AD floor of FCA3120 option C ?

I plan to use FCA3120 counter to measure ~10GHz signal against a very good external reference (AD@1s ~10^-13)  What is the instrument measurement floor with an external reference? An AD chart from 1ms to 100ks would be ideal to see.  I found the instrument's datasheet shows a stability chart with various quartz oscillators (page 7) but I do not think this is the floor limit.  Thank you.  Anatoliy.

Sorry for the delayed response. It took us awhile because we checked throughout the company to find some help for you.  Please note that the datasheet has the most accurate and detailed information.

I looked through all the pages and I did not find an allan deviation curve of 10-20GHz signal vs itself (which is the noise floor of the instrument). Maybe I just missed it. Can you point me at the specific page of the datasheet which speaks about the x-band noise floor, please?

Hi Anatoliy,

Unfortunately, we currently only provide the Allan deviation measured at 10 seconds with the time-base references we provide, as you found in the datasheet.
The measurement floor of the instrument is not provided directly.

So, the instrument is not currently specified for such high stability measurements. You might still be able to use it for your measurement, but you will have to test the measurement floor of your FCA+external reference setup yourself.