E-Layer Ionisation On 80m
QRP Hours Contest held on the night of 14 April 2012, conditions
on the 80m amateur radio band were not ideal for QRP operation (ie
low power operation where the transmitter output is 5W or
less). A number of stations reported in their contest logs
that received signals exhibited deep fading, and receive noise
levels were high. Ionospheric soundings taken at the time in
the Australasian region suggest that these adverse conditions were
possibly due to sporadic E-layer ionisation.
This page examines the ionospheric
conditions prevailing during the contest period. As an
introduction, it also examines the means
by which ionograms are generated, and identifies the components shown
on an ionogram taken during the QRP Hours Contest. The
sporadic E on radio communications are discussed, and the extent of sporadic E reported in the
Australasian region during the contest period is examined.
Finally; the page looks at an example of a phenomenon
known as "E-layer screening", followed by references for further reading.
Back to Miscellaneous Technical
conditions during the QRP Hours Contest
The ionogram in Figure 1 below
shows the ionospheric conditions present above Hobart at 1105 UTC
on Saturday 14 April 2012, during the QRP Hours Contest conducted
on the 80m amateur radio band. The discussion which follows
examines how an ionosonde operates and how it generates an
ionogram, and what this particular ionogram can tell us about the
ionosphere and resulting propagation conditions prevailing on that
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||Figure 1 - Hobart Ionogram for 1105 UTC on 14
April 2012. This ionogram was obtained
from the Ionospheric
Prediction Service (IPS) website. Like
many of IPS's ionosondes, the one in Hobart generates an
ionogram every five minutes. A means of generating an
ionogram like this one, and how to understand the
information it contains, is explained below.
like that shown in Figure 1 above is a record generated by a Vertical Incidence (VI) Ionosonde,
which is a vertical-sounding radar sweeping in frequency from
about 1.7 MHz up to around 17 MHz. The radar emits a pulse
of energy upwards and measures the time taken for it to reflect
(actually refract) off an ionospheric layer and return to the
radar receiver. Figure 2 below shows the concept - for ease
of depiction, the radar is shown having separate transmit and
technique to determine the height of the ionospheric layer is
relatively simple. The time taken from when the ionosonde
transmits the pulse and subsequently receives it is called the Round-Trip Time (RTT). The RTT is quite
short - in the order of milliseconds. The Round-Trip Distance (RTD) -
the distance from the ground up to the ionospheric layer and back
down to the ground - can be calculated using the RTT and the speed
of light in the atmosphere. In radio terms, much of the
atmosphere traversed by the radio wave (the troposphere,
stratosphere, and neutral or non-ionised regions of the
ionosphere) is considered "free space", so the value of 300 000 km
per second is used. The RTD, and resulting Virtual Height (H) of the
ionospheric layer, are calculated as follows:
2 - The Vertical Incidence Ionosonde. This
simplified depiction of a VI ionosonde shows the
transmitter (Tx) sending a signal upwards into the
ionosphere, which is reflected from the ionospheric
layer and returned to the receiver (Rx). If the frequency is too
high, the radar pulse will penetrate the ionospheric
layer and continue into space - the frequency at which
this just occurs is termed the "critical frequency" for
that ionospheric layer.
The height is "virtual" because it is somewhat different from the
physical height of the ionospheric layer. As stated above; in radio terms,
much of the atmosphere traversed by the radio wave is "free
space". * However; the radio wave propagates more slowly
in an ionospheric layer (that is, its speed is less than 300 000
km/s) than it does in the rest of the Earth's atmosphere;
therefore the time taken by the radar pulse from leaving the
transmitter to arriving at the receiver will be slightly longer
than if the radar pulse did not traverse an ionospheric
layer. The ionogram is a graph of virtual height versus
frequency - it plots the virtual height for each pulse frequency
transmitted by the ionosonde as it sweeps across its frequency
range (approximately 1.7 to 17 MHz). This form of ionogram
is known as a Virtual Incidence
Ionogram, abbreviated to VI ionogram.
