Re: [time-nuts] General questions about making measurements with time interval counter.

[Bob Camp]

Hi

The most basic issue you are going to run into is that your counter is not high 
enough
resolution / accuracy to give you meaningful data for time intervals under a 
few hundred
seconds. I would focus on improving on that part of things before I went off on 
a major
“test everything” adventure. Simply collecting a lot of data that is resolution 
limited is 
not a lot of fun …..

Bob

> On Jan 11, 2017, at 9:20 PM, Dr. David Kirkby (Kirkby Microwave Ltd) 
>  wrote:
> 
> MY AIMS
> 
> 1) Try to learn about the various statistical tests (ADEV, MDEV etc), and
> how best to compare oscillators, by making some measurements on various
> oscillators I have.
> 
> 2) Investigate the short/medium term stability of the output of  various
> bits of test kit. All are locked to GPS by feeding 10 MHz to their timebase
> inputs, so long term drift should not be relevant.
> 
> These istrumuments are:
> 
> a) The GPS itself - primarily a test of the 5370B time interval counter,
> distribution amplifier and general temperature fluctuations in the lab.
> 
> b) Other GPS(s) when I get 1 or 2 more.
> 
> c) 10 MHz to 20 GHz Microwave signal generator.
> 
> d) 0.001 Hz to 30 MHz function generator.
> 
> e) A VNA that will work at 10 MHz. Turn sweeping off
> 
> f) A VNA that has a minimum frequency of 50 MHz. Again turn sweeping off.
> 
> METHOD - Suggestion for improvements welcome.
> 
> * Where possible set all instruments to 10 MHz, which is the same as the
> GPS reference. (Obviously since one of the VNAs will not go below 50 MHz, I
> would need to use a higher frequency)
> * Feed GPS to the start input of the 5370B TI counter and the DUT into the
> stop input
> * Use the 5370B time interval counter to measre the time difference between
> one output of the distribution amplifier and the output of the instrument
> being tested .
> * Collect data from 5370B and use John's Timelab to plot various graphs and
> try to understand the differences between the various statical measurements
> (ADEV, MDEV etc.)
> 
> MY QUESTIONS.
> 
> 1) Should I use the GPS to provide a reference for the 5370B time interval
> counter,  or would it be better to use the internal OCXO? Currently I have
> the 5370B locked to GPS too, but I am wondering if this is a bad idea and I
> should run it from its own oscillator.
> 
> 2) Is there any advantage in a 10 MHz DUT going into the start or stop
> input? I assume that it is irrelevant, as long as the GPS goes into the
> other. But maybe not.
> 
> 3) If the DUT is higher in frequency (eg 50 MHz) than the 10  MHz GPS,  is
> there any advantage in going in the start ot stop input?
> 
> 4) If the DUT is lower in frequency (eg 5 MHz) than the 10  MHz GPS,  is
> there any advantage in going in the start ot stop input?
> 
> Dave
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[time-nuts] General questions about making measurements with time interval counter.

[Dr. David Kirkby (Kirkby Microwave Ltd)]

MY AIMS

1) Try to learn about the various statistical tests (ADEV, MDEV etc), and
how best to compare oscillators, by making some measurements on various
oscillators I have.

2) Investigate the short/medium term stability of the output of  various
bits of test kit. All are locked to GPS by feeding 10 MHz to their timebase
inputs, so long term drift should not be relevant.

These istrumuments are:

a) The GPS itself - primarily a test of the 5370B time interval counter,
distribution amplifier and general temperature fluctuations in the lab.

b) Other GPS(s) when I get 1 or 2 more.

c) 10 MHz to 20 GHz Microwave signal generator.

d) 0.001 Hz to 30 MHz function generator.

e) A VNA that will work at 10 MHz. Turn sweeping off

f) A VNA that has a minimum frequency of 50 MHz. Again turn sweeping off.

METHOD - Suggestion for improvements welcome.

