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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