I’m using the evaluation board EV-ADF4159EB1Z to understand how the ADF4159 component works and how to program it. I use software ADF4158-59 dated 28.01.2016.
Without setting any modulation , I set the adf4159 to 11GHz, to 12GHz, to 13GHz.
If I set 13GHz carrier, I have the VTUNE output fixed continuous voltage of 13,66 Vdc
If I set 12GHz carrier, I have the VTUNE output fixed continuous voltage of 5 Vdc
If I set 11GHz carrier, I have the VTUNE output fixed continuous voltage of 0,624Vdc
I noticed that for each carrier the spectrum presents a sort of burst modulation as shown in the attachment figure adf4159_2.jpg and highlighted with the red arrow.
If I turned on the evaluation board EV-ADF4159EB1Z without loading the software this phenomenon does not appear. Clearly, the 10.6GHz carrier (default value) is not stable in frequency because the PLL is not locked but there is no modulation. In attachment it is possible to see the image adf4159_default.jpg regarding this situation.
To capture the attachment figures I used the spectrum analyzer ANRITSU MS2725C in burst mode acquisition.
Why do I see this burst modulation?
What should I do to remove this burst modulation?