* Where possible set all instruments to 10 MHz, which is the same as the
GPS reference. (Obviously since one of the VNAs will not go below 50 MHz, I
would need to use a higher frequency)
* Feed GPS to the start input of the 5370B TI counter and the DUT into the
stop input
* Use the 5370B time interval counter to measre the time difference between
one output of the distribution amplifier and the output of the instrument
being tested .
* Collect data from 5370B and use John's Timelab to plot various graphs and
try to understand the differences between the various statical measurements
(ADEV, MDEV etc.)

MY QUESTIONS.

1) Should I use the GPS to provide a reference for the 5370B time interval
counter,  or would it be better to use the internal OCXO? Currently I have
the 5370B locked to GPS too, but I am wondering if this is a bad idea and I
should run it from its own oscillator.

2) Is there any advantage in a 10 MHz DUT going into the start or stop
input? I assume that it is irrelevant, as long as the GPS goes into the
other. But maybe not.

3) If the DUT is higher in frequency (eg 50 MHz) than the 10  MHz GPS,  is
there any advantage in going in the start ot stop input?

4) If the DUT is lower in frequency (eg 5 MHz) than the 10  MHz GPS,  is
there any advantage in going in the start ot stop input?

Dave
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Re: [time-nuts] hm H Maser

[Bob Camp]

Hi

The obvious question would be: What does it cost to set up a line to make a 
proper
set of spherical Rb cells? Doing this as a glassblowing project is a dead end. 
You
need it properly tooled ….

Bob

> On Jan 11, 2017, at 7:05 PM, Bruce Griffiths  
> wrote:
> 
> Angus
> Read the paper I posted on the current state of the art.
> ADEV ~ 2E-13/SQRT(Tau) is feasible with large cells and using a laser instead 
> of rubidium lamp.In principle, one can use the same cell to lock the laser to 
> the rubidium absorption line and lock the microwave signal.Suitable laser 
> diodes are readily available.
> Increasing the contrast of the signal used for locking reduces the noise 
> significantly.One approach is to use an integrating sphere cell and use an 
> optical fibre to bring the laser signal into the cell.Since random scattering 
> in an integrating sphere depolarises the light and virtually eliminates any 
> effect of spatial coherence a multimode fibre should suffice.Laser speckle 
> can be reduced significantly by using a colloidal suspension of titanium 
> dioxide if the colloidal suspension fills another integrating sphere or 
> equivalent.I've tried the latter using plastic optical fibres to transport 
> the laser light into and out of the colloid. Its extremely effective in 
> eliminating speckle in an optical interferometer.
> Bruce 
> 
>On Thursday, 12 January 2017 12:19 PM, Angus  
> wrote:
> 
> 
> On Tue, 10 Jan 2017 21:43:07 -0500, you wrote:
> 
>> 
>> This does get back to state of the art Rb and what that means. In my 
>> suggested case thats measured in terms of ADEV for Tau = 1 to 1,000,000 
>> seconds. If you wanted an Rb with (only) state of the art phase noise at 1 
>> MHz offset … thats a different thing. State of the art for 
>> power consumption and size is also not what Im suggesting in this case. Why 
>> the choice of spec? … this is TimeNuts. 
> 
> Hi,
> 
> Some discussions on the performance that might be practically achieved
> with different designs may be a useful start - as long as it's done in
> the context of a practical unit that could actually get built, rather
> than just a theoretical wish list.
> 
> It would also be good to have some idea of the cost of any special
> parts like cells too. Without that info, it's hard to know how
> practical particular designs would be. 
> 
> Looking at export/technology controls might be useful early on too,
> since we're going for high performance.
> 
> I've often wondered how a 21st century version of a 5065 would
> perform, so it's great to see that I'm not completely alone in my
> insanity!
> 
> Angus.
> 
> 
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> 
> 
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Re: [time-nuts] hm H Maser

[Bruce Griffiths]