* The term "free space" applied to
radio waves means that the matter within a given region does not
change the speed, direction, polarisation, amplitude or other
characteristics of the wave. For high frequency (HF)
radio, the troposphere and stratosphere can be considered to be
"free space". An ionospheric layer is not free space
because it consists of free electrons and positive ions - also
known as a "plasma" - which affect the characteristics of the
radio wave. For example; an electron can be excited by a
radio wave, and as a result it may collide and recombine with a
positive ion to form a neutral atom or molecule - the energy
imparted to the electron is lost from the radio wave,
effectively resulting in attenuation of the radio wave, albeit
by a small amount. However, if enough electrons collide
with enough ions due to excitation, then the attenuation of the
wave may be significant. Also, the Earth's magnetic field
is present in an ionospheric layer, which means the plasma is
"anisotropic" - this means the speed at which the radio wave
propagates in the plasma will depend on the direction in which
the wave is travelling.
ionisation density in an ionospheric layer is strong enough to
reflect the radar pulse back towards the ground with sufficient
energy that it reflects off the ground and back up to the
ionospheric layer. If the pulse survives a second reflection
from the ionospheric layer then it can be received by the
ionosonde's receiver. In this case, the ionosonde does not
distinguish between single and double hops, so it reports the
virtual height as being double the virtual height of the actual
layer. Triple hops and even higher are possible. The
figures below illustrate the concept.
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3 - Double Hop Reflection. The signal
transmitted by the VI ionosonde can reflect from the
ionospheric layer, return to Earth, reflect from the
Earth and ascend again towards the ionosphere, reflect
again from the ionospheric layer, and return to the
receiver. In such a case, the calculated virtual
height of the ionospheric layer is twice the single hop
virtual height because the round-trip time is twice that
of the single hop.
4 - Triple Hop Reflection. This is
similar to the double-hop reflection case, only an
additional hop including an Earth reflection and
ionospheric layer reflection occurs. In this case,
the calculated virtual height of the ionospheric layer
is three times the single hop virtual height because the
round-trip time is triple that of the single hop.
Deciphering the ionogram
the basic knowledge of VI ionosonde operation, and how the
ionosonde does not distinguish between pulse returns based on the
number of hops, we can now look again at the ionogram shown in
Figure 1. At first glance, it still looks like a somewhat
confused mess of traces. The first step to deciphering the
information presented is to identify what are actual ionospheric
layers, and what are "phantoms" ** due to multi-hop reflections
like those shown in Figures 3 and 4. This section of the
discussion does exactly that, and then looks at some very
interesting reflections involving both layers.
** The traces arising
from these reflections are referred to here as "phantoms"
because they do not represent actual ionospheric layers - they
represent apparent layers, as shown in the discussion below.
real ionospheric layers please stand up?
only two actual ionospheric layers shown in the ionogram: a
typical night-time F-layer, and a sporadic E-layer. To
illustrate these, the ionogram shown in Figure 1 above is overlaid
with a mark-up showing these layers in Figure 5.
||Figure 5 - Hobart Ionogram for 1105 UTC on 14
April 2012 with sporadic E-layer (Es) and typical
night-time F-layer (F) highlighted. The
highlighted traces represent the actual ionospheric
layers depicted on this ionogram - the other traces are
"phantoms" arising from multi-hop reflections, which are
reflections from individual layers
Now that the
actual layers are identified, it is quite easy to identify the
multi-hop reflections arising from those layers individually
(which occur as shown in Figures 3 and 4 above). These are
shown for the Es- and F-layers respectively in Figures 6 and 7
below - these figures are shown side-by-side to allow ready
comparison between multi-hop Es- and F-layer returns.
6 - Sporadic
Reflections. The actual sporadic E-layer,
and the double and triple hop phantoms (designated
respectively as "2Es" and "3Es"), are shown highlighted
in this mark-up of the Hobart ionogram for 1105 UTC on
14 April 2012.
7 - F-layer
The actual F-layer and its double hop phantom
(designated as "2F") are shown highlighted in this
mark-up of the Hobart ionogram for 1105 UTC on 14 April
reflections involving both layers
Figures 6 and
7 together show two traces on the ionogram as actual ionospheric
layers, and a further three traces as phantoms of the individual
Es- and F-layers arising from multi-hop propagation between the
ionosonde and the ionospheric layers. This leaves two traces
- both are situated at heights between the F-layer trace and its
double hop phantom. The lower (fainter) of these traces looks
like a weak replica of the F-layer trace; while the higher of these
traces looks very similar to the F-layer double hop phantom.
This description gives a clue as to how these traces arise.
