Here's a reason why you might "want" (as opposed to "need"!) another
standard beyond the GPSDO.
An Rb or Cs is self-contained. The GPSDO relies on an external factor,
the presence of GPS. Holdover mode may be good to keep thing close for
a while, but over the long term the GPSDO without GPS is no better than
its crystal oscillator.
The Rb is a secondary standard and therefore isn't "correct" by
definition, but it has a low aging rate and gives you something
independent of GPS to use for measurements. Monitor it against GPS for
a while to learn its offset and drift characteristics, and then you can
extrapolate its performance out over a much longer time than you could
with an OCXO.
You may not require that independence, but it gives you additional
measurement capability. For example, comparing the output of two GPSDO
may not be meaningful because their frequencies could be correlated by
their common view of the GPS constellation. Using an Rb reference would
eliminate that common mode error and reveal information about the
GPSDO's short and medium term stability that would otherwise be hidden.
John
----
Joseph Gray wrote:
I know I don't "need" any of this stuff. I was just wondering what I
could do with a rubidium vs what I already have.
On Mon, Oct 5, 2009 at 10:58 AM, J. Forster <[email protected]> wrote:
From an engineering point of view:
Very few people really "NEED" a Rb or Cs as they are not really doing
anything that requires that level of precision in frequency or accuracy in
time (me included). These days a BC-221 or WWB is not good enough, but 1
Hz at X-Band is for almost all practical uses.
_______________________________________________
time-nuts mailing list -- [email protected]
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
