So 657khz is a number station?
657khz is not a number station per say. it is the strong watt broadcast of Radio Pyongyang with regular programming all day. However, it plays the numbers just after the station ID, usually starting around 5 minutes after midnight Japan Time daily. The DPRK bitch who reads them out to the spies in Japan goes on for about four or five minutes. There is a site on the internet; somebody in Japan once recorded it and audio streams it online