Aircraft Enhancement explained

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VK2ZRH
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Aircraft Enhancement explained

Post by VK2ZRH » Mon Jan 12, 2009 12:02 pm

The means by which signals between distant amateur VHF-UHF stations are "enhanced" by the presence of an aircraft flying on a path between them have been comprehensively examined and debated since the mid-1980s.

The principal mechanism is attributed to forward scatter from the aircraft, while it has also been shown that refraction via the aircraft's exhaust plume can contribute to signal enhancement.

Two papers, available online, provide good explanations. The list of references in each provides further reading (and, yes, a paper of mine - from 1985 - is in there).

Aircraft Enhancement – Some Insights from Bistatic Radar Theory, by Rex Moncur VK7MO, GippsTech Proceedings 2000. Available here: http://www.users.bigpond.com/anvdg/ENHA ... 0final.doc

Aircraft Scatter, by Guy Fletcher VK2KU. Available here: http://www.vhfdx.radiocorner.net/docs/A ... catter.pdf

Analysis of the contribution by an aircraft's exhaust plume was detailed by Ian Cowan VK1BG in Amateur Radio magazine in the March and July 1989 issues.

VK7MO's analysis ". . . is based on some major approximations. . . based on the target being much larger than a wavelength and in many cases the parts of an aircraft that are used for scattering will be of the order of a wavelength or less. Secondly, the method of approximating the complex shape of an aircraft has its limitations. Given these approximations we should see bistatic radar theory as applied in this paper as guiding us to what might be expected rather than providing exact answers."

Rex concludes:

1. Bistatic radar theory, can explain significant signal enhancements due to aircraft compared to those that are calculated on the basis of normal radar reflection. On 2 meters, 70 cms and 23 cms enhancements of 20 to 30 dB can be expected.

2. Based on bistatic radar theory one can build a simple model to predict aircraft enhancement.

3. Large enhancements will only occur when the aircraft is very closely aligned between the transmitter and receiver. This means the aircraft needs to being flying along the path if it is to keep within the forward scattering lobe for a useful period. Under these conditions typical enhancements are of a few to several minutes duration and more than sufficient to complete a QSO

4. At shorter wavelengths there is a significant increase in the potential enhancement, but the alignment must be improved to gain the benefit. Given that Earth curvature prevents close alignment it is likely to be much more difficult to use aircraft enhancement at microwave frequencies.

VK2KU's recent analysis looks at the different lobes scattered from an aircraft and their effect on what operators experience in the duration of enhancement.

Posted in the interests of sharing the knowledge around.

73, Roger Harrison VK2ZRH

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Re: Aircraft Enhancement explained - Bibliography

Post by VK2ZRH » Wed Jan 14, 2009 10:17 pm

For the edification of all interested, here's a list of all the salient articles by Australian authors, published in Australia.

Aircraft Enhancement of VHF/UHF Signals
Doug McArthur VK3UM
Amateur Radio, July 1985

Enhanced VHF/UHF Signal Levels Due to Aircraft
Gordon McDonald VK2ZAB (now VK3EJ)
Amateur Radio, October 1985

Aircraft Enhancement Propagation of VHF/UHF Signals - Preliminary Observations
Roger Harrison VK2ZTB (now VK2ZRH)
6UP, Vol.5 No.1 1985

Aircraft Enhancement of VHF/UHF Signals - towards a propagation model
Roger Harrison VK2ZTB (now VK2ZRH)
Amateur Radio, November 1985

Propagation via Reflections From Aircraft
Gordon McDonald VK2ZAB (now VK3EJ)
Amateur Radio, February 1986

Aircraft Enhancement - Another View
Ian Cowan VK1BG
Amateur Radio, March 1989

Signals Reflected via Aircraft
Gordon McDonald VK2ZAB (now VK3EJ)
Amateur Radio, May 1989

More on Aircraft Enhancement
~ in "Comments" column, Amateur Radio, July 1989
Correction to May 1989 article, Gordon McDonald VK2ZAB (now VK3EJ)
More on Aircraft Enhancement, Ian Cowan VK1BG; rebuttal to May 1989 article

Aircraft enhancement- some insights from Bistatic Radar Theory
Rex Moncur VK7MO
Proceedings of the GippsTech Conference 2000
http://www.users.bigpond.com/anvdg/ENHA ... 0final.doc

Aircraft Scatter
Guy Fletcher VK2KU
VHF DX Group website, 2006
http://www.vhfdx.radiocorner.net/docs/A ... catter.pdf

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Re: Aircraft Enhancement explained - Bibliography

Post by VK2OMD » Thu Jan 15, 2009 9:30 am

VK2ZRH wrote:For the edification of all interested, here's a list of all the salient articles by Australian authors, published in Australia.
...
Thanks Roger, well done.

