Doesn't the US run stations like this as well. The "numbers" station. Basically they're for covert communications. Operatives that need orders will tune in at a specific time and use their one time pad book to translate the message.
The reason they transmit all of the time is that they know other spies listen to the station, and they don't want to make it apparent when they're sending more messages than usual, so non-broadcast time is filled with just random data.
IMHO, these stations have been running for far too long to be an art project. They were also much too obscure, even for the insular art world.