On 11/03/2016 04:07 PM, Bert Kehren via time-nuts wrote:

What about instead establishing an open-source hardware project for a
frequency standard fusor?  I was researching COTS solutions for this for
my rubidium ensemble and could only find this one product, which
obviously should be exorbitant in cost:
http://vremya-ch.com/english/product/indexe817.html?Razdel=11&Id=54

-Ruslan

Hi

Since you can buy a working Rb that runs to a given level. My assumption is that
the objective is to do something that is significantly better than you can get for $100
or less.  I see no point in setting up to build a device that it 10X worse and costs 10X
more money.

Making the physics package of a good Rb takes a lot of custom tooling. It also takes
a bunch of engineering experiments to get the process running on that tooling, You
also need to train the operators on how to do this or that with the setup.  If good performance
is the goal, you probably need some sort of quality process backing it all up.

If you look at a modern CPU as “just a handful of sand and some stuff”, it seems
pretty easy to build one in the kitchen after an hour or two of setup. When you dig
into the nasty details the line costs rapidly spiral off into the stratosphere. Atomic
standards are not quite as complex, but there still is more than just a little custom
equipment involved. $1M sounds a bit on the low side of what it might take.

Bob

On 11/3/2016 1:07 PM, Bert Kehren via time-nuts wrote:

I was on the design team for the HP 10816 mini rubidium
which leveraged the production capabilities of the
HP 5065 such as glass blowing, etc., although what we
called "glassware" was much smaller in the 10811
than the 5065.  IMHO, the glassware
is the critical item.  Of the glassware, the lamp is
probably the most finicky.  The glassware used some
glass type (forgot the number) that was only slightly
removed from fused quartz.  Very difficult to work
with.  Also, one of the Rb isotopes is slightly radioactive.
35 years ago, the guy in the next cubicle got away with
storing it under his desk.  He also happily smoked
cigarettes all day at his desk.  Another ERA.

HP IIRC supplied "RVFR" assemblies to customers who wanted
to roll their own electronics to use in military applications
where the 5065 wasn't suitable.  I would consider approaching
current manufacturers of Rb standards to see if they would
make glassware to order.

Another thing to consider is optically pumped Rb.  This is
now possible with available lasers.  There are some DARPA
projects in this area that I know of.  I can put you in
contact with the right person.  Optical pumping gets rid of
the lamp hassle and the radioactive isotope for the filter
cell.

The rest of the standard can be built in a garage using various
contract manufacturers available online.  If I can give any advice
about this project, feel free to throw me some questions.

Rick Karlquist N6RK

On Thu, 3 Nov 2016 16:07:59 -0400
Bert Kehren via time-nuts time-nuts@febo.com wrote:

I challenge your cost estimate! :-)

My guestimate on the cost for a Rb vapor cell standard would be somwhere
in the region of 2000€ to 5000€, per unit. If you add some experimentation
it might become something like 10k€ for the first unit. How do I come to
this number? A vapor cell is quite cheap, 300-500€ can buy you an off
the shelf cell. They will not have the best buffer gas filling, but they
will be good enough for at least to get a reasonable stability.

population trapping standards.

For the dual resonance standard, a cavity is required. As the vapor cell
has a predetermined form, that cannot be changed (unless one goes for
full custom cells from the beginning), the cavity has to be adapted to the
cell. This means a cavity that is resonant at the 6.9GHz, yet fits the
cell has to be designed. My guess is, that this can be done by someone
with enough experience in microwave resonant cavities/filters and simulated
using tools like OpenEMS for verification. Producing them using aluminium
should be in the order of 200-1000€ plus cost of aluminium which I guess
to be less than 100€. Excitation of the cell can be done using either
the way the super-5065 with its filter, or tuning the laser diode. Both
way work and as far as i can tell are mostly a matter of taste with a
slightly increased complexity in the control loop for the tuned laser diode.
The detection electronics for the signal can be build for probably less
than 300€/board in batches of 10, definitely less than 1000€. Complexity
should be relatively easy to handle, as we have today access to the nice
UHF devices from Hittite, which handle all the 6.9GHz and bring it down
to easy to handle frequencies. Add a uC, some ADC and DAC and you are
basically done. For advanced features a small to medium sized FPGA (~20-50€)
can be added. If you want to be fancy, add an OCXO (like Abracon AOCJY4 or
Axtal AXIOM10HP/AXIM15) to the equation. What is missing is the magnetic
shielding, which is probably cheapest by using multiple layers of soft-iron.
Maybe using a composite of soft-iron and ferrite pads could improve things
at moderate costs. I don't think that mu-metal would be a good choice,
as it will in almost all cases need to be anealed which is not something
you can easily do (needs a furnace that goes to IIRC 800°C and can be
flooded with hydrogen)

