Multiple LNB's on a 12' BUD.

[123tim]

Recently I was offered a 12' BUD (mesh) which I think that I'm going to take.
I was wondering about the possibility of attaching multiple ku-band LNB's to track adjacent satellites. Does a BUD has too tight a focal point to allow for the separation (spacing)?
I hope this question makes sense. I don't know much about this, and I don't think that I worded it very well. I guess that I should just ask if multiple lnb's can be done on a BUD.


Thanks in advance for any replies.

 

[PSB]

Here is one way to do it!



http://community.webshots.com/photo/100919814/1130616190051497581kAELDc

 

[Stefan]

Recently I was offered a 12' BUD (mesh) which I think that I'm going to take.
I was wondering about the possibility of attaching multiple ku-band LNB's to track adjacent satellites. Does a BUD has too tight a focal point to allow for the separation (spacing)?
I hope this question makes sense. I don't know much about this, and I don't think that I worded it very well. I guess that I should just ask if multiple lnb's can be done on a BUD.


Thanks in advance for any replies.

One thing you have to remember is that what we call the "focal point" of a dish is the focal point whenever the incoming signals is coming in directly at the dish from the position the dish is directly pointed at (on a prime focus dish of course). If the angle at which the signal is coming at the dish changes then the focal point for that particular signal moves. This is actually how a parabolic refelctor is able to focus onto the satellites it's aim at and not others. The off axis signals will be focused at different focal points away from the location of the central feedhorn and thus are rejected. So, for a multifeed application like your thinking of a large dish like you have is actually better. The reason a larger dish has a narrower beamwith is because as the direction of the incoming signal moves off axis the focal point for that signal moves more and further from the central focal point. This is why a larger dish rejects off axis signals better and has a narrower beamwidth. So, on your large dish the spacing of your multiple feeds will actually need to be wider apart than it would be on a smaller dish. Anyway, your idea should work just fine though it may require some experimenting and trial and error in finding the proper placement for each feedhorn.

Of course all of this is assuming your dish has a surface that's true and accurate and isn't warped. If that's not the case then you might have trouble with Ku regardless of whether you use multiple feeds or a single feed.

 

[rdel]

You may want to check how far apart the mesh is on the dish, I've never had a c-band dish but I've read about (on satguys forum) if the mesh is to far apart it won't
reflect the ku-band.
You may want to check with the experts (iceberg and psb) before you undertake such a large project.

 

[PSB]

As long as a pencil will not fit through the mesh you should be good for Ku signals. Smaller the mesh the better for Ku!

 

[123tim]

Pete, Stefan, and rdel,
Thank you for the replies. I'm glad to know that it can be done. I appreciate the pictures, and the explanation of signal rejection.

It appears that the scalar ring has been cut to insert the KU lnb's (in the photographs). I would think that this would cut down on the C-band signal strength. Is this an incorrect assumption?

By the way....the mesh in my dish does have small holes. Lucky me.

 

[PSB]

I think no loss in C-Band signal quality was reported with the above modification to the scalar ring. You are removing part of a scalar ring and replacing it with a smaller scalar ring.

A scalar ring just really blocks adjacent satellite signals and helps direct the signal into the C-Band LNB. As long as they do not block any incoming signal I do not see any problems.