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Purpose of the World Direct Dish?


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66 replies to this topic

#51 OFFLINE   P Smith

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Posted 19 January 2011 - 04:31 PM

137 LNB skew 18.5
139 LNB skew 20.5
177 LNB skew 44.5
Again these are for a single LNB dish, so why the variation of skew?

because those sats 'seat' on a curve from your one point of view and you're not on equator ;)
Try to create a picture of vert polar signal from each two or three sat to your location and you will see three angled lines with same common middle point at your home.Same for horizt signal.

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#52 OFFLINE   veryoldschool

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Posted 19 January 2011 - 06:40 PM

because those sats 'seat' on a curve from your one point of view and you're not on equator ;)
Try to create a picture of vert polar signal from each two or three sat to your location and you will see three angled lines with same common middle point at your home.Same for horizt signal.

"Exactly", and why if the linear polarization was used on the 99/101/103/119 birds, that each LNB would need to be adjusted for this after "tilt" was done.
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#53 OFFLINE   BattleZone

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Posted 19 January 2011 - 08:45 PM

"Exactly", and why if the linear polarization was used on the 99/101/103/119 birds, that each LNB would need to be adjusted for this after "tilt" was done.


And since that isn't really very practical in a multi-sat dish with integrated LNB, that's one reason why an "integrated 95 Slimline dish" doesn't exist.

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#54 OFFLINE   prestone683

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Posted 19 January 2011 - 08:56 PM

I'm no rocket scientist, but I guess the reason I was asking was because it just seems that since the international dish looks, shape wise, nearly identical as the slimline, it would be seemingly possible. The tilt I believe is virtually the same for the two dishes, except the 95 (in this area) is 113, and the slims are 65. But both birds in the sky are in the same orbital line, in the Clark orbit belt. If you can get the 95, you can also get the 101, then you are also getting the 99, just no LNB to receive and convert it.......

I'm no rocket scientist, but since you can center your dish on the 101, and its capable of reaching as far as 119 (18 degrees down from it), then logic dictate, that you can, (and probably already are) getting the 95, just 6 points the other direction of the 101. Again, all you are missing is the LNB.

But I guess I don't full understand how they are reflected back into the LNB.

Dunno.

Inquisitive minds wonder...

#55 OFFLINE   veryoldschool

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Posted 19 January 2011 - 08:56 PM

And since that isn't really very practical in a multi-sat dish with integrated LNB, that's one reason why an "integrated 95 Slimline dish" doesn't exist.

What you're trying to bring this thread full circle? :lol:
A separate "skew-able" 95W LNB "might work". :)
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#56 OFFLINE   veryoldschool

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Posted 19 January 2011 - 09:04 PM

But I guess I don't full understand how they are reflected back into the LNB.

Dunno.

Inquisitive minds wonder...

As I've tried to work through here, it's not really how the signal reflects back to the LNB, but whether the LNB needs to have an angular alignment to the SAT. Linear polarization, which the 95W uses, requires this, where circular polarization [all the others] doesn't.

the 95 (in this area) is 113, and the slims are 65

"Virtually the same"? Not even close as this is 48 degrees.
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#57 OFFLINE   Kevin F

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Posted 19 January 2011 - 09:42 PM

Is it possible for the 95 bird in the sky to be tweaked to emit circular polarization instead of linear? Probably not without launching another satellite.

Just a thought...
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#58 OFFLINE   bobnielsen

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Posted 19 January 2011 - 09:48 PM

Is it possible for the 95 bird in the sky to be tweaked to emit circular polarization instead of linear? Probably not without launching another satellite.

Just a thought...


No. Just as the Directv satellites use right-hand and left-hand circular, many other satellites use vertical and horizontal polarization. The transmitting antennas are different (circular polarization has both vertical and horizontal components).

#59 OFFLINE   veryoldschool

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Posted 19 January 2011 - 09:48 PM

Is it possible for the 95 bird in the sky to be tweaked to emit circular polarization instead of linear? Probably not without launching another satellite.

