Re: [time-nuts] Segal law: freq difference for GPSDO

[Vlad]

I tried to see the 1PPS on my oscilloscope. Here is the series of 
screenshots from that experiment:


https://www.patoka.ca/OCXO/TBvsSL/

I also tried to catch something using HP5386A. However I was not able to 
measure the pulse.


Regards,
Vlad


On 2016-03-29 18:53, Henry Hallam wrote:

If you put the PPS outputs of the two GPSDOs into an oscilloscope and
trigger on the leading edge of one of them, what does the other look
like?

Henry

On Tue, Mar 29, 2016 at 12:56 PM, Vlad  wrote:



Hello,

I am looking for for the advise regarding some strange difference in
frequency between of two GPSDO: Trimble Thunderbolt and Datum Starloc 
II


Measuring by HP 5386A counter it shows something around 0.014 
delta.

If I connect TB as REF source then I am getting numbers like this:
10.01396 Mhz
If I connect StarLoc II as REF source then I am getting following:
9.98612 Mhz

May be somebody could recognize, what 10.014 Mhz could be used for 
?


TB Lady Heather screenshot
http://www.patoka.org/OCXO/TB-LH-Mar.png

Allan Deviation for several hours looks like this:
http://www.patoka.org/OCXO/TB-SL.png


I connected both GPSDO to Rigol DS1102E Oscilloscope to see the phase
difference. And its shows me the ellipse which change its orientation 
left

to right and vice versa.

Its classical case of Segal's law: "A man with a watch knows what time 
it
is. A man with two watches is never sure". This is exact situation. 
Now I am

not sure which GPSDO (if any) is more accurate.

I have no third GPSDO (or equivalent) to compare. TB and Starloc 
connected
to the same GPS Antenna distribution amplifier. So basically both 
using the
same antenna. Both of them was turned on at relatively the same time 
and

both was warmed up for few days.

I have a theory, that may be StarLoc II was customized somehow to 
produce

the freq. slightly different from 10Mhz. But its just a theory.
Is it worth to compare 1PPS outputs using something like AD8302 + DAC 
+ MCU

?

--
WBW,

V.P.
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--
WBW,

V.P.
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Re: [time-nuts] Segal law: freq difference for GPSDO

[Tom Van Baak]

> May be somebody could recognize, what 10.014 Mhz could be used for ?

It sort of looks more like an unlocked OCXO than a magic frequency.
Measure phase instead of frequency; see how the phase drifts over time.
Also check if the magic frequency varies or drifts over time.
See if the offset is constant in spite of a one hour power cycle of either 
GPSDO.

> Its classical case of Segal's law: "A man with a watch knows what time 
> it is. A man with two watches is never sure". This is exact situation. 
> Now I am not sure which GPSDO (if any) is more accurate.

Yes, and www.leapsecond.com for where this madness ends up.

> I have a theory, that may be StarLoc II was customized somehow to 
> produce the freq. slightly different from 10Mhz. But its just a theory.
> Is it worth to compare 1PPS outputs using something like AD8302 + DAC + MCU ?

The TBolt/LH screen seems ok. Send some RS232 commands to the StarLoc. Verify 
they are both receiving a good number of SV, and maybe even a lot of the same 
set of SVN.

You can also remove the antenna on one or both units. See if the unusual 
frequency offset and the ADEV curve looks the same with or without antenna.

/tvb
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Re: [time-nuts] Trimble Thunderbolt GPSDO Troubleshooting

[Ryan Stasel]

Hi Charles (et al),

So, I did see that post, but I'm not entirely sure how it works. If I 
understand, the FPGA is generating the 9.7khz clock (which I can see on the 
test pad he indicated), running it through some logic to square it up, then a 
low pass filter, then into the op-amp similar to this: 
http://ww1.microchip.com/downloads/en/AppNotes/00538c.pdf (and this: 
http://www.ti.com/lit/an/spraa88a/spraa88a.pdf) ?

So where does the 5v reference play in? I see on the newer models apparently 
U14 is fed power by that reference? Maybe that's the same here...

Anyway, I lifted the 5v reference pin and fed the pad with the 5v supply. While 
it did keep positive, it was still being pulled down to just over 3v. So 
wherever that pin goes is pulling a fair amount of current. The 5v reference 
pin, while lifted, hovered just a few millivolts above 0v, and the disciplining 
of the OCXO remained the same 26hz high.

I'm starting to think the LT1014 is also bad, which I'm glad I have one on 
order along with the reference. Just in case, I did reflow all the pins on the 
opamp, reference, associated transistors, and the flip flop (U14) (which looks 
to be okay given its input and output appear to be there) I'm starting to think 
the previous owner accidentally plugged -12v into the +12v supply (maybe fully 
reversing them)? That doesn't explain the MAX232 dying, but it would probably 
nuke the 5v reference and the opamp. Mixing up any of the others (swapping +/- 
12v for 5v) probably would have left far more casualties. :/ Reconnecting the 
5v ref pin returned it right back to -0.6v (yes, negative).

The FPGA, I'd think, is probably okay given it's putting out a good 9.7khz. But 
I haven't ever troubleshot one of those before, so maybe part of it could be 
dead. :(

Anything else I might want to look at?

And thanks for all the responses!

Ryan Stasel
IT Operations Manager, SOJC
University of Oregon

Sent from my iPhone

On Mar 29, 2016, at 02:01, Charles Steinmetz 
> wrote:

Ryan wrote:

Also confusing is the quad op-amp seems to be saturated at the negative rail. I 
can see this Opamp feeds the adjust pin on the OCXO, but I'm not sure what 
feeds it. Guessing the FPGA? I still can't find the DAC
all I see are these
pictures [ ] but the pictures aren't of the DAC, unless the DAC is a resistor 
ladder (hadn't thought of that until now). Now I'm starting to realize this is 
probably the case.

Stewart Cobb described the operation of the DAC (actually, PWM) in a post on 
Nov 2, 2013 ("Subject: [time-nuts] Thunderbolt tuning DAC theory of 
operation").  Check the list archive.

Does it seem likely the 5V reference is dead?

If the output is at 0.6v, as you say, then either the reference chip is bad or 
something on the load side of the 5v reference bus is drawing too much current 
and dragging it down.

I don't really want to just lift the output of the 5V reference and leave 
whatever it feeds floating.

Why not lift the output pin and connect the PC trace to the 5v logic supply 
through, say, 470 ohms?  This will limit the current through the load to ~10mA 
if the load side is bad.  Then measure the voltages on the referrence output 
pin and the PC trace.  One or the other should be ~5v (unless the reference and 
the load side are both bad).  The one that is low will tell you which side 
(reference or load) is the problem.

