On a dish it is usually weak signal caused by misalignment or weather. Is it on the roof where it could be blown by wind?Or on a wall low enough for a window cleaner to bash it with a ladder? Check cabling for breaks or loose connections.
Also during the summer, be aware that our little buzzy friends the wasps can crawl into the feed horn of the LNB if it doesn't have a cover over it, this causes signal loss as well, I get this a lot!
Also check which channels its affecting, is it all of them or just one or two? If its the latter it is definitely signal drop out - the broadcaster has changed the strength of the signal, we get this on itv 2,3,4 and some of the regular sat channels like Really and Drama even though we have a 3 metre dish!