[time-nuts] Thermal impact on OCXO

[Mark Sims]

Several years ago I replaced the OCXOs in some Tektronix DC5010 counters with 
surplus Oscilloquartz 8663 DOCXOs.   The darn things have freaky good aging 
characteristics.   They have been on 24/7 (except for a few brief 
power-outages) for over 3 years.   After a month I set their freq against a 
cesium oscillator.   They still show 10 MHz out to 8 or 9 decimal places.

I just got in an Oscilloquartz Star-4 ATDC (automatic temperature / drift 
compensation) that uses the same DOCXO.   They take 24 hours from a cold start 
before the ATDC learning kicks in (you can fake it out by power cycling during 
that interval and it thinks it was a brief outage and reports a 1 hour learning 
delay).   After an unspecified time (at least several days) the device learns 
the compensation characteristics and the holdover performance status switches 
from POOR to IN-SPEC.   I have not yet gotten it past the learning stage...

Oh,  and Lady Heather now speaks Star-4 management interface commands which are 
also used on a NEC GPSDO that shows up on Ebay... I have one of those on order.

---

> OSA8663: per year, 3.0E-8, in 10 years < 30.0E-8
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Re: [time-nuts] Excel logarithmic function (was Thermal impact on OCXO)

[Scott Stobbe]

Hi Lars,

I agree with you, that if there is data out there, it isn't easy to find,
many thanks for sharing!

Fitting to the full model had limited improvements, the b coefficient was
quite large making it essentially equal to the ln(x) function you fitted in
excel. It is attached as "Lars_FitToMil55310.png".

So on further thought, the B term can't model a device aging even faster
than it should shortly after infancy. In the two extreme cases either B is
large and (Bt)>>1 so the be B term ends up just being an additive bias, or
B is small, and ln(x) is linearized (or slowed down) during the first bit
of time.

You can approximated the MIL 55310 between two points in time as

f(t2) - f(t1) = Aln(t2/t1)

A = ( f(t2) - f(t1) )/ln(t2/t1)

Looking at some of your plots it looks like between the end of year 1 and
year 10 you age from 20 ppb to 65 ppb,

A ~ 20

The next plot "Lars_ForceAcoef", is a fit with the A coefficient forced to
be 2 and 20. The 20 doesn't end-up fitting well on this time scale.

Looking at the data a little more, I wondered if the first 10 day are going
through some behavior that isn't representative of long-term aging, like
warm-up, retrace (I'm sure bob could name half a dozen more examples). So
the next two plots are fits of the 4 data points after day10, and seem to
fit well, "Lars_FitAfterDay10.png", "Lars_1Year.png".

If you are willing to share the next month, we can add that to the fit.

Cheers,

On Fri, Nov 18, 2016 at 1:26 PM, Lars Walenius 
wrote:
>
> Hopefully someone can find the correct a and b for a*ln(bt+1) with
stable32 or matlab for this data set:
> Days ppb
> 2   2
> 4   3.5
> 7   4.65
> 8   5.05
> 9   5.22
> 12 6.11
> 13 6.19
> 25 7.26
> 32 7.92
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Re: [time-nuts] Thermal impact on OCXO

[Azelio Boriani]

One starting point to figure out the 10 years aging can be the
datasheet of an OCXO:
MTI240: per year, 3.0E-7, in 10 years must be less than 30.0E-7
MTI220: per year, 1.0E-6, in 10 years < 10.0E-6
Bliley NV26R: 17 years, 5.0E-6
OSA8663: per year, 3.0E-8, in 10 years < 30.0E-8

