Prime Focus set-up

G0JCN

G0JCN

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#1
Hi all.

Some of you will already be aware of my saga chasing a decent dish and the result is that I now have a 1.8 mt pf dish. The next problem is that the last owner was using it for C band so I have to make a LNB hoder. My question........ when I clamp the feedhorn and LNB together it has to be mounted at the "focal point"..... Where do I mesure this? Is it the center of the parabol to the front of the feedhorn, or to the LNB, or maybe even an imaginary point somewhere inside the feedhorn. Can anyone help please?

Want to get it right...:)

Many thanks,

Martin
 
Lancelot

Lancelot

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125cm Gibbi with Channelmaster feedhorn and Inverto C120 twin.
36v H to H 62E - 61.5W
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#2
Martin - can you post some pictures of the 'bits' you got with it, as you may already have what you need there without messing about.


L.:)
 
Rob

Rob

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Technomate TMS-1500 CI+ "patched" receiver, 90cm p/f 36v motorised dish, Inverto C120 0.3db LNB, Moteck V-Box 2, Packard Bell 6052 XP Home computer, Toshiba A60 laptop, and lots of Russian Vodka !
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Essex
#3
Do we have a tutorial on how to set-up a prime focus dish, in my case with an actuator.
I did a search and nothing, so if someone knows where there is one, let us know.

Thanks
Rob
 
Lancelot

Lancelot

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My Satellite Setup
SS1.
125cm Gibbi with Channelmaster feedhorn and Inverto C120 twin.
36v H to H 62E - 61.5W
My Location
South central
#4
CH is probably your man Rob.
Have you tried the LNB that came with the dish yet?. The feed you got with the dish may be already set to optimum focal length and just needs a universal C120 bolting on if the original is a gonner.


L.:)
 
Rob

Rob

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Technomate TMS-1500 CI+ "patched" receiver, 90cm p/f 36v motorised dish, Inverto C120 0.3db LNB, Moteck V-Box 2, Packard Bell 6052 XP Home computer, Toshiba A60 laptop, and lots of Russian Vodka !
My Location
Essex
#5
Hi L, No doubt your right, but at the moment it is not fitted up yet (Saturday week), and am planning to change the old analogue lnb, for a new digital one.
So the answer to your question is not yet, but my question was more about fitting the actuator and that sort of stuff.
Should be pretty easy to figure out, but I was an old boy scout:- Be Prepared.:)
 
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rmhms

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#6
Hi,
I had an old prime focus dish connected to an analog receiver, so the lnb was not usable. I got some frequencies but all out of place and not all of them, so i had to replace the lnb. The feed was not usable as the feed from the old lnb attached directly to it, so i had to get a new one, but if you have an old one, you should be able to use it, as long as you can attatch a C120 to it. i just placed the new C120 lnb with the feed on the same position the other was and everything was ok. As for the motor, the dish was motorised with an actuator, so i just got a V-BOX and connected it to the receiver, so now i can control it with DiSeq 1.2 and everything is working ok.
 
Channel Hopper

Channel Hopper

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#7
Lancelot said:
CH is probably your man Rob.
Thanks a bunch

Without knowing the make of dish, its possible this was originally a Cband system for a good reason - it wont perform at Ku band.

Is it solid or mesh ?
Is it a single piece or petalised design ?
Do you have any other markings on it, or can post a picture ?

The feed distance on a prime focus dish is given by the formula D x D / 16 d

D = Diameter
d = depth of dish (surface - rim - to deepest part of dish)
keep the same dimensions in each part of the equation mm to mm, " to ".
 
G0JCN

G0JCN

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My Satellite Setup
Home brew PC, Fortec Star FSCI-5100 plus + ultra sat RX. triax 110 motorised dish
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#9
Thanks for the formular, thats great.... but where do we messure to? is it the front of the feedhorn? (most likley i think) or some imaginary point along the wave guide to the LNB?
 
Rob

Rob

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My Satellite Setup
Technomate TMS-1500 CI+ "patched" receiver, 90cm p/f 36v motorised dish, Inverto C120 0.3db LNB, Moteck V-Box 2, Packard Bell 6052 XP Home computer, Toshiba A60 laptop, and lots of Russian Vodka !
My Location
Essex
#10
Here's some more pictures, before I stripped it down.

It's a Uniden 90cm prime focal motorised dish with an 8" actuator.
 

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Orthoclipse

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#11
Rob said:
Do we have a tutorial on how to set-up a prime focus dish, in my case with an actuator.
This is a link to a 5MB zip file containing a word doc with lots of good pictures on setting up a 2.3M mesh dish with actuator and C-band LNBF posted on the Vetrun forum. The principles are the same for your dish - just remember that this was written for Australia so some things are back to front for Northern hemisphere.

h**p://www.vetrun.com/competition/tutorial.zip
 
R

Rd100

Guest
#12
Hi if you are useing the feedhorn he was useing for c-band you can not that the feedhorn for H&V ku band you will need a h&v ku-band feedhorn for that dish



G0JCN said:
Hi all.

Some of you will already be aware of my saga chasing a decent dish and the result is that I now have a 1.8 mt pf dish. The next problem is that the last owner was using it for C band so I have to make a LNB hoder. My question........ when I clamp the feedhorn and LNB together it has to be mounted at the "focal point"..... Where do I mesure this? Is it the center of the parabol to the front of the feedhorn, or to the LNB, or maybe even an imaginary point somewhere inside the feedhorn. Can anyone help please?

Want to get it right...:)

Many thanks,

Martin
 
Rob

Rob

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My Satellite Setup
Technomate TMS-1500 CI+ "patched" receiver, 90cm p/f 36v motorised dish, Inverto C120 0.3db LNB, Moteck V-Box 2, Packard Bell 6052 XP Home computer, Toshiba A60 laptop, and lots of Russian Vodka !
My Location
Essex
#13
Thanks for that Orthocliipse, have printed it out and will use when putting the system up on Saturday week.

Once again thanks
Rob
 
G0JCN

G0JCN

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My Satellite Setup
Home brew PC, Fortec Star FSCI-5100 plus + ultra sat RX. triax 110 motorised dish
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Forest of Dean, Gloucestershire
#14
Yeh I realise that the c band feed horn is no use, you could probably get a Ku one inside it.....:)

Still one question not answered though, just where ecactly do we mesure the focal length to. bearing in mind the dimension is in millimeters, and the LNB/feedhorn assembly is quite long, just where on this assembly do we messure. Am i correct to assume the front face of the feedhorn?

M
 
Channel Hopper

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#15
The rule of thumb is about 3mm inside the feed surface, this varies depending on the depth of the dish (altering the f/d ratio).

Start there and work to improve using the weakest signal you can find.
 
G0JCN

G0JCN

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My Satellite Setup
Home brew PC, Fortec Star FSCI-5100 plus + ultra sat RX. triax 110 motorised dish
My Location
Forest of Dean, Gloucestershire
#16
Cheers for that. I will try to make up the holder to give a bit of movement either side of that then.

Thanks
M

Just found this link.....
h**p://hjem.get2net.dk/ole_nykjaer/oz2oe/10ghzparabol/prime_focus_geometry.jpg

Good diagram.

G0JCN
 
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