Marconi transmitter c.1897

Elecraft KX3  c.2012

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Guglielmo Marconi

Callsigns: MAA-MZZ

Experimental Radio Communications

From 1895-1937


Callsign: G0ISW

(Ex G1MOG)

Amateur Radio Communications

 Since 1985




This website relates to the recreational pastime and hobby of Amateur Radio, promoting the science of experimental radio communications & related technology, founded by the famous Guglielmo Marconi, in 1895.

This website was originally created over 16 years ago, on 1st September 2000, by Philip G0ISW to assist other Radio Amateurs to experiment, research and achieve Very High Frequency (VHF) and Ultra High frequency (UHF) DX (long distance) communications in the 50 MHz, 70 MHz, 144 MHz & 432 MHz bands, as well as being a useful operating aid, having essential propagation information on one page. It has since expanded to also cover HF frequencies too. Additionally the site has been designed not only for current Radio Amateurs, but also for members of the public who are not licensed to transmit, but who may have an interest in some of the topics discussed or are aspiring to join the hobby.

If you cannot see the full index shown on the left edge of your screen, please go to my main page at


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 16 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





The 'magic' with VHF signals is that Amateur Radio signals in the frequency bands 50 MHz, 70 MHz, 144 MHz, & 430 MHz are predominantly 'line of sight', typically short range distances at ground level between 0-45 km and are blocked easily by obstacles such as mountains or buildings. If these signals are not obstructed and are sent from ground transmitters into the air they will travel straight out into Space for significantly greater distances.

Using experimental techniques and 'enhanced propagation' it is possible to regularly bend these VHF signals back to Earth at distances of up to 2,300 km and to reflect them from Meteor trails, Auroras, Aircraft, Satellites, the Moon, the International Space Station (ISS) or once every 11 years at the peak of the Solar cycle the Earth's 'F2 layer' making it possible to extend the range of VHF signals to many thousands of km and even reach all Continents, including Australia!


Did you know that most International Space Station (ISS) Astronauts and Cosmonauts undergo Amateur Radio training and are licensed to send and receive amateur radio transmissions whilst orbiting Earth?

Voice transmissions can often be heard on the downlink frequency of 145.800 MHz FM

Packet/AX25 data transmissions can often be heard on the uplink/downlink simplex frequency of 145.825 MHz FM

ISS Packet/AX25 - BBS not in use by the International Space Station crew

Please DO NOT attempt to connect to or use the very old International Space Station 'Packet' AX25 mode BBS system, callsign RS0ISS-11, as you will block the whole 8 minute pass for every other European station, who can digipeat only if the BBS is not being used. It takes several successful lengthy transmissions just to enter a 'subject', let alone then leave any message, so chances of total success are very low anyway.

The ISS BBS was established many years ago before the advent of e-mail, the crew DO NOT READ MESSAGES ON THIS BBS, so please don't cause QRM or waste your time trying to connect using packet.

In order to obtain an ISS QSL card you only have to  'digipeat' once through the onboard system using the callsign RS0ISS-4. This allows multiple amateurs greater success within the 8 minute orbital pass over Europe, as each digipeated signal is completed within less than 3 seconds.


If you are old enough to remember the pre digital (before 2007-2012 switchover) 'analogue' TV signals here in the UK in the frequency range 470 MHz to 790 MHz, you might recall the BBC weather forecasters sometimes announcing during extended periods of high air pressure and fog that your TV reception was suffering from 'co-channel interference' from the Continent.

This was caused by unusual enhanced propagation, caused by the weather conditions allowing TV stations in France, Holland or Germany to be received here, but sharing the same frequencies as our own TV stations they created unintended difficulties for viewers such as receiving their pictures and/or sound. However this announcement by the BBC was always good news for VHF Radio Amateurs because we would know it was an opportunity to greatly extend our own radio transmission ranges to the Continent.

These pages will explain how VHF DX is possible and show experimentation continues to this day with new technologies and developments such as special 'Weak Signal' software allowing us to combine radio transceivers with computers to detect signals that otherwise would be missed.

This site has for several years now also contained sections dedicated to High Frequency (HF) Worldwide communications in the 1.8 MHz - 30 MHz range, where World-wide communication is much easier and a regular every day occurrence.








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.