Just a thought...

Well, let me put on my jetpack and grab another antenna, and then.... :lol:
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#60 OFFLINE   bobnielsen

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Posted 19 January 2011 - 09:56 PM

Well, let me put on my jetpack and grab another antenna, and then.... :lol:


Back in the 1960s (when the space shuttle was only in the planning stages) NASA was considering using the shuttle to service geosynchronous satellites. Of course, the shuttle doesn't have the capability to reach that high an orbit but it would have been interesting to see what could have been accomplished (I was working at Hughes at the time and we were asked what kind of tests we might run on the failed Syncom I satellite if it could be recovered).

#61 OFFLINE   HoTat2

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Posted 20 January 2011 - 10:38 AM

No. Just as the Directv satellites use right-hand and left-hand circular, many other satellites use vertical and horizontal polarization. The transmitting antennas are different (circular polarization has both vertical and horizontal components).


I guess given the additional LNB skew adjustment complexities discussed here, the question should be asked why communications satellite designers past and present ever chose linear polarization over circular to begin with?

I was even taught way back in my college days that a linearly polarized satellite signal or other microwave transmission can even experience an affect called "Faraday Rotation," when transiting the ionosphere to or from space, where in severe cases can cause a signal originally transmitted as horizontal to be received vertically. :eek2:

#62 OFFLINE   BattleZone

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Posted 20 January 2011 - 10:39 AM

Is it possible for the 95 bird in the sky to be tweaked to emit circular polarization instead of linear? Probably not without launching another satellite.


Impossible to change the existing sat, and hugely unlikely that the sat's owners (DirecTV only leases space here) would replace it with a circular-polarized sat, since there's a huge installed base of users with linear setups.

IMO, it would be FAR more likely for DirecTV to simply move the content over to an existing DBS satellite that they already own, which is why many of us speculate an eventual move of this content to 110 and 119.

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#63 OFFLINE   veryoldschool

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Posted 20 January 2011 - 11:48 AM

I guess given the additional LNB skew adjustment complexities discussed here, the question should be asked why communications satellite designers past and present ever chose linear polarization over circular to begin with?

I don't really have the answer, but if you're working with a single SAT and single receiver/transmit location, it isn't that big of a deal.
"Back in 1980", I had to learn/deal with a circular polarized antenna for the aircraft to use the SATCOM radio. It was much more complex than the other radios. Because of the mobile nature of the aircraft, circular polarization was the only option.
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#64 OFFLINE   doctor j

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Posted 20 January 2011 - 11:49 AM

Anything is possible.

The Directv LA Broadcast center has a 50+ ft Dish with LNB's for just about every SAT horizon to horizon that it uses to collect its "feeds" prior to retransmitting to their SATs and us.

Check out monster receive dish in center. The others are smaller (11 meter and 9 meter) transmit dishes.

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#65 OFFLINE   BattleZone

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Posted 20 January 2011 - 04:50 PM

Anything is possible.


Sure. Local cable franchises use the same type of dish.

But POSSIBLE doesn't mean PRACTICAL. Who wants that thing bolted to their roof, and who is going to pay $75,000 for installation?

A World Direct dish costs DirecTV about $20. Do the math.

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#66 OFFLINE   HoTat2

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Posted 20 January 2011 - 06:07 PM

Sure. Local cable franchises use the same type of dish.

But POSSIBLE doesn't mean PRACTICAL. Who wants that thing bolted to their roof, and who is going to pay $75,000 for installation?

A World Direct dish costs DirecTV about $20. Do the math.


Bolted to the roof? Those monsters will surely collapse just about any residential roof :lol:

Even at the CATV headends or satellite earth stations they're pretty much mounted on the ground from all the installs I've seen ... :)

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#67 OFFLINE   BattleZone

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Posted 20 January 2011 - 08:48 PM

Maybe this guy:

Posted Image


or maybe these folks:

Posted Image

or these:

Posted Image

:)

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