[time-nuts] Rubidium (Rb) or Caesium (Cs)

Tom Van Baak tvb at LeapSecond.com
Mon Oct 3 21:36:23 EDT 2011

> What I'd like to find out is how accurate a GPS Disciplined_Rb_Osc can be made compared to the typical Cs out there.


Most modern GPSDO will outperform rack-mount Cs in stability
as the tau grows beyond a day or a week. Of course, it depends
quite a bit on the particular GPSDO or the brand of Cs but in
general GPSDO's are really good and always "win" in the end
because they are locked to UTC and a free-running Cs isn't.

Some of my 5071A flicker out at 5e-15. It takes a 4 ns RMS
GPS timing receiver about 10 days to get to the same point.

Remember that a GPSDO is a really just a radio receiver, a
time-transfer device, a slave repeater; not strictly a "clock".
So their superior long-term performance isn't surprising. It
also explains why there's a huge market for GPSDO products
and a very small market for large stand-alone Cs standards.

The surplus Z3801A and Thunderbolts that hit the eBay market
this decade have been the greatest treat any amateur could
possibly have hoped for!

I have a couple of suggestions for you; in another posting.


More information about the time-nuts mailing list