two modes of propagation at 50MHz
 - E-layer and sporadic-E
by Ken G4IGO

I would like to point out before starting this article that I am not a scientist, nor am I, as an Amateur looking for contacts with faraway places, interested as to what may or may not be causing "Sporadic E" - I am interested in making long distance contacts by using the results of my observations. I have been studying propagation at 50MHz for the last 17 years on a detailed basis, backing up my observations with some input from other local amateurs and from reports in the amateur press.

From these observations I have come to the conclusion that for many years we have been too readily applying old ideas that, whilst working well on HF and fitting the models of propagation at those frequencies, do not always work at 50MHz and above.

As far as I can remember we have called the Ionospheric propagation that operates in the summer months on 50MHz and above "Sporadic E" - I now believe that two distinct modes apply. First and most prevalent is E layer (operating in a similar way to F layer i.e. for a given height and frequency, a given range will be workable and at a given date and time a given direction will be workable) and second is the well known overrated Sporadic E. The Sporadic E/E Sporadic is best used to describe the mode of propagation that affects frequencies in excess of 100MHz - more on this later. It has become clear, particularly over the last few years that at certain times and days, certain directions (target areas) will propagate. This can not be coincidence. We do not term the predictable F layer propagation that exists in the peak of the sun spot cycle as "Sporadic", so why do we term the predictable E layer propagation as "Sporadic" - force of habit is my answer.

When it is predicted, that at certain times of the cycle the F-layer MUF will reach 50MHz, it is referred to as "ordinary" F layer propagation, so why, if the Es MUF rises to 50MHz in June or July (i.e. between 1800 to 2400 for North America and 1600 to 1800 for the Middle East) do we refer to it as "Sporadic"? It is also quiet probable that the path to 7Q7 around 1700 is also an E layer path - more on this later. The above times are reliable - the only thing that is not, is whether or not the MUF reaches 50MHz, but the same applies to the F layer! I believe that a large number of openings recorded at 50MHz and called "Sporadic E" are in fact ordinary E layer.

The E layer openings are usually characterised by the following:-

• Usually weaker, longer paths (2200kms+). For example when do you hear 4X/5B at the same strength as Italians or EH stations (from G).

• The time frame for a particular direction (target area) is predictable.

• Directions are predictable.

• Slow rise and fall times of events and gentle QSB rates.

The "Sporadic" openings are usually characterised by the following...

• 1) Usually very strong and short paths (300-2000kms) at S9++.

• 2) The time frames are not predictable.

• 3) The directions are not predictable (sporadic).

• 4) Fast rise and fall times of events and very deep QSB rates.

The old rule of HF Sporadic E states that as the skip shortens, the MUF must rise (e.g. if the skip is short on 28 or 50MHz the MUF could be at 144MHz). I believe this to be largely false. From my observations, when Sporadic E is present the same target zone from a given location is present at all frequencies up to the MUF/MOF. (opening on 12/06/93 with OK on 28/50/144MHz or 12/05/93 with SV on 50 & 144). With E layer propagation it would appear that the rule is valid - most obvious when the signals to North America decline, if not disappear on 28MHz, at the times when the band opens on 50MHz, much the same as F layer propagation. I believe that we are, for the most part, unable to see (hear) the E layer propagation, which is bringing in the weak long range signals due to the very strong Sporadic E signals that are masking them. There are exceptions to this, giving us a clue to what is occurring. One of these events is the occurrence over the last few years (totally due to the fact that amateurs are now QRV) of the path to 9K, which is workable through the QRM from I/YU etc. Other openings are those deep into Russia (mainly TV), North America, the openings to the Caribbean and those to ZD8. The last three have the advantage of not too many intermediate areas of high density amateur activity.

The HF model of E layer height (sporadic or otherwise) at 110-120kms does not allow a single hop to account for these longer distances and therefore encourages us to believe that multiple hops are the obvious answer. We always look for simple answers to problems and usually find them. I believe that we just have to accept that both the E and sporadic E layer propagate at various heights up to 1000kms. This is supported by information I have seen in other articles - at any rate why should it not be so simple? Over the past 3-4 years I have had many discussions with Roger (G4HBA), we feel that most of the main, long distance propagation can be explained by accepting three components, two of which have been observed (1 &3 below).

• The bulk of events occur on the grey line.

• We assume that the height of the layer is above 110 kms.

• The path is at nearly 90 degrees to the grey line.

Figure 1.

We have used a term between us to describe a situation that we can easily visualise. We call this event "Mare’s tails". This is easy to visualise - just think of the very high cirrus clouds we see in the Troposphere - these are named Mares tails. The important fact is the layer gradually increases in height and splits into 2, or more "tails" (Fig 1). Let us examine some examples.

Take the path from southern UK to 9K. With observations so far this path would seem to occur very reliably between 1600-1700 (1500-1800 at the extremes). At this time the grey line is between SV and 4X and is at 90 degrees to the path. Under the old model of E layer propagation this path would either a) not be possible or b) only be explained by the very accurate lining up of at least 2 clouds or reflecting zones within the layer at just the right point. Are we to believe that this occurs regularly at the same time? It is clear that for any individual, his target point in the E layer is extremely small, so for two points to line up accurately to provide a very long path is asking a lot. The most logical explanation is that as the earth turns, the effect of the sun at E layer height (110 kms) is at a range of approx. 1250 kms. As the sun sinks on the active layer the active area rises and tries to catch the sun (or the sun drags the active area higher). This is what happens to the F layer at sunset so why should it not happen to the E layer? We believe that the layer both rises and splits into a number of distinct areas/reflecting points that allows a range of extensions from 2500 - 5000km+ (fig 2).

Figure 2.

If we look at another direction - from southern UK, to North America - a similar pattern emerges. The main time frame is 2000-2300, this coincides with the onset of sunset and the grey line moving over the UK. Of interest is the observation that between about 1800-2100 9H and I can be heard working North America over our heads (sometimes weak signals are detected) this is well after grey line has passed over them. At times signals from North America have been heard as late as 0100 - this is sunset in VE land! - again well after the passing of the grey line. One unusual observation noted is from our end the target area is quite small (some of this may be due to amateur activity of course) but from the other side the target area is large. For example Bob, VE1YX can be heard working into OK/ON/G/F/DL/SM and all in the space of a couple of minutes (see fig.2). We believe that the following is happening. From Bob’s viewpoint, he is able to "see" 2,3, or 4 of these "tails" which therefore bring in 2,3 or 4 areas at the same time, whereas from our side we can only see one of these tails at any one time, but as the grey line moves, so another comes into view, which moves the target area further west. It would also appear that, when looking from west to east the reflecting area diverges the signals into a cone/triangular shaped area whereas looking from east to west the signals are converged. Perhaps this is a function of the tilting of the "tails"? - the focusing/lens effect noted by other observers. These are our thoughts for the present which we are building on and with your help and comments you can see if our observations are accurate. Remember that we are in southern UK, but we believe similar effects should occur, with minor modifications, anywhere dependent on the amateur population in the target range.

On the subject of night time Es, I suggest that although the sun may have set at a location, as far as the E layer is concerned it is still daylight, or in a few extreme cases the E layer is so excited, it does not have time to die. We look forward to any comments that you may wish to make, either to my home address (G4IGO QTHR 1994) or through the pages of Six News. May I thank Roger G4HBA, John GW4LXO, Lyn GW8JLY in particular and many other locals (and not so) for their views and observations over recent years.

73 Ken, G4IGO

UKSMG Six News issue 42, July 1994