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AD9361 Internal LO Phase noise when Rx=Tx

Question asked by rsizeland on Feb 10, 2016
Latest reply on Feb 11, 2016 by rsizeland

We have an application where we are using internal LOs and the Tx LO is the same frequency as the Rx.  First, is there a way to only use 1 LO to drive both Tx and Rx?  I don't think so, but thought I'd ask.

 

The problem we are seeing is the excess phase noise on the Tx signal, around 50% of the time (see spectrum analyzer screen shot of CW signal).  Changing frequency or power cycling the unit can clear / cause the high phase noise state.  I'm guessing there is some kind of in phase / out of phase interaction between some leaked and divided signal between the LOs which changes randomly when re-locking, but can't say for sure. The poor phase noise signal gives ~2 % worse EVM on the Tx signal.

 

Any advice?

 

Thanks,

Rob.

 

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