On Fri, Nov 18, 2016 at 11:48 PM, Bob Camp  wrote:
> Hi
>
>
>
>> On Nov 18, 2016, at 1:31 PM, Lars Walenius  wrote:
>>
>> Hi Bob (and all others),
>>
>> I agree to all your points but am curious to your comment: ”that OCXO is 
>> aging a lot for one that has been on that long”.
>> As I have only done this test and seen no other test of OCXO´s powered over 
>> at least ten years, I have no idea what is reasonable. I also guess I will 
>> not do another test of an OCXO powered and measured over ten years again.
>>
>> Could you give some examples what is reasonable for aging after ten years? 
>> Maybe others have data? I have searched internet and it isn´t easy to find 
>> long-term data on OCXO’s (at least for me).
>
> The only people I know of that have the gear and the interest to run a number 
> of OCXO’s are oscillator manufacturers. They also track parts
> in the field by various methods. The data takes real effort to collect and 
> thus is “part of our IP”.
>
> Bob
>
>>
>> This oscillator drifted about 60ppm between 1month on to ten years on . Do 
>> others have figures what is reasonable over this time span?
>>
>> For point 1: Is it possible from the aging curve to have some ideas what is 
>> going on??
>>
>> Lars
>>
>> >Från: Bob Camp
>> >Skickat: den 17 november 2016 01:03
>> >Hi
>>
>> >Your data demonstrates a couple of things:
>>
>> >1) There are a number of different things going on with that OCXO and some 
>> >things are a lot less predictable than others.
>> >2) Oscillators do drop rate while on power.
>> >3) Oscillators that age a lot are easier to model (yes, that OCXO is aging 
>> >a lot for one that has been on that long).
>>
>> >Bob
>>
>> >> On Nov 16, 2016, at 2:41 PM, Lars Walenius  
>> >> wrote:
>> >>
>> >> FWIW. Between 2001 and 2011 I run a 5MHz OCXO (in a box). It is a 2x3inch 
>> >> type without EFC marked OFC MC834X4-009W with date code 97. Probably it 
>> >> was from some base station testing and it had been sitting in my shelf 
>> >> since 98. The OCXO were battery backed but at two occasions (2004 and 
>> >> 2007) we had power fails that drained the battery as can be seen in the 
>> >> graph.
>> >>
>> >> Just out of curiosity I yesterday put just the first thirty days (like in 
>> >> the pdf mentioned below) and let Excel calculate the logarithmic 
>> >> function. If I extrapolate that to 10 years it seems that the drift would 
>> >> be 6E-13/day but as can be seen in the aging graph it was more like ten 
>> >> times higher.
>> >>
>> >> Some days ago I started the OCXO again after it had been on the shelf for 
>> >> more than 4 years. Enclosed is a graph for the first 7 days. After six 
>> >> and half days it seems to be a jump of about 1.5E-10 and as I have no 
>> >> indication of anything else I believe it is from the OCXO.
>> >>
>> >> /Lars
>
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Re: [time-nuts] Thermal impact on OCXO

[Bob Camp]

Hi



> On Nov 18, 2016, at 1:31 PM, Lars Walenius  wrote:
> 
> Hi Bob (and all others),
>  
> I agree to all your points but am curious to your comment: ”that OCXO is 
> aging a lot for one that has been on that long”.
> As I have only done this test and seen no other test of OCXO´s powered over 
> at least ten years, I have no idea what is reasonable. I also guess I will 
> not do another test of an OCXO powered and measured over ten years again.
>  
> Could you give some examples what is reasonable for aging after ten years? 
> Maybe others have data? I have searched internet and it isn´t easy to find 
> long-term data on OCXO’s (at least for me).

The only people I know of that have the gear and the interest to run a number 
of OCXO’s are oscillator manufacturers. They also track parts
in the field by various methods. The data takes real effort to collect and thus 
is “part of our IP”.

Bob

>  
> This oscillator drifted about 60ppm between 1month on to ten years on . Do 
> others have figures what is reasonable over this time span?
>  
> For point 1: Is it possible from the aging curve to have some ideas what is 
> going on??
>  
> Lars
>  
> >Från: Bob Camp
> >Skickat: den 17 november 2016 01:03
> >Hi
>  
> >Your data demonstrates a couple of things:
>  
> >1) There are a number of different things going on with that OCXO and some 
> >things are a lot less predictable than others.
> >2) Oscillators do drop rate while on power.
> >3) Oscillators that age a lot are easier to model (yes, that OCXO is aging a 
> >lot for one that has been on that long).
>  
> >Bob
>  
> >> On Nov 16, 2016, at 2:41 PM, Lars Walenius  
> >> wrote:
> >>
> >> FWIW. Between 2001 and 2011 I run a 5MHz OCXO (in a box). It is a 2x3inch 
> >> type without EFC marked OFC MC834X4-009W with date code 97. Probably it 
> >> was from some base station testing and it had been sitting in my shelf 
> >> since 98. The OCXO were battery backed but at two occasions (2004 and 
> >> 2007) we had power fails that drained the battery as can be seen in the 
> >> graph.
> >>
> >> Just out of curiosity I yesterday put just the first thirty days (like in 
> >> the pdf mentioned below) and let Excel calculate the logarithmic function. 
> >> If I extrapolate that to 10 years it seems that the drift would be 
> >> 6E-13/day but as can be seen in the aging graph it was more like ten times 
> >> higher.
> >>
> >> Some days ago I started the OCXO again after it had been on the shelf for 
> >> more than 4 years. Enclosed is a graph for the first 7 days. After six and 
> >> half days it seems to be a jump of about 1.5E-10 and as I have no 
> >> indication of anything else I believe it is from the OCXO.
> >>
> >> /Lars

