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

[Wilko Bulte]

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 <F1CHF at free.fr> wrote:
> 
> error in the Link ?
> is it the good one ?
> tks
> 
> 
> https://www.eevblog
> 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 <attila at kinali.ch> wrote:
>>> 
>>> On Thu, 23 Dec 2021 12:14:48 -0500
>>> Bob kb8tq <kb8tq at n1k.org> 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
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