There is a new DXSummit cluster page and application, please click on image below to adjust viewing for your desired choice of bands


Status Status Status Status


VHF Tropo Ducting Index

(Click on image below for full 6 day preview)

Historical image shown courtesy of William Hepburn

   Click here for latest 6 day preview

Great example above of a Tropo Ducting path potentially open between Spain and South America on Tuesday 25th June 2013. That evening lots of 144 MHz DX being worked between mainland Spain and the Canary islands, mistakenly reported on the DXclusters as via Sporadic-E, as even on 50 MHz the Es had been extremely poor throughout Europe all day long.


VHF 144 MHz Tropo propagation openings map

(Click on historical image below for current map)

Click here for last 1 hour Live Map

Above a VHF Tropo propagation map using 144 MHz APRS signals, by Jon Harder NG0E, shown on the morning of Wednesday 26th June 2013 indicating pathways. Interestingly the Tropo ducting paths are still open from Portugal and the Azores to the Canary Islands.

Historical image shown courtesy of John Harder NG0E


Sporadic Es and Ionospheric chart for Rome

Showing daily height of Sporadic Es clouds (h'Es) and MUF.

For the Northern hemisphere, between April to September, MUF (3000)F2 frequencies greater than 18 MHz generally indicate potentially good 50 MHz Sporadic Es conditions. It is possible for the MUF to exceed 30 MHz in Winter at the peak of the solar cycle, but this does not guarantee any Sporadic Es propagation. Also shown, if present, is the height of the Sporadic-Es reflecting layer usually between 104-115 km.



Sporadic Es and possible Jet stream association

(Click on historical image below for current live jet stream map)

There is one current theory in 2016 (amongst many others) that wind shear from the Jet Stream at altitudes of between 9-16 km above ground level over mountains may have an association with Sporadic Es, the so called 'wind shear' theory. Using the above live wind chart and setting the wind height altitude to 500 hPA  (11 km) should allow observations and comparisons to be conducted in real-time with Sporadic Es cluster maps to support or discount any such correlation.

I am personally very sceptical and doubtful about the 'wind shear' theory, as my own observations show clearly that Sporadic Es is very seasonal in the Northern hemisphere between about April to August each year, with a pronounced peak in June, whereas the jet stream is all year round and there is also a significant difference in heights between the jet stream at 11 km and Sporadic E reflecting layers at 104-115 km.

Sometimes I see a correlation with Es reflecting areas and thunder storms generating extensive lightning activity (another theory), but by no means do they coincide every time. On the morning of 3rd May 2016 there was a clear 50 MHz ES reflecting layer centred over the Baltic states, but no wind shear nor any thunder storm lightning activity found using live data, so what caused it?

In June 1989, during a particularly intense radio Es event on 144 MHz, I observed the distant DX stations heard to slowly all shift SW over the course of two hours, in a direction not associated with the jet stream, but either consistent with the Earth's rotation in relation to the Sun or possibly due to the Sporadic Es layer descending over time and reducing the distance of stations' signals observed reflected via it.

The generally accepted height of the Sporadic Es reflecting layer is around 90-115 km, which is very significantly higher than the jet stream altitude of 11 km. Although annual the intensity of Es events varies by year and in recent years has been very poor compared with the 1980's and 1990's, despite peaks and troughs of the solar cycle.

I definitely think there is a connection with the intensity of the Sun due to the seasonal Summer nature of the event in the Northern hemisphere. Also the Es events tend to only occur during daylight hours at VHF. A 3 day cycle pattern of building up to a Es peak also seems quite prevalent, possibly a charge/discharge cycle period perhaps.

Sometimes Sporadic-E is mentioned as having occurred several times in December each year, in the Northern hemisphere, this would conflict with the summer sun correlation, but I think from my own observations that sometimes Sporadic-E propagation can be confused with very high level meteor scatter propagation. My rationale is that when I participated in the fantastic Leonids November 2002 meteor shower event, with over 700+ meteors per minute, the intensity was such that the whole 144MHz band was wide open for many hours with the high signal strengths associated with Sporadic-E signals. I have also observed other meteor showers tricking me into thinking there was a Sporadic-E opening, as happened most recently in April 2017 during the peak of the Lyrids meteor shower, no other mention of Sporadic-E by stations until May, but the signal strengths I observed that day were very high and prolonged again, for an hour or so.

The long standing mystery of what exactly causes Sporadic Es propagation continues, since it was first observed in the 1930's.


Tropo and Air pressure charts

(Click on historical image below for current chart)

Click here for llatest Air Pressure charts

Above an Air Pressure chart from the UK Met Office for Wednesday 26th June 2013 showing the very large system of High pressure between Africa and South America leading to good Tropo ducting opportunities.

