[time-nuts] Fury Realhamradio listing

SAIDJACK at aol.com SAIDJACK at aol.com
Mon Aug 20 19:04:24 EDT 2007

In a message dated 8/20/2007 12:47:02 Pacific Daylight Time,  
tvb at LeapSecond.com writes:

>I  could be wrong, but diurnal perturbations sound like antenna,
>location,  or placement more than receiver. 12h or 24h  period?

Hi Tom,
hard to say. I run all my units from the same antenna/feed using an HP  
1-to-8 splitter, so I don't think it's the antenna. It may be the Auto-Survey  thoug
h, since I don't hard-code the position but rather let the receivers  
determine it themselves. Maybe the M12M's have better Auto Survey  precision?
I have tested three different M12M's on different Fury's, and all are  better 
than the M12+'s.
What we noticed is a fairly significant reduction in long-term  (say >5 
hours) EFC voltage activity with the new receivers, which  seemed to be related to 
thermal changes, which are diurnal of course, 24 hour  periods.
I expect the reason for the lower EFC voltage activity to be a better  
accuracy of the 1PPS signal since the OCXO's are extremely good (6.6E-012 change  
per degree C for the OCXO itself) and we also electronically measure and  
compensate for the residual thermal coefficient of the electronics on the Fury  
GPSDO. With this electronic compensation we expect less than 2E-012/Deg  C thermal 
sensitivity of the unit (excluding the GPS receiver  itself).
The new receivers also have less hold-over, and generally a much reduced  
Standard Deviation error as indicated by GPSCon.
My theory is that the older M12+'s were just quite sensitive to thermal  
changes, which show up as diurnal errors. Randy also confirmed that the old  
M12+'s had a significant thermal sensitivity in their TCXO's. The M12M's are  much 
To test this using my Cs or Rb's is difficult, since my Cs is somewhat  
thermally sensitive, and the Rb is running of GPS as well (sigh). Wish I had a  
maser, or 5071A etc.

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