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Guest Message by DevFuse

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Purpose of the World Direct Dish?


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66 replies to this topic

#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:

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#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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