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Re: [time-nuts] Excel logarithmic function (was Thermal impact on OCXO)

[Bob Camp]

Hi


> On Nov 18, 2016, at 4:36 PM, Magnus Danielson  
> wrote:
> 
> Hi Lars,
> 
> Now, consider f(t) = a*log(b*t+1), then the derivate is a*b/(b*t+1) and 
> second derivate - a * b^2 / (b*t + 1)^2.
> 
> Forming first f'(t) and second f"(t) derivate estimates from data is trivial. 
> Given that we can estimate a and b using
> 
> a = - f('t)^2 / f"(t)
> 
> b = - f'(t) / (f'(t) * t - a)
> 
>  = - f"(t) / (f("t) * t - f'(t))
> 
> A bit of paper and pen work or you get Maxima to do some work for you.
> I haven't seen how any real estimator of this drift function is implemented,


By far the most common implementation of the equation as an estimator is in 
factory test of OCXO’s that
are built to the 55310 spec. It also is fairly common to use it on commercial 
OCXO’s as well. Put another way:
It’s how you answer “Does it meet the 20 year aging spec?” in less than 20 
years. 

Bob


> but I wanted to provide some notes from note-book of stuff being unfinished.
> 
> Cheers,
> Magnus
> 
> On 11/18/2016 07:26 PM, Lars Walenius wrote:
>> Bob wrote:
>>> As mentioned earlier in this thread. The function that has been used in 
>>> several posts
>>> isn’t the right log function. The proper fit is to ln(bt+1)
>> 
>> You are absolutely right. It was my mistake to use the ln(t) in the graph. 
>> As that was what I know in Excel and I don´t have Stable32 or MatLab. In 
>> Excel I actually double checked that (a*ln(bt+1)) with b 5 to 1000 gave 
>> about the same as (a*ln(t)) for my data set (only the offset was largely 
>> different).
>> 
>> Hopefully someone can find the correct a and b for a*ln(bt+1) with stable32 
>> or matlab for this data set:
>> Days ppb
>> 2   2
>> 4   3.5
>> 7   4.65
>> 8   5.05
>> 9   5.22
>> 12 6.11
>> 13 6.19
>> 25 7.26
>> 32 7.92
>> 
>> It would also be interesting if I could get the drift after 10 years to see 
>> if it is about 6E-13/day as with the ln(t).
>> 
>> 
>> Peter wrote:
 I'm not very good with Excel, but this curve-fitting function sounds very
 useful.  Could you please tell me how it's done?
>> 
>> In the graph I only right-clicked the curve and selected ”add trendline” 
>> here I checked the logarithmic and show equation.
>> 
>> Lars
>> 
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[time-nuts] TDOP impact on accuracy of receiver's 1PPS

[Bob Stewart]

I can't help but notice that there is an impact on the measured phase error 
every time the TDOP reported by the LEA-6T changes.  What I don't know is how 
to characterize the impact.  Is the impact more of a change in the error band, 
rather than a bias in one direction or the other?  Would a variable dead-band 
filter be an appropriate response to these changes?  I've experimented with a 
dead-band filter in the past with mixed results, but I never coupled the width 
of the dead-band to the TDOP.

Bob - AE6RV -
AE6RV.com

GFS GPSDO list:
groups.yahoo.com/neo/groups/GFS-GPSDOs/info
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Re: [time-nuts] Excel logarithmic function (was Thermal impact on OCXO)

[Magnus Danielson]

Hi Lars,

Now, consider f(t) = a*log(b*t+1), then the derivate is a*b/(b*t+1) and 
second derivate - a * b^2 / (b*t + 1)^2.


