Ku linear polarization lnbf skew

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Has anyone seen a graphic representation of Ku lnbf skew, as
it relates to linear polarization? Would like to better
understand how "positive" skew has been determined to be
CCW on satellites west of my location.

 

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On 20 Jul 2004 17:04:03 -0700, rose122550DONTSPAM@yahoo.com (rose)
wrote:

>Has anyone seen a graphic representation of Ku lnbf skew, as
>it relates to linear polarization? Would like to better
>understand how "positive" skew has been determined to be
>CCW on satellites west of my location.

It is simply measuerd in degrees from horizontal. There is usually a
mark on the LNBF to indicate the vertical polarity.

 

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rose wrote:

> Has anyone seen a graphic representation of Ku lnbf skew, as
> it relates to linear polarization? Would like to better
> understand how "positive" skew has been determined to be
> CCW on satellites west of my location.

Here's one:

http/cobaltqube.org/goods/basketball01.jpg

Imagine you're looking at a picture of the earth, and the
line that says "cobalt networks" represents the equator;
the line perpendicular to that represents the north-sole
pole.

Now, imagine a point some distance above the earth's equator,
and then picture a plane going through that point, parallel
to the equator, but hitting the earth some distance north of
the equator.

The intersection of that plane and the earth is represented
by the curved line above the "equator". That line also
represents horizontal planar polarization. In addition,
the angle between any point on that line and a line parallel
to the equator is representative of the skew.


Now, if you just meant why is "positive" skew one way and
"negative" another, well, that's just by convention, as far
as I can tell.

Here's some more info:

http/www.satsig.net/polangle.htm

 

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Archived from groups: alt.video.satellite.mpeg-dvb (More info?)

Thanks for taking a stab at it, was hoping that someone had
created a specific graphic describing it. It's tough to
describe in words.

One of the details I was looking for, concerns the actual
vertical transmitting element of the transponder in orbit.
Is it aligned perpendicular to a plane passing through the
equator, or is it aligned perpendicular to a plane passing
through a point on the surface of the earth (possibly near
the center of the intended footprint)?

If the transmitting element is perpendicular to a plane passing
through the equator, it appears that (without a graphic), by
pointing the dish (and linear polarization lnbf) down (as
compared to an elevation due south of my location), to a
satellite west of me, that the skew (as viewed from the rear
of the dish), should be counter clockwise. This is exactly
opposite from what I understand is being published.

Zoyburg <rats@attib.com> wrote in message news:<KcnLc.150359$Oq2.99134@attbi_s52>...
> rose wrote:
>
> > Has anyone seen a graphic representation of Ku lnbf skew, as
> > it relates to linear polarization? Would like to better
> > understand how "positive" skew has been determined to be
> > CCW on satellites west of my location.
>
> Here's one:
>
> http/cobaltqube.org/goods/basketball01.jpg
>
> Imagine you're looking at a picture of the earth, and the
> line that says "cobalt networks" represents the equator;
> the line perpendicular to that represents the north-sole
> pole.
>
> Now, imagine a point some distance above the earth's equator,
> and then picture a plane going through that point, parallel
> to the equator, but hitting the earth some distance north of
> the equator.
>
> The intersection of that plane and the earth is represented
> by the curved line above the "equator". That line also
> represents horizontal planar polarization. In addition,
> the angle between any point on that line and a line parallel
> to the equator is representative of the skew.
>
>
> Now, if you just meant why is "positive" skew one way and
> "negative" another, well, that's just by convention, as far
> as I can tell.
>
> Here's some more info:
>
> http/www.satsig.net/polangle.htm

 

[Guest]

Archived from groups: alt.video.satellite.mpeg-dvb (More info?)

rose wrote:

> Thanks for taking a stab at it, was hoping that someone had
> created a specific graphic describing it. It's tough to
> describe in words.
>
> One of the details I was looking for, concerns the actual
> vertical transmitting element of the transponder in orbit.
> Is it aligned perpendicular to a plane passing through the
> equator, or is it aligned perpendicular to a plane passing
> through a point on the surface of the earth (possibly near
> the center of the intended footprint)?
>
> If the transmitting element is perpendicular to a plane passing
> through the equator, it appears that (without a graphic), by
> pointing the dish (and linear polarization lnbf) down (as
> compared to an elevation due south of my location), to a
> satellite west of me, that the skew (as viewed from the rear
> of the dish), should be counter clockwise. This is exactly
> opposite from what I understand is being published.

You can use the picture I referenced before:

http/cobaltqube.org/goods/basketball01.jpg

to visualize why it is clockwise.

Looking at the curved line in the northern hemisphere, if you
are pointed at a satellite that is due south, then you will be
at the bottom of the curve, and the skew will be zero degrees.

If you want to imagine now pointing at a satellite that is to
the west of your location, then effectively you can consider
that you are moving east along the curve. The curve has turned
up, or counterclockwise as you face the earth, or clockwise if
you were turned the other way around and were facing the satellite.

With regard to your first question, I don't really know, but it
doesn't really make any difference. Vertical polarization is
still parallel to the earth's axis, while horizontal is still
parallel to the earth's horizon at the longitude of the satellite.