Angus
Read the paper I posted on the current state of the art.
ADEV ~ 2E-13/SQRT(Tau) is feasible with large cells and using a laser instead 
of rubidium lamp.In principle, one can use the same cell to lock the laser to 
the rubidium absorption line and lock the microwave signal.Suitable laser 
diodes are readily available.
Increasing the contrast of the signal used for locking reduces the noise 
significantly.One approach is to use an integrating sphere cell and use an 
optical fibre to bring the laser signal into the cell.Since random scattering 
in an integrating sphere depolarises the light and virtually eliminates any 
effect of spatial coherence a multimode fibre should suffice.Laser speckle can 
be reduced significantly by using a colloidal suspension of titanium dioxide if 
the colloidal suspension fills another integrating sphere or equivalent.I've 
tried the latter using plastic optical fibres to transport the laser light into 
and out of the colloid. Its extremely effective in eliminating speckle in an 
optical interferometer.
Bruce 

On Thursday, 12 January 2017 12:19 PM, Angus  
wrote:
 

 On Tue, 10 Jan 2017 21:43:07 -0500, you wrote:

>
>This does get back to state of the art Rb and what that means. In my suggested 
>case thats measured in terms of ADEV for Tau = 1 to 1,000,000 
>seconds. If you wanted an Rb with (only) state of the art phase noise at 1 MHz 
>offset … thats a different thing. State of the art for 
>power consumption and size is also not what Im suggesting in this case. Why 
>the choice of spec? … this is TimeNuts. 

Hi,

Some discussions on the performance that might be practically achieved
with different designs may be a useful start - as long as it's done in
the context of a practical unit that could actually get built, rather
than just a theoretical wish list.

It would also be good to have some idea of the cost of any special
parts like cells too. Without that info, it's hard to know how
practical particular designs would be. 

Looking at export/technology controls might be useful early on too,
since we're going for high performance.

I've often wondered how a 21st century version of a 5065 would
perform, so it's great to see that I'm not completely alone in my
insanity!

Angus.


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Re: [time-nuts] hm H Maser

[Bob Camp]

Hi

> On Jan 11, 2017, at 6:07 PM, Angus  wrote:
> 
> On Tue, 10 Jan 2017 21:43:07 -0500, you wrote:
> 
>> 
>> This does get back to “state of the art Rb” and what that means. In my 
>> suggested case that’s measured in terms of ADEV for Tau = 1 to 1,000,000 
>> seconds. If you wanted an Rb with (only) state of the art phase noise at 1 
>> MHz offset 
> that’s a different thing. State of the art for 
>> power consumption and size is also not what I’m suggesting in this case. Why 
>> the choice of spec? 
> this is TimeNuts. 
> 
> Hi,
> 
> Some discussions on the performance that might be practically achieved
> with different designs may be a useful start - as long as it's done in
> the context of a practical unit that could actually get built, rather
> than just a theoretical wish list.
> 

The biggest issue with doing this is that *if* there is a magic formula that 
tells you 
“these parts give you that ADEV” …. it’s in the same vault as the formula for 
Coke. 
That sort of thing (if it even exists) would be the gold standard of corporate 
IP for
a company making atomic clocks. 

About all you can really say is “they did this and the units the shipped did 
that”. There
are some obvious thing like “bigger cells work better”. Coming up with an 
equation that
correctly predicts a cell of this odd geometry functioning at these dimensions 
for 10,000
second ADEV ….not so much. 

> It would also be good to have some idea of the cost of any special
> parts like cells too. Without that info, it's hard to know how
> practical particular designs would be. 

The most likely course would be to cut out a major chunk of cost and find 
somebody
who is willing to make up a couple hundred sets of cells. There has already been
a proposal to do this floated on the list. I don’t recall the exact numbers, 
but $2,000
is what comes to mind. Apologies if this is a bogus number. 

> 
> Looking at export/technology controls might be useful early on too,
> since we're going for high performance.

Indeed, if you get to crazy you could get in trouble. My guess is that a 
standard the 
size of a 5065 or larger is unlikely to set off alarm bells. 