Best regards,

Charles


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Re: [time-nuts] high rev isolation amps

[Bruce Griffiths]

With most of these old circuits reducing the LF noise contribution to the 
emitter/collector current by the biasing circuit by utilising lower noise power 
supplies and/or using improved biasing methods can improve the clse in PN 
significantly.
The PZT3904 and PZT3906 are still available.
Bruce
 

On Wednesday, 30 March 2016 1:00 PM, Bob Camp  wrote:
 

 Hi

There were (and maybe still are) SOT-89 versions of the 2N3804 and 3906. They 
will handle more
power than most of the other versions. That gives you better Vce on the string. 
They also have less
package inductance which helps tie the base to ground. If you are building some 
of those circuits, they
are worth looking for.

Bob

> On Mar 29, 2016, at 6:47 AM, Charles Steinmetz  wrote:
> 
> See below for schematics of the NIST isolation amplifiers from 1990 and 1997. 
>  NIST reported the isolation as >120dB.
> 
> I built isolation amplifiers similar to these (with lower-noise power 
> supplies and biasing tinkered slightly for better dynamic range), and with 
> careful construction achieved isolation substantially better than 120dB (see 
> my post of 11/25/14 for more details).
> 
> Best regards,
> 
> Charles
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Re: [time-nuts] Phase noise test set reference articles

[Bruce Griffiths]

I dont believe that the LF IF port output resistance of the minicircuits phase 
detectors is 500 ohm.Its just that this IF port load provides aa reasonable 50 
ohm match at the RF/LO ports.
The IF port LF output impedance is likely to be 100 ohms or less some of which 
will be intrinsic (having a effective thermal noise resistance of 1/2 its 
value) to the diodes and some of which is bulk resistance (a few ohms).To be 
sure one would need diode models as well as transformer/balun models.My crude 
simulations using ideal transformers (k=1) and HSMS2810 diode models reproduce 
all the effects that various NIST papers claimed as far as the effect of IF 
port load on the phase detector characteristics but not the claimed noise 
effects.
I need to find the MPD1's I have and run some tests for IF port output 
impedance at low frequencies with both RF ports saturated by the same 10MHz 
signal.

Bruce
 

On Wednesday, 30 March 2016 12:04 PM, Gerhard Hoffmann  
wrote:
 

 Am 29.03.2016 um 16:53 schrieb Charles Steinmetz:
>
> (10)  Phase_detector_with_low_flicker_noise_BARNES_etal_NIST_2011: 
> Describes a DIY double-balanced mixer phase detector using 
> diode-connected 2N transistors.  [Note that only the flicker noise 
> is improved -- the white noise floor is actually significantly higher 
> than with DBMs using diodes.  NB: There are much better transistors 
> than the 2N for this application.]
... and they are NOT really used as diodes. They are used as switching 
transistors with most current flow C-E, saturation enforced.
That turns faster on than the diode exp-law.
Somewhere they also say that they use 50 Ohm load.

I really wonder where all that ring mixer noise is to come from. The 
diodes are just switches, the transformers
have close to no loss and behave properly in power dividers, and even 
when the diodes are resistors for a moment,
their noise is only half-thermal.

I find it easy to believe that high power mixers produce more noise. In 
that app note by Watkins-Johnson that everybody copies,
there it is clearly shown that they may use resistors to generate bias 
voltages.

If I use two 1:4 Wilkinsons, 4 low power ring mixers and put the outputs 
in series, will it also turn worse? I don't think so.

Are there anywhere musings about the equivalent noise resistance of a 
ring mixer IF output?
If it is really something like 500 Ohms, even a single AD797 may be 
excessively over-optimized
for voltage, and not current noise.

regards, Gerhard
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Re: [time-nuts] Phase noise test set reference articles

[Alexander Pummer]

Hello Gerhard
look that: http://cp.literature.agilent.com/litweb/pdf/5989-8999EN.pdf
http://rfic.eecs.berkeley.edu/~niknejad/ee242/pdf/ee242_mixer_noise_design.pdf
and also STEPHEN MAAS has very good book on mixers...  Microwaves101 | 
Mixers

www.microwaves101.com/encyclopedias/mixers
Mixers. Check out our book recommendation page and order Stephen Maas' 
masterpiece on mixers!

73
KJ6UHN
Alex

On 3/29/2016 3:28 PM, Gerhard Hoffmann wrote:

Am 29.03.2016 um 16:53 schrieb Charles Steinmetz:


(10) Phase_detector_with_low_flicker_noise_BARNES_etal_NIST_2011: 
Describes a DIY double-balanced mixer phase detector using 
diode-connected 2N transistors.  [Note that only the flicker 
noise is improved -- the white noise floor is actually significantly 
higher than with DBMs using diodes.  NB: There are much better 
transistors than the 2N for this application.]
.. and they are NOT really used as diodes. They are used as switching 
transistors with most current flow C-E, saturation enforced.

That turns faster on than the diode exp-law.
Somewhere they also say that they use 50 Ohm load.

I really wonder where all that ring mixer noise is to come from. The 
diodes are just switches, the transformers
have close to no loss and behave properly in power dividers, and even 
when the diodes are resistors for a moment,

their noise is only half-thermal.

I find it easy to believe that high power mixers produce more noise. 
In that app note by Watkins-Johnson that everybody copies,
there it is clearly shown that they may use resistors to generate bias 
voltages.


If I use two 1:4 Wilkinsons, 4 low power ring mixers and put the 
outputs in series, will it also turn worse? I don't think so.


Are there anywhere musings about the equivalent noise resistance of a 
ring mixer IF output?
If it is really something like 500 Ohms, even a single AD797 may be 
excessively over-optimized

for voltage, and not current noise.

regards, Gerhard
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Re: [time-nuts] Phase noise test set reference articles

[Alexander Pummer]

and here is with very good literature: 
https://www.google.com/search?q=Haas+Mixer+noise=utf-8=utf-8#q=Maas+Mixer+noise


On 3/29/2016 3:28 PM, Gerhard Hoffmann wrote:

Am 29.03.2016 um 16:53 schrieb Charles Steinmetz:


(10) Phase_detector_with_low_flicker_noise_BARNES_etal_NIST_2011: 
Describes a DIY double-balanced mixer phase detector using 
diode-connected 2N transistors.  [Note that only the flicker 
noise is improved -- the white noise floor is actually significantly 
higher than with DBMs using diodes.  NB: There are much better 
transistors than the 2N for this application.]
.. and they are NOT really used as diodes. They are used as switching 
transistors with most current flow C-E, saturation enforced.

That turns faster on than the diode exp-law.
Somewhere they also say that they use 50 Ohm load.

I really wonder where all that ring mixer noise is to come from. The 
diodes are just switches, the transformers
have close to no loss and behave properly in power dividers, and even 
when the diodes are resistors for a moment,

their noise is only half-thermal.

I find it easy to believe that high power mixers produce more noise. 
In that app note by Watkins-Johnson that everybody copies,
there it is clearly shown that they may use resistors to generate bias 
voltages.


If I use two 1:4 Wilkinsons, 4 low power ring mixers and put the 
outputs in series, will it also turn worse? I don't think so.


