[time-nuts] DMTD using TBolts

WarrenS warrensjmail-one at yahoo.com
Thu Oct 20 22:05:00 UTC 2011

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



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