The authors who have published online will get a better airing. How about it Roger, can your articles be made available for online viewing? Perhaps even a revised / updated article if the context has changed, or you have learned more on the subject.

I am probably not the only one who would enjoy the read OM!

Barry might have a story to tell. He seems to have become quite good (expert even!) at predicting when paths probably exist, even indirect paths if I understand correctly.

Owen

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Re: Aircraft Enhancement explained

Post by VK3HZ » Fri Jan 16, 2009 4:04 pm

This was discussed some years ago (well, many times over the years :roll: ) on the VK-VHF Reflector.

At the time (2003) I managed to hunt down the copies of AR, scanned the articles and put them online for all to read. I also attempted to contact the authors for their OK on reprinting this stuff - most were OK with it, the others I didn't hear from ...

So, I've thrown it all up again direct from the archives.

You'll find them at: http://home.exetel.com.au/dwsmith/aep/ae.htm

Regards,
Dave.

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Re: Aircraft Enhancement explained

Post by VK2ZRH » Sat Jan 17, 2009 11:11 am

Thanks for restoring the articles to view, Dave.

I was in the process of obtaining permission for posting from all of the authors (all agreed), and from the AR Editor (not yet - I believe he's gone field-daying), but you've done the job for me . . . and page views have increased :D

73, Roger Harrison VK2ZRH

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Re: Aircraft Enhancement explained

Post by VK3PF » Sat Jan 17, 2009 7:32 pm

Hi Roger,

Not playing Field Day.... Well, not yet!

Spent some time in the last week trying sort issues with microwave gear in between organising the Jan/Feb issue of AR. Guess what arrived last night - the proofs for checking..... You can guess the rest.

Sounds like I need not officially respond, as it appears to be a fait accompli.

Peter VK3KAI

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Re: Aircraft Enhancement: the ionised exhaust myth

Post by VK2ZRH » Sun Jan 18, 2009 8:32 am

There was a belief held in recent years that ". . . exhaust fumes from the aircraft ionise the air immediately behind it for a short time, and reflexions (sic) happen at that layer (similar to a meteor trail)". [Author not identified, to prevent distraction].

It's an idea that seems attractive - perhaps even plausible - at first.

Even if the exhaust from aircraft engines had sufficient energy to ionise the atmosphere at the flight heights where aircraft enhanced propagation is observed (ie. 10-12km), the recombination time for ions in the atmosphere here is *milliseconds*. Any ions and free electrons would hardly make it down the exhaust tube, whether in jet turbine or internal combustion/prop engines.

With a meteor trail, and any other type of ionospheric reflection/refraction, your Tx signal spins the free electrons, which re-radiate the signal. The ions are too heavy. Meteor ionisation trails, which mostly occur around 100-110 km, don't last very long because wind in the E-region neutral atmosphere cause the non-ionised molecules to collide with the positively-charged ions, pushing them hither and yon. The electrons, being negatively-charged, follow suit - or try to. The geomagnetic field tries to prevent them moving directly towards the ions and so the electrons are forced to move at an angle to the ions' attractive force. Hence, the electrons spiral across the sky. :) The wind disperses the meteor trail till the flock of electrons is too under-dense for detectable reflection. In addition, many electrons find their way close to a nearby ion and they recombine. Some electrons will attach themselves to neutral air molecules, giving up their freedom. Your signal won't budge them. Meteor ionisation trails are literally blown away and mopped up :D

Ionisation of the aircraft exhaust - if it happens at all - would be so rapidly consumed by recombination and attachment that your VHF-UHF signal wouldn't get the chance to spin any free electrons - not even within quarter of the RF cycle.

Posted in the interests of clarifying the issue.

73, Roger Harrison VK2ZRH

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Re: Aircraft Enhancement explained

Post by VK3BJM » Tue Jan 20, 2009 10:14 am

Barry might have a story to tell. He seems to have become quite good (expert even!) at predicting when paths probably exist, even indirect paths if I understand correctly.
True - I probably could tell some stories. It would depend if this thread remains focussed on the technical theory of how AE occurs, or whether it veers wildly into the "How to make practical use of AE" area. I do have certain views about AE and how to exploit it, and so far they seem to have borne fruit...