For coherent population trapping, the cavity goes away. The excitation
is either done using a single laser that is modulated with 3.5GHz and
tuned like above, or by using two lasers that are locked to eachother
using an opto-electronic PLL (basically direct both beams at an avalance
photodiode, then use an ordinary PLL to control one of the laser).
For enhanced perfromance the two laser variant can use extenernal cavities
to narrow the laser linewidth from 10-100MHz of an "raw" laser diode
to 10-100kHz. Descriptions how to build such ECDL are available on the
net, including mechanical drawings. The price for the single diode
version is the same as the dual resonance approach, minus the cavity.
The double laser diodes add a slight cost for the OPLL (probably <100€).
An external cavity would probably be in the order of 200-500€ each.

All that said, if someone would want to tackle this project, I would
be willing to help with knowhow and electronic design. Unfortunately
due to limited finances I would not be able to invest much money.

		Attila Kinali

--
Malek's Law:
Any simple idea will be worded in the most complicated way.

On a somewhat related note....

Several years ago I pondering getting a Cs standard.  After considering the performance of my references and my stack of time interval counters I concluded that in practice I could more or less get the level of measurement accuracy I wanted by comparing the "device under test" to a reference and at the same time comparing the reference to several other references.  I wouldn't want to use this technique in a professional setting but for my hobby use I believe it met my needs.

In hindsight though I expect I could have bought a fairly nice Cs unit for the money I sunk into the time interval counters and the various references but that wouldn't have been as much fun.  The wear out aspects of used Cs standards are also a bit of a concern for me.  That being said a few of my time interval counters have also stopped working properly so I seem to have just traded one set of issues for another but I'm considerably more optimistic of being able to repair / re align a couple of my HP5370's than trying to revive a dead Cs standard.

All the best
Mark S

Kickstarter?

On Thu, 3 Nov 2016 16:37:06 -0400
Ruslan Nabioullin rnabioullin@gmail.com wrote:

You don't need a hardware project for this, as long as a paper clock
is enough for you. Just buy a couple of kiwi-sdr (or anything similar),
provide all of them with a common clock source and you get a comparison
of all your atomic clocks with minimum effort and can build from that
a paper clock easily. The paper clock can than be used for the measurement
you do, using one of the atomic clocks (preferably the one with the lowest
phase noise) as reference.

If you really want to have a physical realization, things become quite
interesting and not easy to handle. There are two parts of the problem,
one is to steer an frequency source accurately, and the other is to
generate the steering value in realtime. Neither of those is trivial.
Especially for the latter one, there is still a lot of research going on.

		Attila Kinali

--
Malek's Law:
Any simple idea will be worded in the most complicated way.

On 11/3/16 1:54 PM, Bob Camp wrote:

Two books everyone contemplating this should have:

Procedures in Experimental Physics, John Strong
Roll your own, in the 30s and 40s.

Building Scientific Apparatus, Moore, Davis, Coplan, and Greer
Vacuum systems, Ion optics, Temperature control, etc. etc.

https://www.amazon.com/Procedures-Experimental-Physics-John-Strong/dp/0917914562

https://www.amazon.com/Building-Scientific-Apparatus-John-Moore/dp/0521878586

I figure everyone on this list is already sufficiently knowledgeable
about oscillators, amplifiers, etc.

On Thu, 3 Nov 2016 16:54:24 -0400
Bob Camp kb8tq@n1k.org wrote:

Not necessarily. There is a large corpus of knowledge available on
how to build vapor cells standards and what is a good idea and what
isn't. Most of it is documented in papers of the PTTI, EFTF and IFCS.
The former two are freely available (for PTTI until 2010, but that
should be good enough). Getting access to those papers behind a
paywall, you only need to know someone with access to a university.
(not for PTTI post 2010 though, ION has quite anal access rules)

Additionally, the people in the time and frequeny community are very
open to discussion and exchange of knowledge. You can almost always
just walk up to someone and ask questions with a high chance of getting
not only answers but help in how to proceede.