> 
> I've often wondered how a 21st century version of a 5065 would
> perform, so it's great to see that I'm not completely alone in my
> insanity!

Which obviously is an itch many of us share. The gotcha of course is that each 
of 
us has (likely incompatible) ideas about how to do it. We may even have 
incompatible goals in terms of “what’s good”. Based on many decades of 
designing 
things like this, feature creep and elastic goals will kill a project dead 
(usually after
a lot of money has been spent). 

Lots of Fun

Bob

> 
> Angus.
> 
> 
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Re: [time-nuts] hm H Maser

[Angus]

On Tue, 10 Jan 2017 21:43:07 -0500, you wrote:

>
>This does get back to “state of the art Rb” and what that means. In my 
>suggested case that’s measured in terms of ADEV for Tau = 1 to 1,000,000 
>seconds. If you wanted an Rb with (only) state of the art phase noise at 1 MHz 
>offset … that’s a different thing. State of the art for 
>power consumption and size is also not what I’m suggesting in this case. Why 
>the choice of spec? … this is TimeNuts. 

Hi,

Some discussions on the performance that might be practically achieved
with different designs may be a useful start - as long as it's done in
the context of a practical unit that could actually get built, rather
than just a theoretical wish list.

It would also be good to have some idea of the cost of any special
parts like cells too. Without that info, it's hard to know how
practical particular designs would be. 

Looking at export/technology controls might be useful early on too,
since we're going for high performance.

I've often wondered how a 21st century version of a 5065 would
perform, so it's great to see that I'm not completely alone in my
insanity!

Angus.


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Re: [time-nuts] hm H Maser

[Bob Camp]

Hi

A spherical set of cells is going to be a massive pain to fabricate. I believe 
you can hit < 5x10^-12 / sqrt(tau) with 
a fairly normal cell design and cavity design. There are some very basic issues 
with the photo detector’s S/N that
also tip things towards a coaxial approach.

Bob

> On Jan 10, 2017, at 10:43 PM, Bruce Griffiths  
> wrote:
> 
> A  spherical cavity resonator with a spherical Rubidium cell configured as an 
> integrating sphere (to enhance the SNR of the optical absorption signal) is a 
> potential option. Its also possible to use the same cell to lock a 795 nm 
> laser to the desired wavelength. Fiber coupling the laser light could also be 
> useful.Note that with an integrating sphere (or any other random scattering 
> process eg scattering from colloidal particles undergoing Brownian motion) 
> laser polarisation isn't preserved which may be convenient.One potential 
> issue with an  integrating sphere is the longevity of the diffusing coating 
> (typically Barium sulphate with an organic binder). Roughening (fine grind  
> followed by HF etch for stress relief) the outer surface of the cell is also 
> advisable to eliminate light pipe effects in the cell wall.
> Bruce 
> 
>On Wednesday, 11 January 2017 3:54 PM, Bruce Griffiths 
>  wrote:
> 
> 
> A goal with ADEV ~ 1E-13/Tau (for Tau <1000sec) may be feasible as its 
> already been done as part of a PhD thesis.Using as large a cavity as possible 
> is probably useful so that a large cell can be employed.What resonant mode is 
> desirable in the cavity?Do we need to avoid field reversal as in the hydrogen 
> maser?
> Bruce  
> 
>On Wednesday, 11 January 2017 3:43 PM, Bob Camp  wrote:
> 
> 

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Re: [time-nuts] hm H Maser

[Bob Camp]

Hi

A cryo pump will get you into reliability issues if run 24/7. It also is 
doubtful 
that you will be able to maintain the vacuum level over long periods.

