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

[Magnus Danielson]

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