Tapping into this knowhow would avoid the need to try out the whole
solution space and concentrate on the few parts that are unkown or
not well enough understood and optimize those. And by doing so safe
a lot of money.

		Attila Kinali

--
Malek's Law:
Any simple idea will be worded in the most complicated way.

There is at least one recent thesis where a dual resonance rubidium vapor cell was built and used to lock a low noise OCXO,The machining of the cavity didnt appear particularly challenging nor did the locking of the laser to the relevant wavelength using an auxiliary rubidium vapour cell.IIRC thee performance was better than the telecom market rubidium standards.
Bruce

On Friday, 4 November 2016 11:34 AM, Attila Kinali <attila@kinali.ch> wrote:

On Thu, 3 Nov 2016 16:54:24 -0400
Bob Camp kb8tq@n1k.org wrote:

Not necessarily. There is a large corpus of knowledge available on
how to build vapor cells standards and what is a good idea and what
isn't. Most of it is documented in papers of the PTTI, EFTF and IFCS.
The former two are freely available (for PTTI until 2010, but that
should be good enough). Getting access to those papers behind a
paywall, you only need to know someone with access to a university.
(not for PTTI post 2010 though, ION has quite anal access rules)

Additionally, the people in the time and frequeny community are very
open to discussion and exchange of knowledge. You can almost always
just walk up to someone and ask questions with a high chance of getting
not only answers but help in how to proceede.

Tapping into this knowhow would avoid the need to try out the whole
solution space and concentrate on the few parts that are unkown or
not well enough understood and optimize those. And by doing so safe
a lot of money.

            Attila Kinali

--
Malek's Law:
        Any simple idea will be worded in the most complicated way.

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and follow the instructions there.

Hi

Not many people have had exposure to Rb’s or Cs standards actually being
built. That leaves a major gap in who you can call when you run into a problem.

Until you have tried to build one it’s not at all clear just how much “missing information” there
is in all those papers. It’s very much like the semiconductor business. Lots of
information is published. There are indeed lots of gaps. At some point you must
build tooling and get it all working.

Again, we are talking about a device that is at least as good as a 5065 and not
something that just barely works. If you could build something better than a 5065
for a thousand or two dollars, it would be on the market today.

Bob

Attached graph indicates ADEV achieved with a 25mm double resonance Rb vapour cell 
Performance appears somewhat better than HP5065A (even Corby's souped up version).
The thesis (by  Thejesh N. Bandi) on this double resonance Rubidium vapour cell in a Magnetron style cavity was completed at the University of Neuchatel.
Bruce

On Friday, 4 November 2016 11:58 AM, Bruce Griffiths <bruce.griffiths@xtra.co.nz> wrote:

There is at least one recent thesis where a dual resonance rubidium vapor cell was built and used to lock a low noise OCXO,The machining of the cavity didnt appear particularly challenging nor did the locking of the laser to the relevant wavelength using an auxiliary rubidium vapour cell.IIRC thee performance was better than the telecom market rubidium standards.
Bruce

    On Friday, 4 November 2016 11:34 AM, Attila Kinali attila@kinali.ch wrote:

On Thu, 3 Nov 2016 16:54:24 -0400
Bob Camp kb8tq@n1k.org wrote:

Not necessarily. There is a large corpus of knowledge available on
how to build vapor cells standards and what is a good idea and what
isn't. Most of it is documented in papers of the PTTI, EFTF and IFCS.
The former two are freely available (for PTTI until 2010, but that
should be good enough). Getting access to those papers behind a
paywall, you only need to know someone with access to a university.
(not for PTTI post 2010 though, ION has quite anal access rules)

Additionally, the people in the time and frequeny community are very
open to discussion and exchange of knowledge. You can almost always
just walk up to someone and ask questions with a high chance of getting
not only answers but help in how to proceede.

Tapping into this knowhow would avoid the need to try out the whole
solution space and concentrate on the few parts that are unkown or
not well enough understood and optimize those. And by doing so safe
a lot of money.

            Attila Kinali

--
Malek's Law:
        Any simple idea will be worded in the most complicated way.

time-nuts mailing list -- time-nuts@febo.com
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Hi

Do you believe that they could produced in volume for < $1,000 each without
any significant setup investment?

Bob

It would obviously be larger than a homebrew Cs, but why not a homebrew
Hydrogen Maser Frequency standard?

