Fibo Gregorian 1.2 conversion to multi lnb

Toyboy

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I'm thinking of doing away with the 2nd reflector & single C120 quad lnb on my dish and adding a multi lnb bracket with 4 Quattro LNBs and a diseqc switch to feed 4 receivers. But I think I'll have to extend the arm that holds the 2nd reflector/lnb to focus directly to the new lnbs. The dish will remain fixed of course even tho' the motor still works. Anyone know what length the arm would need to be to focus on the new lnbs ? Could be trial & error I guess.
 

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Wait a minute.... you are going to remove sub-reflector and install multifeed instead of it?This is not so wise idea IMHO. This is great dish, great Gregorian design and would be sad to see it spoiled.
 

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Wait a minute.... you are going to remove sub-reflector and install multifeed instead of it?This is not so wise idea IMHO. This is great dish, great Gregorian design and would be sad to see it spoiled.
Yes I know but rather than having a single lnb with the dish swinging away I'd rather have it fixed with access to 4 Sats. Also, the moving part of the polar mount seized up a while ago, took some leverage to make it rotate again but the nylon sleeves between the fixed & moving parts got trashed so now it's not a snug fit & there's some play and metal-metal contact.
 

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That is pity and will certainly be step backwards. But if this is your decision there is my offer: I make multifeed system (for 4 LNBs) for your dish and send it to you. You send me subreflector, feedhorn and LNB from your dish. Costs lay where they fall.
 

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That is pity and will certainly be step backwards. But if this is your decision there is my offer: I make multifeed system (for 4 LNBs) for your dish and send it to you. You send me subreflector, feedhorn and LNB from your dish. Costs lay where they fall.
Appreciate your help but I'd rather keep the sub reflector, feedhorn & LNB in case I find replacement nylon sleeves and restore dish to it's former glory
 

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I'd rather keep the sub reflector
Happy to hear it! At least some chance you can go back to Gregorian design some day. So, back to your original question.... focal point of your dish is located 627mm from lower point of its working area and 1246mm from the upper point of the working area. You could put 2 threads (627 and 1246mm) and visualize where you should have central LNB installed.
 

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One thing I didn't like about the 2nd reflector is that the signal is partially blocked by the feed horn. Wonder what would happen if the 2nd reflector was replaced with a big feedhorn the same size as 2nd reflector & the lnb behind it ?
 
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One thing I didn't like about the 2nd reflector is that the signal is partially blocked by the feed horn. Wonder what would happen if the 2nd reflector was replaced with a big feedhorn the same size as 2nd reflector & the lnb behind it ?
You'd still be suffering from lower signal quality the derives from having the spherical wavefront distortion from the reflector, which get corrected by the second reflector. (which is why there *is* a second reflector).
Incidentally, the dish was also available in a multi-LNB, non-gregorian configuration. Just what you are asking for. The one's I've seen was branded Philips. But they are comparable to any other 100cm dish, so there's not much gained there. The real difference is made by the Gregorian feature.

Edit: Sorry, I meant comparable to any other 1.2 meter dish.
 

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the signal is partially blocked by the feed horn.
It is not true. That is beauty of the Gregorian design that signal is not blocking nether by subreflector nor feedhorn.
 

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Multi lnb set-up is also possible in front of the sub .
I tried it once with succes for 23.5 / 19.2º with a modded 6º monobloc .
As you can see , only one lnb is in the centre , so for shure a third lnb (13.0º) will work , maybe even four (28.5º)

gregmonobloc 003.jpg
 

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To give a idea where to put lnb if you dont use the sub .
At first the dish with sub and fibo horn was pointed to a certain satellite , than I tried to find the lnb position with a adjustable 4D lnb stand for use without the sub .
As you can see its more close to the dish than the sub is .

no sub.jpg

4D stand.jpg
 

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To give a idea where to put lnb if you dont use the sub .
At first the dish with sub and fibo horn was pointed to a certain satellite , than I tried to find the lnb position with a adjustable 4D lnb stand for use without the sub .
As you can see its more close to the dish than the sub is .

View attachment 100685

View attachment 100684

I like the way you work trust, you think well and your works very good, a pleasure to read your tests and see your designs :)
 

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Looks like what I'm looking for, I thought the multi LNBs would have to be further away from the dish with no 2nd reflector? I was thinking about using a 4 lnb bracket with the weakest signal lnb at the main focal point and stronger signals either side to the other 3 LNBs. Been off the air for quite a while now so not sure what's up there these days but Thor/Sirius (TV1000) was my favourite, Hispasat was good but needed a dish swing. Now I'm thinking Hotbird, Eutelsat, Astra 19.2, ??
 

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Do you really want to waste a good dish like the 1.2m Fibo on these strong satellites? Any 80cm dish with a more multi-LNB friendly arrangement will do there.

That said, I am using a 55cm version for Sky, so I am not one to talk...
 

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Good point, I also have a 1m alloy dish which I'll now use for Sats I mentioned. My Sky dish is a mere 60cm, better than the mesh crap they supply.
 
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As you can see its more close to the dish than the sub is .
I seem to remember from somewhere that sub-reflectors are placed beyond the focal point, instead of "in front of" the focal point. Your measurements seem to confirm this.
 

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Is it so that the polarities don't screw up with the double reflection?
 
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I'm thinking of doing away with the 2nd reflector & single C120 quad lnb on my dish and adding a multi lnb bracket with 4 Quattro LNBs and a diseqc switch to feed 4 receivers. But I think I'll have to extend the arm that holds the 2nd reflector/lnb to focus directly to the new lnbs. The dish will remain fixed of course even tho' the motor still works. Anyone know what length the arm would need to be to focus on the new lnbs ? Could be trial & error I guess.
In fact, the Fibos where sold in a non-gregorian config as well.
You can see a picture of what it should look like here:

Advice Needed - Gregorian dishes
 

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Pictures from Fibo-owners site .

multifeed rail fibo.jpg

multifeed rail rods fibo.jpg
Is it so that the polarities don't screw up with the double reflection?
only with LH and RH circulair signal
 
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Pictures from Fibo-owners site .
I like how the gentleman taking the pics has at least four Fibos leaning against each other in the living room.
Would never fly here... :D

Even if I was single, I'd probably still not have the dishes in the living room.
Have nice out-house for that.
What about you all. Dishes in living room?
 
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