Are there anywhere musings about the equivalent noise resistance of a 
ring mixer IF output?
If it is really something like 500 Ohms, even a single AD797 may be 
excessively over-optimized

for voltage, and not current noise.

regards, Gerhard
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Version: 2016.0.7497 / Virus Database: 4545/11913 - Release Date: 
03/29/16


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Re: [time-nuts] Phase noise test set reference articles

[Magnus Danielson]

You should add some of the NIST writings on cross-correlation, both 
traditional and newer. In particular, the more recent papers describe 
the newly discovered danger of cross-correlation which currently is an 
open research field. Cross-correlation can give over-optimistic values.

Never the less, the cross-correlation technique is very useful.

Cheers,
Magnus

On 03/29/2016 04:53 PM, Charles Steinmetz wrote:

Since there seems to be some interest in DIY phase noise test sets, I
put together the following list of references relevant to such a
project, with some comments.  I have a ZIP file of these items (about
35MB), but so far have been unsuccessful in uploading it to Didier's
site.  If anyone has suggestions for hosting it, please let me know
*offlist*.

For those who are in a rush, most of these should be easy to find on the
web with a search engine (but note that my file names are often not the
exact paper titles, so don't make your searches too literal).

Note that the "dual source" quadrature method is not the only practical
way to make sensitive phase noise measurements.  Interested DIY-ers
should also look at the "delay line discriminator" method.  It is
substantially simpler, although its ultimate noise floor is typically
not as good as the "dual source" method.  But it may well be good
enough, depending on the PN of the oscillators you are measuring.

(1)  Correlation_based_PN_measurements_RUBIOLA_2000:  Describes a system
for making interferometer-based PN measurements, for a lower noise floor.

(2)  HP_AN150-4_SA_noise_measurements_1974  [see especially pp. 19-25]:
A good introduction to using a spectrum analyzer to characterize the
phase noise of oscillators.

(3)  HP_AN246-2_PN_measurement_with_HP_3585A:  A good introduction to
the advantages and limitations of using a spectrum analyzer to
characterize the phase noise of oscillators.  For those fortunate enough
to own an HP 3585A or B, this reference provides much useful information
about using this particular instrument.

(4)  HP_art_of_phase_noise_measurement_SCHERER_1985:  An excellent
introduction to the subject.  Explains the operation, advantages, and
disadvantages of the "dual source" and "delay line discriminator" methods.

(5)  HP_Phase_Noise_Measurement_Techniques_2000:  More detailed
treatment than the Scherer 1985 reference, including direct PN
measurements with SAs, as well as the "dual source" and "delay line
discriminator" methods.  Provides specific sensitivity/noise floor
information about various HP instruments.

(6)  HP_phase_noise_seminar_1985:  Even more detail than the two
references above.  Discusses four different measurement methods in
substantial detail and provides specific sensitivity/noise floor
information about various HP instruments.

(7)  Low_cost_phase_noise_measurement_Wenzel:  Describes a practical,
low-cost "dual source" PN measurement system, with links to schematics
of the building blocks.  Provides useful insight into calibration.

(8)  Measurement_of_frequency_PN_AM_noise_WALLS_NIST:  More theoretical
treatment, discussing five PN measurement systems.

(9) Phase_and_AM_noise_measurement_in_frequency_domain_LANCE_etal_1984:
Another theoretical treatment of both dual source and single source
measurement methods, including a dual delay line system to improve the
noise floor.

(10)  Phase_detector_with_low_flicker_noise_BARNES_etal_NIST_2011:
Describes a DIY double-balanced mixer phase detector using
diode-connected 2N transistors.  [Note that only the flicker noise
is improved -- the white noise floor is actually significantly higher
than with DBMs using diodes.  NB: There are much better transistors than
the 2N for this application.]

(11)
Phase_Noise_Measurement_Using_Phase_Lock_Technique_Motorola_AN1639_1999:
A good general treatment of the "dual source" quadrature method,
including insights into avoiding a number of sources of error.

(12/13/14)
Phase_noise_measurement_with_amateur_instruments_2010_(Italian)  [and
English translations]:  Slides from a presentation by Eraldo Sbarbati,
I4SBX (SK) to Italian hams.  Practical orientation.

(15)  Phase_Noise_Measurements_NELSON_NIST_2011:  Slides from a
conference presentation.  More a discussion of the finer points of PN
measurements, less about the basics.

Oops, missed one:

(16)  DEMPHANO_phase_noise_measurement_fixture_MAKHINSON_CQ_1999: DIY
construction article for a "dual source" quadrature test fixture that
the author uses as a front end for an HP 3585A spectrum analyzer.

Best regards,

Charles

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Re: [time-nuts] Phase noise test set reference articles

[Magnus Danielson]

On 03/30/2016 12:28 AM, Gerhard Hoffmann wrote:

Am 29.03.2016 um 16:53 schrieb Charles Steinmetz:


(10)  Phase_detector_with_low_flicker_noise_BARNES_etal_NIST_2011:
Describes a DIY double-balanced mixer phase detector using
diode-connected 2N transistors.  [Note that only the flicker noise
is improved -- the white noise floor is actually significantly higher
than with DBMs using diodes.  NB: There are much better transistors
than the 2N for this application.]

.. and they are NOT really used as diodes. They are used as switching
transistors with most current flow C-E, saturation enforced.
That turns faster on than the diode exp-law.
Somewhere they also say that they use 50 Ohm load.

I really wonder where all that ring mixer noise is to come from. The
diodes are just switches, the transformers
have close to no loss and behave properly in power dividers, and even
when the diodes are resistors for a moment,
their noise is only half-thermal.


The diodes as not "just switches". The "switches" analogy is not 
helpful. It has an exponential function from voltage to current.


There is thermal noise because they have resistance.

There is flicker noise, as current flows through the semiconductor.

Cheers,
Maguns
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Re: [time-nuts] high rev isolation amps

[Bob Camp]

Hi

There were (and maybe still are) SOT-89 versions of the 2N3804 and 3906. They 
will handle more
power than most of the other versions. That gives you better Vce on the string. 
They also have less
package inductance which helps tie the base to ground. If you are building some 
of those circuits, they
are worth looking for.

Bob

> On Mar 29, 2016, at 6:47 AM, Charles Steinmetz  wrote:
> 
> See below for schematics of the NIST isolation amplifiers from 1990 and 1997. 
>  NIST reported the isolation as >120dB.
> 
> I built isolation amplifiers similar to these (with lower-noise power 
> supplies and biasing tinkered slightly for better dynamic range), and with 
> careful construction achieved isolation substantially better than 120dB (see 
> my post of 11/25/14 for more details).
> 
> Best regards,
> 
> Charles
> ___
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Re: [time-nuts] Segal law: freq difference for GPSDO

[Hal Murray]

> I have no third GPSDO (or equivalent) to compare.

There is the crystal in your 5386A.  Can you use that to measure the time 
between PPS pulses? (Some counters/timers don't go over a second and if the 
crystal is fast, the PPS will look slightly longer than a second.)

If both GPSDOs agree, you can calculate the actual frequency of the 5386A.

Then you can measure the 10 MHz signals and compute the actual frequency.