The commercial Cs units always seemed objects of pure miniaturized hi-tech
materials science magic, while the Hydrogen Masers I've seen seem much
larger-scale\ and more a matter of vacuum plumbing. Obviously the materials
cost for the copper microwave cavity will be very large, and I'm sure
Teflon-coating a quartz chamber is an art, but the pumps and magnets are
very familiar from my years in grad school working with plasma kettles and
mass spectrometers.

Tim N3QE

On Thu, Nov 3, 2016 at 4:07 PM, Bert Kehren via time-nuts <
time-nuts@febo.com> wrote:

Hi

Ok, how many full performance Hydrogen Masers can you build (size is not an issue) and
deliver for < $10,000 (2X Bert’s number) ?

Bob

Zero. But the answer is also zero for a Rb or Cs cell!

On Thu, Nov 3, 2016 at 8:59 PM, Bob Camp kb8tq@n1k.org wrote:

Suitable ECDL laser for Rb clock:https://www.sacher-laser.com/home/industrial-lasers/point_and_line_laser_module.html
the 784.8 nm version has 0.2nm of tuning range,
Bruce

On Friday, 4 November 2016 2:43 PM, Tim Shoppa <tshoppa@gmail.com> wrote:

Zero. But the answer is also zero for a Rb or Cs cell!

On Thu, Nov 3, 2016 at 8:59 PM, Bob Camp kb8tq@n1k.org wrote:

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Hi Bert:

Have you looked into the Stanford Research PRS-10?  It a current production Rb standard with internal provision to sync
to 1 PPS.
http://prc68.com/I/PRS10.shtml
You can choose to run it like a GPSDO but it needs an external 1 PPS for that (there is no GPS receiver in the PRS-10).
Or, you can time stamp an external 1 PPS.

The company was founded by a physicist and they hire mostly physicists rather than engineers.  I like their stuff.
The crystal oscillator in the PRS-10 is the SC-10, also made by SR and comes in many flavors that among other things
trade off aging for stability.  I assume you could order a custom PRS-10 with the desired crystal oscillator specs.

Before spending a lot of money you might want to experiment with the PRS-10 and the best currently available GNS timing
receiver.

I experimented with both hardware and software sawtooth correction and they both have pluses and minuses.  I seem to
remember that CNS Systems had a sawtooth corrected GPS timing receiver that ran TAC32 software, but haven't kept up on it.

--
Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html
The lesser of evils is still evil.

-------- Original Message --------

Yes.  See attached.

On Thu, 3 Nov 2016 22:27:36 -0400, Chris Arnold via time-nuts wrote:

Bill Beam
NL7F

Thanks

Sent from AOL Mobile Mail

-----Original Message-----
From: Bill Beam wbeam@gci.net
To: Discussion of precise time and frequency measurement time-nuts@febo.com; n3izn n3izn@aol.com; time-nuts time-nuts@febo.com
Sent: Thu, Nov 3, 2016 08:46 PM
Subject: Re: [time-nuts] Lady Heather and LeapSecond

Yes.  See attached.

On Thu, 3 Nov 2016 22:27:36 -0400, Chris Arnold via time-nuts wrote:

Bill Beam
NL7F

On Thu, 3 Nov 2016 23:52:00 +0000 (UTC)
Bruce Griffiths bruce.griffiths@xtra.co.nz wrote:

The dissertation in question is:
"Double-Resonance Studies on Compact, High-performance Rubidium Cell
Frequency Standards, bay Thejesh Bandi, 2013
https://doc.rero.ch/record/32317/files/00002318.pdf

		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

You will also share the same challenges as Touchstone semi did, no one
wanted to stick their neck out to design in a little startup.

On Thu, Nov 3, 2016 at 7:49 PM, Bob Camp kb8tq@n1k.org wrote:

Hi

You are indeed effectively either doing a startup or contracting with somebody
already in the business. In a lot of ways, contracting this out might be the easier
approach. The trick there will be having enough business to make it attractive
to them.

Bob

In message 2af27ebe-9200-c348-c89b-b98f9c973974@karlquist.com, "Richard (Rick) Karlquist" w
rites:

Rb87 has a halflife north of the age of the planet as far
as I recall, and the result is a beta which goes nowhere
far and Sr87 which is stable.

He got a lot more ionizing radiation from his cigaretess than he
ever got from the Rb87.

