[time-nuts] Second FTS4060 shows Drift, is it me? Good Links

John Ackermann N8UR jra at febo.com
Tue Feb 7 11:39:31 EST 2006

Hi Brooke --

Did you remove any linear offset before generating thorse plots?  They 
sure look a lot more like an Xtal aging with offset removed, than a Cs.

I wonder if it might be related to your use of the 1MHz output, rather 
than 1pps, to drive the stop input.  Maybe you're slipping cycles due to 
drift in the counter timebase (or some other systemic reason)?  I've 
sometimes seen squirrely results when trying to use a high frequency 
from the DUT to drive the stop signal.  Dividing down to 1pps would 
eliminate that as a possible problem.


Brooke Clarke wrote:
> Hi:
> Sorry for the bad links, here are good ones:
> Today's plot = http://www.pacificsites.com/~brooke/pdf/sn1013_850_Drift2.pdf
> s/n 1227 29 Apr 2005 plot = 
> http://www.pacificsites.com/~brooke/pdf/Cs_Drift0429.pdf
> Brooke
> Brooke Clarke wrote:
>>A year ago I took apart the FTS4060 that was DOA (s/n 1013) because of 
>>rough shipping and used it to figure out most of the interconnect 
>>wiring.  A few months ago I put it back together with the thought of 
>>selling it as a parts unit.  But first powered it up and found that it 
>>now locked and seemed to be working so tried to set the C-field. 
>>For the last couple of weeks it has shown a parabolic plot like s/n 
>>1227, although this time the polarity is opposite that of s/n 1227 which 
>>also showed drift, but that may be a setup difference.  A plot of s/n 
>>1227 is at:   file:///C:/Webdocs/pdf/Cs_Drift0429.pdf 
>>The equation for s/n 1013 is:
>>y = 2.7943x2 - 302.64x + 8969.4 and the quality of fit is
>>R2 = 0.9088.  The x-axis is in days and the y-axis is in ns. 
>>The first derivative of the equation has a first term of 2 * 2.7943 * x 
>>ns/day or +5.3E-14 seconds/seconds drift rate.
>>Today's plot is at:   file:///C:/Webdocs/pdf/sn1013_850_Drift2.pdf
>>The current setup is:
>>SR620 time interval counter doing 500 averages (500 seconds = 8 1/3 
>>Start from Motorola M12+T (9 ns jitter).
>>Stop from FTS4060 1 MHz output.
>>Manually enter into spreadsheet date and time of reading (usually not on 
>>the 8 1/3 minute change, just a random time) and counter value.
>>For most of the test the SR620 was using it's internal oscillator and 
>>just recently I changed it to the PRS10 external standard but that does 
>>not seem to have made any difference.
>>Is there something I'm doing wrong that would cause apparent drift? 
>>Thanks for any thoughts,
>>Brooke Clarke, N6GCE

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