[time-nuts] FE-5680A performance
John Ackermann N8UR
jra at febo.com
Thu Jan 5 14:49:45 UTC 2012
On 1/5/2012 12:33 AM, John Miles wrote:
> Grab the latest release from www.miles.io/timelab/readme.htm if you like --
> it will acquire from the TSC 5125A for as many hours/days as the TSC's
> Ethernet connection will stay up. (Which sometimes isn't very long.)
> TimeLab generates its frequency-difference plot from the acquired phase
> data, so it will give you various display and filtering options that the
> 5125A itself will not.
All the wonders of the TSC boxes aside, there is one really annoying
thing you need to keep in mind when working with the phase data: the box
applies an arbitrary phase offset that reflects through to the phase
data output. It appears as a linear frequency offset that needs to be
removed prior to doing frequency analysis. That's not a big problem for
normal stability measurements, but in some cases it makes it a lot
harder to extract the data you want.
To get around this, you can use the TSC's frequency counter output which
gives 14 or 15 digit measurements. However, you need software to
manually poll for the fcounter data, and you can't get precise tau from
it since the updates don't seem to happen synchronously. I ended up
writing a perl script that grabs and logs the fcounter data every 10
seconds by default, and that has worked well.
John, could you expand on your comment about the ethernet connection? I
have seen random instances where the TSC seems to lose its TCP/IP
settings, but so far it's never happened during a measurement run, so
has been annoying but manageable.
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