This page is intended to show that you do not need large amounts of RF power or massive antenna arrays to work stations far away.

Here in the UK the maximum RF power permitted without a special exemption for 'Full' licence holders is 400 Watts, that is nearly equivalent to a single bar of an electric fire! In some Countries they permit an even higher maximum of 1 kW.

The maximum power I have ever used for SSB speech on HF is 100 Watts, although for many years now I use nothing more than 50 Watts as that significantly reduced for me cases of RFI breakthrough, TVI etc. This 50 Watts is the maximum permitted power level for 'NOVICE' licence holders and is plenty enough for all of my needs too.

I have in recent years used the PSK31 data mode on HF in preference to Speech and use an even less 5 or 25 Watts.

QRP Low Power is defined usually as using 5 Watts or less and this is what I am going to talk about on this page and provide you with some of my experiences.

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Firstly, on VHF and using the 144 MHz (2 metres) band you will find that your height above ground level (AGL) and a clear unobstructed line of sight (LOS) path can permit QRP level transmissions to travel significant distances. I live on the edge of the Lake District National park and often carry a handheld transceiver with me. I have managed to easily work stations on the Isle of Man (GM) and as far away as North Wales (GW), just using the handheld and its own helical aerial.

Your antenna height above sea level will affect how far your signal can travel, try the VHF/UHF Line of sight calculator by G4VWL to see for yourself how far your signals can travel from home via conventional line of sight propagation. Don't be concerned that you do not live at a great height above sea level! This will only affect your ability to work greater line of sight distances up to a maximum of 100km, even more important is your ability to have an unobstructed view of the horizon. Believe me it is better to be located in Norfolk than amongst the valleys of the Lake District, from a VHF DXer's perspective.

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.

For more serious VHF DX though, you will need a multimode transceiver capable of Single Sideband (SSB) transmissions and you will also need a horizontally polarised beam antenna, which has significant gain compared to a dipole. Probably the best and most commonly used is a Tonna 9 element beam. Ideally you will also need a rotator so that you can point your aerial at the station or Country you are trying to work/hear.

Using your multimode radio in Upper Side Band (USB) and calling initially on 144.300 MHz it is possible daily to have speech contacts in the region of 50-500km using Tropo scatter propagation, depending on where you are in the UK you may be able to have regular QSO's with amateurs in Europe.

During the months of May to August you may be very lucky to experience a rare form of propagation called 'Sporadic E', which can appear from nowhere and allow you to work vast distances. Distances achievable are in the region of 1100-2350km on 144MHz.

I have managed to work North Africa, EA9IB on 144 MHz USB with only 25 watts and a small Log Periodic aerial (equivalent to a 4 element yagi) via this mode. A distance of 2154 km.

Whilst I used more than 5 Watts I am convinced I would have managed the contact using QRP, it was just calling at just the right time that resulted in me being successful, the power was not so important and the signal levels for Es propagation are typically 59+ in each direction, unlike all other modes.

Many Radio Amateurs have reported success working both the International Space Station and Low Earth Orbiting FM satellites using only handheld QRP radios on 145 MHz uplink and 435 MHz FM downlinks using a portable Arrow II antenna. Click on the images below for some YouTube video clips demonstrating this antenna. K7AGE, in particular, seems to have a wealth of experience and videos on this subject.

I use AGW packet engine software to give me the ability to transmit and receive packet without a TNC and only using my computer soundcard. The UISS software works in tandem with AGW and is a very useful tool for working the ISS or digipeating through it.

UISS software

See the image below, showing my QTH and those of other successful Hams, displayed in real-time, as heard by the ISS. The ISS position is shown and where it will be in 5 minutes later (ISS-5).

I have had great success with my Yaesu FT-817 HF multimode radio from beaches in France using 5 Watts of RF on SSB speech and a Miracle Whip antenna, working around Europe easily. I've also managed to work the USA and South America too.

From home with slightly larger aerials I have had even more success with QRP.

If you already use your computer soundcard for data modes such as PSK31, then you can use WSPR (Distant Whispers) software by K1JT, with your existing hardware. The software transforms your station into an automated beacon and weak signal reception hub.

You will be amazed how far your low power signals can be heard and can see maps in real time. Great for antenna experimentation and comparison too. There is even a searchable WSPR spots database.

Below is an computer screen grab using WSPR software and taken from the WSPRnet pages showing my 5 Watts QRP signals on 10 MHz on Friday 3rd September 2010. Comparing this with my HF vertical aerial I can see immediately better results for working the nearby Continent, which is what I would expect.

