You can program the output frequency from 0Hz to 50MHz, but according to the sampling theory (Shannon, Nyquist) practically, the output is limited to about 45% of the maximum clock rate at which the logic can be operated. This means that the sinus-output can reach from 0 Hz to about 25MHz with a 50MHz crystal. I think that is really good. http://hem.passagen.se/communication/dds.html
Но вопрос - то был не только в этом. Как запустить КВАРЦ на 49,860МГц!!!