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Discussion of precise time and frequency measurement

Fluke/Pendulum Counters - Rubidium Timebase

Ed Palmer

Mon, Jan 16, 2017 10:01 PM

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?

Thanks,
Ed

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? Thanks, Ed

Magnus Danielson

Mon, Jan 16, 2017 10:42 PM

Ed,

On 01/16/2017 11:01 PM, Ed Palmer wrote:

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

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