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

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 > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there.