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AD936x LO Configurations - Valid crystal resonant frequencies range.

Category: Hardware
Product Number: AD9361/AD9363


I searched for this information in many forum posts here, but none of them gave a clear explanation like I need. 

I'm working on an SDR-based project exploring the use of an external reference signal with AD9363 as the core transceiver IC. We currently connect a 40 MHz TCXO to XTALn but are exploring the use of a 10 MHz reference clock as well. 40 MHz works exceptionally well, but a build with a 10 MHz demonstrates phase noise failures and mixing products despite being able to initialize the device. 

In the document AD936xLOconfiguration posted in this group, it's stated that "valid crystal resonant frequencies range from 19 MHz to 50 MHz". Following this, a 10 MHz reference would be invalid, and I wanted to know why. Is there a drastic phase noise issue or other hardware issue that arises with using a lower reference? This isn't really clarified anywhere, including the datasheet. I've seen it said in forums that "10 MHz is a poor choice as a reference". 

Thank you for your time and any help you can offer!