Just for the heck of it, I'd go laser instead of the old UHF lamp.

With respect to precision machining, that space has changed a lot
over the last five years, with precision CNC machines, factory
or home-built, dropping dramatically in price.

--
Poul-Henning Kamp      | UNIX since Zilog Zeus 3.20
phk@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.

On Fri, Nov 4, 2016, at 02:27 PM, Poul-Henning Kamp wrote:

87-Rb has a half life of something like 4.9e10 years — you'll be waiting
a while for that strontium. /gp

On Friday, November 04, 2016 09:27:59 PM Poul-Henning Kamp wrote:

"Richard

Yes, the laser technique is doable even if one has to build an ECDL.
What would be nice would be a scheme that allows the same Rb filled bulb
to be used to both lock the laser to the right wavelength and to detect
that the microwave signal is also locked to the Rb microwave transition.

Bruce

Hi,

On 11/04/2016 10:27 PM, Poul-Henning Kamp wrote:

With a half-life of 49.2 Gigayears compared to universe life around 13.8
Gigayears and the beta-decay within both glas and metal enclosure, I'm
not overly concerned. For all practical purposes it is essentially stable.

The 780 nm laserdiodes isn't all that hard to get, in fact I've got some
lying around. Depolarizing needed with a quarter-wave needed not to get
a Stark-pull.

You need to tune it regardless.

Cheers,
Magnus

Hej Magnus
A quarter waveplate doesn't depolarise, it can however convert a linearly polarised beam to a circularly polarised one.If you really need to depolarise a laser beam, scattering from a colloidal suspension of Titanium dioxide is very effective.There are no macroscopic moving parts.Brownian motion of the colloidal partticels suffices.
Bruce

On Saturday, 5 November 2016 11:28 AM, Magnus Danielson <magnus@rubidium.dyndns.org> wrote:

Hi,

On 11/04/2016 10:27 PM, Poul-Henning Kamp wrote:

With a half-life of 49.2 Gigayears compared to universe life around 13.8
Gigayears and the beta-decay within both glas and metal enclosure, I'm
not overly concerned. For all practical purposes it is essentially stable.

The 780 nm laserdiodes isn't all that hard to get, in fact I've got some
lying around. Depolarizing needed with a quarter-wave needed not to get
a Stark-pull.

You need to tune it regardless.

Cheers,
Magnus

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In message 59dc074a-3a09-6315-29d4-6877c3bf7510@rubidium.dyndns.org, Magnus Danielson write
s:

First:  Yes, but if you pick a sensible vibration mode for your
microwave resonance, that can be done with an screw-in endcap.

Second:  No, I would actually not need to tune it.

Historically resonance cavities were used so that step/avalance
diode multipliers had enough power to excite them.  Today we have
semiconductors which work at those frequencies.

Later people kept the resonance, because it works well with low
power budgets in telecoms/milspec applications.

But the resonanance leads to all sorts of trouble, including frequency
pulling, temperature sensitivities etc.

We're neither space nor power constrained, we'd probably be
perfectly happy if the end result is 4U and 100W, so resonance
is not mandatory.

Third:  A lot of the "everybody knows" about which atoms can be
used for active vs. passive atomic standards comes from the
state of the art electronics about 30 years ago.

Using laser-pumping and modern semiconductors, it might actually
be possible to detect the 6.8GHz photons from the Rb.

They won't be coherent photons, like in a Hydrogen maser, but we
don't need them to be, in fact that just causes the same exact
problems as the tuned cavity anyway, as long as we can measure
the frequency well enough.

(No, I havn't done the math on this, my wife has banned me from
starting any new projects until our house is finished.)

--
Poul-Henning Kamp      | UNIX since Zilog Zeus 3.20
phk@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.

Hej Bruce,

Ah yes, that's it. Sorry for the bad wording.

Cheers,
Magnus

On 11/04/2016 11:41 PM, Bruce Griffiths wrote:

Poul-Henning,

On 11/05/2016 12:04 AM, Poul-Henning Kamp wrote:

Indeed.

Sure, but if you do have a cavity, as you was hinting at, tuning it is
still needed for the cavity pull effect.

Sure, but some behaviors just remains there when still using such setups.

You can avoid the cavity using sidebands of the pumping laser and all
that, yes I know.

Active maser like the hydrogen would be possible naturally, but would
require the resonator.