Forming first f'(t) and second f"(t) derivate estimates from data is 
trivial. Given that we can estimate a and b using


a = - f('t)^2 / f"(t)

b = - f'(t) / (f'(t) * t - a)

  = - f"(t) / (f("t) * t - f'(t))

A bit of paper and pen work or you get Maxima to do some work for you.
I haven't seen how any real estimator of this drift function is 
implemented, but I wanted to provide some notes from note-book of stuff 
being unfinished.


Cheers,
Magnus

On 11/18/2016 07:26 PM, Lars Walenius wrote:

Bob wrote:

As mentioned earlier in this thread. The function that has been used in several 
posts
isn’t the right log function. The proper fit is to ln(bt+1)


You are absolutely right. It was my mistake to use the ln(t) in the graph. As 
that was what I know in Excel and I don´t have Stable32 or MatLab. In Excel I 
actually double checked that (a*ln(bt+1)) with b 5 to 1000 gave about the same 
as (a*ln(t)) for my data set (only the offset was largely different).

Hopefully someone can find the correct a and b for a*ln(bt+1) with stable32 or 
matlab for this data set:
Days ppb
2   2
4   3.5
7   4.65
8   5.05
9   5.22
12 6.11
13 6.19
25 7.26
32 7.92

It would also be interesting if I could get the drift after 10 years to see if 
it is about 6E-13/day as with the ln(t).


Peter wrote:

I'm not very good with Excel, but this curve-fitting function sounds very
useful.  Could you please tell me how it's done?


In the graph I only right-clicked the curve and selected ”add trendline” here I 
checked the logarithmic and show equation.

Lars

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Re: [time-nuts] Thermal impact on OCXO

[Lars Walenius]

Hi Bob (and all others),

I agree to all your points but am curious to your comment: ”that OCXO is aging 
a lot for one that has been on that long”.
As I have only done this test and seen no other test of OCXO´s powered over at 
least ten years, I have no idea what is reasonable. I also guess I will not do 
another test of an OCXO powered and measured over ten years again.

Could you give some examples what is reasonable for aging after ten years? 
Maybe others have data? I have searched internet and it isn´t easy to find 
long-term data on OCXO’s (at least for me).

This oscillator drifted about 60ppm between 1month on to ten years on . Do 
others have figures what is reasonable over this time span?

For point 1: Is it possible from the aging curve to have some ideas what is 
going on??

Lars

>Från: Bob Camp
>Skickat: den 17 november 2016 01:03
>Hi

>Your data demonstrates a couple of things:

>1) There are a number of different things going on with that OCXO and some 
>things are a lot less predictable than others.
>2) Oscillators do drop rate while on power.
>3) Oscillators that age a lot are easier to model (yes, that OCXO is aging a 
>lot for one that has been on that long).

>Bob

>> On Nov 16, 2016, at 2:41 PM, Lars Walenius  wrote:
>>
>> FWIW. Between 2001 and 2011 I run a 5MHz OCXO (in a box). It is a 2x3inch 
>> type without EFC marked OFC MC834X4-009W with date code 97. Probably it was 
>> from some base station testing and it had been sitting in my shelf since 98. 
>> The OCXO were battery backed but at two occasions (2004 and 2007) we had 
>> power fails that drained the battery as can be seen in the graph.
>>
>> Just out of curiosity I yesterday put just the first thirty days (like in 
>> the pdf mentioned below) and let Excel calculate the logarithmic function. 
>> If I extrapolate that to 10 years it seems that the drift would be 6E-13/day 
>> but as can be seen in the aging graph it was more like ten times higher.
>>
>> Some days ago I started the OCXO again after it had been on the shelf for 
>> more than 4 years. Enclosed is a graph for the first 7 days. After six and 
>> half days it seems to be a jump of about 1.5E-10 and as I have no indication 
>> of anything else I believe it is from the OCXO.
>>
>> /Lars

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Re: [time-nuts] Excel logarithmic function (was Thermal impact on OCXO)

[Lars Walenius]

Bob wrote:
>As mentioned earlier in this thread. The function that has been used in 
>several posts
>isn’t the right log function. The proper fit is to ln(bt+1)

You are absolutely right. It was my mistake to use the ln(t) in the graph. As 
that was what I know in Excel and I don´t have Stable32 or MatLab. In Excel I 
actually double checked that (a*ln(bt+1)) with b 5 to 1000 gave about the same 
as (a*ln(t)) for my data set (only the offset was largely different).

