SKEW - Understanding it, how to set it

[마틴신]

http://ftaforums.org/forum/viewtopic.php?f=7&t=14591 

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 compared to where the satellite is at, the direction and angles change. This is why we use a satellite aiming program or site, to calculate these 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 in relation to the satellite(s) we must adjust the angle of the dish and LNB’s to receive a strong signal. For instance, if we want to receive 2 satellites on a single dish and from our location they are at the start of the arc and are about 10 compass degrees apart, we would have to tilt (skew) the dish at a great angle for both LNB’s to receive both signals well. However if we move our location to where the same two satellites are at the top of the arc, we would not have to tilt (skew) 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 and not needed.

TWO or more CIRCULAR 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. 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 Poor mans 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; because the linear satellites transmit signals that are polarized. 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, for best strength. This can be accomplished by either skewing the LNB (without skewing the dish) OR by skewing the LNB and DISH assembly.

NOTE: LNBs used with motorized dishes do not need to be skewed because the dish always skews to the proper angle when it turns on the motor.

//