This website relates to the recreational
pastime of Amateur Radio, promoting the science of
experimental radio communications & related technology,
founded by Guglielmo
Marconi, in 1895.
This website was created, on 1st September
2000, by Philip G0ISW to assist other UK & overseas
Radio
Amateurs to experiment, research and achieve VHF /UHF DX (long distance)
communications in the 50 MHz - 432 MHz range, as well as being a useful operatingaid having essential
propagation information on one page.....
It has for several years now also contained sections dedicated to
High Frequency (HF) Worldwide communications
in the 1.8 MHz - 30 MHz range.
As a visitor to this website please, please
Sign my
Guest Book, as I spend a considerable amount of time maintaining this
site. I really appreciate your positive comments, suggestions etc. Your
Guest Book entries greatly help to maintain my enthusiasm for continuing
this task for over 12
years!
I've had to create a
new Guest Book due to the old Lycos/Tripod service closing down on
01.04.2012.
73 de Philip G0ISW
Operator:
Philip
QTH: Penrith/The Lake
District/Cumbria/IO84OQ
EchoLink Node:
3116 at home or G0ISW/M using iPhone
Worldwide!
Very High Frequency (VHF) and Ultra High Frequency (UHF)
Amateur Radio signals
in the frequency bands
50 MHz, 70 MHz, 144 MHz, & 430 MHz are predominantly 'line of sight',
typically short range and are blocked easily by obstacles such as mountains or
buildings. Using experimental techniques and 'enhanced propagation' it is possible to send
these signals over thousands of kilometres and even to reflect them from Meteors,
Auroras,
Aircraft, Satellites or the
Moon.
This site will show you how.
Please do not attempt to connect to the
old International Space Station Packet BBS system, callsign RS0ISS-11, as you
will block the whole pass for all other European stations who can digipeat only
if the BBS is not being used. The BBS was established many years ago before the
advent of e-mail, the crew do not read it, and in order to obtain a QSL card
from the ISS you only have to now digipeat through it using the callsign
RS0ISS-4.
If you cannot see the full
index shown on the left edge of your screen, please go to my main page athttp://www.qsl.net/g0isw
The section below is designed to be a single
page at-a-glance indicator of current VHF / UHF Propagation conditions,
particularly useful if just home from work or to monitor whilst in your shack.
Different propagation modes enable VHF/UHF signals to travel further than
normal 'line
of sight'
because they are reflecting your signals from different heights, above sea
level, in the Earth's atmosphere.
Tropo Scatter
takes place below
10,000m (10km)
height (Mt. Everest is by comparison
8,850m
high), whereas the majority of
Meteor Scatter takes place at
90km altitude and
Sporadic Escan be up to
110km height, allowing much greater distances to be achieved.
The
exception is
Tropo Ducting,
between 450-3000m
height asl, where the signals are trapped between layers of hot and cold air (temperature
inversion) and if over a good calm sea path may extend for huge
distances. Contacts between Scotland and the Canary Islands on
144MHz
have been achieved this way.
Why
are
Auroral signals shown to typically achieve a lesser distance than
Meteor Scatter even though the reflection takes place at a greater height
in the Atmosphere? They do actually travel further reflected off the Auroral
curtain near the Arctic and back again, but the receiving station may be a lot
closer to you in Europe.
The International space Station and the
Space Shuttle are both over
200km
in height.
This is
the mode by which most of your local 144/432 MHz
FM
simplex conversations will be made, either direct to stations or via
repeaters.
Dependant upon
antenna height above sea/ground level and visible radio horizon distance. Line
of sight (LOS) distance can be increased with height or decreased by
obstructions such as mountains, buildings etc.
Line
of sight is the direct free-space path that exists between two points. Using
binoculars on a clear day, it is easy to determine if visual line of sight
exists between two points that are miles apart. To have a clear line of
sight there must be no obstructions between the two locations. Often this
means that the observation points must be high enough to allow the viewer to
see over any ground-based obstructions.
The following
obstructions might obscure a visual link:
Topographic
features, such as mountains
The curvature of
the Earth
Buildings and
other man-made objects
Trees
If
any of these obstructions rise high enough to block the view from end to
end, there is no visual line of sight.
Obstructions
that can interfere with visual line of sight can also interfere with radio
line of sight.
But one must also consider the Fresnel effect. If a hard object, such
as a mountain ridge or building, is too close to the signal path, it can
damage the radio signal or reduce its strength. This happens even though the
obstacle does not obscure the direct, visual line of sight. The Fresnel zone
for a radio beam is an elliptical area immediately surrounding the visual
path. It varies in thickness depending on the length of the signal path and
the frequency of the signal.
As
shown in the picture above, when a hard object protrudes into the signal
path within the Fresnel zone, knife-edge diffraction can deflect part of the
signal and cause it to reach the receiving antenna slightly later than the
direct signal. Since these deflected signals are out of phase with the
direct signal, they can reduce its power or cancel it out altogether. If
trees or other 'soft' objects protrude into the Fresnel zone, they can
attenuate (reduced the strength of) a passing signal. In short, the fact
that you can see a location does not mean that you can establish a quality
radio link to that location.
