[time-nuts] Re: help reviving Trimble UCCM-LPS GPSDO
I have a couple of Trimble UCCMs. They would not come ready unless pin 39 of the 50 pin ribbon connector is grounded. This selects the 1PPS sync source. Ground is internal, open is external. 73, David N1HAC On 12/24/21 7:39 AM, Wilko Bulte wrote: hi Francois, That EEVblog thread discusses (mainly) the UCCM produced by Symmetricom. If I remember correctly the Symm uses a 12V powered OCXO, likely with another Vref output. I sold my Symm, the two Samsung UCCM I have found to be "just working always". In the meantime I have measured the EFC voltage of the Trimble over a long period (interval 2 sec). Vref is 2.5V, taken from a LM336. In more detail At about 2.5V EFC voltage I measure 10MHz output, plus/minus a couple of mHz. So using a Vref of 2.5V I do get an EFC voltage in the right range. Unfortunately the Trimble never goes GPS locked. LH reports FFOM: Init and Operation mode: Settling. Reported TFOM is 2. No idea why it does not lock, the GPS sees ample sats and is in position lock mode. Ideas welcome! Wilko > On 24 Dec 2021, at 12:41, F1CHF wrote: > > error in the Link ? > is it the good one ? > tks > > > https://www.eevblog <https://nam12.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.eevblog%2F&data=04%7C01%7Cdavid.g.mcgaw%40dartmouth.edu%7C5e368c4bed4442c4c81d08d9c702eb66%7C995b093648d640e5a31ebf689ec9446f%7C0%7C0%7C637759637767230002%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C2000&sdata=wItGRmNR%2F%2BipczR5Fu9sMZftMW6mTl4yXMBN22jBVC4%3D&reserved=0> > com/forum/projects/a-look-at-my-symmetricom-gpsdo-(ocxo-furuno-receiver)/msg3 > 78499/#msg3778499 > > francois > > > > ---Message original--- > > De : Wilko Bulte > Date : 23/12/2021 20:50:36 > A : Discussion of precise time and frequency measurement > Sujet : [time-nuts] Re: help reviving Trimble UCCM-LPS GPSDO > > > >>> On 23 Dec 2021, at 18:58, Attila Kinali wrote: >>> >>> On Thu, 23 Dec 2021 12:14:48 -0500 >>> Bob kb8tq wrote: >>> >>> It’s a pretty good bet that the Vref is 5V >> >> A quick google lead me to this forum post: >> https://www.eevblog <https://nam12.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.eevblog%2F&data=04%7C01%7Cdavid.g.mcgaw%40dartmouth.edu%7C5e368c4bed4442c4c81d08d9c702eb66%7C995b093648d640e5a31ebf689ec9446f%7C0%7C0%7C637759637767239960%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C2000&sdata=pDHdAlHCUGp%2FKIyE21WtGeBpei0yNt6mP0K3XqTWj04%3D&reserved=0> > com/forum/projects/a-look-at-my-symmetricom-gpsdo-(ocxo-furuno-receiver)/1325 > >> >> Looks like the Vref is supposed to be 2.5V > > For the Symmetricom UCCM or for the Trimble? > > These UCCM are form-fit-function compatible but that does not mean the > circuits are the same. Or the OcXO. > > Samsung also produced UCCM, of which I have 2, both working fine. Again > different circuits, different GPS etc. > > Wilko >> >> Attila Kinali >> -- >> The driving force behind research is the question: "Why?" >> There are things we don't understand and things we always >> wonder about. And that's why we do research. >> -- Kobayashi Makoto >> ___ >> time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send > an email to time-nuts-le...@lists.febo.com >> To unsubscribe, go to and follow the instructions there. > ___ > time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an > email to time-nuts-le...@lists.febo.com > To unsubscribe, go to and follow the instructions there.___ > time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com > To unsubscribe, go to and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: help reviving Trimble UCCM-LPS GPSDO
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 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 wrote: >> >> Hi >> >> It’s a pretty good bet that the Vref is 5V >> >> Bob >> >>> On Dec 23, 2021, at 8:42 AM, Wilko Bulte 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 2FFOM >>> 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 AzGPS 13:28:51 23 Dec >>> 2021 >>> 15 71 212 37 5 6 195 >>> 24 45 272 4330 7 85ANT DLY 77 ns >>> 17 28 97 3719 19 124Position >>> >>> 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@lists.febo.com -- To unsubscribe send >>> an email to time-nuts-le...@lists.febo.com >>> To unsubscribe, go to and follow the instructions there. >> ___ >> time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an >> email to time-nuts-le...@lists.febo.com >> To unsubscribe, go to and follow the instructions there. > ___ > time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an > email to time-nuts-le...@lists.febo.com > To unsubscribe, go to and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: help reviving Trimble UCCM-LPS GPSDO
