Empathy List Archives

PS

paul swed

Thu, Dec 23, 2021 7:34 PM

Plus it was temperature stabilised since it was in the oven area.
Regards
Paul
WB8TSL

On Thu, Dec 23, 2021 at 2:16 PM ed breya eb@telight.com wrote:

Many of the older VTOCXOs have the internal reference voltage accessible
simply to use them stand-alone. A remote adjustment pot could be fed
from the reference, and set the fine tuning voltage, without needing any
other support from the system. Nowadays we typically tune from PLLs, and
such, and providing a stable reference is nearly trivial, but way back,
having a good reference right from the unit itself was (and still is) a
handy feature.

Ed

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Plus it was temperature stabilised since it was in the oven area. Regards Paul WB8TSL On Thu, Dec 23, 2021 at 2:16 PM ed breya <eb@telight.com> wrote: > Many of the older VTOCXOs have the internal reference voltage accessible > simply to use them stand-alone. A remote adjustment pot could be fed > from the reference, and set the fine tuning voltage, without needing any > other support from the system. Nowadays we typically tune from PLLs, and > such, and providing a stable reference is nearly trivial, but way back, > having a good reference right from the unit itself was (and still is) a > handy feature. > > Ed > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send > an email to time-nuts-leave@lists.febo.com > To unsubscribe, go to and follow the instructions there. >

BC

Brooke Clarke

Thu, Dec 23, 2021 8:30 PM

Hi:

I'd second this. When I was working at HP on the Kobe Instrument Division products (component testers) the 4352S VCO
tester had a very special power supply for the tuning voltage that was extremely clean so as not to detract from the VCO
under test.

--
Have Fun,

Brooke Clarke, N6GCE
https://www.PRC68.com
axioms:

The extent to which you can fix or improve something will be limited by how well you understand how it works.
Everybody, with no exceptions, holds false beliefs.

-------- Original Message --------

I've always assumed this is because they need to know the reference is
clean and under the OCXO manufacturer's control if it's to meet specs. If
the user had to supply the reference there's no knowing how clean it is.

Andy
www.g4jnt.com

On Thu, 23 Dec 2021 at 17:47, Attila Kinali attila@kinali.ch wrote:

On Thu, 23 Dec 2021 14:42:27 +0100
Wilko Bulte wilko.bulte@xs4all.nl wrote:

A quick experiment learned that the OCXO freq responds to the EFC

voltage.

So, looks like the Vref circuit in the OCXO has died.

A stupid side question: Why do have OCXO a Vref output in the
first place?

I can see that some form of reference might make stabilizing
the power in the crystal easier, but that still wouldn't make
it necessary to have an actual reference output.

And related to that: Would supplying the voltage reference
externally, in case of a broken Vref output, work for whatever
is inside that needs this reference voltage?

                      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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Hi: I'd second this. When I was working at HP on the Kobe Instrument Division products (component testers) the 4352S VCO tester had a very special power supply for the tuning voltage that was extremely clean so as not to detract from the VCO under test. -- Have Fun, Brooke Clarke, N6GCE https://www.PRC68.com axioms: 1. The extent to which you can fix or improve something will be limited by how well you understand how it works. 2. Everybody, with no exceptions, holds false beliefs. -------- Original Message -------- > I've always assumed this is because they need to know the reference is > clean and under the OCXO manufacturer's control if it's to meet specs. If > the user had to supply the reference there's no knowing how clean it is. > > Andy > www.g4jnt.com > > > > On Thu, 23 Dec 2021 at 17:47, Attila Kinali <attila@kinali.ch> wrote: > >> On Thu, 23 Dec 2021 14:42:27 +0100 >> Wilko Bulte <wilko.bulte@xs4all.nl> wrote: >> >>> A quick experiment learned that the OCXO freq responds to the EFC >> voltage. >>> So, looks like the Vref circuit in the OCXO has died. >> A stupid side question: Why do have OCXO a Vref output in the >> first place? >> >> I can see that some form of reference might make stabilizing >> the power in the crystal easier, but that still wouldn't make >> it necessary to have an actual reference output. >> >> And related to that: Would supplying the voltage reference >> externally, in case of a broken Vref output, work for whatever >> is inside that needs this reference voltage? >> >> 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-leave@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-leave@lists.febo.com > To unsubscribe, go to and follow the instructions there. >

JA

John Ackermann N8UR

Thu, Dec 23, 2021 8:33 PM

One thing I've seen on several OCXO and small Rbs is that the EFC pin is
internally wired in the middle of a voltage divider using two fairly
high value (>10K) resistors between Vref and ground. That ties the
varactor to the middle of the EFC range when no external tuning is
required. For external tuning, put the EFC pin on the wiper of a pot
between the Vref pin and ground that has a much lower value than the
internal divider. That stiffer voltage will override the internal divider.