-- 
These are my opinions.  I hate spam.



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Re: [time-nuts] Segal law: freq difference for GPSDO

[Henry Hallam]

If you put the PPS outputs of the two GPSDOs into an oscilloscope and
trigger on the leading edge of one of them, what does the other look
like?

Henry

On Tue, Mar 29, 2016 at 12:56 PM, Vlad  wrote:
>
>
> Hello,
>
> I am looking for for the advise regarding some strange difference in
> frequency between of two GPSDO: Trimble Thunderbolt and Datum Starloc II
>
> Measuring by HP 5386A counter it shows something around 0.014 delta.
> If I connect TB as REF source then I am getting numbers like this:
> 10.01396 Mhz
> If I connect StarLoc II as REF source then I am getting following:
> 9.98612 Mhz
>
> May be somebody could recognize, what 10.014 Mhz could be used for ?
>
> TB Lady Heather screenshot
> http://www.patoka.org/OCXO/TB-LH-Mar.png
>
> Allan Deviation for several hours looks like this:
> http://www.patoka.org/OCXO/TB-SL.png
>
>
> I connected both GPSDO to Rigol DS1102E Oscilloscope to see the phase
> difference. And its shows me the ellipse which change its orientation left
> to right and vice versa.
>
> Its classical case of Segal's law: "A man with a watch knows what time it
> is. A man with two watches is never sure". This is exact situation. Now I am
> not sure which GPSDO (if any) is more accurate.
>
> I have no third GPSDO (or equivalent) to compare. TB and Starloc connected
> to the same GPS Antenna distribution amplifier. So basically both using the
> same antenna. Both of them was turned on at relatively the same time and
> both was warmed up for few days.
>
> I have a theory, that may be StarLoc II was customized somehow to produce
> the freq. slightly different from 10Mhz. But its just a theory.
> Is it worth to compare 1PPS outputs using something like AD8302 + DAC + MCU
> ?
>
> --
> WBW,
>
> V.P.
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Re: [time-nuts] Phase noise test set reference articles

[Gerhard Hoffmann]

Am 29.03.2016 um 16:53 schrieb Charles Steinmetz:


(10)  Phase_detector_with_low_flicker_noise_BARNES_etal_NIST_2011: 
Describes a DIY double-balanced mixer phase detector using 
diode-connected 2N transistors.  [Note that only the flicker noise 
is improved -- the white noise floor is actually significantly higher 
than with DBMs using diodes.  NB: There are much better transistors 
than the 2N for this application.]
.. and they are NOT really used as diodes. They are used as switching 
transistors with most current flow C-E, saturation enforced.

That turns faster on than the diode exp-law.
Somewhere they also say that they use 50 Ohm load.

I really wonder where all that ring mixer noise is to come from. The 
diodes are just switches, the transformers
have close to no loss and behave properly in power dividers, and even 
when the diodes are resistors for a moment,

their noise is only half-thermal.

I find it easy to believe that high power mixers produce more noise. In 
that app note by Watkins-Johnson that everybody copies,
there it is clearly shown that they may use resistors to generate bias 
voltages.


If I use two 1:4 Wilkinsons, 4 low power ring mixers and put the outputs 
in series, will it also turn worse? I don't think so.


Are there anywhere musings about the equivalent noise resistance of a 
ring mixer IF output?
If it is really something like 500 Ohms, even a single AD797 may be 
excessively over-optimized

for voltage, and not current noise.

regards, Gerhard
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[time-nuts] Segal law: freq difference for GPSDO

[Vlad]

Hello,

I am looking for for the advise regarding some strange difference in 
frequency between of two GPSDO: Trimble Thunderbolt and Datum Starloc II


Measuring by HP 5386A counter it shows something around 0.014 delta.
If I connect TB as REF source then I am getting numbers like this: 
10.01396 Mhz
If I connect StarLoc II as REF source then I am getting following:  
9.98612 Mhz


May be somebody could recognize, what 10.014 Mhz could be used for ?

TB Lady Heather screenshot
http://www.patoka.org/OCXO/TB-LH-Mar.png

Allan Deviation for several hours looks like this:
http://www.patoka.org/OCXO/TB-SL.png


I connected both GPSDO to Rigol DS1102E Oscilloscope to see the phase 
difference. And its shows me the ellipse which change its orientation 
left to right and vice versa.


Its classical case of Segal's law: "A man with a watch knows what time 
it is. A man with two watches is never sure". This is exact situation. 
Now I am not sure which GPSDO (if any) is more accurate.


I have no third GPSDO (or equivalent) to compare. TB and Starloc 
connected to the same GPS Antenna distribution amplifier. So basically 
both using the same antenna. Both of them was turned on at relatively 
the same time and both was warmed up for few days.


I have a theory, that may be StarLoc II was customized somehow to 
produce the freq. slightly different from 10Mhz. But its just a theory.
Is it worth to compare 1PPS outputs using something like AD8302 + DAC + 
MCU ?


--
WBW,

V.P.
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Re: [time-nuts] Timelab bug (was: Framework for simulation of oscillators)

[John Miles]

> Here it takes slightly less 3 minutes, but stops at 10M samples.

> Memory consumption of Timelab stays below 350MB the whole time

> and drops to 98MB after it finished.

> 

> OS is windows XP pro

> 

> How many samples did you get? It should have been 14926518 (ie slightly

> less than 15M) 

 

D'oh, sorry, I misunderstood -- I thought you were saying it locked up.
Yes, the normal file-import process stops at 10M samples because that's the
arbitrary maximum value allowed for the Trace Duration property in the
file-import dialog.  I'll go ahead and raise the limit to 100M points for
the 64-bit version.

 

For now, you can work around the 10M-point import limit by using
Acquire->Acquire from live ASCII file instead of File->Import
phase/frequency data.  Most of the same code is used for both cases, but
unlike the static file-import version of the dialog, the live data importer
will let you specify the expected duration yourself.  So you can give it a
duration value that you know will be long enough to cover the whole data set
(10 days in this case.)  

 

To use the live-ASCII acquisition option on a static file, uncheck "Auto"
and check "Include existing file contents" before hitting the Start
Measurement button.  When the file finishes loading, it will sit there
waiting for more data to be appended to the file.  At that point you can hit
the space bar to stop the acquisition, and it will readjust the duration to
correspond to the actual number of points it read.

 



 

 

-- john, KE5FX

Miles Design LLC

 

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[time-nuts] Phase noise test set reference articles

[Charles Steinmetz]

Since there seems to be some interest in DIY phase noise test sets, I 
put together the following list of references relevant to such a 
project, with some comments.  I have a ZIP file of these items (about 
35MB), but so far have been unsuccessful in uploading it to Didier's 
site.  If anyone has suggestions for hosting it, please let me know 
*offlist*.


For those who are in a rush, most of these should be easy to find on 
the web with a search engine (but note that my file names are often 
not the exact paper titles, so don't make your searches too literal).


