The LNB on the end of the satellite dish picks up either a horizontal or a vertical signal.
Your satellite receiver sends an 18volt current to the LNB when it requires a horizontal signal and a 13volt current for a vertical signal. Physically turning the LNB on the end of your satellite dish 90degrees will also alter the signal being received from Horizontal to Vertical. Anywhere in between these two positions and the LNB will pick up a mixture of both signals. This is known as ‘Cross Polar Discrimination’ and causes interference in the signal quality being received.
Due to the curvature of the earth and the position of the satellites in orbit, the LNB may need to be at a very slight angle. As you travel around Europe the correct skew position of the LNB changes.
The main effect of the LNB being out of Skew is a reduction in the ‘Signal Quality’.
With an Auto Skew satellite system there is a GPS receiver built in and a small motor attached to the LNB and the system automatically changes the Skew angle depending upon your current location giving the optimum signal quality possible.