Made a start on my petal extensions ..

lanab · Apr 26, 2012

Raining and cold as hell here in Sweden as well the last days

The last panels doesn't seem to fit as good as the rest

Vipersan · Apr 27, 2012

..Well ..almost that time ...so thought I'd deal with the boiler outlet issue..
Shortened by 3/4 inch ..but retained the cover/cap ..
Used fibregalss bridging compound ..and will tidy up with a file ..and wrap each 'leg' of the cap with aluminium high temp foil tape ..
..this should suffice ..
You can see what a close call it was ..
The Dish is currently at 58West ...and now clears the flue...with fractions to spare..
rgds
VS

Lazarus · Apr 27, 2012

Do you anticipate any flexing of the dish in high winds that might cause contact with the truncated flue?

Vipersan · Apr 27, 2012

Tivù said:
Do you anticipate any flexing of the dish in high winds that might cause contact with the truncated flue?

Not really Gordon ....
The wing should be 1cm closer to the dish as the tripod bracket passes through the edge of the wing..also 58 West is my absolute limit ..
Vbox limit set just 5 clicks beyond this ..and there should be 3/4 inch clear behind the wing and in front of the flue..
I can't see the flue output being particularly hot either ..the cap/vent is actually made of plastic ..and not as I thought ..aluminium..

Christina is rarely parked at 58 West for long periods ..as most channels at this location are encrypted.
So ..short periods ..for DXing ..
I think it'll be ok.
rgds
VS

lanab · Apr 27, 2012

Can't you install the dish on the roof? that would clear obstacles.

I can see what you mean by close, that's only 1cm or so from the object in the wall.

Lazarus · Apr 27, 2012

lanab said:
Can't you install the dish on the roof? that would clear obstacles.

I can see what you mean by close, that's only 1cm or so from the object in the wall.

I feel sure we've mentioned UK Planning Rules on several occasions .......................

sonnetpete · Apr 27, 2012

lanab said:
Can't you install the dish on the roof? that would clear obstacles.

If you wanted to draw attention to it.....yes (regardless of the weight consideration and increased exposure to prevailing strong winds).

lanab · Apr 27, 2012

sonnetpete said:
If you wanted to draw attention to it.....yes (regardless of the weight consideration and increased exposure to prevailing strong winds).

That's not a problem, where do you think most 1.8m dishes were installed in the old days? on roof, if you have houses built to high standards this is not a problem, i know UK doesn't make the best constructions in the world, specially the old ones...

wod · Apr 27, 2012

The dish add ons are starting to look good, have you made a cut out in them for the lnb feed arm fixings, so they will bolt tightly to the panels ?

Vipersan · Apr 27, 2012

lanab said:
That's not a problem, where do you think most 1.8m dishes were installed in the old days? on roof, if you have houses built to high standards this is not a problem, i know UK doesn't make the best constructions in the world, specially the old ones...

I agree with part of what you say Lanab...
But I would suggest the reverse is true regarding older properties ..
From what I've observed ...they are substancially better built than modern houses..
The mare less energy efficient ...but most have stood 100 years plus ...
..
Whereas modern cheap builds are showing movement and cracks after 20 years ..
just my opinion for what its worth.
Give me an old terraced from 1900 over a modern cheap brick and wood timer frame built in the 80s/90s any day..
rgds
VS

Vipersan · Apr 27, 2012

wod said:
The dish add ons are starting to look good, have you made a cut out in them for the lnb feed arm fixings, so they will bolt tightly to the panels ?

yes Wod ..you are correct ...
A slot is cut rather than a piece cut out of the wing ..allowing the tripod mount to pass through the wing ..and act as an extra brace to bolt the wing to the dish..
rgds
VS

Vipersan · Apr 27, 2012

Oh...woe is me ..
The last wing is 1.5cm too long to fit the remaining gap ...
I'd rather it had been a cm too short ..
as I can close up half a cm ..maybe even a cm by elongating the drill holes in the wings ..and closing them up tighter..
I guess it was too much to expect they'd be a perfect fit ...as ALL sizes and curves were guestimated from the start..
If the worst happens ..I'll just have to slighty shorten the last wing and make it customised ..
Still ...a cm error over this entire circumferance..
I'd say that was close to a miracle..
cest la vie
VS

Vipersan · Apr 27, 2012

Baptism of fire for Christinas new clothes ...
65-70 mph predicted Sunday...and this time the wings will remain in place ..though I will add lateral bolts between the wing segments tomorrow..to create a more solid overall structure.
rgds
VS

sonnetpete · Apr 27, 2012

Vipersan said:
Baptism of fire for Christinas new clothes ...65-70 mph predicted Sunday...

Good job it's not on the roof then......

Vipersan · Apr 27, 2012

sonnetpete said:
Good job it's not on the roof then......

