[time-nuts] Lucent KS-24361, HP/Symmetricom Z3809A, Z3810A, Z3811A, Z3812A GPSDO system

Bob Stewart bob at evoria.net
Sat Nov 1 00:38:31 EDT 2014

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?

     From: Bob Camp <kb8tq at n1k.org>
 To: Discussion of precise time and frequency measurement <time-nuts at 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

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.


> On Oct 31, 2014, at 9:26 PM, Brooke Clarke <brooke at 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


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