The lower of these two traces will be dealt with first.
the Es-layer is so strongly ionised that the F-layer above it is
not visible - this phenomenon is known as E-layer screening.
However; this is not the case for the ionogram being examined here
- the Es- and F-layers can be clearly discerned. Obviously
the radar signal is penetrating the Es-layer to reach the F-layer
- this raises the question of whether it is possible for the radar
signal to undergo a double hop involving the two layers and the
Earth's surface before returning to the ionosonde receiver.
Figure 8 below examines two such propagation mechanisms, while
Figure 9 highlights the result in the ionogram - these figures are
shown side-by-side to allow ready comparison between the
propagation mechanism and the corresponding result on the
8 - Double Hop Reflection From Es- and F-layers.
As shown in the left-hand side of the diagram, the
signal transmitted by the ionosonde can reflect from the
Es-layer, return to Earth, reflect from the Earth and
ascend again towards the ionosphere, reflect again from
the F-layer, and return to the receiver. The
right-hand side of the diagram shows the converse
case. In both cases, the calculated virtual height
of the phantom ionospheric layer is the sum of the
virtual heights of the two layers.
9 - Es- and F-layer
The actual Es- and F-layer traces, and the double hop
phantom arising from the combination of single hop
reflections from the Es- and F-layer (designated as
"Es+F"), are shown highlighted in this mark-up of the
Hobart ionogram for 1105 UTC on 14 April 2012. The
height of the "Es+F" phantom trace is equal to the
virtual height of the Es-layer trace shifted upwards by
the virtual height of the F-layer trace; or conversely
virtual height of the F-layer trace shifted upwards by
the virtual height of the Es-layer trace.
The explanations of the multi-hop phenomenon in Figures 8 and 9
leaves only the higher remaining phantom trace to
account for. As stated above, this phantom
trace looks very similar to the F-layer double hop phantom, only
its virtual height does not match a multi-hop phantom of that
layer. The mechanism by which this trace arises is shown in
Figure 10 below, while Figure 11 shows the result on the ionogram
figures are shown side-by-side to allow ready comparison between
the propagation mechanism and the corresponding result on the
10 - Reflection Between Es- and F-layers.
The signal transmitted by the ionosonde can pass through
the Es-layer, reflect from the F-layer, return to
Es-layer and reflect from that, ascend again to the
F-layer and reflect from that, descend through the
Es-layer and return to the receiver. In this case,
the calculated virtual height of the phantom ionospheric
layer is the virtual height of the F-layer summed with
the difference of the virtual heights of the F- and
Es-layers. This virtual height is equivalent to
twice the virtual height of the F-layer minus the
virtual height of the Es-layer.
11 - Multi-hop Reflections between Es- and F-layers.
The actual Es- and F-layer traces, and the multi-hop
phantom arising from the reflections from the F-layer to
Es-layer and back to the F-layer (designated as
"2F-Es"), are shown highlighted in this mark-up of the
Hobart ionogram for 1105 UTC on 14 April 2012. The
"2F-Es" phantom trace height is equal to the height of the F-layer double hop
phantom trace shifted downwards by the virtual height of
the Es-layer trace.
it all together
examined the traces for the actual ionospheric layers - with their
individual multi-hop reflections and the reflections involving
both layers as shown in Figure 12 below - all of the traces can be
identified on the ionogram in Figure 13 below.
Figure 14 below
contains the virtual height data for the Es- and F-layers measured
directly from the ionogram shown in Figure 1 (this is easily
obtained by using the Ionogram Viewer on
the IPS website); and the computed height data for all other
traces depicted in Figure 13 above.
12 - Composite of all Reflections. The
signal transmitted by the ionosonde follows many
different propagation paths between the ground and the
ionospheric layers, and between ionospheric
layers. The horizontal distance between the
transmitter and receiver is exaggerated in order to show
the various propagation paths. The colours for
each path correspond to the resulting traces shown on
the ionogram mark-up in Figure 13.
|Figure 13 - Hobart Ionogram for 1105 UTC on 14
April 2012 with all traces highlighted.
The highlighted traces are presented using the same
colours and designations as shown in the figures above;
and the trace order shown in the legend on the
right-hand side is the same as the height order of the
traces shown in the ionogram.
are example calculations for the phantom trace
virtual heights at 2.0 MHz, using the Es- and F-layer virtual
heights of 106 km and 238 km respectively, as shown in Figure
|Figure 14 - Tabulated virtual height data for
the Hobart Ionogram at 1105 UTC on 14 April 2012.
