Thx for the reply,
As i understand, DDS' SFDR can not be found & measured by observing the spuriouses with spectrum analyzer while you are changing the amplitude of the output.
You are using another way to identfy SFDR of your DDS's. (Like ADIsimADC which is mentioned at
http://www.analog.com/static/imported-files/tutorials/MT-003.pdf )
Could i understand rigth?