[time-nuts] Time interval measurement vs dual mixer method
kb8tq at n1k.org
Sun Jan 21 09:04:36 EST 2018
What level of stability are you trying to measure?
What sort of offset frequency are you running?
What kind (phase noise / spurs / adev) offset oscillator are you using?
What sort of limiter are you running with what sort of pre filtering?
We have run around on a lot of generalities. You may have some issues
that are specific to your setup. There is no “one size fits all” approach here.
If you are running a couple of oscillators it the THz region and trying to look
at ADEV from 1us to two months tau with one setup, a lot of what we have
been saying simply does not apply.
> On Jan 21, 2018, at 4:23 AM, timeok at timeok.it wrote:
> thanks for the information.
> I'm definitely interested in the short therm ADEV but especially for Tau from 1 day and over to test high stability standard over the time.
> I will have further tests.
> Da "time-nuts" time-nuts-bounces at febo.com
> A time-nuts at febo.com
> Data Sat, 20 Jan 2018 16:14:10 -0800
> Oggetto [time-nuts] Time interval measurement vs dual mixer method
> I don't know of a commercial version.
> As you have seen as the two signals move away from close phase
> coincidence the system noise level will increase.
> This is because the common offset oscillator noise will only cancel when
> the phases are closely matching.
> This is mainly important for the lower Tau (like 1 to 10 seconds).
> I will normally adjust the phase of my reference or DUT so that myTIC is
> reading 0.00000XX (close to phase match) and very slowly rising. (with my
> setup most DUT will age downward).
> Then I start logging the data.
> A typical run with a 1 week aged quartz will show the TIC count slowly
> increase (and may wrap) and then as the aging continues the count will
> reverse and eventually go "below" zero and wrap.
> A phase plot will show a nice parabolic looking curve going up and then
> as the aging crosses it will curve down.
> If there are wraps the plotter program can take them out.
> Any long plot of Quartz WILL wrap!
> Now if you plot the AD you will see a normal type plot for a good Quartz.
> If the TIC count increased well past coincidence only the Higher Taus
> will be accurate.
> For the lower Tau you need to cut off the data past where it climbed too
> I typically will setup as described and run a short log of say 5 minutes.
> I might only keep the first 100 Seconds and plot the AD against that.
> This will give you an accurate plot for the lower Tau.
> These two plots can then be combined to give you the whole range.
> The attached plot of an FE405B illustrates this.
> The Red plot is against a very good FTS 1200 (2X10-13th at 1 thru just
> past 10 Sec)
> The blue continuation is against a very good HP 5065A (1.5X10-13th at 100
> So if the lower Tau are important only use logged data that are in near
> phase match!
> Hope this helps!
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