[UK-CONTEST] Aircraft Reflection

[Ray James]

--- On Tue, 22/3/11, John Lemay <john at carltonhouse.eclipse.co.uk> wrote:

> It's too early in the day for me to delve into spherical
> geometry. 

Anytime of the day for me John!

>Is it reasonable to assume that a plane at say 40,000ft at your
mid point is approximately at zero degrees elevation, for both parties?

Yes, that is a reasonable assumption.
I don't have elevation on 23cm but do so on 2m and 70cm and I very often listen to PI7CIS/B on 70cm when aircraft pass through the mid-point from here (just off the coast of Scarborough) and elevation makes little difference. However, I do find a few degrees of elevation helps during UKAC's on 70cm when working or listening for "G's", turning a marginal signal to fully readable in the majority of cases. This is were your spherical geometry would come in but I'm more interested in making the contacts and less in the maths behind it.
I did an experiment on 23cm last year by mounting a single 23el Tonna through my skylight window to the same height as my 4x44el mounted on the gable end to see if the wider beamwidth of the smaller antenna would produce a longer aircraft reflected signal. If it did it was marginal but the much more readable signal off the 4x44's convinced me I had nothing to gain.    

> It occurs to me that for stations located behind a hill ('Morning Bob!),
> the reflection technique could still be useful, but with shorter paths, so long as the plane is not behind the obstruction.

Certainly, though as above, a wee bit of antenna elevation would not go amiss but always worth trying if that's not possible.
As a number on here who have been to my home will know, I'm on the side of a hill with a horrible take-off to the north into immediately rising ground rising another 200'-300' higher within a mile and 1,500' hills some miles beyond. During a contest (UK Microwave Group) at the beginning of this month I managed to work GM8IEM in IO78HF, right up in the north west corner of Scotland on 23cm via aircraft reflection so the moral is, however poor you believe your location is in some directions (Hi Bob!) then aircraft reflection is a method to overcome such disadvantages.

> Could you say a little bit more about equipment requirements? I see that on 70cms you have about 100w and 2 yagis. How is OZ1FF equipped? 
Could you conclude that a more basic station (say 50w to a single yagi) would struggle to make effective use of aircraft scatter ?


There is no substitute for ERP to produce the best results (shortest contest QSO's) but this does not preclude good results with lower power levels, it can just take a bit longer or more than one aircraft to complete a QSO. It is far easier to generate a decent ERP on the likes of 70cm and above due to antenna size. I started off in the 23cm UKAC's running just 10w to a single 23el Tonna and could work numerous stations over 500km on a regular basis. My higher ERP contact partners were usually the ones waiting to get my information through but patience is a virtue that gains points and multipliers! So yes, there can be a struggle using lower ERP but it will still work.
Kjeld OZ1FF runs 145w to a 1.5m dish http://www.oz1ff.dk/Pages/Station/Antennas.htm

Hope that answers your questions John and is of interest to other contesters interested in exploring this means of communication.
I would add that during UKAC's, aircraft numbers reduce quite dramatically from the 8pm start so it is best to utilise aircraft reflection contacts earlier in the contest rather than later.

73 Ray GM4CXM