The Es- and F-layer data was measured directly from the
ionogram at the approximate vertical centre of each
layer for each of the frequencies shown in the
figure. All other trace data, ie for the 2Es, 3Es,
Es+F, 2F-Es and 2F phantoms, was computed from the Es-
and F-layer data. The grey areas represent
frequencies at which the data was not present on the
ionogram for the actual ionospheric layers, or not
computed for the phantom traces. The measured Es- and F-layer data was entered into a
Microsoft Excel workbook; this data and the resulting
calculated virtual heights for the phantom traces were
plotted on charts overlaying the ionograms, thus
generating the marked-up ionograms shown on this
page. The computed trace data shows extremely good
correlation with the phantom traces shown on the
ionograms, as evidenced by the mark-ups shown in the
various figures. The colour coding for the
tabulated virtual height data is the same as the
corresponding trace highlight colour used in the marked-up ionograms.
results, as well as the other phantom trace virtual heights shown
in Figure 14, can be compared with the respective heights plotted
in Figures 6, 7, 9 & 11; or Figure 13.
- 2Es virtual height = 2 x Es virtual height = 2 x 106 = 212 km.
- 3Es virtual height = 3 x Es virtual height = 3 x 106 = 318 km.
- 2F virtual height = 2 x F virtual height = 2 x 238 = 476 km.
- Es+F virtual height = Es virtual height + F virtual height =
106 + 238 = 344 km.
- 2F-Es virtual height = F virtual height + (F virtual height -
Es virtual height) = 238 + (238 - 106) = 238 + 132 = 370
km. (Alternatively: 2F-Es virtual height = 2F virtual
height - Es virtual height = 476 - 106 = 370 km.)
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The impact of
sporadic E on night-time radio communications in the 80m band
section we will examine the effect of sporadic E on some typical
amateur radio communications paths used on 80m at night, and
also examine the effect of the sporadic E-layer critical
frequency (abbreviated to foEs).
ionogram in Figure 1 shows that radio signals propagating from
the ground can reach both the Es- and F-layers, because E-layer screening
is not occurring. For a given radio communications
circuit operating during the ionospheric conditions recorded
in the ionogram; signals emitted by the transmitter can be
reflected by the Es-layer; and also can pass through that
layer to be reflected by the F-layer, where they can pass
through the Es-layer again to reach the ground. This has
implications for signal propagation over multiple paths
simultaneously, which in turn means signals received via
multiple paths can reinforce or cancel depending on the
electrical lengths of those paths.
understand the impact of sporadic-E ionisation, we can consider some radio
communications circuits which are representative of those
routinely used by amateur radio operators for "local"
communications at night on the 80m band. Figures 15, 16,
and 17 below show 1500 km and 500 km circuits using antennas which
provide low, medium and high take-off angles. Each figure
shows a typical propagation path under normal conditions (ie, when
sporadic-E ionisation is not present), and possible propagation
paths which are open when sporadic-E ionisation is present.
Note that there are literally infinite possible propagation paths
- the actual path or paths taken depend on factors such as the
antenna gain patterns at the transmitter and receiver, the
ionisation densities in the Es- and F-layers, the distribution of
ionisation densities in the layers (ie do the densities and
therefore the critical frequencies vary along the paths), the
presence or absence of layer "tilts", and so on.
Accordingly, the propagation paths presented in Figures 15, 16 and
17 are merely a subset of such paths selected to illustrate some
effects of this form of ionisation. Each of these figures is
a scale drawing using the ionospheric layer height data for 3.6
MHz as determined from Figure 1 above.
effect of signals propagating via paths supported by the Es- and
F-layers is of particular interest. In Figures 15, 16
and 17 above; note that the take-off angles for the Es- and
F-layer reflections are similar, so the transmitting and receiving
antennas cannot distinguish between these propagation paths.
If the signal
arriving at the receiver via the F-layer path is in-phase with the
signal (or signals) arriving via the Es-layer path (or paths),
then the received signals will reinforce - at the receiver, the
radio operator will hear a relatively strong signal.
