G0ISW VHF page

Marconi transmitter c.1897

Icom 7800 c.2007

Experimental Radio Communications

1895 - 2008

This website relates to the recreational pastime of Amateur Radio and promoting the, over 110 years old, science of experimental radio communications & related technology, founded by Guglielmo Marconi, in 1895. This site was created, on 1st September 2000, to assist other UK & overseas Radio Amateurs to experiment and achieve VHF /UHF DX (long distance) communications, as well as being a useful operating aid for its creator Philip G0ISW..... It now has additional sections for HF world-wide communications.

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VHF /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 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.

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 VHF DX cluster spots

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Tropo Index

(Click on thumbnail below for full 6 day preview)

Auroral Oval

(Click on thumbnail below)

Real time Geomagnetic activity shown below (Aurora Watch)

Real-time data for today

VHF/UHF QSOs real time maps

(Click on thumbnail below)

Live International Space Station (ISS) position below

(Press Browser refresh for latest image)

Live Meteor Scatter daily activity analysis OSWIN (Berlin) Radar 53.50 MHz 90kW (1 hour - shown below)

Meteor Scatter daily activity analysis 48.250 MHz (This month - shown below)

Meteor Scatter daily activity analysis

Live meteor numbers by height and time (shown below)

G7IZU Live 3D Meteor Spectrogram (Click on thumbnail below)	Virgo Meteor Sky view applet (Click on thumbnail below)

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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

Dependant upon antenna height above sea level

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. Software calculator here

Tropo Scatter

100-500km

Available all the time.

Aircraft Scatter

100-500km

Subject to rapid fading of signals

Aurora

250-1100km

Favours Northern Europe. March often good

FAI

250-1100km

May to August, favours Southern Europe

Tropo Ducting

200-1000km

Sea path possible exceptionally up to 3000km. October often the best month. These Ducts form at heights between 450m to 3000m, but are blocked by higher mountains along the path.

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

Ionoscatter is 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 on 50 MHz with occasional enhancements making it rarely workable for larger EME capability type stations on 144 MHz also.

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!

Meteor Scatter

700-2350km

Summer months best for major showers, but winter months active too.

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. 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.

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.

F2 layer / TEP

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 2011.

VHF DX Year Planner

VHF DXers year planner

The VHF Net Ring	by CT4KQ

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