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 wrote: > > Hi > > It’s a pretty good bet that the Vref is 5V > > Bob > >> On Dec 23, 2021, at 8:42 AM, Wilko Bulte 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 2FFOM >> 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 AzGPS 13:28:51 23 Dec >> 2021 >> 15 71 212 37 5 6 195 >> 24 45 272 4330 7 85ANT DLY 77 ns >> 17 28 97 3719 19 124Position >> >> 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@lists.febo.com -- To unsubscribe send an >> email to time-nuts-le...@lists.febo.com >> To unsubscribe, go to and follow the instructions there. > ___ > time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an > email to time-nuts-le...@lists.febo.com > To unsubscribe, go to and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: help reviving Trimble UCCM-LPS GPSDO
> On 23 Dec 2021, at 18:58, Attila Kinali wrote: > > On Thu, 23 Dec 2021 12:14:48 -0500 > Bob kb8tq wrote: > >> It’s a pretty good bet that the Vref is 5V > > A quick google lead me to this forum post: > https://www.eevblog.com/forum/projects/a-look-at-my-symmetricom-gpsdo-(ocxo-furuno-receiver)/1325/ > > Looks like the Vref is supposed to be 2.5V For the Symmetricom UCCM or for the Trimble? These UCCM are form-fit-function compatible but that does not mean the circuits are the same. Or the OcXO. Samsung also produced UCCM, of which I have 2, both working fine. Again different circuits, different GPS etc. Wilko > >Attila Kinali > -- > The driving force behind research is the question: "Why?" > There are things we don't understand and things we always > wonder about. And that's why we do research. >-- Kobayashi Makoto > ___ > time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an > email to time-nuts-le...@lists.febo.com > To unsubscribe, go to and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: help reviving Trimble UCCM-LPS GPSDO
On Thu, 23 Dec 2021 18:57:10 +0100 Attila Kinali wrote: > On Thu, 23 Dec 2021 12:14:48 -0500 > Bob kb8tq wrote: > > > It’s a pretty good bet that the Vref is 5V > > A quick google lead me to this forum post: > https://www.eevblog.com/forum/projects/a-look-at-my-symmetricom-gpsdo-(ocxo-furuno-receiver)/1325/ > > Looks like the Vref is supposed to be 2.5V Ooops.. stupid me linked to the wrong page (too many tabs open) https://www.eevblog.com/forum/projects/a-look-at-my-symmetricom-gpsdo-(ocxo-furuno-receiver)/1300/ Sorry about that. Attila Kinali -- The driving force behind research is the question: "Why?" There are things we don't understand and things we always wonder about. And that's why we do research. -- Kobayashi Makoto ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: help reviving Trimble UCCM-LPS GPSDO
On Thu, 23 Dec 2021 12:14:48 -0500 Bob kb8tq wrote: > It’s a pretty good bet that the Vref is 5V A quick google lead me to this forum post: https://www.eevblog.com/forum/projects/a-look-at-my-symmetricom-gpsdo-(ocxo-furuno-receiver)/1325/ Looks like the Vref is supposed to be 2.5V Attila Kinali -- The driving force behind research is the question: "Why?" There are things we don't understand and things we always wonder about. And that's why we do research. -- Kobayashi Makoto ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: help reviving Trimble UCCM-LPS GPSDO
Hi It’s a pretty good bet that the Vref is 5V Bob > On Dec 23, 2021, at 8:42 AM, Wilko Bulte 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 2FFOM > 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 AzGPS 13:28:51 23 Dec > 2021 > 15 71 212 37 5 6 195 > 24 45 272 4330 7 85ANT DLY 77 ns > 17 28 97 3719 19 124Position > > 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@lists.febo.com -- To unsubscribe send an > email to time-nuts-le...@lists.febo.com > To unsubscribe, go to and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