Conversely; if the signal arriving at the receiver
via the F-layer path is anti-phase with the signal (or signals)
arriving via the Es-layer path (or paths), then the signals will
cancel - at the receiver, the radio operator will hear no
signal. Slight changes in the virtual heights and ionisation
densities of the two layers result in changes in the electrical
lengths of the Es- and F-layer signal paths, which in turn means a
set of paths resulting in signal reinforcement may change to
producing signal cancellation, and vice versa. This means
the received signals will reinforce then cancel then reinforce,
and so on, over a period of time - this manifests itself as the
deep fading (QSB) with periods of minutes which can be experienced
on the 80m amateur radio band at night when sporadic E ionisation
|Figure 15 - 1500 km circuit
at 3.6 MHz using low take-off angle. The
yellow trace shows a single hop propagation path under
normal conditions, when only the F-layer is present,
serving the 1500 km circuit between the transmitter
(Tx) and receiver (Rx). The low take-off angle for
this path is typical of that exhibited by a vertically
polarised antenna (eg a 1/4 wavelength monopole, also
known as a "groundplane" or "vertical" antenna in
amateur radio parlance). The red trace shows a
possible double hop propagation path when sporadic E
ionisation is present.
||Figure 16 - 1500 km circuit
at 3.6 MHz using moderate take-off angle.
yellow trace shows a double hop propagation path under
normal conditions, when only the F-layer is present, serving the 1500 km circuit between the transmitter
(Tx) and receiver (Rx). The moderate take-off
angle for this path is typical of that exhibited by a
horizontally-polarised antenna (eg a 1/2 wavelength
dipole) installed at a height less than 1/2 wavelength
above the ground. The red trace shows a possible
double hop propagation path when sporadic E ionisation
|Figure 17 - 500 km circuit
at 3.6 MHz using high take-off angle. The
yellow trace shows a single hop propagation path under
normal conditions, when only the F-layer is present, serving the 500 km circuit between the transmitter
(Tx) and receiver (Rx). The high take-off angle for
this path is typical of that exhibited by a
horizontally-polarised antenna (eg a 1/2 wavelength
dipole) installed at a height of approximately 1/4
wavelength or less above the ground. The red and
orange traces show two separate, possible double hop
propagation paths when sporadic E ionisation is present.
complicated view (the effects of angle of incidence and critical
It was stated earlier that the
highest frequency at which the radar pulse from the
vertical-sounding ionosonde is reflected from an ionospheric layer
is termed the "critical frequency" for that ionospheric
layer. A simplistic view of the effect of sporadic E
ionisation on communications using the 80m band could consider
this phenomenon not to be a problem if the critical frequency foEs
is below 3.5 MHz (the lowest frequency in the 80m amateur radio
band). However; this is not necessarily the case. It is possible
that sporadic E-layer ionisation having a critical frequency less
than the frequencies in the 80m amateur radio band can cause
problems for communications circuits using that frequency
band. To understand why, it is useful to examine the
relationship between Maximum
Usable Frequency (MUF) and the critical frequency (fc)
for an ionospheric layer as shown in Figure 18. This
approach may seem counter-intuitive at first, as we're trying NOT
to use the sporadic E layer ionisation in this case, so why would
we be interested in its MUF? It turns out that this same
relation can be used to determine the maximum frequency at which a
radio signal will be reflected by sporadic E layer ionisation.
Using the relationship between MUF, critical frequency
(fc), and the angle of incidence ('theta') presented in Figure
18 above, we can examine what minimum critical frequency, or
foEs, the sporadic E-layer must have at the ionospheric
reflection point in order to cause possible problems for
communications using the 80m band.
||Figure 18 - Simplified path geometry for an
ionospheric hop. The maximum usable
frequency (MUF) is dependent on both the critical
frequency (fc) and the angle of incidence
(designated by the Greek letter "theta"). The
angle of incidence is the angle between the incident ray
path and a line perpendicular to the ionospheric layer
and passing through the highest point that the radio
signal reaches into the ionosphere, and is larger for
longer distances between the transmitter (Tx) and
receiver (Rx). For a given critical frequency, the
MUF increases as the angle of incidence increases; or,
for a given angle of incidence, the MUF changes in
direct proportion to the critical frequency.