WSPR 10 MHz signals dipole 03.09.2010

Using the WSPRnet website and its 'spot database query' research tool, I can enter search parameters for callsign, band, number of spots, and select the order they are displayed in such as timestamp, distance, SNR, km per Watt etc.

In the example below, dated from late 2010, I have selected 5 spots for my signals on the 10 MHz band and placed them in longest distance order. I can see that my best distance was to W3HH at 6751km and I can also see that all 5 spots were using my Sandpiper MV6+3 HF vertical, as I only put up my Racal Military tactical adjustable wire dipole on 1st September 2010.

Spot Database

Specify query parameters

Using spot archive (no automatic refresh). 5 spots:

Timestamp	Call	MHz	SNR	Grid	Pwr	Reporter	RGrid	km	az
2010-08-31 22:22	G0ISW	10.140199	-13	IO84oq	5	W3HH	EL89vb	6751	280
2009-07-23 21:32	G0ISW	10.140223	-26	IO84oq	5	K8CXM	EM79	6074	290
2009-07-23 21:10	G0ISW	10.140214	-25	IO84oq	5	W4JE	FM08qw	5724	285
2010-08-31 23:00	G0ISW	10.140193	-17	IO84oq	5	K8CT	EN83ce	5711	293
2009-07-23 21:32	G0ISW	10.140203	-25	IO84oq	5	K1JT	FN20	5383	284

Query time: 0.004 sec

However, on 14 MHz it is a different story, as I can see from the results shown below that my two best distances were both on dates after 1st September 2010, when I was using my Racal Military tactical adjustable wire dipole. Obviously you have to take into account the variations in propagation, but this software does allow you to compare antenna system performance if tests are carried close in time to each other.

In April 2011, I have returned to using my Sandpiper MV6+3 HF vertical as my primary aerial, as it will tune up on 50 MHz for the Sporadic-E season in April-July, whereas my dipole won't.

Below is a map showing my QRP 5W 10 MHz WSPR signals reaching the USA using a Sandpiper MV6+3 HF vertical on the morning of 6th April 2011.

Below is a map showing my 5W 10 MHz WSPR signals reaching VK1UN in Australia using my 2m tall Sandpiper MV6+3 HF vertical on 8th April 2011.

The Solar Flux for this day is shown as 112. I have since been informed that due to an OTHR system that the 10 MHz band now suffers from severe QRM in Australia, so I will be trying 14 MHz instead.

The WSPRnet database shows my 10.140195 MHz signal to VK1UN in Australia had a SNR of -28 dB and the distance was until recently my best ever at 16947 km.

The WSPRnet database shows my best ever DX signals have all occurred so far on the 10 MHz band and I can tell by the dates that all were achieved using my Sandpiper MV6+3 HF vertical, rather than my dipole. I would expect this due to the low angle of radiation from the vertical aerial which is better suited for long distance (DX) working.

Here below is my 10 MHz signal being received on 16th April 2011 by the man himself K1JT, Joe Taylor, the author of WSPR and WSJT software. I owe a great debt of gratitude to Joe as his software has transformed the experimental side of the hobby for me, making Meteor Scatter immense fun and QRP HF too!

After my Summer holidays I have experimented again with WSPR, this time looking at the 14 MHz band and QRP level 5 Watts of RF. Shown below is a screen grab for the morning of 12th September 2012, using my Kenwood TS-2000 transceiver and Sandpiper MQ6+3 HF vertical antenna, showing where my weak signals have been heard.

Here are the corresponding signal levels, VK3GMZ heard my 5 Watts signal at -25 dB and at a new record distance for me of 16,981 km. In reality due to the height of my 3rd floor house radio station and the distance to the garden ground level where my antenna is situated, with only a long run of lossy and thin RG-58 coaxial cable, I wouldn't expect much more than 3 Watts being radiated.

In October 2011 I started to look at other HF data modes and tried JT65-HF software on 28 MHz just to see what band conditions were like. Wow!

Shown below is a screenshot using PSK Reporter of stations heard by me on 28.076 MHz (10m), using JT65 HF mode, on Tuesday 18th October 2011.Amazing conditions considering we are only a little way out of sunspot minimum and already DX is visible on 4 Continents all at the same time.

Here below is the accompanying JT65-HF software screen grab showing ZS1LS in South Africa, PU3WSF in Brazil and several US stations.



		Send formatted VHF DX Cluster spot
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 © Copyright G0ISW. Page last modified 12th September 2012. All Rights Reserved.