Marconi transmitter c.1897

Elecraft KX3  c.2012

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Marconi

Callsigns: MAA-MZZ

Experimental Radio Communications

From 1895-1937

Philip

Callsign: G0ISW

Amateur Radio Communications

 Since 1985

 

 

 

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 operating aid 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 at http://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.

 

Latest 50 MHz DX cluster spots

 

Latest 144 MHz DX cluster spots

Status Status Status Status

Tropo Index

(Click on thumbnail for full 6 day preview)

Historical image shown courtesy of William Hepburn

Historical image - please click to obtain real time images

Auroral Oval

VHF/UHF QSOs real time maps

(Click on thumbnail below)

Live International Space Station (ISS) position below

 Images provided by Heavens-Above

VHF/UHF spots Real-time maps

ISS position

Radio Meteor Observatories Online (www.rmob.org)

Scatter daily activity analysis  (Click on thumbnail below)

 

 

Scatter daily activity analysis  (preliminary results, not validated)

Meteor Scatter daily activity analysis

NLO Meteor Detection Live 3D Spectrogram

 (Click on thumbnail below)

Virgo Meteor Sky view applet

(Click on thumbnail below)

 

 

VHF/UHF DX clusters

50MHz Cluster

70MHz Cluster

144MHz Cluster 

432MHz Cluster

 50MHz DXcluster analysis live map

Beacon spots Cluster

1.2GHz Cluster

10GHz Cluster

 Digital modes spots Cluster

Satellite spots Cluster

ON4KST 50/70/144/432 MHz Chat, DX cluster and live maps  

144MHz DXcluster analysis map

 Live Aurora/Es/MS last 10 minutes

 144 MHz Sporadic E spots

50/144 MHz Aurora spots

VHF/UHF QSOs real time maps

 

 

 

 

 

Height km

VHF Propagation modes

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 Es can 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.

VHF/UHF Propagation modes explained

Propagation type

Distances

Comments for European stations

Line of sight

0-100km

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

·        Cut down problem trees

 

Click on this link for VHF/UHF Line of Sight range calculator.

 

Knife edge diffraction

1-100km

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'.

More information and software calculator here

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.

 

Tropo Scatter

100-500km

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

100-500km

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

250-1100km

 

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.

More information can be found here.

 

FAI

 

 

 

 

 

 

250-1100km

 

 

 

 

 

 

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.

 

TEP

3000-8000km

Trans-Equatorial Propagation (TEP)

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).

 

Tropo Ducting

200-1000km

 

Exceptionally to 3000km

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.

Click here for atmospheric temperature soundings.

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.

Inversion thickness required
Feet
Metres
Band
MHz
300
91
UHF
432 MHz
600
183
VHF
144 MHz

 

Ionoscatter

900-2000km

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.

NATO Military 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.

DEWLine station in Alaska

 

 Meteor Scatter

 

 

 

700-2350km

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)

50MHz  

500-2350km

(Single hop)

 

 

1000-4700km

(Double hop)

 

 

 

 

 

Around 6000km

(Triple hop Sp-E or SSSP)

 

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)?

 

144MHz

1400-2350km

(Single hop)

 

 

Around 3000km

(Double hop)

144MHz 2,350km is max single hop distance. 144MHz Sporadic E (Es) season is from June to July in the Northern Hemisphere.

 

Rare double hop Sporadic-E up to around 3000km perhaps with ground reflections from large inland waterways such as lakes and rivers as one theory suggests.    Click on link for more information.

F2 layer

50MHz

>3200km

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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