We have a design with two AD9361 and want to synchronize LOs by using an external LO. For this, I apply a sinus from a signal generator to the RX_EXT_LO_IN pins and set the appropriate registers. However, this doesn't work and while debugging we noticed that the bias voltage at our RX_EXT_LO_IN pins is only 0.03V instead of 0.5V as in the FMCOMM2 reference design. TX_EXT_LO_IN is grounded, but grounding the pin on the FMCOMM2 didn't cause a voltage drop. This voltage is generated chip internal, hence my question: What can cause a drop of the bias voltage at the RX_EXT_LO_IN pin?
Did you enable external LO mode?