the radiation that enters our planet’s solar system and that it is also our shield from intense radiation. The intensity of the solar flux governs the amount of ionization that we can get into the F2-layer, and the F2-layer controls the ionization available for the E-layer. We also know that during the very low part of our solar cycle, F2 propagation ceases on 10 and 15 meters because the amount of ionization arriving there is too low to support propagation on those bands.

The sporadic-E type of propagation, however, takes place regardless of the solar-flux readings. Therefore, the sun has nothing to do with sporadic-E—well, not by the previously accepted means. Ionization of the E-layer cannot be changed by radiation from outer space when the observed solar flux level does not change, and it would have to, to have any effect on the E-layer. Extreme flares such as X5 or above can temporarily change things, but only for a couple of days; after that we return to normal. The big thing to come to grips with is that the ionization from the sun has nothing to do with sporadic-E type propagation.

Determining What Produces Sporadic-E Propagation

With this statement as our basis, let us look at what we need to have to determine what produces sporadic-E propagation. First, we need an annual cycle to meet the traditional mid-summer peaks of propagation which occur between the December 10 and January 20 in the Southern Hemisphere and June and July in the Northern Hemisphere. Next, we need a means of varying the propagation direction, such as in the Southern Hemisphere. Examples are:

A. Propagation only from southwest to south on a yearly basis here at 37 degrees south.

B. A means of producing propagation only to the west and south on a yearly basis.

C. A means of producing propagation in all directions also on a yearly basis. A study of my extensive log shows that the described conditions do occur as stated, on a yearly basis. A classic example was during Cycle 23 between summer 1998 and 2000. At that time we constantly had the same weather pattern, one which gave us no propagation to the north. Therefore, during Cycle 23 we seldom made the F2 areas, which in our case are only to the north of us.

D. In addition, we need some means of propagation that is possible even in mid winter.

Now that list was a tall order, but it covered my basic requirements.

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