First thing to check is the dish mount foot. Getting loose? Dish sag from it own weight? Couple of turns of a wrench might straighten things up. But it may be a constant problem if not secured into a house frame member.
Look into installing a pair of monopoles, which I assume you don't have. Will help distribute the weight over a larger area and hopefully allow a longer lag bolt to penetrate a larger house frame stud.boylan said:Thanks, that was it!
The weight of the dish had split the shingle it was screwed into, which allowed the dish to sag downwards. I saw from a level that the mast was tilting forward, away form the house.
I put some shims under the shingle and the signals returned.
This weekend, I'll have to come up with a way to better secure it to the house. It may involve a little bit of construction and painting to make it look acceptable - but at least I know what to do now.