This content of this page contains a mixture of Amateur Radio related topics such as Amateur Radio High Altitude Balloons, Aircraft scatter propagation (ACS) and RADAR, together with other sections about aircraft in general.

I have a personal interest observing aircraft in flight and this page also reflects that and provides a number of useful links to other related sites. I am particularly interested in military helicopters as well as experimental, unusual or exotic aircraft. Living in the Lake District National Park with its many mountains and valleys, provides me with an abundance of jets, helicopters and other aircraft, flying at low level, to and from RAF Spadeadam to see.

My old amateur radio QSL card design, showing my interest in stealth aircraft.

In November 2014 I took advantage of a special discounted offer from Moonraker for an AirNav Radarbox 3-D ADS-B receiver system in order to track in real-time aircraft within approximately 200 miles of my home location.

So far I have been very impressed and have setup alerts for specific aircraft or types of aircraft I am interested in. The system automatically records and logs all aircraft received and downloads pictures from the Internet of them too, for later review.

Shown below is my live AirNav Radarbox 3-D feed, updated every minute when system is switched on.



Aircraft Scatter Propagation (ACS)

Aircraft scatter, occurs where an aircraft is flying in the air along a signal path.  The signal may not be available until the aircraft is at the midpoint, half way between your location and the transmitter, but it can occur at any point.  The metal of the aircraft may be able to reflect the signal, which would otherwise be attenuated along the ground, either because of the large distance involved or because the signal has been attenuated due to nearby terrain. The maximum distances involved are around 800km (500 miles) and the duration can be for several minutes.



The most common effect of aircraft scatter is to cause a rapid flutter of the propagated signal.  An aircraft flying at low altitude travels close to the signal path and begins to affect the received signal.  The fist signs are when the signal becomes choppy.  A rapid flutter becomes audible where the signal fades cyclically.  The cycle becomes shorter and after a minute or so the fades appear to stop.  A few seconds pass and the fluttery fading starts again, becoming more and more rapid until the effect passes.  This happens because the signal is arriving from two angles: from the ground wave and via the aircraft reflection.  The distance travelled by each signal is slightly different and as the aircraft moves around a phase cancellation effect occurs which produces the fading effect.


In order to cause a radio reflection an aircraft must have both the transmitter and receiver within its line of sight "radio horizon." The minimum altitude for a reflection is lowest at the transmitter-receiver baseline midpoint, with the minimum altitude about four times as high over either the transmitter or receiver.


A few examples of the minimum midpoint altitudes are:


Link Distance

Minimum aircraft altitude


20km (65,000 feet)


11km (36,000 feet)


5km (16,000 feet)


1.2km (4,000 feet)


0.3km (1,000 feet)


I have had SSB voice QSOs using this mode usually on 144 MHz (2 metres) and in the region of up to 250km distance and more recently greater success using JT6M data mode on 50 MHz at a distance of around 350km, where the reflections are longer and more stable.


I am on the main transatlantic flight path between Heathrow and the Hebrides as well as being reasonably close to Manchester, Newcastle, Glasgow and Belfast airports. I have RAF Spadeadam, a NATO electronic warfare range just to the North of me so am used to seeing lots of military aircraft and helicopters too.


Most civilian aircraft fly at a cruising altitude of no more than 12,000m or 37,000feet, but there are a few modern military aircraft, which fly much higher. However due to their Radar Absorbing Materials (RAM) and Stealth technology, they are intended to deliberately not reflect back any radio waves and thereby defeat enemy Radar, which might otherwise detect them.





The shorter the distance between the transmitter and receiver, the more levels of air traffic that become available to cause reflections, over a broader geographic area. Due to their slower speed, aircraft tend to have much longer reflection durations, when compared to meteors.



The aircraft will simulate an extremely slow "head" echo, with its associated oscillating diffraction pattern. The stronger the normal atmospheric scatter signal is at the receiver, the more pronounced these oscillations will be. This will create a symmetrical signal of a series of either accelerating or decelerating oscillations. The centre of these oscillations is usually occupied by a large peak which last from about one to fifteen minutes. The higher the operating frequency, the more likely it is for an aircraft to cause a reflection.


An experimental data mode SlowFeldXPAS designed for use specifically for aircraft scatter can be downloaded here. Depending on how close you are to major air routes will affect how many reflections you can detect.



Watch here how Rex VK7MO beat the Australian distance record for Microwave using ACS





Now in March 2013 I have just discovered some fantastic software called AirScout by DL2ALF for live real-time Aircraft Scatter propagation analysis with live mapping too.


Here is a screen shot showing the projected 144 MHz signal path between my station G0ISW at IO84OQ and the GB3VHF beacon at JO0EH. The area for mutual Aircraft scatter propagation, roughly the mid point distance wise between the two amateur radio stations, is shown in the 'Pathinfo' box at the lower part of the screen. Flights in this area will appear in the box. However that potential ACS area is above the set maximum flight height of 12200m set in the software indicated by the dark blue line in the 'Pathinfo' box, so is suggested as being non viable for this distance of 431 km.


For the live aircraft flight tracking, required by AirScout, I used the Flightradar24 website.



In this second alternative screenshot example below the projected 144 MHz signal path between my station G0ISW at IO84OQ and G4VLC at IO81PV, a distance of 311 km, is shown. The maximum aircraft altitude has been set at 12000m in the software, the Aircraft Scatter Propagation (ACS) zone is shown in purple.







