I have an AD-FMCOMMS1-EBZ (REV C) board. In REV C, the ADL5380 output filter C115, C116, C142 and C143 are absent. The C114, C264, C145 and C295 exist for AD9643 input filter (I assume it is the anti-alias filter).
Now begin my test as follow:
ADC and DAC sample rate is 245.76MHz. Direct loopback cable from TX to RX.
ADC and DAC LO=2400MHz; set DDS one tone at 20MHz. Now the 20MHz peak appears normally on the IIO Scope.
ADC LO=2400MHz, DAC LO=2550MHz; set DDS one tone at 20MHz. Now the -75MHz peak appears on the IIO Scope. The peak db is nearly same as step 1.
Does this test means that the Anti-Alias design of AD-FMCOMMS1-EBZ (REV C) is failed?