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FMCOMMS4 RX_A and RX_B swapped?

Question asked by jeffmelville on Mar 30, 2015
Latest reply on Apr 3, 2015 by jeffmelville

I am using an FMCOMMS4 board with the AD9364 chipset on a ZC706 board with the AD reference design. I am using IIO Oscilloscope from another PC over Ethernet.


I'm working with signals outside the 2.4 GHz band so I the RF input is connected to RX-A for the wider bandwidth balun. (By the way, I could not find the balun <-> RF port mapping without looking at the schematics).  For now, I'm just applying a tone into the RX-A connector.


The strange thing is that I have to select "B_BALANCED" from the FMCOMMS2/3/4 tab in IIO Oscilloscope in order to see the signal. If I select A_BALANCED, I just see noise with a lot of spurs. Interestingly, if I select C_BALANCED I see an attenuated version of the input signal.


Alternatively, if I plug the input into the "B" connector, I get the best data when selecting "A_BALANCED." I do see some attenuation in this case but I assume it is because of the performance of the 2.4 GHz balun at this frequency.


What am I doing wrong?