Hopefully someone can find the correct a and b for a*ln(bt+1) with stable32 or 
matlab for this data set:
Days ppb
2   2
4   3.5
7   4.65
8   5.05
9   5.22
12 6.11
13 6.19
25 7.26
32 7.92

It would also be interesting if I could get the drift after 10 years to see if 
it is about 6E-13/day as with the ln(t).


Peter wrote:
>> I'm not very good with Excel, but this curve-fitting function sounds very
>> useful.  Could you please tell me how it's done?

In the graph I only right-clicked the curve and selected ”add trendline” here I 
checked the logarithmic and show equation.

Lars

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Re: [time-nuts] Thermal impact on OCXO

[Rick Commo]

A similar practice at a small East coast microwave company back in the 60s.  
Except the product was magnetrons that were used in the Talos missile system 
(if memory serves).
 
On Nov 18, 2016, at 01:30, David  wrote:

I have only heard of and never observed the problem of manufacturers
cutting the middle out of a gaussian distribution for tighter
tolerance parts.

Robert Pease of National Semiconductor had an even better story:

I recollect the story of one of the pioneering transistor companies,
back in the '60s.  They had agreed to ship to their customers
transistors with an AQL (Acceptable Quality Level) of 2%, which was
pretty good for those days.  So the tester would test 98 good parts
and put them in the box.  Then, following her instructions, she would
add 2 bad transistors to finish off the box, thus bringing the quality
to the exact level desired.  This went on for some time, until one of
the customers got suspicious, because the two bad transistors were
always in the same corner of the box! Then things were changed ...

On Thu, 17 Nov 2016 10:34:06 -0500, you wrote:

> ...
> 
> I once herd a story from once upon a time that, if you bought a 10%
> resistor, what you ended up with is something like this in the figure
> attached.
> 
> Of course 1% percent resistors (EIA96) are manufactured in high yield
> today, but I would guess some of this still applies to OCXOs, you
> aren't likely to find a gem in the D grade parts. After pre-aging for
> a couple of weeks they are either binned, labeled D, or the ones that
> show promise are left to age some more before being tested to C grade,
> etc, etc.
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Re: [time-nuts] Question about AD9832 "I out Full Scale" (what does it mean?)

[Tim Shoppa]

Bruce, I assume you are talking about Figure 12 of UG-313.

If an LCD scope is not in single shot mode it will show a composite of many
cycles which will hide the stairsteps (especially if the frequency control
word is not a nice round binary number) in the fuzz.

I think the 0.1uF capacitor on IOUT on the evaluation board also helps roll
off the stairsteps.

Tim N3QE

On Thu, Nov 17, 2016 at 11:49 PM, Bruce Griffiths <
bruce.griffi...@xtra.co.nz> wrote:

> With no internal PLL to generate a higher internal frequency than the
> 25MHz MCLK, that 1MHz waveform looks a bit too smooth for an unfiltered
> 1MHz output.
> Bruce
>
> On Friday, 18 November 2016 5:12 PM, Richard (Rick) Karlquist <
> rich...@karlquist.com> wrote:
>
>
>  Trying to figure out what "Iout Full Scale" means on the AD9832.
> Some time nuts may have used this one.
>
> On page 7 of this doc:
>
> http://www.analog.com/media/en/technical-documentation/
> user-guides/UG-313.pdf
>
> It shows the AD9832 output as 572 mV peak to peak
> across 300 ohms.  This works out to 1.9 mA peak to
> peak current through the resistor.  But Rset on the
> board is 3.9K, which is supposed to give a value
> for so-called "Iout Full Scale" of 3.878 mA.
>
> I would have thought (just guessing) that peak to
> peak output current would be equal to Iout Full
> Scale, but it appears to be only half of that.
>
> Can anyone clarify this?
>
> Rick
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>
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Re: [time-nuts] A (slightly) different apu2 question

[Wojciech Owczarek]

On 18 November 2016 at 09:21, Martin Burnicki 
wrote:
>
> Just a few thoughts regarding NTP vs. PTP:
>


Oh dear... OK, before this snowballs into a bigger discussion this was not
meant to be:

My original post was _not_ about PTP vs. NTP, it was about the APU2 boards
and hardware timestamping.

