[time-nuts] DMTD using TBolts
magnus at rubidium.dyndns.org
Thu Oct 20 23:46:57 UTC 2011
On 10/21/2011 12:05 AM, WarrenS wrote:
> Tbolt-Tic is what I call a Tbolt when it is NOT used as a GPSDO
> controller but instead used as a high resolution time interval counter.
> (really a time difference logger).
> How do you make a single TBolt-Tic much better?
> Simple, By making a dual TBolt-Tic.
> From an offshoot of my Common view TBolt experiments,
> I connected a common GPS antenna to two Tbolts that both have been
> modified to use an external osc.
> This makes a simple, high performance, DMTD tester with low ps
> resolution using the 'noisy' GPS signal as the common "offset" Osc.
> DMTD and common view both work on the same basic principle.
> The end results is that the noise of the common signal source (GPS in
> this case) tends to cancel when the difference between the two Tbolt
> data streams is use.
> The data difference then gives the freq and the phase difference between
> the two 10 MHz Oscillators that are being compared. (neither of which
> needs to be disciplined or have an EFC input).
> From the phase difference and the PPT Freq difference data, standard
> low noise floor ADEV plots can be made with tau zero = 1 sec.
> No software yet to make it all easy and automatic, but hopefully that
> will happen in a future version of LadyHeather and/or TimeLab.
> Maybe, the existing Plotter S/W can already take the raw data from two
> Tbolts, find the differences by subtracting both the Phase and PPT
> columns and plot the results.
> If not, any volunteer to come up with a SIMPLE routine to do the above
I like this idea. I would need a couple of thunderbolts to try it.
A side-effect is that the transfer oscillator also provides a UTC source.
Care should be taken such that the same birds is selected. I think a
normal mode T-bolt should be used as normal reference and bird-master,
and the selection be forced onto the slave measurement channels. Would
not require very much of a software.
Only works for 10 MHz clocks I guess.
The software could produce a socket for timelab or it could provide data
on a timelab compatible file, since timelab is able to get data from an
The overall processing and parsing should be fairly simple to produce
the raw-data. Sounds like a fun project.
Anyone with a few spare thunderbolts that I could get to try this out?
Bad oscillator isn't a problem.
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