[time-nuts] S200 to S250 Conversion to In/Outs

[martinm]

Success!

Converted to a working S250. Well worth the effort...

http://www.eevblog.com/forum/metrology/symmetricom-s200-teardownupgrade-to-s250/msg1317144/#msg1317144
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Re: [time-nuts] Weird GPSDO behavior - update

[Lars Walenius]

Hello,

If I look on the one hour plot it look like it goes in hold mode due to zero 
used satellites. If my assumption that the light blue graph in the bottom is 
satellites it sees no satellites during about a minute and after that it 
selects a fast time constant. From the TIC offset and DAC changes, a time 
constant of 10-20 secs seems reasonable if it is a PI-loop with a low pass 
filter on the TIC value.

So nothing strange except the jump of the DAC value in hold mode. As always you 
really want to know what the firmware does.

As the satellite constellation is the same every 23h56min I guess it could be 
zero usable satellites every day at about 8am for several days.

Lars


Från: Skip Withrow
Skickat: den 4 oktober 2017 03:17
Till: time-nuts
Ämne: [time-nuts] Weird GPSDO behavior - update

Hello Time-Nuts,

Well, I think I know a little more about my GPSDO problem, but
probably have more questions now than before.  Thanks for all the
replies to the first post with thoughts and suggestions.

I first tried restarting Lady Heather and doing a cold boot on the
NTGS50AA (then entering the same disciplining values). Same behavior.

I let it run over the weekend and the same behavior happened on
Saturday and Sunday morning.

So, yesterday (Monday morning) I changed the gain to the gain of the
oscillator (.0072Hz/V), damping to 1.2, and time constant to 900s.  On
the attached PRS10-2 plot you can see that it quickly settled.  This
morning, it looks like all is well from the plot (about an hour before
the furnace kicks in at the right of the plot).  HOWEVER, when the
plot is expanded there is still funny business going on with the DAC
control voltage at the same time of day.  I just think the changed
parameters limit the disturbance.  The expanded plot is the attached
PRS10-1.

At this point I'm beginning to think that the NTGS50AA is the issue,
but there are lots of questions left.

1. There are various version of the NTBW50AA/NTGS50AA GPS/operating
firmware.  Mine is 10.3 and I notice that it has the LH 'ro'
designation (as does the 10.4 version).  The 10.5 version does not
give the LH ro notice.  Maybe it behaves better with the disciplining?
 I will have to give a 10.5 a try.

2. Why does the glitch occur at 8am in the morning?  Will have to try
powering the NTGS50AA up at different times and see it the glitch
moves around.

3. Which disciplining parameters are affected by this glitch and which are not?

4. Have other people seen this same behavior?  Does it happen on
Thunderbolts too?

I'll update again when I have more data.

Regards,
Skip Withrow

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[time-nuts] S200 to S250 Conversion to in/outs

[martinm]

Link to photos of S200 investigation:

http://www.eevblog.com/forum/metrology/symmetricom-s200-teardownupgrade-to-s250/
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Re: [time-nuts] time-nuts Digest, Vol 159, Issue 3

[Mike Bafaro]

The unit I have is locking intermittently and I see a waveform at TP1 on the 
servo board that is a clipped sine wave when it is locked. The waveform at TP1 
when unlocked is about .2V p-p.  I am concerned that the clipping on the bottom 
of the waveform is a problem with the bias on the sync detector stage.  I am 
just guessing. When the unit is locked the lamp voltage is 10.0V and the 
crystal voltage is 6.5V.  This seems to be OK. But in about 10 minutes it 
breaks lock and it may or may not lock again. But I had to add a .01uf at the 
lamp voltage pin of the main connector to get it to lock at all.  Without the 
.01uf cap it would break lock as soon as  I touched the DVM probe to the lamp 
pin on the main connector.  I was going to enclose the waveform I took but I 
guess it is too big a file.   Also I noticed that the output of middle gain 
stage in the lamp photo diode amplifier is biased at 1.6V which I think should 
be at about 5V.  There must be an issue with the LM324 or the bypass cap
 .  The resistor from +5V to the + input measures OK. 
 
