A Blank TV Screen

I was watching the BBC News tonight when it suddenly went blank. A few seconds later the video reappeared and I caught the last second of a news promo piece about a story on Tibet. A few minutes later, after a story on the Spanish elections the story about Tibet started and the TV screen immediately went blank again. As soon as the story finished, about 2 minutes, the video came back on. Obviously, the Chinese censors are again blocking all incoming news about this subject. It's no wonder why the Chinese people don't have much information about the matter.

What I wonder is how the censors block satellite transmissions. Many of the TV broadcasts received by upscale housing units in China are via technically illegal satellite dishes and the BBC News is not really legal in China. But this law is, like many laws in China, rarely enforced. But how does the Chinese Government block these transmissions through space?