In Figure 15; the angle of incidence for the E-layer
reflection point is approximately 71°; the cosine is
0.321, and the secant ('sec') of this angle is 3.1. For
an E-layer MUF (Emuf) of 3.6 MHz, foEs is only approximately
1.2 MHz! This will not appear on an ionogram, because
the ionosonde does not transmit at such a low frequency.
For Figure 16, where the E-layer reflection point is a
"topside" reflection point, the angle of incidence is
approximately 50°; and the secant of this angle is
1.6. For an Emuf of 3.6 MHz, foEs is only approximately
2.3 MHz. This will appear on an ionogram (strictly
speaking, one would need to refer to a topside ionogram
produced by a topside sounder carried on a satellite, assuming
that the sounding signal could penetrate the F-layer), but is
obviously lower than the frequencies in the 80m band.
In Figure 17, there are two angles of incidence at the E-layer
- the traditional bottomside reflection point and a topside
reflection point. The respective angles of incidence are
approximately 46° and 21°; resulting in secants of 1.4
and 1.1. The respective foEs values are 2.5 and 3.4 MHz
for an Emuf of 3.6 MHz.
It is worth noting that as the range between the transmitter
and receiver shortens, the angle of incidence decreases and
the secant of that angle decreases. This means the foEs
increases towards the operating frequency; with the limiting
case being NVIS propagation where the distance between
transmitter and receiver is so short that the angle of
incidence is approximately 0° (this would be the case
where the transmitter and receiver are separated by a mountain
range or similar geographical feature preventing ground wave
and/or direct line-of-sight propagation between the two
These calculations show that the maximum frequency at which
the sporadic E-layer returns a vertical incidence signal to an
ionosonde located under the reflection point for a propagation
path on the 80m band can be less than the 80m operating
frequency while still resulting in E-layer reflections.
The calculation for the longer distance path involving fewer
hops shows that in some cases the presence of an E-layer
capable of supporting 80m reflections may not show on the
ionogram because the foEs is below the minimum frequency used
by the ionosonde.
observations during weekly, early evening 80m CW and SSB nets
over approximately five years to May 2012 suggests that the
presence of sporadic E-layer ionisation affecting the 80m
amateur radio band is characterised by "sizzling" noise (QRN) up
to strength 9 as observed with some radio receivers, and the
deep and sudden fading (QSB) mentioned above. Also, it
appears that there have been more instances of sporadic E-layer
ionisation occurring in the south-eastern corner of Australia
during the 2011/12 (Southern hemisphere) spring / summer season
than in the previous years since 2006/07. This increased incidence
appears to be extending into the 2012 autumn season.
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Distribution of sporadic E-layer
ionisation during the QRP Hours Contest 2012
An idea of
the geographical spread of sporadic E-layer ionisation during
the QRP Hours Contest over the period from 1000 UTC to 1159 UTC
on 14 April 2012 can be gained by examining the map shown in
Figure 19 below. The following are summarised observations
of ionograms for each of the ionosondes shown in Figure 19,
starting at the most westward location and moving East:
As can be
deduced from the observations summarised above, and the map
showing the ionosonde locations below, the geographical
distribution of this sporadic E incidence was quite
extensive. Also, this incident occurred over a number of
hours, of which the contest period was merely two of them.
(Keeling) Island - sunset was at 1129 UTC, and reviewing the
around that time show that the E-layer cusp featured in the
daytime ionosphere had disappeared completely by 1135
UTC. This was replaced by E-layer ionisation extending
to approximately 3 MHz past 1200 UTC.
- sporadic E was observed from two hours before the contest
start until 1045 UTC. Prior to the contest, foEs reached
up to 10 MHz. After 1045 UTC, only a few incidences were
observed until 1345 UTC.
- Perth -
after sunset and recombination of the daytime E-layer,
sporadic E was consistently observed with a foEs of
approximately 2 MHz until 1130 UTC, when the foEs increased,
reaching 4.4 MHz at 1155 UTC, then decreasing again until no
sporadic E was observed at 1240 UTC.
- sporadic E was observed during approximately five hours
before the contest with foEs reaching a maximum of 16.5
MHz. By the contest start time of 1000 UTC, foEs had
fallen to 5.9 MHz. At times during the contest period,
the layer shown on the ionogram diverged into two layers, with
typical heights of 105 km and 135 km. The sporadic E
persisted until 1155 UTC, and didn't reappear until 1340 UTC.
