Dual and quad scalar ring spacing?

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hank123

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Just got in my dual and quad scalar ring. Does anyone know what the spacing is on them?

How close or far apart do the satellites need to be?
 

primestar31

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You know you can't move satellites in orbit to match the plate, right? LOL

How close/how far apart it "can see" the various satellites you can only determine with YOUR particular dish, and how you set it up. It depends on size of dish, focal point, location on Earth, etc.
 
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hank123

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You know you can't move satellites in orbit to match the plate, right? LOL

How close/how far apart it "can see" the various satellites you can only determine with YOUR particular dish, and how you set it up. It depends on size of dish, focal point, location on Earth, etc.

I was thinking about putting it on the 10-footer. I'm just curious if 2 degrees is too close together and with the maximum stretch I could get out of it is. So can I do something like 97-99 101-103? 107 is about true south of me
 

primestar31

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I was thinking about putting it on the 10-footer. I'm just curious if 2 degrees is too close together and with the maximum stretch I could get out of it is. So can I do something like 97-99 101-103? 107 is about true south of me

It depends on how tightly you can get the lnb spacing and such. The plate itself limits you. It's very unlikely you can get 2 degree spacing. You MIGHT be able to pull off 4 degree spacing, depending on various things.

There's no way we can tell you for sure, it depends on your situation. Make SURE your dish is already 100% set and working perfectly before you start this. I suggest you take a lot of reference photos, and make marks with permanent marker to help figure it all out.

Just get the plate and lnbs installed, and then play around with adjusting things from there. Make your adjustments at the TOP of your arc, at your true south sat.
 
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pendragon

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An ideal parabolic reflector can only bring all of an incoming signal to a single focus point if the source is on axis. In the case of multi-satellite reception, any off-axis source will suffer from coma distortion, which will spread the 'focus' away from the apparent, off-axis reflection. One can model this numerically to find the best locations to place feeds, but there are a lot of factors (signal frequency, dish and feed dimensions, location on the earth, and the specific orbital locations) that play a role. I wrote some software to do this, and it accurately predicts where to place feeds on my dishes, most of which have multiple feeds. This is heavy lifting territory.

Of course one can simply center a dish with a single feed, and start hunting around for the off-axis locations. This is really hit-or-miss, because you can receive an off-axis source in substantial range of locations, but you want to find the one with the smallest 'circle of confusion'. That can be rather counter-intuitive, particularly for sources far off-axis. You can probably get something to work, but in many cases it will not be optimal.

After modeling all sorts of dishes (I have a lot), I can offer several generalizations. Choose a big dish with a high f/D, preferably around 0.4 or higher. This will spread the signals out at the feeds, and you will experience smaller losses off-axis. Something like a Winegard Pinnacle is the polar opposite of what you want, because it has a low f/D (0.275).

As a contrived example, let's say you want to use a quad feed on a 10' Pinnacle to get 4 orbital locations, each separated by 2 degrees. It turns out you can't get C-band feeds close enough to do this, but even if you could, the two inner feeds would have nearly 3.5 dB of CNR loss compared to a single, on-axis feed. This is about the same gain as a 6' dish. The outer feeds would lose nearly 5 dB. You're not going to get anywhere close to 20 degrees at that rate.

Now take a f/D = 0.4, 10' dish. The inner two feeds can be separated sufficiently, and will have a negligible loss compared to a single on-axis feed. The outer feeds will have to be squeezed as they are just slightly too large in diameter, but you'll lose less than 1 dB, roughly equivalent to a 9' dish. As a practical example, I have a feed offset by 8 degrees from center on a f/D = 0.38, 12' dish, and it performs like it would on a 8.5' dish. Not incredible, but usable.

The problem I have with dual and quad plates is they are unlikely to hold feeds where you need them. In most cases the problem is the feed diameters constrain how close one needs to get them spaced, and creative means are needed that cannot work with these plates. But if you end up with a dish 14' or greater, they might actually work.
 
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