[time-nuts] Help with my ADEV measurement setup

Bob Camp kb8tq at n1k.org
Tue Jun 30 21:36:26 UTC 2015


Are you using a PPS as the “start” and the 10 MHz as the “stop” or comparing two PPS signals?


> On Jun 30, 2015, at 2:47 PM, Dan Watson <watsondaniel3 at gmail.com> wrote:
> Hi,
> 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.
> Regards,
> Dan W
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