I know what you are talking about. There are atleast 7 different Tjaden families in The Netherlands and several in northern Germany. I have visited some of these families in both of those countries. My particular branch came from the Aurich, Ostfriesland area. When I was attending a Norweigen college (Luther) at Decorah, Iowa, I had an instructor that was sure the name had Scandanavian roots. My e-mail address is:
btjaden@neotek.net