Bob

> On Jan 11, 2017, at 12:09 AM, Bruce Griffiths  
> wrote:
> 
> One could always use a cryo pump.
> The following paper is a summary of the current state of the art for rubidium 
> vapour frequency 
> standards:http://www.euramet.org/Media/docs/Repository/A169/IND55/micalizio_02182015.pdf
> 
> Bruce 
> 
>On Wednesday, 11 January 2017 5:15 PM, Ole Petter Ronningen 
>  wrote:
> 
> 
> Add to this ion-pumps (in the case of EFOS type masers 2 every ~2 years),
> plus substantial tooling (turbomolecular vacuum pump, anyone?) to service
> the thing - unless you want the manufacturer to do so..
> 
> Ole
> 
> On Tue, Jan 10, 2017 at 11:12 PM, Dr. David Kirkby (Kirkby Microwave Ltd) <
> drkir...@kirkbymicrowave.co.uk> wrote:
> 
>> On 10 January 2017 at 15:35, Ole Petter Rønningen 
>> wrote:
>> 
>>> ... having said that, I for one think I'm with Bob on this one. The thing
>>> about masers are that they are big. At least active masers. And they
>>> require a substantial volume be kept at ultra high vacuum - which is not
>>> trivial, especially not in a homeshop. The cavity needs to be kept at a
>>> temperature stable to 0.001 degree C. With 4-5 magnetic shields. Add to
>>> this costly pumps to keep the vacuum this low even if you succeed at
>>> reaching that vacuum.. There's easily 1-2KUSD running cost per year just
>> to
>>> keep the maser running.
>>> 
>> 
>> Looking at the Microsemi MHM 2010 Active Hydogen Maser data sheet, the
>> maser has a peak power of 150 W and an operating power of 75 W.  Based on a
>> power consumption of 75 W, that is 657 kW hr / year of energy. I pay around
>> £0.20 (GBP) per kW hr for electricity, so that's £131 (GBP) annually. I
>> believe electricity is cheaper in the USA than here in the UK, but
>> converting £131 (GBP) to USD, that's around $161/year in electricity.. So
>> running costs don't seem to be an issue.
>> 
>> But I must admit, the thought of spending a lot of time/money to build
>> something I could have bought for a lot less with higher performance is not
>> that attractive, although of course there would be a satisfaction from
>> building it yourself.
>> 
>> Dave
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Re: [time-nuts] hm H Maser

[Poul-Henning Kamp]

In message <619617e1-aa26-4eb7-b73e-042f22912...@n1k.org>, Bob Camp writes:

>I guess the question then would be: 
>
>Is a H Maser that runs 6.6 x 10^-12 at 1 second worth the trouble? 

I would say absolutely not.

All things considered, I think a trapped-ion type standard would
be both much more feasible and much more worth it.

Heck, just getting an optical comb working would be awesome...

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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Re: [time-nuts] hm H Maser

[Poul-Henning Kamp]

In message <0C641805E0824C499D3C15F67F0B880B@pc52>, "Tom Van Baak" writes:

>To keep a maser room within 1 C or 0.1 C takes much more power [...]

Forget the power:  Look at the installation costs.

If you want to be able to go in and pat your maser, the air volume
and flow has to be big enough that the 100W heating and increased
humidity you bring does not throw your environment system off balance.

For +/- .5K, you can do that in an existing room.

You need something like 20-40 square meters with about 20cm thermal
insulation in all directions, and a two level 10:1 heat/cool
ventilation kit, capable of handling your local climatic excursions.


For +/- 50mK, building-in-building design is required.

You probably need at least 100 square meters in the interior building
if you want to be able to go in there and stay in tolerance and you
can only stand downwind from the maser at all times.

You will need to think a lot about power fluctuations.  Lightning
must be permanent ON and you may need voltage regulation.  Sunlight
through windows are VerBoten.

You will need a three level 100:10:1 heat/cool A/C setup, and the
":1" level is too big for TECs.  You'll need very competent mixing
(I hope your wife likes the look of the Pompidou center) and even
more competent measurement and regulation.

Building-in-building-in-existing-barn is probably the cheapest you
can do this, and the maser is certainly going to be cheaper.

