Elliptical Sky Dish - reason for shape?

[luggagewarrior]

I have been given an elliptical dish, 39cm high by 54cm wide. It had been on the wall of it's previous site for some years. What was the reason for that shape? Is it still compatible with the sats out there? I was thinking of getting a positioner, one of the disecq 1.2 types with the cranked mounting arm.
The LNB is a cambridge industries type with LO freq shifting.
Please help, I'm all on my own here and I know nothing.

Thanks in advance
LW

[Quator2000]

The new dish shape is because of the reflection of the waves back to the LNB. You don't need a whole circle because you are only worried about the east/west not the north/south. Hence you don't need the top and bottom of the dish and less surface area in the wind makes it more stable, lighter and cheaper to make.

[Nibb]

It is s Sky mini-dish, and is not much use with a positioner.

You really need an 80cm minimum dish to get most of the decent channels on the other sats.

[luggagewarrior]

Thanks for those, I have a suitcase size portable maplin system which only looks at about 8 sats close together. I can get all sats with the suitcase dish, so what would be the problem with using this elliptical on a positioner? (apart from the dish edge bumping into the wall)
Ta.
LW

[Nibb]

Well try it then mate....however some channels on certain sats are weaker than others and dependant on that all will not be available on a 60cm mini dish!

And I would certainly expect you to get problems in poor weather conditions.

Check out Lyngsat for minimum dish sizes for certain sats in UK.

[the_wizzard]

Thanks for those, I have a suitcase size portable maplin system which only looks at about 8 sats close together. I can get all sats with the suitcase dish, so what would be the problem with using this elliptical on a positioner? (apart from the dish edge bumping into the wall)
Ta.
LW

whats sat's do you get with it? it wouldnt bump into wall if it was on a pole!

[luggagewarrior]

I can't recall the individual sats, the dish had to be scanned about 30 degrees horizontally from one side to the other to rx them. Astra 28, hotbird, something on 19.2 as well. memories a bit cloudy at the best of times.
It was going to be bracket mounted on our rear south facing wall rather than a pole above the roof. If it scans left to right, then possibly a wide dish (within reason) will foul on the wall if too close.
Experiments are called for I think, starting with borrowing a spectrum analyser from work and looking at the product of the round portable dish when facing due south ( so that polarisation isn't an issue ) then looking via the elliptical dish and seeing if more sats are visible. A colleague said that because it is wider, it sees a 'letterbox' portion of the horizon and a number of sats. Let me say that I'm generally ignorant of all this stuff and can only apply my general RF eng knowledge. ( I work in uhf broadcast repair ).
What is the sat that is due south from the midlands, and what freq does it broadcast on? I'll post my heath robinson findings on here if people are interested.
regards
LW

[Eddie101]

What is the sat that is due south from the midlands

Thor 1W of true South _http://www.lyngsat.com/1west.html ,quite hard to get a good signal from the midlands i would think ,unless your on a 800mm + dish

[luggagewarrior]

OK, thanks, I'll give it a try.

[Eddie101]

If it scans left to right, then possibly a wide dish (within reason) will foul on the wall if too close.

If you are intending using a motor ,it actually throws the dish a good way off the wall ,and on the likes of a 1 m dish ,if your wall is roughly true south ,would allow approx 70 degrees each way .

[Nibb]

You are unlikely to get an eliptical dish above 80cm!

Sky use 80cm in Scotland due to the curvature of the earth affecting the strength.

[Eddie101]

Elliptical dishes go to approx 36" ,which is roughly 90 cm (Force Toroidal 90cm, raven make a few as well) ,i was translating it to a standard high gain dish . You are correct the further you are from the meridian line ,the harder it is to focus the signal ,the link will show you why

_http://science.nasa.gov/Realtime/jtrack/3d/JTrack3D.html

This has most of the sats and tracks them realtime .

Regards

[goggles]

The new dish shape is because of the reflection of the waves back to the LNB. You don't need a whole circle because you are only worried about the east/west not the north/south. Hence you don't need the top and bottom of the dish and less surface area in the wind makes it more stable, lighter and cheaper to make.

It makes no difference the shape of the dish as long as its accurately made and rejects background microwaves and correctly illuminates the lnb feed assy and is correctly aligned.

Look at that old book by Baylin and Gale about KU band sat tv then look at the Pico Kid sat dish and look at weird.Think Sky`s was done like that to be modern looking and less obtrusive.Thats my thought.