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 over 12 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 is also for members of the public who are not licensed Radio Amateurs, 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 http://www.qsl.net/g0isw

 

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

 

 

 

 

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 sometimes to 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 all 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

Packet/AX25 - BBS

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 low anyway.

The BBS was established many years ago before the advent of e-mail, the crew DO NOT READ THIS.

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 '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.

 

Latest 50 MHz(6m) DX cluster spots

 

Latest 70 MHz(4m) DX cluster spots

 

Latest 144 MHz(2m) DX cluster spots

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 propagation openings map

(Click on historical image below for current map)

Click here for last 1 hour Live Map

Above a VHF 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

 

Ionospheric chart for Rome

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

For the Northern hemisphere, between April to September, MUF frequencies greater than 19 MHz generally indicate 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.

 

 

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

(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 (www.rmob.org)

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)

 

 

PRIMARY EUROPEAN METEOR SCATTER FREQUENCIES & WEAK SIGNAL DATA MODES USED

Old Region 1 Band plan had 50.200-50.300 MHz for Meteor Scatter (still largely in use 2013/2014)

FREQUENCY

MODE

COMMENT

50.230 MHz* JT6M

 

95% European activity this mode seen here 2013
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
50.280 MHz* PSK2k

 

New none WSJT mode, difficult to install, but fully automatic
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)

FREQUENCY

MODE

COMMENT

50.325 MHz ISCAT-B Some European activity this mode seen here 2014
50.330 MHz JT6M 5% European activity this mode seen here 2013
50.370 MHz FSK441 No European activity this mode seen here 2013
70.230 MHz JT6M  100% European activity this mode seen here 2013

+/- 10 kHz

70.260 MHz FSK441 90% European activity this mode seen here 2013

+/- 20 kHz

144.360 MHz PS2K 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

NOTES

*As of June 2013 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.

 

 

 

 

PRIMARY EUROPEAN WEAK SIGNAL FREQUENCIES & DATA MODES FOR OTHER PROPAGATION TYPES

FREQUENCY

MODE

COMMENT

50.230 MHz* JT6M Combination Meteor Scatter or Aircraft Scatter (ACS) seen here in 2013
50.250 MHz* PSK31  SPORADIC-E / F2 Transatlantic
50.276 MHz* JT65A  SPORADIC-E / F2 Transatlantic
50.278 MHz* JT9-1  SPORADIC-E / F2 Transatlantic (was 50.293 until 19th July 2013)
50.293 MHz* (+ >1500Hz) WSPR  US / EUROPE*
50.305 MHz PSK31  No PSK31 observed here in 2013 yet
50.333 MHz JT9-1  Japan - US - Japan
50.401 MHz (+/- 500Hz) WSPR  New Region 1 Band plan

NOTES

*As of June 2013 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 where stations remain to work each other.

 

 

 

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

0-110 Km

(Ground)

 

0-390 Km

(Aircraft)

 

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

110-500km

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.

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 1000 km or around 800 km at sea level.

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 radio horizon is 394 km as shown in the calculation below.

Example: Commercial aircraft at 12,192 m (40,000 feet) altitude, carrying Amateur radio transmitter

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

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 disctance could be extended to around 500 km

So for the two legs from ground station to aircraft and scattered back to ground the maximum distance is 2 x(394+110) km = 1008 km.

 

Do any aircraft ever fly higher than 12,192 metres (40,000 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.

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 800-1000 km.

Any DX spots showing aircraft scatter (ACS) over this 1000 km distance can only be operator error and 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

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

 

 

 

350-2350km

Most meteorites have a significant iron content and when they burn up in the atmosphere at heights between 85-90 km they leave metallic ionised trails which reflect VHF signals back to Earth that would otherwise be lost in space.

Summer months best for major showers, but winter months 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 50/144 MHz SSB contacts using WSJT software (JT6M mode for 50 MHz and FSK441 mode for 144 MHz) for long distance contacts. My favourite propagation type!

Meteor Showers

Meteor Showers

Active Period

Approximate activity maximum

Peak recorded Radio reflection hourly rate

Quadrantids

Jan 01-Jan 05

Jan 04

522 (2009)

Delta Leonids

Feb 15-Mar 19

Feb 25

353 (2010)

Virginids

Jan 25-Apr 15

Mar 24

299 (2009)

Lyrids

Apr 16-Apr 25

Apr 22

403 (2010)

eta-Aquarids

Apr 19-May 28

May 05

488 (2005)

Unknown??

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)

Perseids

Jul 17-Aug 24

Aug 12

527 (2009)

a-Aurigids

Aug 25-Sep 08

Aug 26

492 (2007)

Delta-Aurigids

Sep 05-Oct 10

Sep 9

298 (2007)

Piscids

Sep 01-Sep 30

Sep 20

396 (2009)

Orionids

Oct 02-Nov 07

Oct 14

471 (2009)

Leonids

Nov 14-Nov 21

Nov 19

700+ (2002)

Puppid-Velids

Dec 01-Dec 15

Dec 07

306 (2005)

Geminids

Dec 07-Dec 17

Dec 14

521 (2005)

Ursids

Dec 17-Dec 26

Dec 22

243 (2007)

 

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 2002. 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.

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 strong VHF Band 1 TV station video carrier such as 49.750 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 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.

 

 

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 layer of ionisation varying in height between 90 - 130 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.

 

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, 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

50MHz

>3200km

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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GG0ISW Penrith weather webcam

  

In the Penrith weather webcam image above, looking West over the town, various prominent landmarks can be seen in the distance on a clear day.

Looking at the distant horizon starting on the left edge of the webcam view above can be seen:

1. The high summit of Blencathra fell 868m altitude (20 km away) also known as Saddleback fell due to its distinctive shape.

2. Moving slightly right in the dip can sometimes be seen the more distant summit of Skiddaw fell 931m altitude (25 km away) near Keswick.

3. Moving further right in the foreground at the lowest point of the horizon is a much closer wooded fell that is near Greystoke village (8 km away), this latter feature is visible most days unless the weather is really bad.

4. At the far right hand edge of the image is the sharply pointed summit of High Pike fell 658m altitude (20 km away), near Caldbeck.

I am using a Panasonic HC-V110 digital video camera linked to my PC via a Hauppauge USB-Live 2 analogue to video digitiser with AV to USB cable. Despite my video camera being full 1080p HD the webcam display resolution using Weather Display software and this interface only seems capable of a maximum 720x576 resolution, this appears to be a limitation caused by the Hauppauge converter.

 

 

 

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