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Old 10-22-2008, 05:44 PM
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Default Skew, Dish & LNB - Understanding it, How to set it

Skew, Dish & LNB - Understanding it, how to set it:

Background;
The providers satellites are orbiting above the Earths equator. They are moving at the same speed the earth is revolving, so to us the satellite appears to be stationary in the sky. Depending upon where you are on EARTH compared to where the satellite is at, the direction and angles change. This is why we use a satellite aiming program or aiming site to calculate these complex angles for us. If you could see the satellites in the sky, they would appear on an arch, such as a rainbow appears to us. So depending upon where we are ON EARTH in relation to the satellite(s) we must adjust the angle of the dish and LNB’s to match EACH satellite to receive a strong signal.
For instance, if we want to receive 2 satellites on a single dish with 2 LNB's and from our earth location, first the LNB's would have to have the correct aim for the positional DIFFERENCE (119 minus 110 = 9 degrees DIFFERENCE, same for 91/82). If the satellites are at the very top of the arc, we would not have to tilt (skew) the dish. However if the satellites are at the start of the rainbow arch, we would have to skew (Tilt) the LNB's and dish where the white hockey puck noses of the LNB's would have to be completely vertical (one on the top of the other, or Up and down) to match EACH satellite for strong reception of that satellites signal. To help visualize this, extend your arm out and fold in your thumb and center two fingers, this leaves your small and index finger extended and they represent 2 of the LNB's white hocky puck noses. Now follow the imagined rainbow arch keeping each of your "LNB fingers" on the arch, as you move along the arch you must rotate your hand to keep both of your "LNB fingers" on the arch. This "rotation" is the same as the skew on the dish.

There are TWO types of skew, Dish skew and LNB skew.

Dish Skew;
Is the tilt of the Dish on its center axis, is used on multi-LNB dishes (linear or circular). This skew is used to adjust each LNB’s aim to hit the desired satellite in the arc. On the dish that skews, there will be a skew scale near the mounting pole that will be rated in “degrees” of skew. At 90 degrees on this scale the LNB support arm in straight down.

LNB skew,
Is used ONLY on linear satellites. Only non-provider dishes have the provision to LNB skew. The skew is accomplished by the mounting of the LNB by its neck. This allows the LNB to rotate (skew) in its mount. Note: With Linear LNB’s you can use either dish or LNB skew.

RULES for SKEW of FTA Dishes

SINGLE CIRCULAR LNB's dishes are not affected by skew.

TWO or more LNB's on a SINGLE dish REQUIRE DISH SKEW. It can be minimal, like at the top of the arc, but must be calculated for each installation and LOCATION. If the single dish does not skew, the dish is at 90 degrees. If you are adding a second LNB to that dish , such as the Poormans dual dish, to be successful on picking up the second satellite, the skew for the two satellites cannot be more than +/- 15 degrees calculated from the 90 degrees (75 to 105). If outside this window you must use a dish that skews, such as the dish 500.

ALL LINEAR LNB’s REQUIRE LNB skew; The Linear transponder sends the signal from the satelite in a straight "plane", there are two planes used, Horizontal and Vertical. If you could picture a cardboard box with a slit cut in it just slightly larger than a "Frisby" (the thing you throw at the beach). If you place the box with the slit Horizontal and throw the Frisby in a Horizontal plane (and were a great shot) it would go into the box, and If you turned the box with the slit vertical (up and down), to get the Frisby into the box you MUST throw in the Vertical Plane to get it into the box. The transponders send both Horizontal and Vertical signals and the LNB and receiver sorts them out. Our LINEAR LNB's on the dish is the same as the slotted box and our receivers send the LNB the signal to receive the Vertical or Horizontal Signal (turns the box). Because the linear satellites transmit signals that are polarized and are on the orbital ARCH. This means that the signals come into your dish on one plane, and the LNB must be adjusted to the same plane as the signal and adjusted for the arch, for best strength. This can be accomplished by either skewing the LNB (without skewing the dish) OR by skewing the LNB and DISH assembly.

A excellent satellite aiming site that calculates skew :
satcalculator.freehostia.com/

PICTURES BELOW:
Top Left = Circular Left
Bottom Left = Circular Right
Top Right = Linear Vertical
Bottom Right = Linear Horizontal
Attached Images
File Type: jpg Circular%20Vs%20Linear%20sat%20Pictures.jpg (15.0 KB, 107 views)
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