My only point was to highlight the following:

1 This board has got exposed test pads for lots of 1PPS / frequency in /
out pins tied to timestamping hardware making it very easy to tap into
them. This is a great opportunity which begs to be exploited.

2. With a stable 1PPS from GPS or another source, this board can serve
nanosecond time, and that includes NTP in hardware, because the Intel NICs
can timestamp every packet, not just PTP. And yes, this mostly matters for
LAN.

I am fully aware of what you listed. NTP is just a different beast and
silicon vendors jumped onto PTP, and PTP inherently lacks the sophisticated
quorum and trust mechanisms NTP has, and yes, those are key items on the
P1588 WG agenda.

Thanks,
Wojciech

-- 
-

Wojciech Owczarek
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Re: [time-nuts] Question about AD9832 "I out Full Scale" (what does it mean?)

[David G. McGaw]

There is something wrong with the example.  The output is single-ended, 
so using info from the AD9832 data sheet with Rset=3.9K and Rload=300 
ohms as shown in the EVB schematic, it should go from 0 to 3.88mA and 0 
to 1.16V.  Figure 12 shows only half this, including only about .3V DC 
bias instead of .58V.


I apologize.  As a former Analog Devices applications engineer (Digital 
Audio Group), I find this data sheet and user guide poorly written.  
They have a lot of digital and almost no analog information.


David N1HAC


On 11/17/16 11:09 PM, Richard (Rick) Karlquist wrote:

Trying to figure out what "Iout Full Scale" means on the AD9832.
Some time nuts may have used this one.

On page 7 of this doc:

http://www.analog.com/media/en/technical-documentation/user-guides/UG-313.pdf 



It shows the AD9832 output as 572 mV peak to peak
across 300 ohms.  This works out to 1.9 mA peak to
peak current through the resistor.  But Rset on the
board is 3.9K, which is supposed to give a value
for so-called "Iout Full Scale" of 3.878 mA.

I would have thought (just guessing) that peak to
peak output current would be equal to Iout Full
Scale, but it appears to be only half of that.

Can anyone clarify this?

Rick
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Re: [time-nuts] A (slightly) different apu2 question

[Martin Burnicki]

Wojciech Owczarek wrote:
>>
>>
>> NTP does not require softstamps.  NTP can be (and I believe it has been in
>> a product) modified to use "PTP" hardware (hardstamps) and  reasonably
>> current releases can run with "drivestamps" (sampled in the NIC driver)
>> between cooperating endpoints.
> 
> 
> Of course it does not *require* software timestamps, I never said that, it
> is just the fact that most people use it with software timestamps, even if
> the NIC permits hardware timestamps. You need a secondary servo to sync the
> NIC to O/S clock if you want to serve that (or consume that) - or sync the
> NIC to external 1PPS. What you call a "drivestamp", I call a software
> timestamp. If it's not a function of the silicon, it's software. All I
> meant was that there is some unexploited potential.

Just a few thoughts regarding NTP vs. PTP:

IMO NTP can yield pretty good results even over WAN connections
*without* the requirement of special hardware which supports
timestamping of network packets, including special switches and routers,
even over WAN connections, and in the presence of network jitter. For
example from one of my workstation running Linux, here in Germany:

   remoterefid st t when poll reach   delay   offset  jitter

*SHM(0)  .shm0. 0 l48  3770.000   -0.001   0.000
 lt-martin.py.me .MRS.  1 u9   64  3770.095   -0.005   0.020
 ntp-master-1.py .PPS.  1 u   58   64  3770.191   -0.019   0.013
 ptbtime1.ptb.de .PTB.  1 u   11  128  377   11.9270.256  74.533
 ptbtime2.ptb.de .PTB.  1 u   16  128  377   11.7060.085  79.565
 ptbtime3.ptb.de .PTB.  1 u   35  128  377   11.5900.058  74.049
 time-b.timefreq .ACTS. 1 u  103  128  377  198.358   -1.377  91.992

where

- SHM is a local GPS PCI card

- lt-martin and ntp-master-1 are GPS controlled NTP servers on the local
network

- ptbtime{1,2,3} are the public NTP servers operated by the German
metrology institute PTB, reached via 7 network hops

- time-b.timefreq is a public server in the U.S., reached via 9 network
hops, including a trans-atlantic connection.


