This is a recording of the old style mechanical teletypes that were the main way to do RTTY before the PC. It was found by Fred, WA0PBL on http://www.earthstation1.com/sfx/. I hear you really need the smell of hot oil to understand the nostalgia. A major source of info on the "Green Key" machines is at the Nadcomm Museum page at: http://www.nadcomm.com/