[time-nuts] G P S D O

Brian Kirby kilodelta4foxmike at gmail.com
Thu Oct 29 03:32:07 UTC 2009

I have attached a plots of various GPSDO's compared against a HP5065A 

The first plot is of a HP Z3801A.  The left scale spans 36 nanoseconds.

The second plot is of a Trimble Thunderbolt, its running default 100 
second time constant with a 1.2 damping factor.  Its from the group 
purchase.  I changed the scale to span 36 nanoseconds.

The third plot is of Efratom FRS-C rubidium that is controlled by the 
Shera Controller, and its GPS source is an older Motorola Oncore VP, ver 
10.  The scale spans   36 nanoseconds.  Bear in mind this was not his 
stock PIC, but a PIC that we modified for a rubidium.  His stock PIC had 
a update rate of 30 seconds, we tested units at 60, 120 and 240 seconds 
and settled on 120 seconds after the preliminary data.   The time 
constant was set up for mode 7, I believe that works out to  the 
proportional controller time constant around 1/3 of a day  (I'll have to 
find the paperwork and run the calcs).

I tried to present some information earlier, but the only 
instrumentation I had was a HP 53131A, with TAC32, and a Efratom FRK-L 
for reference.  At that time I did not have the computing horsepower, 
plotting capability or some more serious instrumentation.

The instrumentation used in these plots was a HP 5370B, it baselines at 
2x10-11 at one second and drops a magnitude for every decade in tau.  
The recording was done via a Prologix GPIB USB adapter and HyperTerminal 
in Windows.  The plots were generate in DF6JB/Ulrich's Plotter program 
(thanks !).

After generating the plots, I scanned them into PDF at 200 DPI to save 
bandwidth.  I have not been able to generate PDF's directly inside of 
Plotter.  I use version 6 of PDF and it takes an internal error.  AT the 
present, I cannot afford to upgrade it.

I bought a Fury controller a couple of years back and due to personal 
issues I could not put it to use.  My next project it to put the Fury on 
the FRS-C and see how much we can smooth it out....

Brian KD4FM
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