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AD9371 Spectrum Difference between ORX1 and RX1

Question asked by gizmoaudio on Mar 31, 2017
Latest reply on Apr 5, 2017 by sripad

I'm using IIO Scope with the AD9371 eval card and the ZC706. I have set the RX1 and ORX1 channels to the same setup parameters as per sample rates and filtering but am seeing a large difference in the spectrums. ORX1 is much noisier than the RX channel. Also the noise spectrum is not flat for the ORX1. I'm using the SN and RX LOs. I'm running an external sig gen at -40dBm and 2GHz CW into a power splitter into both inputs so there is no difference in their input signals. I also tuned the signal close to the internal LOs so that I would see a noisey "dot" on the constellation display and I see just a dot with no arcs that would indicate a phase noise issue, so the noise is just random noise and not phase noise. The time domain capture shows the large difference in noise level, the noiser signal is the ORX channel. I've attached jpg files showing a time domain capture, the spectrums, and setups. What could be causing the difference in performance? Is there a parameter that I'm not setting correctly?