[time-nuts] Help with my ADEV measurement setup

Bob Camp kb8tq at n1k.org
Tue Jun 30 21:48:08 EDT 2015


Hi

Your OCXO and the TBolt *should* be down around 1x10^-11 to 1x10^-12 at one second. 
That’s a factor of 10 to 100X better than the 53131 can do at a random frequency. At exactly
10 MHz it may be even worse than that. Effectively what you will be doing is measuring the 
noise floor of the counter out to a few hundred seconds. To get useful data, plan on runs of
at least several hours, if not a few days. 

Bob

> On Jun 30, 2015, at 8:05 PM, Dan Watson <watsondaniel3 at gmail.com> wrote:
> 
> I tried both the PPS and the 10MHz signal on channel 1, with the 10MHz DUT
> on channel 2. Tom emailed me and it turns out the software was not
> detecting the units correctly from the serial string. (What are 6 powers of
> ten between friends, right? :) ) Likely a settings mistake on my part, I
> sent him a screen cap to see what's up.
> 
> None the less, I manually enter the time units and was able to plot some
> data. I attached a new screen cap. How does this look?
> 
> Thanks
> 
> Dan
> 
> On Tue, Jun 30, 2015 at 5:36 PM, Bob Camp <kb8tq at n1k.org> wrote:
> 
>> Hi
>> 
>> Are you using a PPS as the “start” and the 10 MHz as the “stop” or
>> comparing two PPS signals?
>> 
>> Bob
>> 
>>> 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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> <adevplot_PPS.png>_______________________________________________
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