I am using FMCOMMS1 with KC705 carrier board. For my design, it is critical to find the loopback delay. I sent a sinc signal to find out the latency in terms of cycles. Here is the snapshot from chipscope.
In the above, The received signal (top 2 signals) has negative I, positive Q values. And The signs of the received IQ signals differ time to time. The latency between sent and received signals also changes. It is not constant.
Why does the latency change time to time?
Why does the received signal change time to time?