Direct Digital Synthesizer

can we use OCVCXO (Oven controlled voltage controlled crystal oscillator) as a reference clock for DDS? Or the use of fixed frequency oscillator is necessary?

You can surely use it, but what should be the benefit?

How about posting your questions with a more specific title? Having a burst of threads with identical title can't be but confusing.

i need reference clock having as low as possible phase noise(round about -155 dBc @ 100kHz offset). Bliley "Zeus" series OCVCXO(frequency range from 30MHz to 130MHz) have very low phase noise..meeting my requirements..but i never saw VCO's being used directly as reference clock...they are always used in PLL's and then a fixed frequency clock source is used as reference clock(according to my perception). Is there any problem using them directly as a reference?

The requested phase noise figure can be expected from good standard OCXOs.