I was going to link to an article about North Korea jamming a signal intended for Japanese abductees, but yomiuri.co.jp moved or removed the article so that I can't find it.
However, Media Network Weblog has a similar article about the jamming. Quoting: "The group, known as the Investigative Commission on Missing Japanese Probably Related to North Korea, broadcasts the programme Shiokaze twice a day on shortwave ... It can be heard in North Korea, as well as in areas near the North Korean border in China and in the northern part of South Korea."
Here's a quote from the Yomiuri article which I can no longer find: "The jamming transmission is coming from North Korea and appears to have started from May 5 at the latest," [Chief Cabinet Secretary Shinzo] Abe said. "It's regrettable if North Korea is jamming the broadcasts because the commission is trying to send messages to as many missing Japanese as possible."
I also located THINK: Abduction by North Korea Resource Site while researching this article.