my suggestion would be to purchase a scalar feed with dual lnb set up for prime focus. http://www.prosat.com/Dish_Network.html
the price is 50 + 8 s&h.
if you use a lnb removed from an offset dish, .6 f/d ratio, then you are not getting
a very good illumination of the feed.
the feed i suggested can be adjusted to match your dish f/d ration for max.