The above list of published works on the theory aspect is pretty comprehensive.

Just after I started mucking around in Western NSW with AE, I was asked to present something at GippsTech 2001 about my portable operations, which I did. Much more to the point, Chris Morley, then VK3KME and now VK3CJK, gave a presentation on tools that may be useful for predicting AE; aircraft route "maps" (ERC's), pilot handbooks, etc, etc. This presentation is in the 2001 GippsTech Proceedings.

My presentation, at the 2008 GippsTech, on the potential use of ADS-B receivers in aiding AE contacts will be in the 2008 Proceedings. (I know, 'cos I've already typed it up and submitted it to Peter... :D )

And there are the articles in AR magazine about my AE-related trips, if you're after more anecdotal stuff. They have background information on why I chose the places I went to. Sorry - I can't remember the Vol/Ed numbers, or the month/year of the earlier ones - I'll need to refresh my memory and post later. The Flinder Ranges article was December 2008 (so relieved I can remember that far back... :shock: )

73,
Barry
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Re: Aircraft Enhancement explained

Post by VK2ZRH » Fri Jan 23, 2009 6:40 am

Hi Barry,

That was an intriguing and informative presentation you gave at last year's GippsTech. Using an ADS-B receiver to track aircraft movements certainly beats the old maps-rule-pencil methodology (as in "string and sealing wax science"). :mrgreen:

It's a pity that the technology is kind-of expensive and the software proprietary. :(

Finding those past articles you cite and posting a list here would probably help others interested in aircraft enhancement. :wink:

73, Roger Harrison VK2ZRH

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Re: Aircraft Enhancement explained

Post by VK3KH » Fri Jan 23, 2009 7:35 am

Hi All,
It's a pity that the technology is kind-of expensive and the software proprietary.
I have an ongoing interest in AE, and have been utilising an ADS-b reciever. There is no doubt this option that may not be for everyone.
However, there is an option that is open to everyone to access the data that we are seeing and it will cost around 25 Euro. This amount will allow you to obtain the Planeplotter program and this program has open sharing of ADS-b info. So any user can see the data others with recievers are collecting and sharing back to the server. You do not need your own reciever.
David 3HZ has an entire section on this forum, in the Radio Site Display area, about using Plane Plotter and then taking the info onto Google Earth so you can look at the aircraft, and the position of Amateur stations you may be intersted in working, to see if the plane flys over the path midpoint.
I suggest the whole section on Radio Site Display is worth reading, and particularly the section on Plane Plotter if you are intersted in AE.
viewtopic.php?f=51&t=8119

Here is an inexpensive way for anyone interested in predicting flight paths over Australia, to get real time info. Its amazing.

VK3KH
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Re: Aircraft Enhancement explained

Post by VK3BJM » Sat Jan 24, 2009 5:41 am

Ok, finally dug out the magazines in question.

The first article, regarding an AE-based trip to Waukaringa in SA, was in AR Vol.70, No.11 - November 2002.

The second article, regarding AE in far-western NSW, was published in two parts. The first was in AR Vol.73, No.11 November 2005; the second was in AR Vol.74, No.3 March 2006.

And the Flinders Ranges trip article (which may contain traces of AE) was in AR Vol.76, No12 December 2008.

Perhaps Dave could scan and add these in a sub-section to his page?

73,
Barry
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Re: Aircraft Enhancement explained

Post by VK3PF » Sat Jan 24, 2009 9:33 am

Barry (& Dave),

For the December 2008 article, perhaps your friendly AR Editor might hunt out the final proof pdf & extract the pages in question....... :wink:

Will try to get it done this weekend....

Cheers,

Peter VK3KAI

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Re: Aircraft Enhancement explained

Post by VK3HZ » Thu Jan 29, 2009 8:01 am

Thank you to the friendly AR Editor for supplying the article.

On the web page, I've now added 4 articles by Barry VK3BJM and a corrected version of the paper by Rex VK7MO, together with a link to Guy VK2KU's paper.

Once again: http://home.exetel.com.au/dwsmith/aep/ae.htm

Regards,
Dave

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Re: Aircraft Enhancement explained

Post by VK2ZRH » Thu Jan 29, 2009 8:46 am

Good work! All the articles, all in one place.

Thanks Dave.

73, Roger Harrison VK2ZRH

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