Re: [time-nuts] CF cards cloned S250

[Bob Darlington]

Think they'll boot in my S300 that fails at start up?

-Bob

On Sep 27, 2017 2:49 PM,  wrote:


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[time-nuts] TNS-BUF

[Vasco Soares]

Hi All,

Is there any TNS-BUF Isolation Amplifier boards available out there?

Regards,
VS
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[time-nuts] Weird GPSDO behavior

[Mark Sims]

A couple of things to try...

Turn on the OSC plot (G O) and see what that looks like... usually like a lot 
of noise.   Try with the display filter turned on (like F D 60).

The "&" menu lets you set the disciplining parameters.  It will also bring up a 
display of all the parameters.  You can see what the jamsync threshold id set 
to.  ESC or space should get out of param display mode.
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Re: [time-nuts] Weird GPSDO behavior

[Lars Walenius]

If I look on the TIC graph it looks like something happen at about + or - 
500ns. Could it be that the software change algoritm? Like a ”Jam Sync”. Seems 
like it tries to get the TIC to zero quick by changing the DAC. Maybe it thinks 
it gets enough close in frequency and stops and goes back to the PI-loop with 
2 secs time constant? As the frequency seems to be off 0.7ppb the excursion 
to about 6-7 us with a 2sec PI-loop make sense and it takes about a day to 
get back in phase (to + or - 500 ns and a new cycle begins).

If the above is correct the parameters for the PI-loop work but not for the 
other ”algoritm” that has a factor of 100 wrong oscillator sensitivity.

Changing to another time constant might give another cycle different from a 
day?? But will not solve the problem I guess.

Best Regards
Lars


Från: Skip Withrow
Skickat: den 28 september 2017 22:25
Till: time-nuts
Ämne: [time-nuts] Weird GPSDO behavior

Hello Time-Nuts,

I have a NTGS50AA GPSDO (close cousin to the NTBW50AA and Thunderbolt)
with the OCXO removed and a SRS PRS-10 rubidium oscillator in its
place.  I have been running Lady Heather 5.0 and have changed the
damping, gain, and time constant to give me a 20,000 second time
constant with a damping of .6.  I have attached a Lady Heather screen
shot of the weird behavior.  You can see that my GPS antenna is in a
very none ideal location (window on the west side of the building).

Once per day (about 8am) something disturbs the system.  So, the GPSDO
spends much of its time recovering and never gives me anywhere near
the performance that this system is capable of.  I would think that it
is not the PRS-10 as it has no knowledge of time.  I would also think
that it is not the GPS system or receiver, since the GPS constellation
repeats twice per day.

Kind of the two things that I am left with are a glitch by the power
company every morning (there is some large industrial machinery across
the street (but then I would kind of expect glitches at 8am and 5pm),
and perhaps Lady Heather doing something funny.  This system has been
running for quite some time, I have not tried restarting Lady Heather
yet.

Anybody seen anything like this, or have any good ideas?

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Re: [time-nuts] Weird GPSDO behavior

[Charles Steinmetz]

Skip wrote:


I have a NTGS50AA GPSDO (close cousin to the NTBW50AA and Thunderbolt)
with the OCXO removed and a SRS PRS-10 rubidium oscillator in its place.

Once per day (about 8am) something disturbs the system.  So, the GPSDO
spends much of its time recovering and never gives me anywhere near
the performance that this system is capable of.  I would think that it
is not the PRS-10 as it has no knowledge of time.  I would also think
that it is not the GPS system or receiver, since the GPS constellation
repeats twice per day.


I'm interested in the temperature trace.  If I'm reading the plot 
correctly, it appears that it starts oscillating up and down about 0.5C 
6 or 7 hours from the beginning of the plot, then around the same time 
as the DAC voltage steps it shoots up 5C in 6 or 7 hours with a peak up 
to +6.5C, then falls back to near where it started over ~15 hours, at 
which point the cycle repeats.  According to what we can see, it appears 
that this may be a two-day cycle, with an amplitude of 2 or 3C on "odd" 
days and ~6C on "even" days, but there isn't enough data here to say 
conclusively.


Is this an environmental effect, or self-heating within the '50AA?  6.5C 
seems like an awfully big temperature shift for something indoors, 
unless it is in direct sun. I'm not sure how it relates to the DAC and 
PPS changes, but it seems to be on the same schedule so it appears to be 
related somehow.


In my experience with Tbolts, I have found that damping of 0.6 is WAY 
too low for good performance generally, and *especially* at time 
constants >500s.  I suggest you try damping of 10 or 20.  I'm not 
suggesting that this will fix your problem, but it may, and if not, even 
after you fix what's wrong I'd advise at least trying it.  You can 
always go back.


Finally, you may get better results by putting the OCXO back into the 
GPSDO and then feeding the GPSDO PPS into the PPS synch input of the 
PRS10, rather than having LH try to discipline the PRS10 directly.  I 
have had superb results that way, after playing around with the PRS10's 
internal disciplining routines.  The PRS10 manual gives the relevant 
details.


Best regards,

Charles


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Re: [time-nuts] Weird GPSDO behavior

[John Hawkinson]

I would have thought the easy test is to run the GPSDO on battery power 
(perhaps with a UPS). Maybe that's not so easy?

--jh...@mit.edu
  John Hawkinson
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