-- 
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Re: [time-nuts] 5ms glitch on WAN ntp server peerstats at around 01:00 UTC today

[Mike Cook]

Hi Dan,
Everything seems pretty much back to normal this morning. I’ll have to take 
another look at yesterdays data to see when that happened. I’ll add a suitable 
graph to my site as an example of wide area routing induced offset glitches.
Mike

> Le 11 janv. 2017 à 00:14, d...@drown.org a écrit :
> 
> On Jan 10, you wrote:
>> I saw 5ms offset jumps on most of the internet ntp servers that I am using 
>> at about 01:00UTC today. The servers are as widespread as NIST Boulder, NPL 
>> UK, Hungary, Scotland, Spain, France, Czechoslovakia.
> 
> Did the RTT change at the same time?  5ms offset change might show up as a 
> 10ms increase or decrease in latency.
> 
> I saw a jump a few hours later reaching utcnist2.colorado.edu:
> 
> 
>   Date (UTC) Time IP Address   L St 123 567 ABCD  LP RP ScoreOffset  
> Peer del. Peer disp.  Root del. Root disp.
> 
> 2017-01-10 02:57:48 128.138.141.172 N  1 111 111   10 13 1.00 -1.260e-02  
> 4.826e-02  1.003e-06  2.441e-04  4.883e-04
> 2017-01-10 03:15:02 128.138.141.172 N  1 111 111   10 13 1.00 -9.482e-03  
> 5.012e-02  1.003e-06  2.441e-04  4.883e-04
> 2017-01-10 03:32:19 128.138.141.172 N  1 111 111   10 13 1.00 -1.173e-02  
> 4.629e-02  1.003e-06  2.441e-04  4.883e-04
> 2017-01-10 03:49:35 128.138.141.172 N  1 111 111   10 13 1.00 -1.268e-02  
> 4.887e-02  1.003e-06  2.441e-04  4.883e-04
> 2017-01-10 04:06:51 128.138.141.172 N  1 111 111   10 13 1.00 -1.256e-02  
> 4.922e-02  1.003e-06  2.441e-04  4.883e-04
> --- RTT (Peer del.)/Offset changes here
> 2017-01-10 04:41:15 128.138.141.172 N  1 111 111   10 13 0.88 -5.550e-04  
> 2.369e-02  1.002e-06  2.441e-04  4.883e-04
> 2017-01-10 04:58:23 128.138.141.172 N  1 111 111   10 13 0.78 -1.634e-03  
> 2.340e-02  1.687e-06  2.441e-04  4.883e-04
> 
> https://dan.drown.org/vps3/latest/remote-statistics.128.138.141.172.png
> 
> You can see from the graph this offset change was most likely a change in 
> both routes (request and response) between my server and the utcnist2 server.
> 
> I saw one other server change latency at around the same time.  It's possible 
> one of the backbone networks was doing maintenance work.

"The power of accurate observation is commonly called cynicism by those who 
have not got it. »
George Bernard Shaw

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[time-nuts] WWVB Simulator

[M. Simon via time-nuts]

After doing some more design work on my WWVB simulator I came up with a DC way 
to change output levels from 2 V to 2 uV (p-p). in 20dB steps. That would be at 
"full power" output. Reduced output will be 17 dB down from that. Well into the 
weeds at low signal levels. That would be quite some trick with computer 
simulation. 

Of course the 2 uV is going to be noisy. When isn't that the case? 

That should be good for testing receivers across the whole range of possible 
amplitude inputs. Note that the results may be problematic at and below below 
200 uV. Still, an indication is better than no results. 

I'm also looking into an absolute value circuit vs a Costas Loop and gating to 
get the phase of the received signals correct. It should be easier in some 
respects (no temporary glitches when the phase changes). And harder in others - 
frequency response will be a trick - and a pair of very well matched resistors 
is needed. They are not very expensive these days. 

Fortunately neither absolute accuracy nor accuracy across a band of frequencies 
is necessary. The circuit just needs to be stable (enough). And respond equally 
to positive and negative cycles. 

When I get my test set built and tested I'm going to do some experiments.  
Engineering is the art of making what you want from what you can get at a 
profit. 
I like Polywell Fusion.
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