From Wikipedia:
Radio and TV sets in North Korea are supplied pre-tuned to government stations and radios must be checked and registered with the police, though some North Koreans have bought radios tuned to foreign broadcasts.[8] Stations not tuned to government broadcasts are not permitted. There are 4 television stations: Korean Central TV, Mansudae Television (a cultural station only available in the capital), Korean Educational and Cultural Network, and Kaesong Television (targets South Korea).[41] State television is always off air until its 5pm evening news broadcast, except on Sundays which start at 6am, and in emergency events or live events.[42]
All broadcast media in some way promotes the regime's ideologies and positions, such as juche, and regularly condemns actions by South Korea, Japan, Israel, the United States, and other nations. The media in recent years condemns the United Nations, and its position against the country's nuclear program. In recent years the North Korean media portrays the rest of the world as an "enemy", and claims that every foreign nation is conspiring against the regime.
Due to the economic conditions in the country, radio is the most widely-used medium. In 2006, there were 16 AM, 14 FM and 11 shortwave radio broadcast stations. Radio stations include Pyongyang Radio, Central Radio and Propaganda Radio – the latter of which purports to be broadcasting from South Korea when it actually broadcasts north of the Korean Demilitarized Zone.[43] According to recent UN data, only 55 of every 1,000 North Koreans have a television in their home. Some foreign broadcast radio stations (see external links) that target North Korea are often jammed, though this can vary. The authorities designate such media as "enemies of the regime".[8]
South Korean programmes cannot be received in North Korea due to incompatibilities between the television systems and the sets being pretuned, but watching them on VHS VCRs smuggled from China is relatively popular.[8] South Korean soap operas, movies and Western Hollywood movies according to defectors, are said to be spreading at a "rapid rate" throughout North Korea despite the threat of punishment; inspection teams are regularly bribed or allowed to watch the cassettes themselves.[44][45]
Residents living in border areas can pick up TV and radio signals from South Korea and China to find out about world events, which are largely ignored in the official media.[17] North Korean broadcasts have been picked up in South Korea,[46] and are monitored by the Unification Ministry in Seoul, which handles cross-border relations and media exchanges.[47]
From Wikipedia section on South Korean Jamming:
The South Korean government constantly jams most radio broadcasts from North Korea on medium-wave. According to the National Security Act in South Korea, it is illegal to tune into or publish frequencies of North Korean broadcasts. Despite the fact, one cannot be easily punished for just listening to those broadcasts individually. However, public listening and distribution of the recordings are criminal offences. A listener in the South Korean Metropolitan area (Seoul, Incheon, and Gyeonggi Province) or near the DMZ who tunes across the MW band may hear strange signals on several MW frequencies, mixing with North Korean radio broadcasts. These include 657 kHz (PBS Pyongyang), 720 kHz (KCBS Wiwon), 819 kHz (KCBS Pyongyang), 882 kHz and 1080 kHz (KCBS Haeju).
The South Korean government broadcasts several bizarre-sounding jamming sounds (usually warbling or chugging)[1] in an attempt to prevent their citizens from hearing radio broadcasts from the North. The medium-wave jamming by the South is sometimes too weak to completely block the North Korean broadcasts (the jamming transmission power seems to be between 20 and 50 kilowatts, while the targeted North Korean transmissions are of much higher transmission power—typically over 500 kilowatts). On shortwave, jamming is not as severe; only a very few North Korean frequencies are slightly jammed. FM jamming is also carried out, but it is not very effective.
Television jamming in South Korea was widespread before the introduction of Digital Multimedia Broadcasting (i.e. DMB) in South Korea. In Seoul, one could see colour bars on particular channels of the VHF band used by (North) Korean Central Television. Now jamming with random signals on those channels is not done, but the channels are used for DMB broadcasting. The digital broadcasts provide reliable portable digital television multimedia broadcasts, but cause severe interference with the North Korean analogue signals.
From Wikipedia article on North Korean Jamming:
Since it is illegal for North Koreans to listen to anything other than state-run radio, all legal radio receivers are sold fixed so they can tune only to channels approved by the government.[2] Because the receiver channels are fixed, North Korea does not need to jam any South Korean private television and radio broadcasts (such as MBC, SBS, etc.). North Korea does jam some of South Korea's state-owned radio and television broadcasts. Before the (early 2007) closure of South Korean shortwave domestic radio broadcasts (which were often targeted at the North) 3930 kHz KBS Radio 1 and 6015 and 6135 kHz KBS Radio Korean Ethnicity (formerly KBS Radio Social Education) had been severely jammed by the North.
The type of the jamming on shortwave is 'Jet Plane Noise', which makes it very hard to hear the radio broadcasts. North Korea also jams South Korea's clandestine shortwave broadcast, Echo of Hope, and the South Korean international shortwave broadcasts of KBS World Radio on 5975 kHz (discontinued as of early 2007) and 7275 kHz. The South Korean national radio channel, KBS Radio 1 on 711 kHz medium-wave is also jammed by the North. Before the bilateral declaration in 2000, KBS Radio 1 used to deliver certain programmes (merged with then KBS Radio Social Education) which condemned the North Korean regime at midnight. A visitor to coastal areas of the Yellow Sea (covering coastal parts of Gyeonggi Province, Incheon, Chungcheong, and sometimes Jeolla regions) who tunes into 711 kHz (KBS Radio 1 Seoul) may hear strange beeping sounds, which seem to be jamming signals from the North.
Strangely, the North does not usually jam the medium-wave transmissions of South Korea's broadcast towards-the-North, KBS Radio Korean Ethnicity (formerly KBS Radio Liberty Social Education) on 972 and 1134 kHz. KBS Radio Korean Ethnicity actually no longer targets North Koreans since the North-South Korea Joint Declaration on 15 June 2000. As of 15 August 2007, the radio channel has changed to a special radio broadcast for the Russian Far East and Northeast China, where nearly three million Koreans in China and several hundred thousand Koryo-saram (ethnic Koreans in Central Asia) live.
North Korean jamming of television broadcasting is relatively unusual, although the North Korean regime once severely jammed a South Korean state-owned television broadcast (KBS TV1 on VHF ch. 9 in Seoul) in the 1970s.[3] Currently there seem to be some strange signals on VHF ch. 9 in Seoul which seem to be North Korean's jamming, especially in the evening. This jamming is not very effective.
Because of electricity shortages in North Korea, the radio jamming activities are not always consistent and are sometimes interrupted by power failures[citation needed].