Now I can see why my dish won't align

[Vipersan]

..Thanks Robbo ...but not convinced in my own mind that moving the dish slightly arround the stub to compensate ..would work if the error was too great ..
Certainly it wouldn't matter for sats within the centre of the arc ..but Im sure it would throw a big spanner in the works at the extremes ..say 40 degrees to 60 either East an west .
on one side it would cause the dish to dip to low ..and on the other ..too high ..
..and of course this would be made worse by a larger dish being mounted ..as the beam width is tighter..
maybe ..its just me ..but I can 'imagine' the errors ..particularly as I tried evey which way for a month to align it ..and couldn't fathom why it was happening..
I can now ....now that I've seen the bracket.
rgds
VS

 

[Robbo]

Having the bend in the bracket does exactly that, it lowers the arc one side and raises it the other, making it lopsided. Twisting the dish round a bit, would put the dish face straight with the motor stub again and there would be no error, surely.

Try it and see.;)

 

[Vipersan]

..Well ..all I can describe is my own experience but I did try rotating the dish ..off the centre marker line on the stub ..during my many attempts..
I checked and double checked the pole for plumb ...and got it so I could track the arc perfectly from 58deg west to 19 deg East ...
I could just about pick up 28deg East ..but at a much reduced sig level ..it being the loudest thing up there ..
but nothing from any other sat East of 19 deg ..except a weak 28 deg ..
Any attempt to tweak the east side of the arc removed all sats 30 deg westward and reduced signal on hispasat ..
So ..my confusion remains ..and I still couldn't trac the arc correctly ..
One of the reasons Im starting over with a new location for the dish ...and a new motor ..
..and the chances are I didn't need any of it ...just a new bracket on the TD110
c'est la vie ..

rgds

 

[Vipersan]

Hi Robbo ..
I can see the logic in what you are saying ...and it would be true if the motor stub pointed vertically down ...
..but because it is at an angle due to geographical location ..
..and assuming the motor to be at zero..
..moving the dish/bracket around the stub to compensate and bring the dish face back into line..would effectively be pre-empting the the dip of the arc ..(you would already be part way down it ..even though the motor was still at the apex) ...and this error would only get worse at the extremes ..
At least ..thats how I see it ..
Im happy to be corrected ...and am enjoying the debate
rgds
VS

 

[Robbo]

LOL,

Where's the error?

The dish is on the motor stub, say it points left a bit because the bracket's bent. You twist the clamp to the right a bit by the same amount. Now, wherever you are on the arc the dish points the same way as it would have done without the bent bracket.

I.E as long as the dish face is aligned to the motor stub, all will be OK, what is in between is unimportant.

 

[Vipersan]

..I think we will have to agree to differ here m8..
If you stick a pole vertically in the ground and rotate a clamp around it with a pointer at right angles ..it remains at the same height ..
If you tilt the pole backwards about 10 degrees ..and rotate a clamp around it ..even by a couple of degrees ...the elevation changes ..
..thus you are manually doing the job of the polar motor ..
so compensating for the brackets irregularity ..you are already ahead of the motors rotation by a couple of degrees ..
You could theoretically compensate for this by increasing motor elevation ever so slightly ..or decreasing dish declination ..a tiny bit ...but the motor and dish would never tuely follow the arc ..
I realise these are tiny amounts ...but I can't see it any other way..
rgds
VS

 

[Robbo]

..I think we will have to agree to differ here m8..

Yes, I think so.

If you stick a pole vertically in the ground and rotate a clamp around it ..it remains at the same height ..
If you tilt the pole backwards about 10 degrees ..and rotate a clamp around it ..even by a couple of degrees ...the elevation changes ..
..thus you are manually doing the job of the polar motor ..

Yep, no probs

so compensating for the brackets irregularity ..you are already ahead of the motors rotation by a couple of degrees ..

No your'e back where you would have been, had the bracket not been irregular.


Or am I gooing insane!

 

[Vipersan]

..well ..if nothing else ...at least I made you larrrff ;)
rgds

 

[Robbo]

So when you getting the Gibby then?;)

 

[Vipersan]

..Thing is m8 ...Im still conviced the the triax has slightly more gain ..and might have a go at straightening and bracing the bracket first .
If it fails ..then as soon as 'piggy bank' will allow for the Gibby..
Do we know if the Gibby is the same dimension height to width ?
..
If it is round as opposed to eliptical ..then maybe the overall surface area will be close to the triax ..

 

[Robbo]

No, Satelliteman won't climb onto his roof to go and measure his.2

But I have fitted a Gibby 1m and it is the same shape as the Triax, i.e taller than it is wide, like most offset dishes.

 

[Vipersan]

No, Satelliteman won't climb onto his roof to go and measure his.2

But I have fitted a Gibby 1m and it is the same shape as the Triax, i.e taller than it is wide, like most offset dishes.

...which just makes me wonder if the 1.04 refers to width or height ..
I think SM should do the honourable thing and visit his roof ...
..just so we know
;)

 

[Robbo]

Yes, I think he should too ( Although I have seen where it's at, and it's a bit awkward to get to)

 

[Vipersan]

Oh well ..time for some ZZZs or I'll not get up for work tomorrow ..
Cheers for the banter ...and for snapping a picture of the extra metalwork on your triax ..
much appreciated Robbo..
VS

 

[Robbo]

Ahh, 97 x 104cm according to the spec sheet

_http://www.gibertini.it/en/frameset.php?p=/actived3/pages.php&s=2&l=2&doctop=/en/prodotti.top

 

[Vipersan]

Ahh, 97 x 104cm according to the spec sheet

_http://www.gibertini.it/en/frameset.php?p=/actived3/pages.php&s=2&l=2&doctop=/en/prodotti.top

Interesting ...
Followed the link you provided Robbo ..to get the gain figure for the dish ..
It does compare quite favourably with the triax ..

Triax TD110 (@ 11.75ghz) gain = 40.3db

Gibertini OP100L (@ 10.95ghz) = 39.4db

so the gibby has 1db less gain than the triax ..
..how this would translate in terms of signal loss on fringe satellites is debateable ..
I suppose it could be compared to a 1db differance in lnb gain ..
rgds

 

[Robbo]

I don't think that you can make a direct comparison though, as the gain has been specified at different frequencies.

I think the real proof would be a direct comparison once set up.

 

[Vipersan]

I don't think that you can make a direct comparison though, as the gain has been specified at different frequencies.

I think the real proof would be a direct comparison once set up.

I totally agree ..
pity Gibby chose the low end of the ku spectrum to specify gain figures ..
The Triax option to quote for mid spectrum makes more sense to me ..
rgds

 

[Vipersan]

Just add a little more confusion ..
I was searching fleabay for the gibby ...and found Brymar quoting 'Illumination Efficiency: 70% - Gain: @ 10.95 GHz: 39.8 dB ' for the 1m Alluminium Gibby they stock ..
Is it a different model ..?
maybe the figure I noted was for the steel version..
and possibly the ally version is slightly higher gain than the steel version ..??
but why ?
rgds

 

[purplemarina]

If you go for the gibby its worth considering the matched feedhorn, you can use a cm. feed as well. i found on my 1m that it made a difference on the marginal channels and more stability in bad weather,although i havent measured it with a meter so dont know the figures % wise!.