John

On 12/23/21 12:51 PM, Andy Talbot wrote:

I've always assumed this is because they need to know the reference is
clean and under the OCXO manufacturer's control if it's to meet specs. If
the user had to supply the reference there's no knowing how clean it is.

Andy
www.g4jnt.com

On Thu, 23 Dec 2021 at 17:47, Attila Kinali attila@kinali.ch wrote:

On Thu, 23 Dec 2021 14:42:27 +0100
Wilko Bulte wilko.bulte@xs4all.nl wrote:

A quick experiment learned that the OCXO freq responds to the EFC
voltage.
So, looks like the Vref circuit in the OCXO has died.

A stupid side question: Why do have OCXO a Vref output in the
first place?

I can see that some form of reference might make stabilizing
the power in the crystal easier, but that still wouldn't make
it necessary to have an actual reference output.

And related to that: Would supplying the voltage reference
externally, in case of a broken Vref output, work for whatever
is inside that needs this reference voltage?
                     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-leave@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-leave@lists.febo.com
To unsubscribe, go to and follow the instructions there.

One thing I've seen on several OCXO and small Rbs is that the EFC pin is internally wired in the middle of a voltage divider using two fairly high value (>10K) resistors between Vref and ground. That ties the varactor to the middle of the EFC range when no external tuning is required. For external tuning, put the EFC pin on the wiper of a pot between the Vref pin and ground that has a much lower value than the internal divider. That stiffer voltage will override the internal divider. John ---- On 12/23/21 12:51 PM, Andy Talbot wrote: > I've always assumed this is because they need to know the reference is > clean and under the OCXO manufacturer's control if it's to meet specs. If > the user had to supply the reference there's no knowing how clean it is. > > Andy > www.g4jnt.com > > > > On Thu, 23 Dec 2021 at 17:47, Attila Kinali <attila@kinali.ch> wrote: > >> On Thu, 23 Dec 2021 14:42:27 +0100 >> Wilko Bulte <wilko.bulte@xs4all.nl> wrote: >> >>> A quick experiment learned that the OCXO freq responds to the EFC >> voltage. >>> So, looks like the Vref circuit in the OCXO has died. >> >> A stupid side question: Why do have OCXO a Vref output in the >> first place? >> >> I can see that some form of reference might make stabilizing >> the power in the crystal easier, but that still wouldn't make >> it necessary to have an actual reference output. >> >> And related to that: Would supplying the voltage reference >> externally, in case of a broken Vref output, work for whatever >> is inside that needs this reference voltage? >> >> 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-leave@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-leave@lists.febo.com > To unsubscribe, go to and follow the instructions there. >

R(

Richard (Rick) Karlquist

Fri, Dec 24, 2021 2:57 AM

When I designed the HP E1938A, I put a 2.5V reference IC inside the oven
and brought out both terminals of it. This was intended to provide a
reference voltage to the external DAC that generated the tuning voltage
for the loop that locked it loosely to GPS. It had its own return path
that was not only independent of the oven but the oscillator as well.
The oven in the E1938A had a thermal gain to the crystal in the 100's of
thousands. The thermal gain to the reference was no where near this
value, but still very substantial compared to anything on the outside.

Rick N6RK

When I designed the HP E1938A, I put a 2.5V reference IC inside the oven and brought out both terminals of it. This was intended to provide a reference voltage to the external DAC that generated the tuning voltage for the loop that locked it loosely to GPS. It had its own return path that was not only independent of the oven but the oscillator as well. The oven in the E1938A had a thermal gain to the crystal in the 100's of thousands. The thermal gain to the reference was no where near this value, but still very substantial compared to anything on the outside. Rick N6RK

WB

Wilko Bulte

Fri, Dec 24, 2021 9:43 AM

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@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@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

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To unsubscribe, go to and follow the instructions there.

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@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@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@lists.febo.com -- To unsubscribe send an email to time-nuts-leave@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-leave@lists.febo.com > To unsubscribe, go to and follow the instructions there.

F

F1CHF

Fri, Dec 24, 2021 10:31 AM

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@kinali.ch wrote:

On Thu, 23 Dec 2021 12:14:48 -0500
Bob kb8tq kb8tq@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

time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send

an email to time-nuts-leave@lists.febo.com

To unsubscribe, go to and follow the instructions there.

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email to time-nuts-leave@lists.febo.com
To unsubscribe, go to and follow the instructions there.

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@kinali.ch> wrote: > > On Thu, 23 Dec 2021 12:14:48 -0500 > Bob kb8tq <kb8tq@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 > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-leave@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-leave@lists.febo.com To unsubscribe, go to and follow the instructions there.

