I have an ADF4351 eval board and I cancelled the onboard oscillator as written in its datasheet in order to to use my own reference input. I use a 50Mhz input clock and using the programming software I set it up for 250mhz output as seen on the settings attached. But the oscilloscope measurement says that the output is 276Mhz.Why is it different from 250 Mhz why I cant get exact frequency I want. I also tried for 1Ghz and 900mhz and mixed these two signals but the lowpass filtered output is 2.5mhz where it should be 100Mhz (1Ghz-900Mhz) normally. I dont have a spectrum analyzer and a high sampling rate oscilloscope but it is obvious that it is not generating the desired output. What could be the reason?