[time-nuts] 10MHz Rubidium reference source for frequency counter

SAIDJACK at aol.com SAIDJACK at aol.com
Mon Oct 27 19:23:10 EDT 2014


Karen,
 
a good double oven OCXO such as Morion etc will give you much better short  
term stability than most Rudidiums can give you. By a factor of 10 or even 
100  sometimes below 10s measurement interval.
 
The Rb's are better anywhere from 100s to many 1000 seconds.
 
bye,
Said
 
 
In a message dated 10/27/2014 13:57:14 Pacific Daylight Time,  
ra3apw at mail.ru writes:

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.
Karen, ra3apw    

> 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:
> http://www.prc68.com/I/ThunderBolt.shtml
> 
>  Another crystal based GPSDO is the HP Z3805:
>  http://www.prc68.com/I/Z3805A.html
> 
> 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.
>  http://www.ebay.com/itm/171504585820
> 
> 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.
> http://www.prc68.com/I/PRS10.shtml
> 
> 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.
>  http://www.prc68.com/I/TandFTE.shtml#SR620
> Mail_Attachment --
>  Have Fun,
> 
> Brooke Clarke, N6GCE
>  http://www.PRC68.com
>  http://www.end2partygovernment.com/2012Issues.html
>  http://www.prc68.com/I/DietNutrition.html

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