[time-nuts] Re: help reviving Trimble UCCM-LPS GPSDO

[Bob kb8tq]

Hi

If it’s a 5V supply then indeed 2.5 is a better bet.

Bob

> On Dec 24, 2021, at 4:43 AM, Wilko Bulte <wkb at xs4all.nl> wrote:
> 
> The OCXO is powered from the 5V rail of the UCCM, so I wonder how a Vref=5V would work? A bit of headroom wouod be required to make a reference circuit work.?
> 
> Wilko
> 
>> On 23 Dec 2021, at 18:15, Bob kb8tq <kb8tq at n1k.org> wrote:
>> 
>> Hi
>> 
>> It’s a pretty good bet that the Vref is 5V
>> 
>> Bob
>> 
>>> On Dec 23, 2021, at 8:42 AM, Wilko Bulte <wilko.bulte at xs4all.nl> wrote:
>>> 
>>> hi,
>>> 
>>> I am currently trying to revive a Trimble UCCM-LPS ex-telco GPSDO.
>>> The model is a 57963-D according to the PCB silkscreen.
>>> 
>>> Got the board without its OCXO but luckily my stash of surplus I have
>>> discovered a Trimble OCXO labeled 72345-86. Given that that OCXO also has a
>>> label UCCM-LPS it "should work".
>>> 
>>> Joining the two resulted in:
>>> 
>>> UCCM >syst:status?
>>> 
>>> -------------------------------------------------------------------------------
>>> 57964-86     serial number  S35DB68332   firmware ver  1.0.0.1-01 Ext
>>> mode
>>> -------------------------------------------------------------------------------
>>> Reference Status __________________________   Reference Outputs
>>> _______________
>>> XX Ext Ref   : [LOS]
>>>                                            TFOM     2            FFOM
>>> 3
>>>                                            UCCM A Status[OCXO WARMUP]
>>> 
>>>>> GPS: [phase:-2.8E-09, settling]
>>> ACQUISITION ...................................................[GPS 1PPS
>>> Valid]
>>> Tracking: 8 ____   Not Tracking: 3 ________   Time
>>> ____________________________
>>> PRN  El  Az  C/N   PRN  El  Az                GPS      13:28:51     23 Dec
>>> 2021
>>> 15  71 212   37     5   6 195
>>> 24  45 272   43    30   7  85                ANT DLY  77 ns
>>> 17  28  97   37    19  19 124                Position
>>> ________________________
>>> 13  55 140   38                              MODE     Hold
>>> 14  39  58   39
>>> 23  33 291   44                              LAT      N  51:xxx
>>> 10  17 324   40                              LON      E   5:xxx
>>> 12   7 212   34                              HGT               +27.54 m
>>> (MSL)
>>> 
>>> 
>>> 
>>> 
>>> ELEV MASK  5 deg
>>> -------------------------------------------------------------------------------
>>> 
>>> Command complete
>>> 
>>> Unfortunately it never went GPS locked. Longer story short: the pin of the
>>> OCXO that (I think) should produce a Vref for the EFC circuitry produced
>>> some random ~ 266mV. 
>>> 
>>> A quick experiment learned that the OCXO freq responds to the EFC voltage. 
>>> So, looks like the Vref circuit in the OCXO has died.
>>> 
>>> Now the question: has anyone a working unit that they can measure the
>>> correct Vref voltage from?  
>>> 
>>> For now I have fitted a 2.5V LM336 vref and I
>>> see the EFC voltage go up and down a bit, with the output freq hovering
>>> around 10MHz (+/- 4mHz roughly).
>>> 
>>> tia,
>>> Wilko
>>> _______________________________________________
>>> time-nuts mailing list -- time-nuts at lists.febo.com -- To unsubscribe send an email to time-nuts-leave at lists.febo.com
>>> To unsubscribe, go to and follow the instructions there.
>> _______________________________________________
>> time-nuts mailing list -- time-nuts at lists.febo.com -- To unsubscribe send an email to time-nuts-leave at lists.febo.com
>> To unsubscribe, go to and follow the instructions there.
> _______________________________________________
> time-nuts mailing list -- time-nuts at lists.febo.com -- To unsubscribe send an email to time-nuts-leave at lists.febo.com
> To unsubscribe, go to and follow the instructions there.