[time-nuts] Fluke/Pendulum Counters - Rubidium Timebase

Magnus Danielson magnus at rubidium.dyndns.org
Tue Jan 17 19:45:24 EST 2017


Ed,

I will make sure to forward your thanks to Stefan.

A small OCXO could be supported by the built-in PSU, so that might be 
more practical. Really depends on what you want to do.

One of these days I will work on the calibration stuff on the 
CNT-81/PM6681 I have.

Cheers,
Magnus

On 01/17/2017 05:13 PM, Ed Palmer wrote:
> Magnus,
> Thanks for the info and please pass my thanks on to Stefan.
>
> Yes, I usually do use an external timebase for the PM6681. I need to do
> some troubleshooting on the  unit and thought I'd do a timebase upgrade
> while I was in there.  I want to make some measurements that are
> independent of my house standard (an Efratom FRK).
>
> I haven't quite decided whether the upgrade will be an OCXO or a Rb.  I
> have both LPRO and X72 Rb units sitting on the shelf so the cost will be
> minimal.  If I go with a Rb, I'll just find a small power supply that
> will fit rather than looking for the distribution board.  There appears
> to be enough info in the service manual that figuring out the
> connections shouldn't be a problem.
>
> Ed
>
> On 2017-01-17 8:14 AM, Magnus Danielson wrote:
>> Ed,
>>
>> On 01/16/2017 11:01 PM, Ed Palmer wrote:
>>> >I have a Fluke PM6681 counter that just has the basic oscillator.  I
>>> was
>>> >thinking of upgrading it to the Rubidium timebase.  From the service
>>> >manual, it appears to use an LPRO, but there's nothing obvious
>>> regarding
>>> >heat sinking.  Does anyone have pictures of this installation or, at
>>> >least, seen it?  Is there any heat sinking at all?
>>> >
>>> >I realize the firmware won't report it as a PM6681R and there will be a
>>> >few non-standard work-arounds required, as well as an auxiliary power
>>> >supply (the original needs this as well), but I don't see any
>>> >showstoppers here.  Does anyone have any warnings or advice?
>> Asked the former Fluke/Pendulum service engineer Stefan Ledberg, and
>> here is his comments:
>>
>> The built in Rubidium can use basically any source and have on earlier
>> models used a Datum or Efratom LPRO-101 model (no heatsink), and later
>> models used Spectratime LPFRS-01 special Heatsink and adapter from DSUB
>> to LPRO-equivalent. PSU is added internally that is sharing PCB with the
>> output amplifier for the additional 10Mhz output on the rear panel. The
>> PSU and output is no longer in production and I doubt there are any left
>> at the factory... I can make an inqury if really important, Internally
>> 10Mhz is connected to a 2 pin header and Source is selected with a
>> jumper. however as stated firmware will still claim std or ocxo
>> timebase.  However my recommendation is to power a Rubidium timebase
>> externally with off the shelf PSU and just feed the PM6681 on "Ext Ref
>> in" this will accept most levels of Signal and no fuss needed.
>>
>> Cheers,
>> Magnus
>
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