Sealand is a self-declared but unrecognized nation-state. The US does not recognize them, nor does anyone else that I know of. Their territory is Roughs Tower, a former Sea Fort located in the North Sea about six miles off the coast of Suffolk UK. Additionally it claims territorial waters of a standard twelve-nautical-mile radius. Sealand is occupied by the family and associates of Paddy Roy Bates. The population of Sealand is about five. They are perhaps the worlds only novelty nation being smaller than the Vatican and funnier than Luxembourg. Only England would put up with this.
As small as it is, Sealand still uses radio. They provide a maritime radio service. Following operational trials and international consultation, they opened a Maritime Radio Service to ships within its territorial waters and surrounding areas. This Service is provided to aid safety at sea and to facilitate ships' movements; vessels transmitting Sealand waters may also obtain relevant navigational and Sealand weather information.
Sealand Radio Shore-to-Ship services are available as follows:
Channel 16: (Emergency): Continuous watch, 0900-2100 GMT
Channel 84: (Operational): Continuous watc, 0900-2100 GMT
Radio on Sealand probably began as maritime wartime broadcasts during WWII. But those are lost to history. In 1965 millionaire fishing magnate Roy Bates first occupied the platform, hoping to make it the base for his pirate radio station, Radio Essex. Then England legalized commercial radio, pirate stations lost much of their appeal.
More on England's long history of off-shore pirate radio here.