Mike  

-Original Message-
From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Andre
Sent: Tuesday, October 3, 2017 1:51 PM
To: time-nuts@febo.com
Subject: Re: [time-nuts] time-nuts Digest, Vol 159, Issue 3

Whats up with it? There are related manuals for these around and one common 
problem is bad 10K resistor on the lamp board.
Apparently the heat does them in over time.

Interestingly a lot of "military surplus" units can in fact be probed using a 
random generator over serial port to see what comes back.
Takes a while but can yield results as commands although undocumented can 
sometimes be brute forced by comparing with known similar units.


Does anyone know where I can get a service manual for an EFRATOM part number
100318-001 or -003.  This is used in the EFRATOM model PRFS102.  The manual for 
the base model may have the data on the oscillator.



Thanks,

Mike Bafaro WA9ZEO

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Re: [time-nuts] sine to square wave circuits - performance data?

[Mattia Rizzi]

Hello,

I think that the important point about sine-to-square converter is about
how you measure the phase noise.
If you use such converter, you don't care about the signal noise when the
output is clipped. But phase noise analyzers care about that too.
That's why Linear characterized LTC6957 additive phase noise using the REF
input port of phase noise analyzer. That port is connected to the LO input
of the internal mixer, therefore it cares only rising/falling edges.
And the worst thing is that push-pull CMOS stage are not operated in
high-gain, so no PSRR.



> For cycle-to-cycle jitter what matters is the white noise floor.
  Ie everything above 100Hz-1kHz, as this is the largest contributor
  of "short" tau jitter. This is the component that limits e.g. the
  single shot resolution of time-interval counters.

Not to be pedantic, but time-interval counters are sensitive to something
similar to *period jitter*, i.e. if phi(t) is the random phase fluctuation,
then they are sensible to phi(t+T)-phi(t), where T is the measurement time.
Period jitter has the same definition, but the "T" is the nominal period of
the clock signal. Indeed, the phase noise contribution starts to be
relevant above kHz.

cheers,
Mattia




2017-10-04 18:49 GMT+02:00 Attila Kinali :

> On Wed, 4 Oct 2017 11:01:31 -0400
> Bob kb8tq  wrote:
>
> > This gets into the “other side” of the whole comparator / squaring
> circuit
> > test process. What matters for ADEV and what matters for phase noise at
> > 100KHz offset likely are not the same thing. A lot of circuits do quite
> well
> > inside 100 Hz, but not so well above that offset.
>
> Yes. Definitely something one should consider.
>
> For completeness:
>
> * For cycle-to-cycle jitter what matters is the white noise floor.
>   Ie everything above 100Hz-1kHz, as this is the largest contributor
>   of "short" tau jitter. This is the component that limits e.g. the
>   single shot resolution of time-interval counters.
>
> * For ADEV/TDEV at "long" taus >1-100s what matters is the close-in, 1/f^a,
>   flicker noise. As white noise averages out with sqrt(n), with n
>   being the number of samples taken, but 1/f^a noise does not.
>
> When the transistion to from short to long taus happens depends as much
> on the noise as on the rate of measurement. If we measure a 1PPS, the
> the ADEV at tau=1s will be dominated by white noise and at tau=10s it
> could be still a significant portion of the noise seen. On the other
> hand, if we measure a 1kHz signal (at that rate), the tau=1s will be
> (most likely) dominated by the flicker noise.
>
>
> > Driving a 5V powered CMOS gate with 5.5V p-p does a pretty good job ….
>
> If you have this much signal, yes. Not everyone has the luxury of an
> steady +19dBm input signal. Part of the reason why I am looking into
> this is because I wanted a squaring circuit that can work down to +2dBm,
> where, so I have been told, CMOS gates do not work well anymore.
>
>
> Attila Kinali
> --
> It is upon moral qualities that a society is ultimately founded. All
> the prosperity and technological sophistication in the world is of no
> use without that foundation.
>  -- Miss Matheson, The Diamond Age, Neil Stephenson
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