[time-nuts] Why would I want a rubidium

Joseph Gray jgray at zianet.com
Mon Oct 5 18:02:24 UTC 2009


Thanks, John. That was the type of information I was looking for.

Joe Gray
KA5ZEC

On Mon, Oct 5, 2009 at 11:34 AM, John Ackermann N8UR <jra at febo.com> wrote:
> 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 <jfor at quik.com> 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.
>
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