Made a start on my petal extensions ..

[nelson_b]

hi vipersan
sorry i,m not at home to test/compare -- i,m away on holiday in north west scotland and will be staying here untill the weather changes -- good forcast untill the middle of next week for this area

this dongle for my laptop is a bit of a pain though GPRS speed only this far north

regards nelson.b.

 

[Vipersan]

hi vipersan
sorry i,m not at home to test/compare -- i,m away on holiday in north west scotland and will be staying here untill the weather changes -- good forcast untill the middle of next week for this area

this dongle for my laptop is a bit of a pain though GPRS speed only this far north

regards nelson.b.

No probs m8 ...
Enjoy your weekend ..and don't get washed away in a storm..next week
;)
rgds
VS

 

[Channel Hopper]

Do I have this right ..that focal distance should not change ...at least not by this much ..
Assuming this is true ..then I have to add more 'tilt' to the wings to make them point slightly more inwards ..thus increasing the depth from 36cm ...to 37 cm..

If the parabola is maintained, then the focal point shouldn't change.
It does appear the surface properties of the reflector has changed in adding the extenders, but it may be that the original dish design was incorrect.
The improved reception could be more to do with the extenders forming a better focal point rather than simply increasing the area.

There are two possible checks

1. Make a parabolic profile card based on the original dish design, extended out to the new radius and check if the extenders follow the formula.
2. Leave everything as it is wrt to the extenders and build a new central reflector based on the revised calculations, then test for improvement of the signal.

 

[lanab]

How heavy are those extension panels? are you sure they are not sagging the dish with all mounted? that could be the reason it loses performance.

 

[Vipersan]

If the parabola is maintained, then the focal point shouldn't change.
It does appear the surface properties of the reflector has changed in adding the extenders, but it may be that the original dish design was incorrect.
The improved reception could be more to do with the extenders forming a better focal point rather than simply increasing the area.

There are two possible checks

1. Make a parabolic profile card based on the original dish design, extended out to the new radius and check if the extenders follow the formula.
2. Leave everything as it is wrt to the extenders and build a new central reflector based on the revised calculations, then test for improvement of the signal.

..Good ideas CH ..
I did something similar earlier whereby I placed a long flat plastic stip on the original dish interior curve...pushed hard down to the original dish surface by hand...allowing it to extend outward beyond the original surface and over the wings ..
there are gaps under the plastic strip on some wings but not on all ..
I concluded therefore that some wings needed lifting a little ..which I'll do once the threatened winds have passed..
Interestingly ..though not a perfect proof ..the gaps under the plastic strip above the wings which sit too low are uniform ..so I'm thinking they fairly acurately follow the curve ..
I'll post a picture tomorrow to show what I mean ..
too dark to do it now ..
Plenty to do ..but I do feel progress is being made.

cheers
VS

 

[Vipersan]

How heavy are those extension panels? are you sure they are not sagging the dish with all mounted? that could be the reason it loses performance.

Light enough to be hung on my little finger without any discomfort ..
absolutely no way they would alter the dish shape ..
Fibreglass panels aren't heavy enough to mishape 2mm+ thick ribbed aluminium.
cheers
VS

..and I should have added ..the dish hasn't lost performance ..
Its improved dramatically overall..
Its just not as efficient as I envisaged ...at least ...not yet

 

[aceb]

@ Nelson ..
Would you mind checking Metro TV and or Silverbird at 37West ?

I'm probably too far south for the test to be relevant VS but I can check here if it's any use?

Now I'm up I've just checked anyway, Silverbird comes in at 8.9dB SNR using Crazyscan and Metro is 15.1dB. Looking at it in Dream it's actually one of the strongest signals I receive on C band at 95/100% and considerable stronger than Silverbird at 90/35SQ although the latter is 8PSK of course.

 

[Vipersan]

I'm probably too far south for the test to be relevant VS but I can check here if it's any use?

Now I'm up I've just checked anyway, Silverbird comes in at 8.9dB SNR using Crazyscan and Metro is 15.1dB. Looking at it in Dream it's actually one of the strongest signals I receive on C band at 95/100% and considerable stronger than Silverbird at 90/35SQ although the latter is 8PSK of course.