There are several
options to establish or improve the line of sight:
·Raise the
antenna mounting point on the existing structure
·Build a
new structure, i.e. radio tower.
·Increase
the height of an existing tower
·Locate a
different mounting point, i.e. building or tower, for the antenna
Your LOS signal, which can be blocked by
high terrain can sometimes be diffracted or bent over the top of the
obstruction, particularly in mountainous areas if the top of the obstruction
is 'sharp', hence the term 'Knife-edge diffraction'.
I live in a mountainous area and have
experienced a few instances where contacts have been made with stations that
should have been totally obstructed by high mountains in between.
This propagation mode is available all the time and is the main one for longer
contacts, particularly at 144 MHz on SSB within
the UK or to mainland Europe. Slow fading of signals often apparent and
reasonable signal strengths.
This
propagation mode was used by NATO, from around 1956 to the late 1980's, as
part of the ACE HIGH
Troposcatter system on frequencies between 832 MHz
and 959 MHz, in a chain of
49 stations running
from Norway to Turkey. Transmitting power was around 10 KW and huge dish
antennas were used!
I
remember seeing the huge dishes at
Cape Greco (JCGZ) in
SE Cyprus in the late 1980's, but am struggling to find any photos of them
apart from this one.
Looking at Google Earth imagery below, from 2003, it appears the dishes have now
been removed.
Aircraft scatter propagation is subject to rapid fading of signals and not particularly easy to catch or use.
You can liken it to bouncing your radio signals off the metal aircraft body,
which will be travelling extremely fast, in the same way you would bounce
light off a mirror.
RADAR (Radio Detection And Ranging) has used radio signals since before WW2
to determine the flight path of aircraft. Early German WW2 radar used
frequencies near to the amateur 144 MHz band.
Modern stealth aircraft such as the US Air Force F-117 were designed so that
their shape would not easily reflect Radar signals back to the receiving
station, by avoiding having any vertical angles.
Some experimentation has been done by
SM6FHZ and his
website detailing how to work regularly via this mode, using flight
timetables is here.
Frequencies of 144 MHz,
432 MHz and 1296 MHz have all been used
successfully. Some imagery and an explanation of how you can experiment to
listen yourself can be found on the website of
G3CWI here.
Aurora favours Northern
Europe. March is often a good month. You need to point your antenna between
North and East and reflect your signal off the moving Auroral curtain.
Speak much slower than normal and
compensate for the Doppler shift, which makes everyone sound like Daleks!
50 MHz is particularly good for this mode,
144 MHz is useable and
432 MHz is extremely difficult due to the high Doppler shift.
Field
Alignment Irregularities (FAI), can occur in the late afternoon from
May to August, and favour Southern Europe. The signal is usually
very weak and the scatter area is located at a height of approximately
110km.
During
exceptional VHF openings some amateurs worked DX stations located
8000 km away crossing the Equator. Imagine:
From Southern Europe to South Africa on 50MHz
or even 144MHz ! This phenomenon seems to occur
when both stations are located at equal distances North and South of the
Equator and experiencing a high level of electron density in Autumn and
Spring, during periods of solar maximum activity and the equinoxes.
The
stations located over 45° of latitude north (or south) are usually too far
off the geomagnetic equator to make use of F-layer FAI. Sometimes however,
these latitudes can be worked via an additional sporadic-E hop, even if
signals are usually weak and typically exhibit the fluttery and hollow like
sound of pure FAI.
It was
observed that there were two distinctly different types of TEP that could
occur:
The
first type occurred during the late afternoon and early evening hours and
was generally limited to distances under 6000 km.
Signals propagated by this mode were limited to the low VHF band (<60
MHz), were of high signal strength and suffered moderate distortion
(due to multipath). Single sideband voice communications were possible with
this mode.
The
second type of TEP occurred from around 1900 to 2300 hours local time.
Contacts were made at 144 MHz, and even very
rarely on 432 MHz.
The
signal strength was moderately high, but subject to intense rapid fading,
making morse code (narrow band CW) the only possible communication mode. One
amateur described the signal quality in the following words: "we tried SSB
but there was so much distortion that not a single word could be identified.
[this mode] has a lot of flutter and fading and ... even the morse comes
through like a breathing noise, not a clear tone" (from the Dawn of Amateur
Radio in the UK and Greece by Norman F Joly).
Signals can be quite strong. Look for periods of high air
pressure over the UK and Europe. Often extensive fog can indicate the right
conditions for this propagation mode. Once established paths can be open for
many hours or days. Often you may hear far away 144
MHz/432 MHz repeaters that normally cannot be heard.
Sea path possible
exceptionally up to 3000km on
144MHz SSB, paths between Scotland and the Canary
Islands have been worked.
October often
the best month.
