[time-nuts] 10MHz Rubidium reference source for frequency counter
ra3apw at mail.ru
Mon Oct 27 16:01:19 EDT 2014
Many thanks for all your recommendations.
Let me provide more details for understanding of my task.
I am playing with a GPSDO project on base of uBlox NEO-7M (http://www.ra3apw.ru/ublox-neo-7m-ocxo-gpsdo/) - sorry, text in Russian.
One of the main step – ADEV measurement of a developed GPSDO.
My ADEV measure stand consists of a frequency counter Pendulum CNT-91 with TimeBase option 19 + GPIB interface + KE5FX TimeLab software (TNX again John).
As option for CNT-91’s reference source I can use a homemade GPSDO on base of G3RUH design.
IMHO, in this condition a frequency stability of my GPSDO project should be higher than a stability of CNT-91’s reference OCXO.
Taking into account that rubidium source has a better short range stability than OCXO or GPSDO I hope to find an external rubidium as 10 MHz reference source instead of internal OCXO of counter.
If my reasoning is not right could you please correct them as I am not an expert in this area.
> Date: Sun, 26 Oct 2014 14:45:00 -0700
> From: Brooke Clarke <brooke at pacific.net>
> Hi Karen:
> The ones you mention are all stand alone Rb oscillators that need to be
> calibrated to set their frequency.
> This was the historical way that crystal oscillators were calibrated every year
> or so. The great advantage of Rb over crystal oscillators is that their drift is
> specified in months instead of days.
> A much better - more modern idea - is the GPS Disciplined Oscillator (GPSDO).
> It keeps the oscillator "calibrated" in real time.
> A popular crystal based GPSDO is the Trimble ThunderBolt:
> Another crystal based GPSDO is the HP Z3805:
> There are many more commercial GPSDOs and this list has discussions that
> show they can be a do it yourself project for under maybe $10, but require a
> number of sophisticated skills.
> I have the just released LTE-Lite GPSDO Evaluation Kit with 10MHz TCXO on
> order. Seems to offer good performance for the dollar.
> The only advantage of a Rb GPSDO over a crystal GPSDO is for the case
> where the GPS updating has not happened for some time.
> This might be due to a power failure lasting some days or that the oscillator
> will be used where there's no GPS access and it only gets "calibrated" then
> used much later.
> The Stanford Research PRS-10 Rb oscillator can be used stand alone where it
> time stamps an external 1 Pulse Per Second input, or as part of a GPSDO
> where an external GPS receiver supplies it with a 1 PPS input.
> The Thunderbolt can be custom modified to drive an external Rb oscillator,
> like the ones you mentioned, but that requires some technical sophistication.
> Note the ThunderBolt and Z3805 are complete GPSDOs in a box, just connect
> power and a GPS antenna.
> The PRS-10 requires an external GPS receiver and antenna. A a practical
> matter that means it's more work to maintain the PRS-10 because there's
> more opportunity for problems like disconnecting a cable.
> PS Stanford Research offered a version of their SR620 Time Interval counter
> that included a Rb oscillator (not a GPSDO) that some government agencies
> purchased, but for normal use you really don't need a Rb oscillator, so the
> CNT-91R appears to be a similar way so sell it to a government with a lot of
> money to spare. So don't feel pressured to use an Rb oscillator.
> Mail_Attachment --
> Have Fun,
> Brooke Clarke, N6GCE
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