A passive direct observation would also possible, but detection will be
harder and then you would run into S/N issues.

Probably a wise thing.

Cheers,
Magnus

The N resonance discussedd in:http://walsworth.physics.harvard.edu/publications/2005_Smallwood_HUBAThesis.pdf

May be a better bet than traditional CPT.
Bruce

On Saturday, 5 November 2016 12:17 PM, Magnus Danielson <magnus@rubidium.dyndns.org> wrote:

Poul-Henning,

On 11/05/2016 12:04 AM, Poul-Henning Kamp wrote:

Indeed.

Sure, but if you do have a cavity, as you was hinting at, tuning it is
still needed for the cavity pull effect.

Sure, but some behaviors just remains there when still using such setups.

You can avoid the cavity using sidebands of the pumping laser and all
that, yes I know.

Active maser like the hydrogen would be possible naturally, but would
require the resonator.

A passive direct observation would also possible, but detection will be
harder and then you would run into S/N issues.

Probably a wise thing.

Cheers,
Magnus

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On Fri, 04 Nov 2016 14:39:54 -0700, you wrote:

Various online sources say that natural rubidium is radioactive enough
to fog photographic film in 1 to 2 months but that is also the case
with unprocessed uranium ore so I would not worry about it at all.

In message c57q1c5engv94amimot7pu3l8romu6g2p0@4ax.com, David writes:

Yes, that sounds about right for an isotope with a 40 billion years
half-life.

1 to 2 months is a LOOOONG time for photographic film.

--
Poul-Henning Kamp      | UNIX since Zilog Zeus 3.20
phk@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.

On 11/4/2016 4:04 PM, Poul-Henning Kamp wrote:

A great deal of complexity in the 5061 went into
exciting an SRD at 90 MHz and getting a sufficient
line at 9180 MHz to put on a sideband at 9192.
I spent a lot of time trying to do this during the
5071 project and was never able to get anywhere
near the efficiency that the 5061 waveguide structure
was able to do.  It was designed by a visiting Korean
professor, so he wasn't around to mentor me.
The 10816 also used an SRD, and it was also a
struggle, although I was able to make it work.

Fortunately, we were able to replace all this with a
DRO and PLL, and that was 25 years ago.  At this time,
it is even more of a no brainer that you don't want
to knock yourself out trying to make an SRD multiplier
work.  Also, these days, it is harder than ever to
purchase good SRD's.

Rick

On 11/4/2016 5:24 PM, Poul-Henning Kamp wrote:

The problem with the half life number is that the cylinder
still was marked "radioactive" complex with the radiation
symbol.  Radioactivity (for legal purposes) is a binary
property.  We used to mark CBT's "cesium device, non radioactive"
because the work "cesium" means "cesium 137 nuclear fallout"
to many people.

Reminds me of an interesting Jack Kusters story.
There was some customer who was having problems with
his atomic clocks being noisy (I don't remember exactly
the story) but the bottom line was that they determined
it was because of helium contamination.  Kusters was
called in to answer to the customer about this contamination
and how they were going to fix it.  Kusters measured the
air in the customer's plant and found that in contained
helium.  But the customer did not use helium at all in the
plant.  Kusters pointed out that that could mean only one
thing:  the plant had a radon problem, and radon breaks down
into helium.  Kusters told the customer that if they
dropped the complaint, he wouldn't have to say anything
about radon to anyone.  That was the last heard about the
helium problem.

Rick

Not to mention there is not so sensitive film, sensitive film and really sensitive film.

Good old orthographic film took minutes in bright light.

Rick on the pll DRO I agree with you for today.
So is it built for 9180 and then the 12.63 is mixed with it? Or is it
actually a direct PLL precisely at the frequency so not even the
synthesizer is used?
Regards
Paul
WB8TSL

On Fri, Nov 4, 2016 at 9:40 PM, bownes bownes@gmail.com wrote:

On 11/4/16 5:27 PM, Richard (Rick) Karlquist wrote:

You can get a nice GaAs VCO that will tune 9GHz with no sweat, and the
PLL parts to go around it. I'm not sure what the DRO market is these
days - You can probably build a synthesizer with lower DC power with a
DRO than using GaAs (although CMOS is getting ever better and getting up
to that kind of range).  There are probably low cost low precision
(unlocked) designs like LNBs that use a DRO.