Historical image shown courtesy of UK Met Office




Auroral Oval


North Auroral Forecast Image

(Images provided by NOAA)


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 (

Scatter daily activity analysis  (Click on thumbnail below)



SKiYMET Meteor Scatter daily activity analysis

NLO Meteor Detection Live 3D Spectrogram

 (Click on thumbnail below)

Virgo Meteor Sky view applet

(Click on thumbnail below)




Old Region 1 Band plan had 50.200-50.300 MHz for Meteor Scatter (still largely in use as of 2017)




50.230 MHz* JT6M (30s periods)


Most European MS activity was seen here in 2016, but in 2017 has declined dramatically in favour of MSK144 mode on 50.280 MHz.
50.235 MHz* ISCAT-B Some European activity this mode, seen here 2013, better performance than JT6M but not adopted by many users yet
50.270 MHz* FSK441


Not ideal for 50MHz use, JT6M mode superior for longer reflections found on 6m
50.260 MHz* PSK2k


Newer none WSJT mode, difficult to install, but fully automatic. Moved up to 50.360 MHz in 2015
50.280 MHz* (+/- 15 kHz) MSK144 (15s periods) 99% European activity this mode and frequency, seen here in 2017, with 15s periods and extremely popular. Software in use is either WSJT10 by K1JT or the newer MSHV by LZ2HV
50.325 MHz* ISCAT-B Some European activity this mode, seen here 2014, better performance than JT6M but not adopted by many users yet

New Region 1 Band plan since 2012 suggests 50.320-50.380 MHz for Meteor Scatter

(largely not adopted yet by European MS community)




50.325 MHz ISCAT-B Some European activity this mode seen here 2014
50.330 MHz JT6M Much more European activity this mode seen here 2015
50.360 MHz  



100% European activity this mode seen here 2015
50.370 MHz FSK441 No European activity this mode seen here 2013
70.230 MHz JT6M  100% European activity this mode seen here 2013, 2016

+/- 10 kHz

70.280 MHz FSK441 European activity this mode seen here 2017

+/- 5 kHz

144.360 MHz PSK2k Unofficial PS2K frequency, 100% European activity this mode seen here 2013
144.370 MHz FSK441 100% European activity this mode seen here 2013 +/- 20 kHz


*The new Region 1 (European) band plan, that came into effect on 1st January 2012, is largely being ignored by the VHF community, as all data modes in Europe were recommended to move above 50.300 MHz to free up space for more SSB voice, however 50 MHz is often capable of Intercontinental communications and there remains much US JT65 data activity below 50.300 MHz so that is where European stations remain to work them.









50.230 MHz* JT6M Combination Meteor Scatter or Aircraft Scatter (ACS)or Sporadic-E, very active in 2016
50.250 MHz* PSK31  SPORADIC-E / F2 Transatlantic / Tropo active 2017
50.276 MHz* JT65A  SPORADIC-E / F2 Transatlantic
50.278 MHz* JT9-1***  SPORADIC-E / F2 Transatlantic (was 50.293 until 19th July 2013) (Poor mode at 50 MHz die to doppler shift making signals not being decoded)
50.293 MHz* (+ >1500Hz) WSPR  US / EUROPE*
50.305 MHz PSK31  No PSK31 observed here in 2013 yet
50.330 MHz JT6M 5% European activity this mode seen here 2013
50.360 MHz PSK2k  SPORADIC-E / F2 Transatlantic

Europe calls 1st 15 second intervals (2015)

50.401 MHz (+/- 500Hz) WSPR  New Region 1 Band plan


*The new Region 1 (European) band plan, that came into effect on 1st January 2012, is largely being ignored by the VHF community, as all data modes in Europe were recommended to move above 50.300 MHz to free up space for more SSB voice, however 50 MHz is very often capable of Intercontinental communications and there remains much US data activity below 50.300 MHz so that is possibly why stations have remained on the old frequencies to work each other.

*** From my own observations JT9 mode does not work at all well on 50 MHz, compared with JT65A which does work well, this appears to be due to JT9 signal drift/doppler and leads to signals not being easily decoded, if at all, despite being strong on your display.








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 90 km altitude and Sporadic Es can be up to 115 km 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 200 km in height.

VHF/UHF Propagation modes explained

Propagation type


Comments for European stations

Line of sight

0-110 Km



0-390 Km



0-618 Km

(HA Balloon)

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.

Due to the curvature of the Earth there is a limit to how far VHF/UHF signals can travel before disappearing into space.