Thanks for checking Paul ..
The ratio looks to be about the same for the 2 channels ..but as you say being considerably further South would make the comparison less relevant ..
Good to know we are in the same 'ball park' with the numbers ..and gives me numbers to aim for..
;)
cheers
VS

 

[Vipersan]

Ok ..most unpleasant outside today ..
Gusting winds and cold rain..
Braved it just long enough to grab these pics ..
I realise this isn't a foolproof accurate nor scientic test..
But it does give a rough idea how well the curve is being followed...and the height discrepency between 2 adjacent wing segments .
that almost 1 cm clearance under the plastic strip would make all the difference when calculating the focal length ..
lifting the wing would make the dish deeper ..so 36 ..would be 37 cm ..and the focal distance when calculated would be closer to 82cm..
So small errors like these ..could well account for the quirks I'm seeing.
rgds
VS

...Chad says..."Wotno feedback ?"... ;)

 

[Vipersan]

Not able to play-out today ..
..the weather forbids it ..
But took some time to watch for any signs of stress or movement on Christina ..
So far she just shrugs off the windy/gusty onslaughts..
The TD110 is tied down ..but still bobs around like a cork on a rough sea..
Very pleased the wings are so solid ..at least thus far..
rgds
VS

 

[Vipersan]

..The sun came out today as promised by Gordon...

Cheers m8 ...any chance you could arrange it for the whole week ?


..Didn't stop the windy gusts though ..
Strong enough to blow bits of fibreglass matt all over the yard...and tip over a freshly mixed pot of resin ..
but hey ..there's this huge yellow ball in the sky ...and its scaring the crap out of me ..
Perhaps I should drop to my knees and worship...

Joking aside ...I've started to mod the last panel ..
You can see by the pic how much too long it is ..
The red arrows show the new end wall being built up ...and I may well still have issues with the flue ..
The blue arrow shows the outer flange which might just foul the dishes track at the extreme west..
Thought shortening the flue was enough ..but looks like I'm wrong ..
Didn't take the flange into account ..so may well have to change the outer curve of this one panel by a cm or so ..
Everyone makes mistakes ..as the Dalek shouted climbing off the dustbin...
rgds
VS

 

[sonnetpete]

The red arrows show the new end wall being built up......

VS, I know you're justifiably proud of your extended dish but how did you manage to blag an air display??

 

[Vipersan]

...and thats the efficiency of fibreglass/resin ..
30 minutes and a good cuppa T later...
...end chopped and the new wall hard enough to work on ..
Building the new wall before cutting the old one loose ..doesn't allow the panel to change shape..
rgds
VS

 

[Vipersan]

VS, I know you're justifiably proud of your extended dish but how did you manage to blag an air display??

Errrr....friends in ^ high ^ places ...????

Buhbumm..

 

[Bajasur]

A very interesting project!

If you want to check the accuracy of you "as built" petal extension, there are a couple of ways you can do it.

Lawrence Mayes published an excellent article on parabolic antenna pattern making using a graphical approximation excel sheet (graphical calculus).
His procedure calculates both the parabolic curve to any accuracy you specify (step length) and the generation of the petal surface area pattern (great for unsupported surface areas).

_http://vzone.virgin.net/ljmayes.mal/var/parabola.htm

the embedded downloadable excel sheet is used for the calculations.

For the parabolic arc:

Cut the parabolic form out of a sheet of thin plywood and use it as a guide to check the parabola.

For the parabolic surface:

Cut surface area petals from construction paper or other thin, flexible material and tape them on the antenna. If the design is correct, each paper petal will exactly meet at their edges. Any gaps or overlaps, indicate a construction error.

 

[Vipersan]

Thanks for the link Bajasur...and a big welcome to the forum to satgeeks in Mexico..
Very inspirational ..and has stirred an idea in my grey matter..

This is very doable I think for testing reasonably accurately the reflecting properties of the ...hopefully parabolic dish and wing segments ..
see the attached pic ..
its fairly self explanatory
rgds
VS

 

[Vipersan]

Well friends ...
..here it is ..the last (customised) wing fitted but not yet laminated ..
A full picture taken at 40W ...and the gap to the flue shown at 40W..
Christina was then shuffled very slowly to 55West ...
and the gap to the flue then shown from front and reverse..
It ain't that far to 58West ..my western limit ...but might well be a million miles away ..unless I either shorten the flue some more ..to shape the wing to allow it to close the gap..
I will of course try nudging her past the flue tomorrow to 58west ..with the advantage of daylight ...but I have my doubts ..
..its a _very_ close call indeed.
So near yet so far.
...but ain't Christina beautiful in her new outfit ?

rgds
VS

 

[nelson_b]

yes -- it looks like the pipe may need a slight trim ---
but that can only be a small job compared to all the hours you have put into making the extensions -
it realy does look very good now --
i look forward to seeing the dish close up - the next time i,m in greater manchester ---

cheers nelson.b.

 

[lanab]

Is that the pipe to the toilet?

 

[Vipersan]

Is that the pipe to the toilet?

Sadly no its not Lanab ...it was discussed earlier in the thread ..
Had it been waste ..or water ..it would have been re-routed..
Its a balanced flue outlet from a gas boiler ...so only minor tweaking is possible ..or indeed ..safe.
rgds
VS