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
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
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)
Directions are predictable.
Slow rise and fall times of events and gentle QSB rates.
The "Sporadic" openings are usually characterised by
1) Usually very strong and short paths (300-2000kms) at
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
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.
We have used a term between us to describe a situation that we
can easily visualise. We call this event "Mares
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).
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 Bobs 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