Hi,
For just 13E and 28E, you are better off with a fixed dish, but most of use would never be satisfied with just those two.
With the average 80 to 90cm ish dish you can normally have up to 20 degrees and up to 4 satellites with a standard DiSEqC 1.0 switch. The advantage is fast zapping, i.e no waiting for the motor to work its way round.
The advantage of a motor is obvious- more choice, at the expense of time when it moves.
The best option is to have a fixed and a motorised dish, but that is being greedy.
Robbo
