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Guest Message by DevFuse

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International equipment needed?


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29 replies to this topic

#21 OFFLINE   veryoldschool

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Posted 17 March 2014 - 12:21 PM

Well I'll try ... :)


Hope my I explanation went well ... :D       

Not really. Might be better to use compass degrees, "but" I seemed to have found something with dishpointer and listed skew differences between the World Direct and WD with the 101 LNB.

 

Sierra Vista AZ is about 110

 

Phase III     Dish Skew [?]:  90.5° 

SL5            Dish Skew [?]:  104.7°
95W & 101 Dish Skew [?]:  113.2°
95W            LNB Skew [?]:  -23.2° 
 
 

A.K.A VOS

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#22 OFFLINE   mnassour

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Posted 17 March 2014 - 08:54 PM

On the content side, one really nice thing about the International Dish is that you get MHz Worldview on 2183 for no extra charge...newscasts and entertainment from around the world 24/7 in English.



#23 OFFLINE   HoTat2

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Posted 18 March 2014 - 03:00 AM

 

Not really. Might be better to use compass degrees, "but" I seemed to have found something with dishpointer and listed skew differences between the World Direct and WD with the 101 LNB.

 

Sierra Vista AZ is about 110

 

Phase III     Dish Skew [?]:  90.5° 

SL5            Dish Skew [?]:  104.7°
95W & 101 Dish Skew [?]:  113.2°
95W            LNB Skew [?]:  -23.2° 
 
 

 

Well .... sorry, did my best to clarify ... :(

 

And really don't see how using magnetic coordinates for Az. can help clarify the issue.  

 

Thought the concept was quite simple really. Horiz. polarized linear signals for N-S aligned satellites emanate at the same angle the Clarke belt makes with a receiving earth station viewing it. So naturally a feedhorn on the receiving dish must be oriented the same way.    

 

But anyhow as to those examples, dishpointer appears to be using two different angle conventions.

 

For the DIRECTV multi-LNB dishes P.III, SL-5, and 95w & 101, "dish skew" which is the same as the dish's "tilt" setting in this case, is measured in a range of 0° to +180° CCW when standing behind the dish.

 

The single 95w dish listed last is apparently for a round dish with a single LNBF where the skew adjustment is made by rotating only the LNBF (and not the dish) in its mount using the angle convention as described here;

http://www.satsig.ne...t/polangle.htm 

 

Straight up vertical is 0° with negative angles measured by rotating the LNBF CCW from the 0° reference point when viewed from behind the dish, and positive angles are CW from the point


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#24 OFFLINE   veryoldschool

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Posted 18 March 2014 - 09:00 AM

The two "scales" on dishpointer "should be" simply 90 degrees different, where the dish at vertical is 90 and the LNB is zero.

 

Your link has this:

"If you are in the northern hemisphere:   Face the equator (by looking south) and you can envisage the geostationary orbit as curved line across the sky starting in the south east, rising to say 35 deg elevation at due south and falling in the south west.  The polarisation of satellites located to the east will be tilted anticlockwise, satellites to the west clockwise.  Only a satellite due south of you will have its polarisation aligned vertical."

 

"I'd say" this is the root of "our problem". We're looking at arcs from off axis. 


A.K.A VOS

#25 OFFLINE   HoTat2

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Posted 18 March 2014 - 10:44 AM

The two "scales" on dishpointer "should be" simply 90 degrees different, where the dish at vertical is 90 and the LNB is zero.

 

Your link has this:

"If you are in the northern hemisphere:   Face the equator (by looking south) and you can envisage the geostationary orbit as curved line across the sky starting in the south east, rising to say 35 deg elevation at due south and falling in the south west.  The polarisation of satellites located to the east will be tilted anticlockwise, satellites to the west clockwise.  Only a satellite due south of you will have its polarisation aligned vertical."

 

"I'd say" this is the root of "our problem". We're looking at arcs from off axis. 

Exactly;

 

Which is what makes the orientation of the satellite *appear* to vary other than its actual straight N-S, E-W orientation that is only seen by an earth station if the satellite is at the local longitude, or 180° true Az. 

 

Also as a side note, (and again AIUI :) ) what many may not realize is that since a multi-LNB dish is actually viewing a portion of an "arc" as illustrated for the northern hemisphere;

 

view-of-orbit-usa.gif

 

 

Dishes like the P.III, SL-5, and Dish's 1000.x must have their feedhorns positioned in an inverse curved arc to match the reflected signals from the Clarke belt and not actually inline with one another.

 

Thus the 110° feedhorn I notice is positioned slightly lower than the two outer ones for 101° and 119° on the DIRECTV LNBFs. And likewise the 72.7° or 119° feedhorns for the Dish 1000.x is lower than the two outer 61.5° and 77° (1000.4 EA) or 110° and 129° horns (1000.2 WA) respectively on each dish. 


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#26 OFFLINE   HoTat2

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Posted 18 March 2014 - 10:59 AM

Although on a different but related issue, I am curious as to what would be the advantage of using an elliptical dish with a single LNBF for a service that uses circular polarization like I see some Ka band satellite internet services doing?

 

Like the Dishnet internet ODUs I notice going up around my area lately for instance.

 

Could this article perhaps be the reason why?

 

http://www.satsig.ne...rientation.htm 

 

 


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#27 OFFLINE   P Smith

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Posted 18 March 2014 - 11:27 AM

perhaps to exactly reduce interference from adjusted satellites



#28 OFFLINE   veryoldschool

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Posted 20 March 2014 - 11:11 AM

"Hopefully" this might get put to rest with a couple of screen grabs off dishpointer

 

95W 0.PNG 95W 40.PNG

 

 

"True" AZ + LNB skew = 180


A.K.A VOS

#29 OFFLINE   HoTat2

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Posted 21 March 2014 - 10:49 AM

"Hopefully" this might get put to rest with a couple of screen grabs off dishpointer

 

attachicon.gif95W 0.PNGattachicon.gif95W 40.PNG

 

 

"True" AZ + LNB skew = 180

Alright;

 

But I still see dishpointer here indicating the same thing. Whether an earth station is at or well north of the equator, a "normal" N-S vertically aligned satellite at a station's local noon longitude meridian will have any vertically linear polarized signals in the same N-S plane and thus exactly perpendicular to the Clarke belt and thereby horizontally polarized ones are parallel to the belt of course.

 

Thus a dish's horn antenna must naturally be oriented the same way to receive the desired linear signal polarity.      


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#30 OFFLINE   veryoldschool

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Posted 21 March 2014 - 11:08 AM

Alright;  

I think it's been a long way to get to "the same place".

The "feed horn" has to align with the SAT, which is perpendicular to the Clarke Belt "at its location".

Dish "tilt" for multi-SATs isn't exactly the same.


A.K.A VOS




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