(Source: DailyNK via Andrea Borgnino)
North Korea has been from the beginning of March continually signal jamming radio broadcasts on the shortwave frequency used by the South Korean non-profit broadcaster Unification Media Group (UMG). Given the present situation, in which North Korean residents might be influenced by outside information condemning the regime and explaining the purpose of the sanctions imposed by the United Nations, the regime has showed the will to block sources of outside information that might cause unrest.
The shortwave frequency […] in question, 7515 [kHz], has been actively jammed starting on March 1st making it extremely difficult for North Korean listeners to tune in. On the 15, UMG organization began using three receivers to test out reception at that and adjacent frequencies on a daily basis and was able to confirm that the exact signal is being jammed.
The blocking effort is being concentrated on the time period from 10pm- midnight. Specifically, from 10-11pm the jamming is very strong. The signal jamming is undetectable from midnight to 1am. The signal blocking became weaker at midnight on March 15, from which point onward the entire three hour broadcast was audible. Starting on the 17, UMG moved the frequency, but the jamming operators seemed not to notice because the interference continued on the old wavelength.
North Korea is limited to how many frequencies they can jam at one time. The only way to deal with it is by jamming up the jammers to where it effects broadcasts from Voice of Korea.
Now while all radios sold in the DPRK are all pre-tuned to only government channels. There are hundreds of radios smuggled in from China each week for sale on the black market.
The penalty for being caught with such a radio is a very long prison sentence not for just the owner, but also his or her family. A large number of defectors have said that there are more of these smuggled radios than people think.