I am using a AD-FMCOMMS1-EBZ REV B with a Digilent Zedboard and the problem is that sometimes in the DAC output appears the frequency of Reference Clock from the FPGA (33 MHz). You can find attached a screenshot from the spectrum analyzer. In this screenshot you can see the 33 MHz tone (1), the tone I really want to use (90 MHz is "my signal" (2)), and two more tones are 245.76 MHz - 33 MHz (3) and 245.76 MHz + 33 MHz (4) (this frequency, 245.76 MHz is just the ADC sampling frequency and the half of the DAC sampling frequency (491.52 MHz)). I have bypassed the RF section in DAC and ADC.
I don't know why this is happening. It would be great if anyone can help me.