Note that the "dual source" quadrature method is not the only 
practical way to make sensitive phase noise measurements.  Interested 
DIY-ers should also look at the "delay line discriminator" 
method.  It is substantially simpler, although its ultimate noise 
floor is typically not as good as the "dual source" method.  But it 
may well be good enough, depending on the PN of the oscillators you 
are measuring.


(1)  Correlation_based_PN_measurements_RUBIOLA_2000:  Describes a 
system for making interferometer-based PN measurements, for a lower 
noise floor.


(2)  HP_AN150-4_SA_noise_measurements_1974  [see especially pp. 
19-25]:  A good introduction to using a spectrum analyzer to 
characterize the phase noise of oscillators.


(3)  HP_AN246-2_PN_measurement_with_HP_3585A:  A good introduction to 
the advantages and limitations of using a spectrum analyzer to 
characterize the phase noise of oscillators.  For those fortunate 
enough to own an HP 3585A or B, this reference provides much useful 
information about using this particular instrument.


(4)  HP_art_of_phase_noise_measurement_SCHERER_1985:  An excellent 
introduction to the subject.  Explains the operation, advantages, and 
disadvantages of the "dual source" and "delay line discriminator" methods.


(5)  HP_Phase_Noise_Measurement_Techniques_2000:  More detailed 
treatment than the Scherer 1985 reference, including direct PN 
measurements with SAs, as well as the "dual source" and "delay line 
discriminator" methods.  Provides specific sensitivity/noise floor 
information about various HP instruments.


(6)  HP_phase_noise_seminar_1985:  Even more detail than the two 
references above.  Discusses four different measurement methods in 
substantial detail and provides specific sensitivity/noise floor 
information about various HP instruments.


(7)  Low_cost_phase_noise_measurement_Wenzel:  Describes a practical, 
low-cost "dual source" PN measurement system, with links to 
schematics of the building blocks.  Provides useful insight into calibration.


(8)  Measurement_of_frequency_PN_AM_noise_WALLS_NIST:  More 
theoretical treatment, discussing five PN measurement systems.


(9) 
Phase_and_AM_noise_measurement_in_frequency_domain_LANCE_etal_1984: 
Another theoretical treatment of both dual source and single source 
measurement methods, including a dual delay line system to improve 
the noise floor.


(10)  Phase_detector_with_low_flicker_noise_BARNES_etal_NIST_2011: 
Describes a DIY double-balanced mixer phase detector using 
diode-connected 2N transistors.  [Note that only the flicker 
noise is improved -- the white noise floor is actually significantly 
higher than with DBMs using diodes.  NB: There are much better 
transistors than the 2N for this application.]


(11) 
Phase_Noise_Measurement_Using_Phase_Lock_Technique_Motorola_AN1639_1999: 
A good general treatment of the "dual source" quadrature method, 
including insights into avoiding a number of sources of error.


(12/13/14) 
Phase_noise_measurement_with_amateur_instruments_2010_(Italian)  [and 
English translations]:  Slides from a presentation by Eraldo 
Sbarbati, I4SBX (SK) to Italian hams.  Practical orientation.


(15)  Phase_Noise_Measurements_NELSON_NIST_2011:  Slides from a 
conference presentation.  More a discussion of the finer points of PN 
measurements, less about the basics.


Oops, missed one:

(16)  DEMPHANO_phase_noise_measurement_fixture_MAKHINSON_CQ_1999: 
DIY construction article for a "dual source" quadrature test fixture 
that the author uses as a front end for an HP 3585A spectrum analyzer.


Best regards,

Charles

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Re: [time-nuts] Oleg' s PN test Re: A new member & PN test set

[Jean-L. RAULT]

Hi Oleg

Le 29/03/2016 07:18, Oleg Skydan a écrit :
 I also tried DL4YHF Spectrum Lab - it works, but lacks of logarithmic 
frequency scale (or I just did not find how to enable it).


Just right-click on the frequency scale, then click on "more ...", and 
then tick on "logarithmic" in the "Options for the frequency axis" window.


Simple, isn't it ?  o:)

Jean-Louis F6AGR
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Re: [time-nuts] high rev isolation amps

[Charles Steinmetz]

See below for schematics of the NIST isolation amplifiers from 1990 
and 1997.  NIST reported the isolation as >120dB.


I built isolation amplifiers similar to these (with lower-noise power 
supplies and biasing tinkered slightly for better dynamic range), and 
with careful construction achieved isolation substantially better 
than 120dB (see my post of 11/25/14 for more details).


Best regards,

Charles
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Re: [time-nuts] Oleg' s PN test Re: A new member & PN test set

[Bruce Griffiths]

NIST indicate in several early papers that using 50 ohm in series with a 
capacitor increases the noise over that achieved by capacitively terminating 
the IF port at the sum frequency (LO + RF) as you have done. NB the RF and LO 
port match will be improved somewhat with suitable low value series resistors.
However 50 ohms to ground at the LC filter output shouldn't be necessary.
 A somewhat larger value should suffice. Despite assertions by Both 
minicircuits and Watkins Johnson a mixer connected as a phase detector doesnt 
act like a current source at the IF output (this  is obvious from the plot of 
the phase detection characteristic as a function of IF port low frequency load 
resistance on the WJ mixer/PD paper. Also the minicircuits assertion that 
amplifiers apply a voltage offset to the mixer port that can only be attenuated 
by a resistor in series with the amplifier input plus a lower value shunt 
resistance at the output of the IF port LC  filter is errant nonsense with an 
opamp based amplifier.
There should be no problems with a parallel connected Buffer amp driving the 
PLL circuitry at the LC filter output that's the way Wenzel does it for 
example.Note that the Wenzel low noise amp can be improved significantly using 
the same components in a slightly different topology.
NIST have used an RF noise source for calibration and to measure the frequency 
response.
Bruce 

On Wednesday, 30 March 2016 12:12 AM, Oleg Skydan  
wrote:
 

 Hi, Bruce,

Thank you for the comments and useful link. Probably you did not understand 
the goal and positioning of this "project" and I did not tell the history of 
how it was build :)

So, the solely goal of making this "test set" was to assist with the design
of the synthesizer unit for my HF transceiver. The synthesizer PN goals are 
to archive PN better then -145..-150dBc/Hz@1kHz offset and better 
then -150..-155dBc/Hz@5kHz and farther. So I do not need something perfect 
to measure parts of the synthesizer or the complete unit.

Now some words how it was build. Several years ago I experimented with the 
voltage regulators and needed to measure their noise. So I made an AD797 LNA 
for my soundcard. Later I added the mixer which I used (along with the 
signal generator) as a selective meter or primitive spectrum analyzer. 
Several months ago I started to work at the synthesizer project, so I needed 
PN "test set". I found a board with two TL071 in suitable configuration in 
my "junk box" and after several minutes of soldering I had the PLL board :) 
Usually I am not a fan of such construction methods, but that time it solved 
problem quickly.

> 1) The chosen mixer isnt as low noise as the various Minicircuits phase
> detectors.
I just used what I have. There are some very bad things here :( (it is way 
out of the list theme), so buying parts (especially ones not widely used) is 
not a simple task here. The Minicircuits parts are expensive and exotic 
here.