The formula for calculating your 'radio horizon' for an 'unobstructed path' or maximum line of sight distance is

Horizon Km = 3.569 x √ height in metres

Example 1: Person standing at ground level (sea level) holding a handheld radio

Horizon Km = 3.569 x √ 1.80 metres  = 4.78 Km

Example 2: My home amateur radio station, located 154m ASL and antenna a further 5m AGL

Horizon Km = 3.569 x √ 159 metres  = 45 Km

Example 3: Person standing on summit of Helvelyn mountain, holding a handheld radio

Horizon Km = 3.569 x √ 950 metres + 1.80 metres  = 110 Km



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


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

My own radio horizon is obstructed by nearby hills and mountains as you can see in the charts below, with the blue line being the profile of the mountains as viewed and the red line being horizon distances. Near 120 degrees I have an almost totally unobstructed path in the region of a maximum 45 Km, whereas immediately behind my house to the North I have a hill  that blocks my signals in that direction.


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

Obviously if the transmitter is not located on the ground, but instead is in an aircraft or balloon the line of sight distances can be vastly increased.

Example 4: Light aircraft at 3,000 m altitude, carrying Amateur radio transmitter

Horizon Km = 3.569 x √ 3,000 metres  = 195 Km

Example 5: Commercial aircraft at 12,192 m altitude, carrying Amateur radio transmitter

Horizon Km = 3.569 x √ 12,192 metres  = 394 Km

Example 5: Helium filled Amateur Radio High Altitude Balloon (ARHAB) transmitter at altitude of 30,000 m

Horizon Km = 3.569 x √ 30,000 metres  = 618 Km



Knife edge diffraction

1-110 Km

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. Single knife edge or rarer double knife edge diffraction observations have been made by me over the Pennine Mountains between Penrith and Hexham. The image below shows the cross section and the distinct knife edges.


Tropo Scatter


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.

Where your 'line of sight' distance has been exceeded due to the curvature of the Earth or obstructions, this mode is the one most likely to be found by radio amateurs, but does require typically horizontal steerable antennas and SSB, rather than FM.

Particularly useful on the 144 MHz band where from the UK it is possible to work nearby stations in France and Belgium all the time. With high gain antennas and sensitive receivers Germany and Denmark also become within range.

However this propagation type doesn't favour 50 MHz so well and can be disappointing.

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

100-1000 Km

Aircraft scatter propagation (ACS) has been regularly used successfully on frequencies of 50 MHz and above. It can be subject to rapid fading of signals at 144 MHz and higher frequencies and may not be particularly easy to catch or use.

Imagine bouncing your radio signals off the metal aircraft body, which will be travelling at between 500-600 mph, in the same way you would bounce light off a mirror. Due to the speed of aircraft transit, maximum 30 second transmit periods are recommended and data modes such as JT6M (30s periods) or ISCAT-B (30 or 15 second periods) will probably yield the best results.

I have often found using 50 MHz and JT6M data mode that identified Boeing 747 airliners are sufficiently large, with their 64m wingspan, to produce good aircraft scatter. The scatter period on 50 MHz can last up to around 1 minute if crossing the direct path between stations and significantly longer if flying along the direct path.

Due to the curvature of the Earth and VHF signals being line of sight there is a maximum distance limit as to how far Aircraft Scatter (ACS) propagation can be used. This maximum distance is approximately 758 km for Civilian commercial aircraft reflections.

Also this maximum theoretical distance using commercial airliners does not take into account any path attenuation.

Using the calculations seen before for VHF line of sight signals we find that for a signal from a commercial aircraft altitude to sea level, the theoretical maximum radio horizon is 379 km as shown in the calculation below.

Example: Commercial aircraft at normal maximum 11,276 m (37,000 feet) altitude, carrying Amateur radio transmitter

Horizon Km = 3.569 x √ 11,276 metres  = 379 km (235 miles)

However, from my own recorded results the very best distance line of sight to a Civilian commercial aircraft I have obtained has been 338 km (210 miles) due to nearby ground obstructions i.e. mountains.

This zone of no line of sight could be referred to as a Radar Shadow Area (RSA), see image below for a better understanding how closer aircraft can be hidden yet further away higher aircraft ADSB transmissions can be observed.


Some modest increase in theoretical distance will be exhibited by amateur radio stations being at an elevation above sea level. However even the top of mountains will only add about 110 km more so the distance could be extended to nearly 500 km

So for the two legs from ground station to aircraft and scattered back to ground the maximum distance is 2 x(379+110) km = 978 km.