- sporadic E was observed in the hours before the contest, but
was not observed during the first 20 minutes. Thereafter
it reoccurred from time to time, with foEs reaching
approximately 6 MHz, up to and beyond 1200 UTC.
- sporadic E was observed with foEs up to 5.9 MHz from sunset
up to the start of the contest, and was consistently presented
during the entire contest period.
- sporadic E was observed from sunset through to almost the
end of the contest.
- sporadic E was observed throughout the contest period.
- sporadic E was observed with foEs reaching 13.5 MHz from
sunset until the start of the contest. Sporadic E was
observed (albeit with lower foEs) throughout the contest
period and beyond.
Island - sporadic E was observed throughout the contest period
with foEs up to 7.9 MHz.
Island - sporadic E was observed before, during and after the
- sporadic E was observed before,
during and after the contest period.
- Niue -
was observed before, during and after the contest period.
An hour or so
after the QRP Hours Contest finished (at 1159 UTC); the sporadic
E-layer ionisation lived up to its "sporadic" name - the
propagation conditions experienced at Gundaroo, NSW, returned to
what would normally be expected for the 80m band at this time of
the year, and the author was able to work VK6 (Western Australia)
on SSB using 100W PEP output fed to the same antenna as that used
during the contest.
|Figure 19 - Map showing the distribution of
stations participating in the QRP Hours Contest 2012,
and some of the ionosondes in the IPS network. This
is a "Great Circle" projection centred on
Australia. The area encompassing the ionosondes
shown on this map at which sporadic E-layer ionisation
was observed during the contest period of 1000 - 1159
UTC covers approximately 93° of longitude and
42° of latitude, centred at 143°26'E 33°21'S
marked with a red-coloured cross (in south-western NSW).
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An example of
mentioned above that occasionally the sporadic
E-layer ionisation is dense enough to render the F-layer above
invisible on the ionogram; and this phenomenon is known as E-layer screening.
Figure 20 below shows a somewhat spectacular example of this.
Back to top
||Figure 20 - Canberra Ionogram for 0858 UTC on
16 February 2012 showing E-layer screening.
This VI ionogram recorded by the IPS ionosonde in
Canberra, just before 7 pm Australian Eastern Standard
Time (AEST), shows the sporadic E-layer ionisation at a
virtual height of approximately 115 km, reflecting
vertical incidence signals at frequencies ranging from
approximately 1.7 MHz to 9.4 MHz. Only the lowest
trace represents an actual ionospheric layer - all other
horizontal traces are phantoms due to multi-hop
reflections between the Es-layer and ground. The
ionisation density is sufficient for the ionosonde to
detect the quintuple hop reflection (ie the radar return
due to the pulse bouncing five round-trips between the
Earth and E-layer and back) giving rise to an
approximate virtual height of 575 km. The typical
early evening / night-time F-layer cannot be seen on the
ionogram, even though it actually exists - it is
completely screened from ground-based radar signals by
the densely-ionised E-layer.
references listed below are recommended for readers wanting to
learn more about the ionosphere and how it supports high frequency
(HF) radio wave propagation.
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Government - Bureau of Meteorology - IPS Radio and Space
Services Educational webpage.
to HF Radio Propagation, Australian Government - IPS Radio
and Space Services.
- HF Radio Propagation - Course
Manual, IPS Radio and Space Services,
Australian Government. (I obtained my copy upon
attending IPS's HF Radio
Course. I believe manual this can be ordered
from IPS via their website.)
- The NEW Shortwave Propagation
Handbook; George Jacobs, W3ASK, Theodore J. Cohen,
N4XX, & Robert B. Rose, K6GKU; CQ Communications, Inc;
Hicksville, New York; 1995; ISBN 0-943016-11-8.
- Radio Amateurs Guide To The
Ionosphere; Leo F. McNamara; Kreiger Publishing
Company; Malabar, Florida; 1994; ISBN 0-89464-804-7.
- Ionospheric Radio, IEE
Electromagnetic Wave Series 31; Kenneth Davies; Peter
Peregrinus Ltd; London, UK; 1990; ISBN 0-86341-186-X. (This
is an excellent reference for those at the scientific and
page was created by Mike Dower VK2IG: 30 May 2012; last
updated: 31 May 2012. Material may be copied for
personal or non-profit use only.