> 2) The 50 ohm load after the filter merely serves to halve the phase 
> detector
> gain. The IF port is terminated by a 15nF capacitor at RF and LO 
> frequencies
> and their harmonics. This produces a frequency dependent gain, however it 
> will
> likely be relatively flat over the sound card bandwidth.
I know it does not terminate mixer correctly, but it is simple and it works.. 
I tried the termination suggested in the NIST papers (with 50Ohm RF 
termination and 1kOhm DC/AF one) with no success - the noise floor of the 
"test set" was higher. As for the gain flatness, I checked it - you can see 
the results of the quick test here 
http://skydan.in.ua/PNTestSet/Screen(432)-e.png (it was 60MHz LO + signal 
generator slowly tuned around 60MHz, the SA was set to peak and hold mode). 
It completely satisfies my needs.

> 3) Saturating both mixer ports increases the phase detector gain 
> substantially
> and has the lowest noise
>
In this case the simple and reliable calibration method I use will not work, 
cause the mixer output will not be sinusoidal anymore. Another problem is 
the signal levels - two good RF LNAs will be needed to amplify signals up to 
the necessary levels to saturate mixer.

> 4) Cascading the PLL circuitry with the preamp causes interaction between 
> the
> Preamp gain settings and the PLL bandwidth. Driving the PLL circuit in
> parallel with the preamp input directly from the low pass filtered mixer 
> output
> avoids this issue as well as your 0.1x amplifier in the PLL section.
I see no reason to use 20dB preamp gain for measurements (the sound card 
noise will have too much influence with this setting), so it useful only for 
calibration or the other LNA use (not in PN test set). On the other hand if 
the PLL circuit connected to the LNA output we have minimal 
components/wires/traces/connections in the most sensitive part of the test 
set, so the chance to pick up some external noise is also minimized.

I can add that other good and simple/cheap 

Re: [time-nuts] Meaning of MTBF (was: Reliability of atomic clocks)

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 28 March 2016 at 00:32, Attila Kinali  wrote:

>
> Yes, the MTBF is a very simplicistic measure and there are a couple
> of assumptions in its calculation which do not hold generally (or
> rather, it's rather seldom that they hold).



It get's "interesting" when you look at the MTBF times on hard disks. Some
of the figures quoted in hours related to an MTBF of over 100 years. From
what I read before, this was based on you replacing the drive at the end of
its service life (typically 3 years for consumer drives and 5 years for
enterprise grade disks). So no individual drive was ever expected to last
100 years, but if you kept replacing the drives ever 3~5 years, the average
time of an unexpected failure would be 100 years. I guess its a bit like a
car - the engine might run for 250,000 miles, but if you never change the
oil or the camshaft belt, it is not going to last.

I note Seagate have dropped the use of MTBF:

http://knowledge.seagate.com/articles/en_US/FAQ/174791en?language=en_US

changing to an Annualized Failure Rate  (AFR). I don't think Seagate will
ever get a real measure of this, as in many cases people are just going to
throw a hard disk in the bin if it fails, even if under warranty. In many
cases the warranty is with an OEM, so even if you buy a new drive sold
originally to Dell, you can't return it unless you are Dell. Also with hard
drive capacities growing quite fast, if a drive does fail you will probably
chose to replace it with one of higher capacity.



Dr. David Kirkby Ph.D CEng MIET
Kirkby Microwave Ltd
Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, Essex, CM3 6DT,
UK.
Registered in England and Wales, company number 08914892.
http://www.kirkbymicrowave.co.uk/
Tel: 07910 441670 / +44 7910 441670 (0900 to 2100 GMT only please)
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Re: [time-nuts] Trimble Thunderbolt GPSDO Troubleshooting

[Tom Van Baak]

> Stewart Cobb described the operation of the DAC 
> (actually, PWM) in a post on Nov 2, 2013 
> ("Subject: [time-nuts] Thunderbolt tuning DAC 
> theory of operation").  Check the list archive.

https://www.febo.com/pipermail/time-nuts/2013-November/081058.html

/tvb
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Re: [time-nuts] Oleg' s PN test Re: A new member & PN test set

[Oleg Skydan]

Hi Magnus,



Would not GNUradio be a good platform to encode the calibration stuff a 
little more gift-wrapped?

I never used the GNUradio. Basically you can use any SA software/hardware
which has the necessary capabilities.


What spectrum-analyzer software do you use? (Just curious)
It is an old SpectraLAB (which is now as far as I know SpectraPLUS). I also 
tried DL4YHF Spectrum Lab - it works, but lacks of logarithmic frequency 
scale (or I just did not find how to enable it). I think, from time to time, 
about writing specialized software with some special features, but there are 
always more important things to do :).


All the best!
Oleg 


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Re: [time-nuts] Oleg' s PN test Re: A new member & PN test set

[Oleg Skydan]

Hi, Bruce,

Thank you for the comments and useful link. Probably you did not understand 
the goal and positioning of this "project" and I did not tell the history of 
how it was build :)


So, the solely goal of making this "test set" was to assist with the design
of the synthesizer unit for my HF transceiver. The synthesizer PN goals are 
to archive PN better then -145..-150dBc/Hz@1kHz offset and better 
then -150..-155dBc/Hz@5kHz and farther. So I do not need something perfect 
to measure parts of the synthesizer or the complete unit.


Now some words how it was build. Several years ago I experimented with the 
voltage regulators and needed to measure their noise. So I made an AD797 LNA 
for my soundcard. Later I added the mixer which I used (along with the 
signal generator) as a selective meter or primitive spectrum analyzer. 
Several months ago I started to work at the synthesizer project, so I needed 
PN "test set". I found a board with two TL071 in suitable configuration in 
my "junk box" and after several minutes of soldering I had the PLL board :) 
Usually I am not a fan of such construction methods, but that time it solved 
problem quickly.



1) The chosen mixer isnt as low noise as the various Minicircuits phase
detectors.
I just used what I have. There are some very bad things here :( (it is way 
out of the list theme), so buying parts (especially ones not widely used) is 
not a simple task here. The Minicircuits parts are expensive and exotic 
here.


2) The 50 ohm load after the filter merely serves to halve the phase 
detector
gain. The IF port is terminated by a 15nF capacitor at RF and LO 
frequencies
and their harmonics. This produces a frequency dependent gain, however it 
will

likely be relatively flat over the sound card bandwidth.
I know it does not terminate mixer correctly, but it is simple and it works. 
I tried the termination suggested in the NIST papers (with 50Ohm RF 
termination and 1kOhm DC/AF one) with no success - the noise floor of the 
"test set" was higher. As for the gain flatness, I checked it - you can see 
the results of the quick test here 
http://skydan.in.ua/PNTestSet/Screen(432)-e.png (it was 60MHz LO + signal 
generator slowly tuned around 60MHz, the SA was set to peak and hold mode). 
It completely satisfies my needs.


