Prior to attempting to point the dish at the satellite you need to pre-set the polarization angle (also called skew) of the RF feed horn assembly. The NOC (Network Operations Center) should be able to tell you what polarization of the receive and transmit signal i.e Rx Horizontal and Tx Vertical for linear cross pol.
A straightforward way to tell the polarization is to look at the thin side of the waveguide as this will be aligned with the antenna in the LNB and BUC. Look at the picture below and look to see what the Rx and Tx pol are.
VSAT Pol (Skew) Alignment Steps
- Calculate the polarization angle for your location.
- Loosen of the RF feed assembly bolts.
- Rotate the feed to the nominal position.
- Place an inclinometer on the BUC. If you do not have one the use a smartphone or just estimate the angle.
- Move the feed to the calculated position. The position will be given in ‘positive’ or ‘negative’ degrees. This is set as if you are looking towards the satellite in the sky i.e you are looking in to the feedhorn from the dish.
- Ignore any degree marking on the feed assembly.
- Positive + degree rotation mean that the feed needs to be rotated clockwise and negative vice versa.
- During the link commissioning you will be asked to move the feed in small steps (typically 1 or 2° steps). The satellite operator will be measuring the isolation to the opposite pol to make sure you are not causing any interference. You normally have to achieve at least 30dB of isolation to pass.
- Tighten the feed bolts taking care that you do not move its position.
- Mark the feed position with a permanent marker pen so that it can be used for future reference.