Do any aircraft ever fly higher than 11,276 m (37,000 feet)

Yes, historically the supersonic Concorde used to fly at a cruise altitude of 18,900 m (62,000 feet) and the US Air Force SR71 Blackbird reconnaissance aircraft set an altitude record in 1976 of 25,950m (85,135 feet) although it is likely it could fly higher, but that maximum remains classified.


Some smaller modern military jet fighters apparently have a service ceiling of 65,000 feet, but stealth radar absorbing materials used to avoid enemy detection by radar will also prevent amateur radio aircraft scatter.

The only aircraft I have observed at significantly higher altitudes have been rare U2 flights passing over the United Kingdom with a transmitted height of 60,000 feet, although they could have been at a different higher altitude apparently as anything over 60,000 feet is deliberately not shown.


There may be other classified experimental military aircraft operational today, but due to the limitations of having air-breathing engines they too are limited in maximum altitude.

If we use 25,950m (85,135 feet) as the maximum possible, but most unlikely, theoretical and practical altitude then the radio horizon would be:

Horizon Km = 3.569 x √ 25,950 metres  = 575 km and for ground to aircraft scatter and back to ground that distance would be doubled to 1150 km in theory!

Also the aircraft size is key to whether or not is offers enough surface area for the transmit frequency in use, at 50 MHz (6m) it appears an aircraft the size of a Boeing 747 with a 64m wingspan is required for good results.

Smaller identified aircraft such as Boeing 737, with 34m wingspan, have not been observed by me to have as much success on 50 MHz, surprisingly.



Realistically for all amateur radio purposes a practical maximum for aircraft scatter (ACS) propagation remains around 700-1000 km.

Any DX spots showing aircraft scatter (ACS) over this 1000 km distance can only be operator error and should be discounted, with another propagation mechanism such as MS or Es being the actual medium used.

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 early 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 by him. Some imagery and an explanation of how you can experiment to listen yourself can be found on the website of G3CWI here.

Also the website of PA0EHG provides a fascinating account of his experimentation at 1296 MHz a frequency particularly well suited to ACS propagation, as well as his use of SM7LCB online Path and Scatter maps.

Since 2013 a fabulous new piece of software called AirScout has been written by Frank DL2ALF especially for Aircraft Scatter propagation. You get moving aircraft over a map in real-time as well as a plot showing where your signal and the station you are trying to work have a mutual reflective scatter zone into which the aircraft can fly and their times predicted.

Additionally a path profile is generated which shows obstructions such as mountains. This software is a superb tool to assist others for ACS research and real-time working and of course fun!

In the Summer of 2013 I first experimented with this software and using WSJT JT6M data mode on 50 MHz SSB was able to take advantage of regular aircraft scatter (ACS) between the UK and Ireland at a distance of 350 Km. The 30 second transmission periods for JT6M fitted perfectly the 1 minute long observed reflections, with fairly stable strong signal strengths seen. Happy days!

Since then I have had many successful contacts on 50 MHz using aircraft scatter and have even been able to predict the reflections timed to the minute using AirScout software by DL2ALF.

Signal strengths have been often observed at 6-12 dB.





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.
















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.




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



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
432 MHz
144 MHz




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





Most meteorites have a significant iron metal content and when they burn up in the atmosphere at heights between 85-90 km they leave behind metallic ionised trails which reflect VHF signals back to Earth, that would otherwise be lost in space. Signals are typically of very short duration, but can be strong typically from -2 to +13db. During the most intense meteor showers the duration of signal reflections and be several minutes or even hours and can be confused for Sporadic-E propagation.

Summer months are best for the major showers, but winter months are active too. Random meteors occur all the time, day or night, and there are far more meteors than can be seen visually. Can be a mode that can revolutionise 50/70/144 MHz SSB contacts using software such as WSJT or MSHV by LZ2HV (latest MSK144 mode with 15 second intervals, is very popular in 2017) for long distance contacts. My favourite propagation type!

The lowest distance 200 km MS contacts can be very difficult to complete due to the high angles required, fewer meteors trails being in just the right place and nearby radio signal obstructions such as mountains, mid distance MS contacts around 600-1000 km being far easier.

Whilst most stations use directional horizontal beams and 100W or more, success can be achieved with omni-directional antennas such as horizontal loops and surprisingly even with vertical colinears.