3) Saturating both mixer ports increases the phase detector gain 
substantially

and has the lowest noise

In this case the simple and reliable calibration method I use will not work, 
cause the mixer output will not be sinusoidal anymore. Another problem is 
the signal levels - two good RF LNAs will be needed to amplify signals up to 
the necessary levels to saturate mixer.


4) Cascading the PLL circuitry with the preamp causes interaction between 
the

Preamp gain settings and the PLL bandwidth. Driving the PLL circuit in
parallel with the preamp input directly from the low pass filtered mixer 
output

avoids this issue as well as your 0.1x amplifier in the PLL section.
I see no reason to use 20dB preamp gain for measurements (the sound card 
noise will have too much influence with this setting), so it useful only for 
calibration or the other LNA use (not in PN test set). On the other hand if 
the PLL circuit connected to the LNA output we have minimal 
components/wires/traces/connections in the most sensitive part of the test 
set, so the chance to pick up some external noise is also minimized.


I can add that other good and simple/cheap additions will be the integrator 
reset button, two buttons to move integrator in positive or negative 
direction manually (to speed up the initial lock in some cases, or shift the 
output voltage into the necessary EFC range), potentiometer for the manual 
VCO/VCXO frequency control (for the calibration) with the switch to 
close/open PLL.



An OCXO like the 10811A has an EFC gain of around 0.1Hz/volt.
The PLL bandwidth should ideally be less than 1/10 of the lowest offset
frequency for which the PN is to be measured.
If the system frequency response is measured then the PLL bandwidth can be 
a
little higher albeit with a reduction is sensitivity and an increase in 
system

PN at the low offset frequency end of the range.
AS is the PN noise of this test set is far too high to measure the PN of 
state

of the art OCXOs or indeed most modern OXCOs.
Ohh... I am not a time nut (or maybe not a time nut YET ;). I did not try to 
make something "state of the art" - my goals were/are different (see 
earlier).


As for the PLL BW of cause one should be aware what the BW is. In my 
measurements the PLL BW is less then 30Hz. I am not interested in PN closer 
then 1kHz, so no need for any additional correction of the results.


Much more sophisticated system can be made - better ADC, better LNA, RF LNAs 
to push mixer in saturation, better software, two channels with cross 
correlation and etc. Or we can even use two high speed ADC and move more 
things into digital domain. But it can not be done in one evening 

Re: [time-nuts] Trimble Thunderbolt GPSDO Troubleshooting

[Charles Steinmetz]

Ryan wrote:

Also confusing is the quad op-amp seems to be 
saturated at the negative rail. I can see this 
Opamp feeds the adjust pin on the OCXO, but I’m 
not sure what feeds it. Guessing the FPGA? I 
still can’t find the DAC… all I see are these 
pictures [ ] but the pictures aren’t of the DAC, 
unless the DAC is a resistor ladder (hadn’t 
thought of that until now). Now I’m starting to 
realize this is probably the case.


Stewart Cobb described the operation of the DAC 
(actually, PWM) in a post on Nov 2, 2013 
("Subject: [time-nuts] Thunderbolt tuning DAC 
theory of operation").  Check the list archive.



Does it seem likely the 5V reference is dead?


If the output is at 0.6v, as you say, then either 
the reference chip is bad or something on the 
load side of the 5v reference bus is drawing too 
much current and dragging it down.


I don’t really want to just lift the output of 
the 5V reference and leave whatever it feeds floating.


Why not lift the output pin and connect the PC 
trace to the 5v logic supply through, say, 470 
ohms?  This will limit the current through the 
load to ~10mA if the load side is bad.  Then 
measure the voltages on the referrence output pin 
and the PC trace.  One or the other should be ~5v 
(unless the reference and the load side are both 
bad).  The one that is low will tell you which 
side (reference or load) is the problem.


Best regards,

Charles


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Re: [time-nuts] Trimble Thunderbolt GPSDO Troubleshooting

[Bruce Griffiths]

There aren't enough resistors for a high resolution R-2R DAC so its likely to 
be something like 4 (or more) x 4 bit (R, 2R, 4R, 8R) sub dacs with weighted 
resistive summing of the sub DAC outputs.
Bruce
 

On Tuesday, 29 March 2016 6:09 PM, Ryan Stasel  wrote:
 

 All,

Yay progress (one step forward into the next wall). I got the MAX232 chip 
replaced with a MAX202 (pin compatible, better ESD and Latchup protection). 
That got the serial working, and I was able to watch the unit do a survey, and 
then confirm it saw that the Osc was off by ~ -2700ppb, and the PPS. I did a 
factory reset as well.

After it did a full survey, it came back and confirmed that the oscillator 
adjustment was at a rail. It read the DAC 4.90. But the output of the 
reference was still -0.6V. So I’m guessing that chip is toast. I’ve got one on 
order. Also confusing is the quad op-amp seems to be saturated at the negative 
rail. I can see this Opamp feeds the adjust pin on the OCXO, but I’m not sure 
what feeds it. Guessing the FPGA? I still can’t find the DAC… all I see are 
these pictures http://www.leapsecond.com/pages/tbolt/photos.htm but the 
pictures aren’t of the DAC, unless the DAC is a resistor ladder (hadn’t thought 
of that until now). Now I’m starting to realize this is probably the case. =P

So, any input on where I might want to look? Does it seem likely the 5V 
reference is dead, or just being down below ground? Tracing the board out is 
proving rather beyond my ability. I don’t really want to just lift the output 
of the 5V reference and leave whatever it feeds floating.

Any help would be greatly appreciated.

Thanks!

-Ryan Stasel

On Mar 27, 2016, at 4:59 PM, Ryan Stasel 
> wrote:

All,

So, ended up pulling the 232 chip, and it seems to test okay as far as 
resistance between pins, and the board still only shows 65ohms or so between 
+5v and ground around that chips pads (support caps, pads, etc). I’m not sure 
if that’s “normal”, but it doesn’t seem like it is to me. Nothing seems to be 
getting abnormally warm. =/ I’m half curious if my meter (Keithley 196, and a 
Fluke 189) is turning on a transistor partially. =/

I do see what appears to be TTL level serial communication on the inputs to 
that chip. The replacement should be here on Monday, but at this point I'm 
wondering if my meter might be turning on some transistor (it shouldn't), 
or...? I would think a shorted cap would itself heat up.

There's a thread online relating to MAX232 type chips suffering from latchup 
under certain conditions 
(https://e2e.ti.com/support/interface/etc_interface/f/392/t/233847). But the 
low resistance between power and ground rails has me a bit concerned. :/

I did leave the unit running for about an hour, and the 10Mhz never came down 
from its 26hz high. Seeing that, I looked at the adjust pin on the OCXO, and 
it’s pegged at -10.25V. That also appears on all the outputs from the LT1014. 
=/ Also in that area is the 5V reference, and checking the output of that shows 
-0.6V (should be 5V). I’m… really starting to worry this whole thing is toast. 
All the rails appear fine, so I can’t help but think the previous owner hooked 
up the power wrong, and either -12V or +12V got applied to the 5V parts. =/ I’m 
fine replacing these two other LT parts, I’m just starting to worry that 
something not as easy to replace could be damaged (the FPGA, the Trimble chip, 
etc). Where is the actual DAC (is that in the FPGA)? Though I suppose if the 5V 
reference is dead, that would probably prevent the DAC from functioning. I 
guess the question would be if something is pulling the ref down (below 
ground), or is it just borked?

