I've confirmed from the model number that the GPS module on these is indeed an Oncore UT+. There's a Synergy engineering note available regarding Oncore battery backup, and one place a copy can be found is here... http://f6fgz.free.fr/Fichiers/GPS/Backup_Battery_Considerations.pdf If so desired, it would be possible to retrospectively convert the UT+ on the Z3811A to take the usual rechargeable battery but the precautions mentioned in the engineering note would need to be implemented. I'm running file checks on my archives right now so can't confirm exactly what's involved, but I think there's one zero ohm SMD chip to be removed at least, and fitting a battery can of course bring its own issues. If anyone's interested, I've just uploaded some detailed photos of the of RFTG-U Ref-1 circuit board to Didier's manuals site. Probably far more detail there than even the nuttiest of us might consider to be sane or healthy but I've got it apart anyway so what the heck.... and they might come in very useful if it decides to self destruct whilst I'm poking it about on the bench:-) Regards Nigel GM8PZR In a message dated 01/11/2014 06:20:00 GMT Standard Time, bob@evoria.net writes: Hi Bob et al, I don't understand the direction this question about the supercap has taken. It's connected to pin 1 of the GPS receiver. It looks to be a UT+, so that's the battery backup power. According to my UT+ manual the current draw on this pin is between 5uA (at 2.5V) and 100uA (at 5V)? How many hours will a .022F supercap keep at least 2.5V at that sort of discharge rate? Unless the cap has gone bad, it seems more likely that Bob's comment about it doing a fast survey and then doing a slower one in the background probably has merit. In fact, my unit goes through its survey mode pretty quickly on power up. So do those current/voltage figures imply several hours on the cap? Bob From: Bob Camp <kb8tq@n1k.org> To: Discussion of precise time and frequency measurement <time-nuts@febo.com> Sent: Friday, October 31, 2014 9:22 PM Subject: Re: [time-nuts] Lucent KS-24361, HP/Symmetricom Z3809A, Z3810A, Z3811A, Z3812A GPSDO system Hi I sort of doubt that a GPS aux supply is quite that low current. I have seen some RTC’s that won’t last a month on a coin cell. My recollection is that the Oncore backup is closer to that category than the “many years on a cap” group. Bob > On Oct 31, 2014, at 9:26 PM, Brooke Clarke <brooke@pacific.net> wrote: > > Hi Bob: > > When HP came out with the 300 series Rocky Mountain Basic computers they were fitted with a super cap to power the RTC. > I will keep time for some months. > http://www.prc68.com/I/HPIB.shtml#300 > > Mail_Attachment -- > Have Fun, > > Brooke Clarke > http://www.PRC68.com > http://www.end2partygovernment.com/2012Issues.html > http://www.prc68.com/I/DietNutrition.html > Bob Camp wrote: >> Hi >> >> The ultra cap is a pretty small one (physical small). You might be able to find a larger (more farads) one that would fit in the same space. It’s not going to help for a hours and hours sort of outage. It might get you from dying in 15 minutes to dying in a half hour. >> >> Bob _______________________________________________ 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.