But things like 10 GHz microwave motion detectors these days use VCOs,
not DROs.

DROs are subject to microphonics and such - yes, the dominant resonance
is the puck, but the cavity it's in affects it too, so vibration and
temperature have effects.

In message 768ee5a7-1c53-06cf-cf36-ec75e290177e@karlquist.com, "Richard (Rick) Karlquist" w
rites:

How would helium make his clocks noisy ?

Isn't it more likely that it was the alphas from the
radon decay that did it by their charge ?

--
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Never attribute to malice what can adequately be explained by incompetence.

On Fri, 04 Nov 2016 23:04:22 +0000
"Poul-Henning Kamp" phk@phk.freebsd.dk wrote:

Yes, it is easier to create the required frequencies with high power
(getting 7GHz with 10dBm is trivial and 30dBm can be readily achieved
with single chip amplifiers) and the signal will be cleaner than what
an SRD setup can achieve (no spurs, comparable close-in phase noise
characteristic). Thus we can use cavities with lower Q which are easier
to build and tune. But we still need to ensure that the field is properly
oriented and homogenous over the whole vapor cell. For this you need
a cavity that is properly designed and most likely will be resonant at 6.9GHz.
(I don't know whether it is possible to design a non-resonant cavity with
the above properties)

Frequency pulling is not so much of an issue for a vapor cell standard
as it is for hydrogen masers or the primary standards. The shifts due
to buffer gas and wall collisions are so large that a calibration is
needed anyways. Frequency pulling just adds another term. Temperature
sensitivity is IIRC lower for frequency pulling than for buffer gas shift,
but I could be mistaken. For high stability applications, temperature
stabilization of the cavity and the cell are advised anyways.

A lot of the "everybody knows" has been challenged and rewritten
in the past 10-20 years. Although, it looks like the vapor cell
standards have not changed in 50 years, there has been a lot of
research going on and people optimized old ideas and came up with
new ones. Yes, a lot of the electronics design is rather crude,
but most of the people working in the field a physicists or electrical
engineers that just graduated, one cannot expect the level of skill
and expertise of someone who has been doing RF designs for 30 years.
Beside, these people are there to do research, not to design electronics.
The circuits are just a tool for the research, not their main topic.
Hence they rather spend 100k€ on a synthesiser from keysight instead
of spending 6 months for designing their own to save money.

You mean an optically pumped active maser? (our vapor cell standards
are passive masers allready) This has been already done in the 60's[1]
and studied later again (eg [2]). I guess this isn't popular because
the short term stability of Rb vapor cell standards is already quite
good and the long term stability does not get improved. So it does not
justify the additional complexity.

If you mean to detect the decay from the 5S hyperfine splitting,
then i have to disapoint you. There will not be much radiation to detect.
On one hand, the lifetime of the hyperfine splitting is quite long, thus
the electrons will just get stuck on the upper level after they fell
down from the 5P state (it's a forbidden transition after all).
A photon to stimulate the fall to the lower state is required, either
provided by spontaneous emission from other Rb atoms or from an external
source. On the other hand, if the photons are not coherent, they will
not build up a signal that one could detect. They will just be spikes
that get burried in noise. Yes, one could build a spectrometer which would
average over a lot of these photons, but that would require a stable
frequency source to be able to avearge for a long time. And I don't think
a simple OCXO is up to this task.

		Attila Kinali

[1] "The Optically Pumped Rubidium Maser", by Davidovits and Novik, 1966
http://dx.doi.org/10.1109/PROC.1966.4628

[2] "Experimental Study of the Laser Diode Pumped Rubidium Maser",
by Michaud Tremblay and Tetu, 1991
http://dx.doi.org/10.1109/TIM.1990.1032908
https://arxiv.org/abs/physics/0508227

--
Malek's Law:
Any simple idea will be worded in the most complicated way.

Am 05.11.2016 um 00:45 schrieb David:

That's next to nothing. A friend of mine with interest in minerals found a
piece of Pechblende (Uranit) simply laying on the street near
St.Joachimsthal
where they used to dig for silver over the centuries and after 1945 for
uranium.

We put it on a sheet of Polaroid film for the Tektronix scope cameras and
sure enough, next morning we could see the silhouette of the stone,
completely white, probably way overexposed.

regards, Gerhard

In message 0e976194-3cc1-2bc7-1289-0d9433132d31@rubidium.dyndns.org, Magnus D
anielson writes:

I don't think they are.

