This is excerpted from a larger AP article on how outside media is starting to affect life in North Korea:
http://m.lvsun.com/news/2012/may/09/us-us-nkorea-media/...
Martyn Williams, who writes the blog NorthKoreaTech.org, said that the government's intense use of its scant resources and electricity to jam foreign news broadcasts reflected its concern about the impact of outside media.
North Korea targets between 10 and 15 frequencies used by international short-wave broadcasters, such as U.S.-funded Radio Free Asia and stations operated by South Korea's government, for up to 18 hours a day, and on major occasions like the April centennial, it jams radio signals around the clock, Williams said.
The North appears to have recently installed more sophisticated transmitters acquired from a Chinese company, although jamming operations have been up and down this year, likely because of technical problems or power shortages, he said.