WB

Wilko Bulte

Fri, Dec 24, 2021 12:39 PM

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@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@kinali.ch wrote:

On Thu, 23 Dec 2021 12:14:48 -0500
Bob kb8tq kb8tq@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

time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send

an email to time-nuts-leave@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-leave@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-leave@lists.febo.com
To unsubscribe, go to and follow the instructions there.

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@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@kinali.ch> wrote: >>> >>> On Thu, 23 Dec 2021 12:14:48 -0500 >>> Bob kb8tq <kb8tq@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 >> _______________________________________________ >> time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send > an email to time-nuts-leave@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-leave@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-leave@lists.febo.com > To unsubscribe, go to and follow the instructions there.

BK

Bob kb8tq

Fri, Dec 24, 2021 2:15 PM

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@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@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@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

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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@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@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@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@lists.febo.com -- To unsubscribe send an email to time-nuts-leave@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-leave@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-leave@lists.febo.com > To unsubscribe, go to and follow the instructions there.

TV

Tom Van Baak

Sun, Dec 26, 2021 7:50 PM

Attila,

Why do have OCXO a Vref output in the first place?

The purpose of Vref is to optionally allow the oscillator to be
fine-tuned using 3 wires to an external user-supplied multi-turn pot,
often hiding behind an access hole at the rear of the instrument.

Note that the internal Vref needs to be good enough not to degrade the
performance of the crystal oscillator, but not much better.

For example, if your OCXO is stable to 5e-10/day and has a tuning range
of 1e-7 with an EFC range of -5 to +5 volts then 1 mV stability on Vref
translates to 1e-7 * 1e-4 = 1e-11 in frequency, far more than adequate
(50x) for the OCXO. Check my math.

By contrast you would not want a cheap Vref that drifted by, say, 50
mV/day because then half the drift of the oscillator might be due to
Vref and half due to the crystal; a waste of a good crystal.

I'll let volt nuts run the actual numbers for Vref that are found inside
various OCXO. But it sounds to me like a Zener would be fine for almost
any OCXO that you own, especially since it's inside an ovenized box.
Using a metrology-grade voltage reference would be a waste of a good
reference.

Here's how to get actual data: disconnect Vref, ground EFC, and then
measure both Vref voltage and Fout frequency once an hour for a few
weeks and compare their normalized daily drift rates.

/tvb

Attila, > Why do have OCXO a Vref output in the first place? The purpose of Vref is to optionally allow the oscillator to be fine-tuned using 3 wires to an external user-supplied multi-turn pot, often hiding behind an access hole at the rear of the instrument. Note that the internal Vref needs to be good enough not to degrade the performance of the crystal oscillator, but not much better. For example, if your OCXO is stable to 5e-10/day and has a tuning range of 1e-7 with an EFC range of -5 to +5 volts then 1 mV stability on Vref translates to 1e-7 * 1e-4 = 1e-11 in frequency, far more than adequate (50x) for the OCXO. Check my math. By contrast you would not want a cheap Vref that drifted by, say, 50 mV/day because then half the drift of the oscillator might be due to Vref and half due to the crystal; a waste of a good crystal. I'll let volt nuts run the actual numbers for Vref that are found inside various OCXO. But it sounds to me like a Zener would be fine for almost any OCXO that you own, especially since it's inside an ovenized box. Using a metrology-grade voltage reference would be a waste of a good reference. Here's how to get actual data: disconnect Vref, ground EFC, and then measure both Vref voltage and Fout frequency once an hour for a few weeks and compare their normalized daily drift rates. /tvb

DG

David G. McGaw

Tue, Dec 28, 2021 12:37 AM

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 F1CHF@free.fr 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 attila@kinali.ch wrote:

On Thu, 23 Dec 2021 12:14:48 -0500
Bob kb8tq kb8tq@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

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

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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 <F1CHF@free.fr> 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 <attila@kinali.ch> wrote: > >>> > >>> On Thu, 23 Dec 2021 12:14:48 -0500 > >>> Bob kb8tq <kb8tq@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 > <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-leave@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-leave@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-leave@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-leave@lists.febo.com > To unsubscribe, go to and follow the instructions there.

time-nuts@lists.febo.com

help reviving Trimble UCCM-LPS GPSDO

John

57964-86 serial number S35DB68332 firmware ver 1.0.0.1-01 Ext mode

ELEV MASK 5 deg

57964-86 serial number S35DB68332 firmware ver 1.0.0.1-01 Ext mode

ELEV MASK 5 deg

Attila Kinali

57964-86 serial number S35DB68332 firmware ver 1.0.0.1-01 Ext
mode

57964-86 serial number S35DB68332 firmware ver 1.0.0.1-01 Ext
mode