[time-nuts] List of time synchronization hardware and software

Tom Van Baak tvb at leapsecond.com
Tue Jan 17 20:42:51 EST 2006

> Can somebody give me a lesson on this area?  Is there a good web page that
> answers questions like these?
> What does a Caesium/Rubidium box cost?  Any reason to prefer one or the
> What sort of lifetime do they have and/or how much care/fiddling do they
> Do they need any calibration or tuning or setup magic, or do I just plug
> in and get a known frequency out?
> Does it make sense for a non-wizard to get something from ebay and if so,
> what do I look for?  Any obvious models/manufacturers to look for and/or
> avoid?
> Any used-gear places have them at reasonable prices?

Nice set of questions.

You can find more info if you hunt around my website:


My very rough guess is that used Rb are available
for $100 to $500 and used Cs are available for $500
to $2500.

Most Rb last longer than a timekeeping hobby lasts.
Rb tend to be much smaller, require less power, are
available in much larger quantities (the used market
is flooded with them; they show up on eBay every day).
Rb have pretty good short-term stability, although a
really good quartz will blow them away. It all depends
on your needs.

Most Rb work when first plugged in and will be accurate
to 9 or 10 digits; they can be calibrated to 10 or 11
digits and will hold that for weeks (they drift).

Most used Cs are dead on arrival. But for those that
work, or can be made to work, the lifetime for a so-called
"high-performance" unit is up to 7 years; the standard
performance unit is up to 20 years. Looks for those by
HP, FTS, Datum, and FEI.

Cs tend to be much larger, heavy, rack-mount-sized
units, require more power and care, and show up on eBay
several times a month. Cs have moderate short-term
stability (Rb are sometimes better; a really good quartz
is often better) but they shine long-term if you want an
independent source of time and frequency.

Any good GPSDO, however, will clean a Rb or Cs's
clock in very long-term accuracy, if that is a factor.

Most surplus Cs, if they work at all will be accurate
to 10 or 11 digits; they can be fine-tuned to 11 or 12
digits and hold that indefinitely (zero drift).

Modern current-product Cs (such as the 5071A) rarely
show up on the surplus market (about once per year
on eBay) and sell for tens of thousands. These are
accurate to 13 digits and stable to 14 or 15 digits.

Many of us who buy surplus Cs on eBay end up
getting more than one unit before we get one that
works right. The repair adventure is part of the fun.

Hope that addresses your questions.


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