[time-nuts] 10MHz Rubidium reference source for frequency counter
brooke at pacific.net
Sun Oct 26 18:01:36 EDT 2014
I've also heard that in order to calibrate rack mount crystal oscillators in instruments they need to be in the same
orientation as when mounted in the rack. So you can not remove the instrument from the rack and turn it on it's side
for the cal. So for some instruments that means mounting them in an empty rack and laying on your back like working
under a car.
Magnus Danielson wrote:
> One use for the R variants of the Fluke/Pendulum counters is/was for calibrating base-stations. They had issues with
> ovens and turning the counter to the side as you lifted it up. A rubidium inside solved that in a nice way.
> It's not all government work you know. :)
> On 10/26/2014 10:45 PM, Brooke Clarke wrote:
>> 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. http://www.prc68.com/I/TandFTE.shtml#SR620
>> Mail_Attachment --
>> Have Fun,
>> Brooke Clarke, N6GCE
>> Karen Tadevosyan wrote:
>>> Hello All,
>>> Can I have your recommendation regarding a choice of 10 MHz rubidium
>>> (available now on eBay like FE-5680; LPRO-101; LPFRS; FRS etc.) as a
>>> reference signal for my frequency counter Pendulum CNT-91.
>>> Thanks in advance.
>>> Karen, ra3apw
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