We are using four AD9361 transceivers on a custom board and we are experiencing an unexpected behavior when synchronizing them.
Initially, all the four transceivers are configured and the data collected by an FPGA, then sent to a PC for visualization. All data looks OK.
When we perform baseband synchronization according to the procedure described at page 88 of UG-570, one or more of the receiving channels shows an evident increase of noise. When the RF connectors are open we found a noise amplitude of the order of magnitude of 0.001 (assuming +1,-1 is the full dynamic of the ADC) before sync. After sync one or more of the eight channels shows a noise amplitude ten times higher. If the sync procedure is repeated the noisy channels changes randomly.
We have also observed that the four data clock becomes synchronous after sync procedure, but the four frame signals are not synchronous.
How can we synchronize the transceiver without affecting the noise level?