Anyway, hopefully I’ll at least be able to hook up serial to it tomorrow 
evening and see what Tboltmon says.

Thanks again for the help. Let me know if you have any other thoughts for 
things I can check.

Ryan Stasel
IT Operations Manager, SOJC
University of Oregon

Sent from my iPhone

On Mar 27, 2016, at 8:53 AM, Robert LaJeunesse 
> 
wrote:

Ryan,

The cap across 1-3 is the one that boosts +5V to +10V, with pin 2 being the 
+10V result. Thus the pins on this "flying" cap swing 5V p-p (pin 3 is 0 to 5, 
pin 1 is 5 to 10). The cap across 4-5 is the one that inverts +10V to -10V, 
with pin 6 being the -10V result. Pin 6 should NOT be at ground. The pins on 
this second flying cap swing 10V p-p (pin 4 is 10 to 0, pin 5 is 0 to -10).

Inputs to the transmitter stages (10 & 11) should be at valid logic levels, for 
the ICL232 these are standard TTL levels. Be aware that other part types that 
do this same function may not have the same logic levels (Vih and Vil) so be 
careful when substituting.

I did not mean to suggest lifting pins 10 or 11, although you might consider 
that last, but pins 7 and 14 should idle near -10V since the transmitter inputs 
have 

[time-nuts] Trimble Thunderbolt GPSDO Troubleshooting

[Mark Sims]

Well,  if you think the 5V ref is bad, you could pull the ref chip and jumper 
the logic 5V to its output pad (through a resistor... maybe 1K) to do a quick 
and dirty test.  If the resistor output is dragged down, you know something is 
loading down the ref voltage.  
___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Re: [time-nuts] Trimble Thunderbolt GPSDO Troubleshooting

[Bruce Griffiths]

Looking at the sample I prepared earlier, except for a single 120 ohm resistors 
all the blue resistors are 10 kohms.  

On Tuesday, 29 March 2016 7:27 PM, Bruce Griffiths 
 wrote:
 

 There aren't enough resistors for a high resolution R-2R DAC so its likely to 
be something like 4 (or more) x 4 bit (R, 2R, 4R, 8R) sub dacs with weighted 
resistive summing of the sub DAC outputs.
Bruce
 

On Tuesday, 29 March 2016 6:09 PM, Ryan Stasel  wrote:
 

 All,

Yay progress (one step forward into the next wall). I got the MAX232 chip 
replaced with a MAX202 (pin compatible, better ESD and Latchup protection). 
That got the serial working, and I was able to watch the unit do a survey, and 
then confirm it saw that the Osc was off by ~ -2700ppb, and the PPS. I did a 
factory reset as well.

After it did a full survey, it came back and confirmed that the oscillator 
adjustment was at a rail. It read the DAC 4.90. But the output of the 
reference was still -0.6V. So I’m guessing that chip is toast. I’ve got one on 
order. Also confusing is the quad op-amp seems to be saturated at the negative 
rail. I can see this Opamp feeds the adjust pin on the OCXO, but I’m not sure 
what feeds it. Guessing the FPGA? I still can’t find the DAC… all I see are 
these pictures http://www.leapsecond.com/pages/tbolt/photos.htm but the 
pictures aren’t of the DAC, unless the DAC is a resistor ladder (hadn’t thought 
of that until now). Now I’m starting to realize this is probably the case. =P

So, any input on where I might want to look? Does it seem likely the 5V 
reference is dead, or just being down below ground? Tracing the board out is 
proving rather beyond my ability. I don’t really want to just lift the output 
of the 5V reference and leave whatever it feeds floating.

Any help would be greatly appreciated.

Thanks!

-Ryan Stasel

On Mar 27, 2016, at 4:59 PM, Ryan Stasel 
> wrote:

All,

So, ended up pulling the 232 chip, and it seems to test okay as far as 
resistance between pins, and the board still only shows 65ohms or so between 
+5v and ground around that chips pads (support caps, pads, etc). I’m not sure 
if that’s “normal”, but it doesn’t seem like it is to me. Nothing seems to be 
getting abnormally warm. =/ I’m half curious if my meter (Keithley 196, and a 
Fluke 189) is turning on a transistor partially. =/

I do see what appears to be TTL level serial communication on the inputs to 
that chip. The replacement should be here on Monday, but at this point I'm 
wondering if my meter might be turning on some transistor (it shouldn't), 
or...? I would think a shorted cap would itself heat up.

There's a thread online relating to MAX232 type chips suffering from latchup 
under certain conditions 
(https://e2e.ti.com/support/interface/etc_interface/f/392/t/233847). But the 
low resistance between power and ground rails has me a bit concerned. :/

I did leave the unit running for about an hour, and the 10Mhz never came down 
from its 26hz high. Seeing that, I looked at the adjust pin on the OCXO, and 
it’s pegged at -10.25V. That also appears on all the outputs from the LT1014. 
=/ Also in that area is the 5V reference, and checking the output of that shows 
-0.6V (should be 5V). I’m… really starting to worry this whole thing is toast. 
All the rails appear fine, so I can’t help but think the previous owner hooked 
up the power wrong, and either -12V or +12V got applied to the 5V parts. =/ I’m 
fine replacing these two other LT parts, I’m just starting to worry that 
something not as easy to replace could be damaged (the FPGA, the Trimble chip, 
etc). Where is the actual DAC (is that in the FPGA)? Though I suppose if the 5V 
reference is dead, that would probably prevent the DAC from functioning. I 
guess the question would be if something is pulling the ref down (below 
ground), or is it just borked?

Anyway, hopefully I’ll at least be able to hook up serial to it tomorrow 
evening and see what Tboltmon says.

Thanks again for the help. Let me know if you have any other thoughts for 
things I can check.

Ryan Stasel
IT Operations Manager, SOJC
University of Oregon

Sent from my iPhone

On Mar 27, 2016, at 8:53 AM, Robert LaJeunesse 
> 
wrote:

Ryan,

The cap across 1-3 is the one that boosts +5V to +10V, with pin 2 being the 
+10V result. Thus the pins on this "flying" cap swing 5V p-p (pin 3 is 0 to 5, 
pin 1 is 5 to 10). The cap across 4-5 is the one that inverts +10V to -10V, 
with pin 6 being the -10V result. Pin 6 should NOT be at ground. The pins on 
this second flying cap swing 10V p-p (pin 4 is 10 to 0, pin 5 is 0 to -10).

Inputs to the transmitter stages (10 & 11) should be at valid logic levels, for 
the ICL232 these are standard TTL levels. Be aware that other part types that 
do this same function may not have the same logic