AD9958 output amplitude variation

Hello Everybody,

I built a board with AD9958 - the way it is suggested in the spec sheet. I need to generate output signals in the range of 30 to 150MHz. I noticed as I change the frequency setting, the output amplitude varies almost two times.

I looked through the spec sheet, but I did not notice amplitude variation vs frequency spec. I would think that amplitude should not change with frequency; there are no specific filters on the DAC's output as far as I see..

I still suspect something wrong with my board, but in general - is there a notion for the output of DDS to stay at the same amplitude over the frequency range?

Thank you,