AD9778 Input Clock Harmonics


I'm using an AD9778 and AD9779, both on custom PCBs. They are both running with the default register settings (with the exception of register 0 set to 0x80 to enable the bi-directional serial interface). As such the internal PLL is disabled, so too is interpolation. My reference clock and data rate is 160 MHz. Unfortunately I am seeing very high (-10 dBm) harmonics of the input clock on the output of the device at 320 and 640 MHz.

Has anyone else had this problem?