Ahem! ...lol Pete ...
;)

Vipersan · Apr 28, 2012

Ok ...
need a little help from experts now ..
needed an assistant so borrowed a neighbour to hold one end of the tape measure ..
Accurately measure the diameter now the panels are bolted together ..
amazingly it measure a fraction shy of 2.2 mtrs ..
Stretched a length of masking tape to span the diameter ..and measured the new depth ..
which was 36cm ..
Using the focal distance formula ..this calculated to be 48400/576 .. = 84cm

Previous calcs when she was but a 1.8 showed the focal distance to be 81.5/82 cm ...
So according to this the focal point is now 2cm further back ..
I was convinced the focal distance should not change so in order to get the same focal distance the depth should be about 37cm not 36
48400/592 =81.8cm

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..

who wants a crack at this ?

..of course ..I could just compromise and set the focal distance at 83cm...
no doubt I'd get results ....and it would be less work ...but just how much gain would I get without accuracy..
rgds
VS

Lazarus · Apr 28, 2012

Sir!

Sir!

Not me, Sir!

joddle · Apr 28, 2012

What you are dealing with as I am sure you know is a parabola - a least part of one. Once you have a parabolic shape there is a defined focus which is the point where parallel lines hitting the surface of the parabola then are bent to converge at a single point - the focus. Extending the sides of the shape without changing the shape of the centre of it mearly allows more parallel lines to converge on the same point - so actually- once you have the basic shape - extending it makes no difference to where the focal point is .

However with a sat dish things get more complicated because an LBN and feedhorn are designed to "see" a specific angle and if you extend the dish without considering this you will simply get the same signal as before - in fact the extention will not do anything.

Think of it in reverse. Imagine a torch pointing at the dish is the lnb and feedhorn and the reflector and lens of the torch concentrate the beam so it illuminates the whole area of the old dish. To get the brightest illumination you adjust the torch beam so it does not spill over the edge of the dish. This is in essence what you have before you extend you dish. Now imagine adding the petals, alas the illuminated area will be the same the new petals will remain unluinated UNLESS you readjust the lens and reflector of the torch so the light spreads more.

Now in reverse, in order to get signal from the new petals you must ensure the lens (ie the feedhorn and scalar rings ) gather the signals from the extended part of the dish. This means changing the scalar rings setting or using an adjusable feedhorn. It becomes a matter of the angle seen by the lnb rather than distance from the dish.

Vipersan · Apr 28, 2012

joddle said:
What you are dealing with as I am sure you know is a parabola - a least part of one. Once you have a parabolic shape there is a defined focus which is the point where parallel lines hitting the surface of the parabola then are bent to converge at a single point - the focus. Extending the sides of the shape without changing the shape of the centre of it mearly allows more parallel lines to converge on the same point - so actually- once you have the basic shape - extending it makes no difference to where the focal point is .

However with a sat dish things get more complicated because an LBN and feedhorn are designed to "see" a specific angle and if you extend the dish without considering this you will simply get the same signal as before - in fact the extention will not do anything.

Think of it in reverse. Imagine a torch pointing at the dish is the lnb and feedhorn and the reflector and lens of the torch concentrate the beam so it illuminates the whole area of the old dish. To get the brightest illumination you adjust the torch beam so it does not spill over the edge of the dish. This is in essence what you have before you extend you dish. Now imagine adding the petals, alas the illuminated area will be the same the new petals will remain unluinated UNLESS you readjust the lens and reflector of the torch so the light spreads more.

Now in reverse, in order to get signal from the new petals you must ensure the lens (ie the feedhorn and scalar rings ) gather the signals from the extended part of the dish. This means changing the scalar rings setting or using an adjusable feedhorn. It becomes a matter of the angle seen by the lnb rather than distance from the dish.

Thanks Joddle...
Well aware of the feed horn issues ..which is why I took 2 months to make an adjustable scalar feed before I attempted the panel extensions ..
However ..no point in playing around with this aspect of the build ..until the focal length is correctly established ..
The adjustable feed is just the icing on the cake ..as it were.

Ok ..still one panel missing ..and there are some quirks noticeable already ..
I noticed a slight _drop_ in gain since the 5th panel was fitted..
My theory fwiw is that the focus is close..so close in fact that there are now standing wave interferences accumilating at or near the focus ..thus reducing some channels reception ..yet building others.
As an example of this ..
I went over 13db on startimes 10E with 4 panels ..but cannot get above 12.5 with the 5th panel added.
However ...I just locked in CDM -4169 V
tp 23 CDM Internacional
DVB-S 3000-3/4
at 58West ..
I don't remember _ever_ locking this before ..and now its locked and stable
here are the pics.

So quirks a plenty ..but then ..the feed assembly has been barely touched yet..
the focal length has yet to be established and optimised..
and...
there is still a panel missing..
rgds
VS

Vipersan · Apr 28, 2012

@ Nelson ..
If you're at home now ..
can you do me a favour ..
I want to compare signal levels on a Linear transponder that we can both access ..
Would you mind checking Metro TV and or Silverbird at 37West ?
I need it for comparison purposes ..
Considerably more than I got previously here..
..and dont want a plate involved in the equation.
Metro TV currently 12.2
Silverbird.. 8.2
I know the scales are not totally comparable ..
These readings being taken on the F15..
But it will help.
rgds
VS

Made a start on my petal extensions ..

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