Interestingly on 12th August 2013 at 0744 UTC I also worked EI9E/P in IO55VD square, 350 km away from me so too close for easy Meteor Scatter. I heard many very brief MS pings from this station but couldn't work him randomly. I then noticed some longer none MS reflections that were random and not Troposcatter, using AirScout software by DL2ALF I was able to observe that all these longer 15-30 second reflections were actually via Aircraft Scatter (ACS) propagation with planes flying over the Irish Sea crossing the path between our two stations.

Looking for a really good flight path I then worked EI9E/P with ease, see screen shot below. Notice the pink coloured mutual scatter zone and the pik coloured aircraft that allowed us the QSO, the metallic body of this plane being an excellent reflector even at 50 MHz. I took the screen shot after the QSO was nearly complete so the aircraft had travelled slightly over the path line. Had I clicked on the aircraft icon I would have known what the flight and aircraft type was.


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.




Of course apart from reflecting your radio signals, the aircraft themselves can also be detected using radio - Radio Detection and Ranging - RADAR







Introduction to RADAR principles



During WW2 the German Freya radar system, which was the first operational early warning radar system, used VHF frequencies very close to the current Amateur 144MHz (2m) range. View the Battle of the beams for more info about WW2 radar development. Or visit this page by LA8AK for an interesting tour of what remains in Norway now of these radar systems.







You can visually observe aircraft scatter for yourself using passive Doppler Radar. Have a look at the site of G3CWI for a full description. Or you may be interested in the new Kinetic Aviation SBS-1 real time virtual radar system, simply plug it into your PC, load the software and it is ready to track aircraft straight away.






Century of Flight


Royal Air Force



Official website


USAF Research Lab


Boscombe Down crash


Military Airshows in the UK

LFA 17


Low flying in the Lakes


The hunt for plane '928'

Tom Mahood the finder of the crash site is a Radio Amateur!

RAF Spadeadam

Electronic warfare range

 UAV overview

Listing of all known UAV programmes

21st SOS 'Dust Devils'



Messerschmitt 262


AirNav Systems tracking software



SimHQ flight simulations


PC flight simulation


Chinook 'Wokka' site


RAF Odiham helicopters

UK aircraft crash sites


Lancashire aircraft investigation team



Zeppelin museum Friedrichshaven





Military aviation & space projects



Fighter Control


For the Military Aviation enthusiast






Global Hawk


High altitude long endurance UAV


X-50 Dragonfly


50% helicopter & 50% plane

X-47 US Navy Pegasus


Unmanned combat aerial vehicle

X-44 Manta


Multi axis No Tail

The X-Hunters

Aerospace archaeology team for Experimental aircraft

Airscene UK

US Military aircraft


Look-up by aircraft designation





US Area 51 research



Desert Secrets


US Area 51 matters


Area 51 imagery


Satellite photos


UK warplane

Forum for UK observers




Scramjet Mach 9.6 (7,000 MPH)



Defence Advanced Research Project Agency



US National UFO reporting centre


WW2 experimental aircraft




Aviation hub


Dryden flight Research centre

MH-53M Pave Low IV


My favourite helicopter








Amateur Radio High Altitude Balloons

University of Cambridge High Altitude Balloon flight predictor


Amateur Radio High Altitude Balloons listing


iHAB Project

Amateur Radio High Altitude Balloons Organisation ARHAB

 The Spirit of Knoxville

Cambridge University Space Flight

 Amateur Radio High Altitude Balloons


Amateur Radio High Altitude Balloons














Exotic Aircraft/Jet packs/Wings/UAV

Artist impression of WW2 German Himmelstürmer jet pack designed to allow 50-70m long jumps over minefields/obstacles, in development 1944-1945

X-15 1961

Boeing X-48

US Navy VTOL XFY-1 Pogo

US Navy XF5U/V-173 'Flying Pancake' 1940's

McDonnell XV-1 Convertiplane






Dragon Warrior








Aircraft spotting / air band monitoring

In the UK it is possible to observe many types of aircraft, often airports will have special observation areas for the public.

It is not permitted to monitor any radio transmissions from aircraft in the UK, but it may be possible to hear these transmissions where a public broadcast facility is provided by the event organisers at major Airshows such as RIAT.

If the laws in your Country do not permit you to monitor radio communications on the Air bands, then it may be possible to hear Aircraft communications using radio receivers around the World, which are linked directly to the Internet and in Countries where it is legal to monitor these transmissions. Please try the DXtuners website to gain such Internet access.


UK Airband frequencies

Civil & Military 1997


Fighter Control

For military aircraft enthusiasts


UK Airfield Viewing Guide

Good guide to spotting

AirNav Systems

Tracking software

 Mil Air audio

Audio recordings


Message board mostly Continental sightings



Internet radio receivers

  Aircraft callsigns

USAF 2003


UK frequency guide

Basic frequency listing


Airband scanners

Scanner reviews

MilAirMan Lakenheath

USAF base activity

Air Supply

Aviation store



Scanner reviews

Monitoring Times

US based scanner magazine

Photavia Press

Excellent books

RAF Wattisham

Frequency guide


Walney Air Show

Excellent free air show


Software mapping for flight restrictions, exercises etc.


Free Software mapping for restrictions, exercises etc.


UK Aviation briefing

UK warplane

UK military aircraft info











50 MHz (6 metres)

70 MHz (4 metres)

144 MHz (2 metres)

432 MHz (70 Centimetres)

G0ISW Ham Radio Station

Send formatted VHF DX Cluster spot


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© Copyright G0ISW. Page last modified 21st November 2014. All Rights Reserved.