The complete signal loss and 11-12-11 code occur on only one of my four receivers and only when changing channels, not at any other time. The problem lasts for 2 - 20 seconds, then hooks up and happens about half the times I change channels. Rebooting receiver by unplugging it does not help. This receiver was replaced two years ago by Dish, but the problem started about six months ago. Check switch and satellite signal strength are OK. No obstructions in front of dish. Any ideas??