[UK-CONTEST] Aircraft Reflection

[Clive Whelan]

Not directly relevant, but I remember many years ago in the Bulletin ( 
probably still was the Bull. back then!) an article on aircraft 
reflections, I believe it was on 144Mhz, using beacons of the era as the 
subject matter.

The article discussed the interference between the direct path and the 
aircraft reflection, giving the familiar variable speed " chuff-chuff " 
sound of the received signal. The author- who was somewhere on the South 
Downs if I recall-. also commented upon the special situation, when the 
" train came into the station", i.e the frequency of the chuff chuff was 
briefly zero, and the signal was steady. iirc He provided a mathematical 
proof that this occurred precisely when the aircraft, the beacon, and 
the receiving station were all on the path of a common ellipse. He then 
showed that there were in fact a number of such ellipses so that the 
train could come into the station, stop, leave and apparently repeat the 
process at a " different station"! Of course, this was in the era when 
thee used to be interesting articles in Radcom as now is, rather than a 
collection of special interest sections, which in totality are probably 
only of interest to the polymath :-(

  In fact, as I write this I am hearing just that sort of reflection on 
the Cornish ( GB3MCB) beacon on 6m, albeit with my ( handraulic) rotator 
fixed to the East. However that particular train has never come into the 
station , suggesting that the aircraft did not cross an ellipse on which 
both myself and GB3MCB (50042.5)  are located, hardly surprising since 
our antennae are mutually at right angles.

Of course, even HF operators in south GW hear not dissimilar 
reflections, on other GW signals in the South ( well on CW anyway), and 
there is little doubt that these are from the hills to the North of each 
of us ( aircraft presumably being too small to reflect HF signals?), but 
why the reflection exhibits a periodicity is not clear to yt, but one 
might postulate that it is something to do with the wx conditions. The 
periodicity of these reflections is interestingly very similar to those 
heard on W6 signals

Zut alors, this is nothing to do with contesting, so I'd better QRT!

73


Clive
GW3NJW

On 21/03/2011 17:50, Ray James wrote:
> Hi all,
> Following my talk at last years convention and on-air activities, I get regular requests for more information on the use of aircraft reflection as a means of nabbing some nice distant contacts under flat tropo conditions and contests on UHF and Microwave bands.
> Much of the content from the memory stick is retained for club talks I do but aircraft reflection appears to be to the most popular personal request.
> I have therefore added a page to my website on the operational side of the subject and trust those interested will find it useful.
>
> http://www.rayjames.biz/gm4cxm/id28.html
>
> 73 Ray GM4CXM
>
>
>
>
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