These Ducts form at heights between 450m to 3000m, but are blocked by higher mountains along the
path. They require stable High pressure areas, fog can be a good indicator.
Select Europe map and then click on
site to view
readings. Gif image to 700mB best. Look for
temperature inversions, where the inversion thickness layer is
wide enough to support ducting at 144 &
432MHz, using the table below.
Not commonly useable by
radio amateurs. Ionoscatter is the scattering
of radio waves in the ionosphere due to irregularities in the electron
distribution, which causes changes in the refractive index. Scattering is most
pronounced in the D-region between 70 and 90 km and is best from
30-60 MHz.
Ionoscatter is a
propagation mechanism available 24H a day like meteor scatter, but it is
different from meteor scatter. Ionoscatter deliverer's a continuous weak
signal and does not have the characteristic bursts in signal strength of
meteor scatter.
Ionoscatter starts about
900 km and extends to almost
2,000 km. Troposcatter works on all frequencies
50 MHz to 10 GHz,
whereas Ionoscatter is only useable on 30-60 MHz.
NATOMilitary radio systems from around the years 1950-1960 used huge aerials and around 40kW of power to
maintain reliable signals via this mode! The Distant Early Warning Line
DEWLine
being a good example. Therefore it is rare for Amateur
Radio transmissions to be powerful enough to utilise this mode. The Military Ionoscatter system was replaced by Troposcatter systems
in the 1960's.
Summer months best for major showers, but winter months
active too. Random meteors occur all the time day or night. Can be a mode that
can revolutionise 50/144 MHz SSB contacts using WSJT
software for long distance contacts. My favourite mode!
Reflections of radio signals can last from around 250 milli seconds (1/4 of
a second) to 30 seconds plus, but the vast majority are extremely brief. It
usually takes a long time to complete a QSO in the region of 30 minutes or
an hour, unless there is a major Meteor shower such as the Leonids in 2001.
To easily hear Meteor
pings tune your transceiver to a strong VHF Band 1 TV station video carrier such
as 55.250 MHz CW and you will hear nothing, until the signal is
reflected briefly by a passing meteor! Please note that during the Summer
months
Sporadic E (Es)
may allow you to hear the TV carrier continuously.
The Spanish TV Transmitter shown above, closed down in 2010, but in 2011 the
TV Transmitter in Prague shown below is still active.
Unfortunately Band
1 analogue TV is being phased out in Europe and so the availability of these
TV carriers is being much reduced for monitoring Meteor Scatter. There are
some alternatives, such as the
French GRAVES
space surveillance radar system on 143.050 MHz CW.
Sporadic E (Es)
at mid-latitudes occurs mostly during summer season, from
May to August in the
Northern hemisphere and from November to
February in the Southern hemisphere. Very strong signal strengths are
common.
There is no single cause for this
mysterious propagation mode. The reflection takes place in a thin sheet of
ionisation around 90 km height. The ionisation patches drift westwards at
speeds of few hundred km per hour. There is a weak periodicity noted during
the season and typically Es is observed on 1 to 3 successive days and remains
absent for a few days to reoccur again. Es do not occur during small hours,
the events usually begin at dawn, there is a peak in the afternoon and a
second peak in the evening. Es propagation is usually gone by local midnight.
Sporadic E (Es)
clouds have been observed to initially occur within approximately
150
km (90 mi) to the East of a severe thunderstorm cell complex in the
Northern hemisphere, with the opposite being observed in the Southern
hemisphere. To complicate matters is the fact that
Sporadic E (Es)
clouds that initially form to the East of a severe thunderstorm
complex in the Northern hemisphere, then move from ESE-WNW and end up
to the West of the severe thunderstorm complex in the Northern
hemisphere.
So one has to look for
Sporadic E (Es)
clouds on either side of a severe thunderstorm cell complex. Things
get even more complicated when two severe thunderstorm cell complexes
exist approximately 1000–2000 miles apart.
Not all
thunderstorm cell complexes reach severe levels and not all severe
thunderstorm cell complexes produce
Sporadic E (Es).
This is where knowledge in Tropospheric physics and weather
analyses/forecasting is necessary.
50MHz 2,350km is max single hop distance.
50MHz
Sporadic E (Es)
season is from
May to August in the Northern Hemisphere. Double hop often seen
vastly increasing the distances worked.
Some distances worked
when at solar minimum in 2007 have been in the order of
6000km, is this triple hop Sporadic-E or something else such as
Short-path Summer Solstice Propagation (SSSP)?
Only open on 50MHz towards the peak of a solar cycle, in the Winter months from
October to April, but possible to work all Continents including Australia.
Next peak due in 2012/2013. Get ready for the
pileups!
For the best and most
comprehensive guide to VHF/UHF propagation studies, I cannot recommend
highly enough the website of Dr. Volker
Grassmann DF5AI ; for practical operating
Udo Langenohl DK5YA and for DX'ers to
meet and chat online in real time the
ON4KST chat pages.
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