Fibo Gregorian 1.2 conversion to multi lnb

T

Toyboy

Member
Messages
20
My Satellite Setup
Extreme Hornet + 1.2m dish
My Location
UK
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.
 
RimaNTSS

RimaNTSS

Super Moderator
Staff member
Messages
5,003
My Satellite Setup
Some SAT-related hardware.
My Location
N-E from Riga
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.
 
T

Toyboy

Member
Messages
20
My Satellite Setup
Extreme Hornet + 1.2m dish
My Location
UK
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.
 
RimaNTSS

RimaNTSS

Super Moderator
Staff member
Messages
5,003
My Satellite Setup
Some SAT-related hardware.
My Location
N-E from Riga
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.
 
T

Toyboy

Member
Messages
20
My Satellite Setup
Extreme Hornet + 1.2m dish
My Location
UK
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
 
RimaNTSS

RimaNTSS

Super Moderator
Staff member
Messages
5,003
My Satellite Setup
Some SAT-related hardware.
My Location
N-E from Riga
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.
 
T

Toyboy

Member
Messages
20
My Satellite Setup
Extreme Hornet + 1.2m dish
My Location
UK
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 ?
 
A

archive10

Guest
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.
 
RimaNTSS

RimaNTSS

Super Moderator
Staff member
Messages
5,003
My Satellite Setup
Some SAT-related hardware.
My Location
N-E from Riga
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.
 
Trust

Trust

Specialist Contributor
Messages
930
My Satellite Setup
1.8 m CM at SMR 1224 + Elev. with 7 lnb changer Ku (lin - circ) - Ka (lin - circ) C (lin - circ)
My Location
Nijmegen Netherlands
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
 
Trust

Trust

Specialist Contributor
Messages
930
My Satellite Setup
1.8 m CM at SMR 1224 + Elev. with 7 lnb changer Ku (lin - circ) - Ka (lin - circ) C (lin - circ)
My Location
Nijmegen Netherlands
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
 
B

blademedia

Member
Messages
1,941
My Satellite Setup
Sky
My Location
UK
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 :)
 
T

Toyboy

Member
Messages
20
My Satellite Setup
Extreme Hornet + 1.2m dish
My Location
UK
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, ??
 
Captain Jack

Captain Jack

Модератор
Staff member
Messages
11,011
My Satellite Setup
See signature
My Location
North Somerset
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...
 
T

Toyboy

Member
Messages
20
My Satellite Setup
Extreme Hornet + 1.2m dish
My Location
UK
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.
 
A

archive10

Guest
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.
 
Captain Jack

Captain Jack

Модератор
Staff member
Messages
11,011
My Satellite Setup
See signature
My Location
North Somerset
Is it so that the polarities don't screw up with the double reflection?
 
A

archive10

Guest
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
 
Trust

Trust

Specialist Contributor
Messages
930
My Satellite Setup
1.8 m CM at SMR 1224 + Elev. with 7 lnb changer Ku (lin - circ) - Ka (lin - circ) C (lin - circ)
My Location
Nijmegen Netherlands
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
 
A

archive10

Guest
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?
 
Top