[time-nuts] Help with my ADEV measurement setup

Dan Watson watsondaniel3 at gmail.com
Tue Jun 30 14:47:45 EDT 2015


I'm trying to take some ADEV measurements with my 53131A, and I'm having
some issues. This is my setup:

- 53131A with the OCXO option. Calibrated against a T-bolt. I also did the
TI Quik cal and it passed
- I'm using RS-232 out with a null modem cable into a Serial-USB converter
- Software is TimeLab in talk-only mode. 53131A check box is checked.
- The counter is in TI mode, with a T-bolt on Channel 1 and DUT on Channel 2
- A delay of 1 second is set on the counter. TimeLab seems to accurately
detect this interval

I started measuring various devices, and could never seem to get better
than around 1x10^-6. Even my Rb was showing a 1 second ADEV of 10^-6.
Finally I put the T-bolt on channel 1 with common mode on to both channels,
and it still measures around 10^-6. A picture of that is attached. Surely
this can't be right.

I tried frequency mode and it gives ADEVs of 10^-12 on the Rb and T-bolt,
as expected. I understand the issues with filtering that the 53131A does
internally on this mode, but at least it shows my setup is working to some
degree. It's TI mode that seems to be wonky.

I'm probably doing something really stupid.

Thanks for any help you all can suggest.


Dan W
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