Made a start on my petal extensions ..

[Vipersan]

You do know the UK is expecting some three days of heavy rain, from tomorrow.

...Rain ain't a problem CH ..
The casts should be waterproof enough..
What _does_ worry me is if its accompanied by high winds..
If anyone hears of anything relating to winds in my area...Manchester...please let me know asap..
I'll chance another day with the wings attached ..so they can fully cure some more ..in the sun...whilst its available.
rgds
VS

 

[Lazarus]

They threw away the mould after they cast you, my boy!

 

[Vipersan]

...Last wing in the mould ...
Sadly I ran short of roving cloth in a single sheet ...so had to piece it in 3 sections ..
I just hope it is as good as the other 5 ..
but then its going to be covered anyway...
..retaining the correct shape is the main worry ..
I'll know tomorrow.
All wing segments now removed from Christina ..in view of the likelihood of some nasty weather for the UK..
rgds
VS

 

[lanab]

Alcoa 2.4m with extension, old pic i found.

 

[Vipersan]

Thanks for the picture Lanab...
She's a beauty..
;)
I doubt my efforts will reproduce what the original with extension panels can do ...particularly as I'm not sure just cloning the last 8 inches of the alcoas dish curve will reproduce the correct parabolic curve ...but ..I'm hoping there will be suffucient extra gain to make it all worthwhile..
In an Ideal world I would have been more likely to get the best results If I'd had a single extension panel to work with ..and able to clone its first inner 8 inches..
but not having one ...I do what I can ..
We shall see..

Difficult takes a long time ....the impossible ...a little longer.
rgds
VS

 

[Vipersan]

Ok ...
We've had this discussion before ...
Time to resurrect it again ...particularly as we have Lanabs picture to reference ..
The debate in the past was ..that adding extension panels would alter the diameter of the dish ...
..but this also changes dish depth ..
So ..presumably the FD ratio remains in balance and ..as Diameter and Depth changes the ratio keeps the focal depth the same ?
..therefore ..the point of focus at the tripods apex remains the same distance from the dish centre.
Do I understand this right ?
rgds
VS

 

[Topper]

As a reminder of the equation etc here is an extract from analyse maths

-http://www.analyzemath.com/parabola/parabola_focus.html

 

[Vipersan]

Well ..even though the last wing had to be pieced ...it came out as well as the others..
Thats it with the odd markings 4th from the front..
Too cold to play out today...
But did managed 1/2 hour to trim the edges neat..

'scuse the mess in the backyard..
..I wont be cleaning up till the weather warms up ..and allows my hands to fully function again.

Couple of days off construction now..as billy wind and roger rain have dictated thus...
rgds
VS

 

[Channel Hopper]

Ok ...
We've had this discussion before ...
Time to resurrect it again ...particularly as we have Lanabs picture to reference ..
The debate in the past was ..that adding extension panels would alter the diameter of the dish ...
..but this also changes dish depth ..
So ..presumably the FD ratio remains in balance and ..as Diameter and Depth changes the ratio keeps the focal depth the same ?
..therefore ..the point of focus at the tripods apex remains the same distance from the dish centre.
Do I understand this right ?
rgds
VS

Can't recall that discussion in full, but no the f/d ratio does change (slightly) as a result of the increased diameter.

If you look at the General Dynamics - ex Prodelin prime focus range - 3.7m and 4.5m antennas, they use the same mouldings, the 4.5 is the same antenna with extension panels, but the f/d ratio changes from 0.37 to 0.3.

Somebody with better maths than me would be able to calculate the change with parabolic formulae.

 

[Vipersan]

Can't recall that discussion in full, but no the f/d ratio does change (slightly) as a result of the increased diameter.

If you look at the General Dynamics - ex Prodelin prime focus range - 3.7m and 4.5m antennas, they use the same mouldings, the 4.5 is the same antenna with extension panels, but the f/d ratio changes from 0.37 to 0.3.

Somebody with better maths than me would be able to calculate the change with parabolic formulae.

Thanks CH ...the discussion I refered to ...we briefly touched on it in a previous thread..
..Probably the lengthy 'Dishaster' thread.
As suspected ..the ratio would change ..but does this also lengthen the focal distance for lnb placement ..?
If it does ..and hopefully not by much ...then I'll have to accomodate the change by lenthening the tripod legs ..since these too are homemade.
Luckilly I used 15mm copper tubing ..so a straight yorkshire coupling would make this easier..
rgds
VS

 

[Channel Hopper]

It won't change the focal point as the parabolic equation remains the same, however the feed needs to be illuminated over a larger area of the dish, meaning the aperture will require changing to retain efficiency.

So you may be experimenting with the scalar rings again.

 

[Vipersan]

Thanks CH ...much as I expected ..
Which is why I made the feed adjustable all those months ago..
Hopefully my hombrew scalar will accommodate the changes.
rgds
VS

 

[Huevos]

VS, as CH say the focal point will be in exactly thge same place. But the scalar rings have to move away from the dish a bit. It is engraved on the side of the lnb. So measure your current depth and work out f/d and then bolt the wings on and measure your new depth and work out f/d for that. If your old f/d was 0.4 and new f/d is 0.35, move the scalar ring set 0.05 away from the dish according to the scale on the side of the LNB.

 

[BM300]

Hope this helps:

Focal length = f Depth = c Diameter = D f = ( D * D ) / ( 16 * c ) Measure the depth using a tight fishing line across the dish and a rule to measure depth c.

 

[Vipersan]

WaaaaaaaHHHHH!!!!!
Just ran out of Resin ...
Ordered another 5kg of the stuff ...but may not arrive before weekend..

Just enough left to start the support struts ...these will be made from 1/2 inch quad mold sticks ..with chopped strand fibre glass draped over them ..as in the pic of the one I managed to do before I ran out ..
also note the re-enforced corners using fibre glass bridging compound..

I should have been more pro-active and ordered earlier in the week ...but never expected the weather to improve as much as it has today.
cest la vie..
VS

 

[Vipersan]

..As expected the lamination process is proving to be the trickiest part ..
Aluminium foil tends not to want to be handled ..plus any air trapped during the foil placement causes blisters and creases ..
This is the first wing laminated ..
If it proves non viable at least it can be rubbed smooth an a new layer bonded..
what is working in my favour is that C band requires less precision accuracy ..
Cosmeticly it wont be a problem ..but to the incoming signal ...maybe..
We shall see..
rgds
VS

 

[Lazarus]

Well I've zoomed in as far as I can and it looks great.

 

[Vipersan]

Well I've zoomed in as far as I can and it looks great.

You'll just have to take my word for it Gordon ...
There are small blisters and creases ...and you know me ...I like perfect
cheers
VS

 

[Captain Jack]

Any early reception reports?

 

[Vipersan]

Any early reception reports?

A bit early to tell yet CJ..
I'll wait until I have at least 3 panels fitted ..before I start playing with the feed..
rgds
VS