Of course, PTP can do *much* better if special hardware is being used.

We have made tests here at Meinberg where we could demonstrate that NTP
yields the same level of accuracy as PTP with a patched ntpd which
supports hardware time stamping of NTP packets. We used an own time
stamp unit which can also time stamp NTP packets.

There are 2 problems with this, though:

1.) While the PTP folks have been requesting support for time stamping
PTP packets in NIC chips as well as specific PTP support by switches and
routers for a long time, this hasn't happened for NTP.

So today we have indeed NIC chips which time stamp PTP packets, and
switches which are PTP-aware and measure the propagation delay of PTP
packets (in transparent clock mode) so that the PTP daemon can
compensate this delay and eliminate the network jitter.

There's no such thing for NTP.

2.) In the original approach introduced by PTP an outgoing packet is
time stamped by the NIC, and then a "followup" packet is sent which
contains that time stamp ("twostep" mode). This eliminates the
processing delay between the time a packet is sent out by the daemon
until it goes onto the network cable.

NTP doesn't support this feature, and introduction of this feature would
either break compatibility of the existing NTP protocol, or would
require the definition of a new protocol version, e.g. NTPv5.
(BTW, I'm aware of ntpd's "interleave" mode, but IMO that's just a hack,
and doesn't even work with normal client/server packet exchanges).

Of course PTP has a "onestep" mode today where a time stamp is taken as
soon as the packet goes out on the wire, and that time stamp is inserted
into the same packet on the fly, so no followup packet is required.

However, this requires even more sophisticated hardware which explicitly
supports this, and even if this was available for NTP this still
wouldn't solve problem of NTP time stamping support missing in NICs and
switches.

So I think NTP still meets the requirements of many users, without
requirement for specific hardware, while PTP can be used to yield a much
higher level of accuracy if you have dedicated hardware available.

Martin

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Re: [time-nuts] Thermal impact on OCXO

[David]

I have only heard of and never observed the problem of manufacturers
cutting the middle out of a gaussian distribution for tighter
tolerance parts.

Robert Pease of National Semiconductor had an even better story:

I recollect the story of one of the pioneering transistor companies,
back in the '60s.  They had agreed to ship to their customers
transistors with an AQL (Acceptable Quality Level) of 2%, which was
pretty good for those days.  So the tester would test 98 good parts
and put them in the box.  Then, following her instructions, she would
add 2 bad transistors to finish off the box, thus bringing the quality
to the exact level desired.  This went on for some time, until one of
the customers got suspicious, because the two bad transistors were
always in the same corner of the box! Then things were changed ...

On Thu, 17 Nov 2016 10:34:06 -0500, you wrote:

>...
>
>I once herd a story from once upon a time that, if you bought a 10%
>resistor, what you ended up with is something like this in the figure
>attached.
>
>Of course 1% percent resistors (EIA96) are manufactured in high yield
>today, but I would guess some of this still applies to OCXOs, you
>aren't likely to find a gem in the D grade parts. After pre-aging for
>a couple of weeks they are either binned, labeled D, or the ones that
>show promise are left to age some more before being tested to C grade,
>etc, etc.
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Re: [time-nuts] Question about AD9832 "I out Full Scale" (what does it mean?)

[Hal Murray]

rich...@karlquist.com said:
> I would have thought (just guessing) that peak to peak output current would
> be equal to Iout Full Scale, but it appears to be only half of that.

> Can anyone clarify this? 

Don't overlook a bug in the data sheet.

The data sheet for the actual part at
  http://www.analog.com/media/en/technical-documentation/data-sheets/AD9832.pd
f
says
  IOUT Full Scale 4 mA nom, 4.5 mA max
  Output Compliance 1.35 V max 3V supply

I didn't find any reference to "peak" on that data sheet, so no peak-to-peak.



-- 
These are my opinions.  I hate spam.



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