Meteor Showers

Meteor Showers

Active Period

Approximate activity maximum

Peak recorded Radio reflection hourly rate


Jan 01-Jan 05

Jan 04

522 (2009)

Delta Leonids

Feb 15-Mar 19

Feb 25

353 (2010)


Jan 25-Apr 15

Mar 24

299 (2009)


Apr 16-Apr 25

Apr 22

403 (2010)


Apr 19-May 28

May 05

488 (2005)

Comet 209P TBC

May 24-May 31 May 24/31 540 (2007)
Pegasids Jul 07-Jul 13 Jul 10 495 (2007)

Southern delta-Aquarids

Jul 12-Aug 19

Jul 28

500 (2007)


Jul 17-Aug 24

Aug 12

527 (2009)


Aug 25-Sep 08

Aug 26

492 (2007)


Sep 05-Oct 10

Sep 9

298 (2007)


Sep 01-Sep 30

Sep 20

396 (2009)


Oct 02-Nov 07

Oct 14

471 (2009)


Nov 14-Nov 21

Nov 19

700+ (2002)


Dec 01-Dec 15

Dec 07

306 (2005)


Dec 07-Dec 17

Dec 14

521 (2005)


Dec 17-Dec 26

Dec 22

243 (2007)


Reflections of radio signals can last from around 250 milliseconds (1/4 of a second) to 30 seconds plus, but the vast majority are extremely brief. It can take a long time to complete a QSO in the region of 30 minutes or an hour, unless there is a major Meteor shower. In November 2002 the Leonids shower was the best ever with over 700+ meteors each hour. So many meteors were striking the atmosphere that an almost continuous reflective layer was formed with amazing easily completed verbal QSO's, almost like Sporadic-E signals that lasted for many hours continuously.

For Meteor Scatter the 50 MHz band is by far the best, 144 MHz is usable too but more difficult and 432 MHz and higher almost unheard of.

To easily hear Meteor pings tune your transceiver to a distant strong VHF Band 1 TV station video carrier or VHF FM Radio station 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 or radio carrier continuously.

The Spanish TV Transmitter shown above, closed down in 2010, but in 2011 the TV Transmitter in Prague shown below was active. Sadly almost all Band 1 TV stations are closing down, replaced by UHF digital instead.

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.


It is also possible to carry out some interesting Radio Astronomy using the signals from Band 1 TV carriers and your Radio receiver to detect Meteor reflections and create imagery of the fireballs or meteors burning up in the atmosphere using SpectrumLab software.


Sporadic E (Es)



(Single hop)




(Double hop)






Around 6000km

(Triple hop Sp-E or SSSP)


Sporadic E (Es) at mid-latitudes occurs mostly during summer season, from April 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 layer of ionisation varying in height between 90 - 115 km above Earth, (average 110 km) the lower the height of the Es cloud the greater the distance the distance that can be worked as the angles of reflection are shallower.

The ionisation clouds can 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, a bit like charging up a battery and then depleting it.

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.

For the UK 50 MHz Es propagation favours stations located furthest South, however openings for Northern based stations do occur, but interestingly often an hour or more later than for stations in the London area. This can result in big pileups with stations around London being worked by the DX station, only for an hour later stations in the North getting a look in! This can be most frustrating as the DX station may well go QRT by then or the pileup is so huge that the more Southerly stations with stronger signal strengths are the only ones heard.

Sporadic E (Es) clouds have been observed to initially occur 'sometimes' 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 may 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 10002000 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, peaking in June. 'Double' or 'triple' hop often seen vastly increasing the distances worked.

Some distances worked when at solar minimum in 2007 or solar maximum in 2013 have been in the order of 6000km, is this triple hop Sporadic-E or something else such as Short-path Summer Solstice Propagation (SSSP)? On 20th June 2013 there was a 50 MHz Es opening from Europe to the Caribbean that vastly exceeds double hop distances.

Some theories suggest these double hop Es occur from the Es layer clouds not being flat, but having an irregular or bumpy surface which can reflect the radio signals to other clouds before returning to Earth. Or some theories favour reflections from bodies of water on the ground back to the Es cloud layer. Sporadic E remains a mystery, since first observed in the 1930's.




(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, with the peak in June. Signals often very strong but areas within the reflection zone are very pronounced, often spots are seen in one part of the UK with other parts not having the same luck.


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



Only open on 50MHz at the peak of the 11 year solar cycle. For the Northern hemisphere in the Winter months open from October to December and possible from Europe to work all Continents, including Australia. Next peak due in 2013/2014. 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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