With hydrogen, hitting the excited electron with the right frequency
increases the probability of coherent emission of the photon enough
that you get to the "SE" we know from LASER and MASER.

As I understand it not all excited modes of all atoms and molecules
have the not-quite-pinned-down quantum-thaumagic property to do that.

And I remember reading somewhere that the alkali atoms have been
poked and prodded to no end about this, in the hope of creating
active Cs, Rb or Sr frequency standards, but the very reluctant
(and expensive) conclusion was that hydrogen is the only one in the
family which knows the trick.

--
Poul-Henning Kamp      | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG        | TCP/IP since RFC 956
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Never attribute to malice what can adequately be explained by incompetence.

On 11/5/16 2:59 AM, Attila Kinali wrote:
But we still need to ensure that the field is properly

isn't a TEM cell, as used in EMI/EMC testing, something like this?  It's
a tapered transmission line and produces a uniform field within an area
inside the line.

On Sat, 05 Nov 2016 12:25:35 +0000
"Poul-Henning Kamp" phk@phk.freebsd.dk wrote:

They are. It took a while, but they have been a thing since '64.
Though all of them have been using vapor cells.

Nope, the problem, as far as I understand it, is not that you cannot
get the atoms to emit, but to keep them in one place without perturbing
them. For hydrogen, a teflon coating does a very good job and the atom
can go for many wall collisions without losing its state/phase. Even the
early hydrogen maser got to >10^4 collisions and modern coatings offer
something like 10^6 IIRC, ie the life time is measured in seconds
to minutes.

Until recently, there didn't exist such a coating for Rb or Cs [1] and
relaxation time was measured in milliseconds. For comparison, have a look at
page 37 of Bandi's dissertation[2], the broadening due to wall collisions
is stated as 300Hz for the wall coated, evacuated cell, while the buffer
gas collision broadening is a mere 10Hz (yes, I am cheating here, the
correct comparison would be the total broadening which is 350Hz vs 600Hz).
Yes, the wall shift is smaller than the buffer gas shift (4000Hz vs 300Hz)
but this is in first order approximation a constant.

Additionally, all the coatings have rather low temperature limits
(the hydrocarbon coatings are very similar to parafin wax) and the
high temperatures that were needed for the Rb lamps didn't work togheter.
And even for modern laser pumped systems, you still need a rather high
temperature (40-90°C are usual) to get a high enough amount or Rb in the cell.

I guess you can understand that people have not been using vapor cell
active masers because they do not offer the long term stability one
seeks (due to buffer gas changes) and their short term stability is
not any better than the passive masers (limited by buffer gas relaxation).

Probably, with the new coatings and laser pumping one could build a usable
Rb active maser with evacuated cells instead of buffer gas. But sofar
nobody has tried that yet (as far as I am aware of). I guess it's more
sexy to investigate optical standards than something as old as Rb.
Especially as there are already Rb fountains[3] which offer quite a
high stability already.

		Attila Kinali

[1] "Polarized Alkali-Metal Vapor with Minute-Long Transverse
Spin-Relaxation Time", by Balabas, Kraulanov, Ledbetter, Budker, 2010
http://dx.doi.org/10.1103/PhysRevLett.105.070801

[2] "Double-Resonance Studies on Compact, High-performance Rubidium Cell
Frequency Standards", by Thejesh Bandi, 2013
https://doc.rero.ch/record/32317/files/00002318.pdf

[3] "The USNO rubidium fountains", by Peil et al. 2015
http://dx.doi.org/10.1088/1742-6596/723/1/012004

Malek's Law:
Any simple idea will be worded in the most complicated way.

I think this is all described in the 1992 FCS papers,
but the executive summary is that a direct synthesizer
on 9192.63177 is to be avoided at all costs because
of the danger of it leaking into the CBT cavity.
This is also the reason why you don't multiply up
a subharmonic of this frequency.
It would also have made the synthesizer a lot more
complicated.  We multiplied 10 to 320 and then used
an SRD to get to 9280 and applied a sideband at 87.36
MHz to it.  The 87.36 MHz synthesizer was a phase
locked VCXO using a 5th OT crystal.

It took me a long time for me to sell this to Len Cutler.
It was pretty advanced for 1989.

Rick

On 11/4/2016 7:12 PM, paul swed wrote:

On Sat, 5 Nov 2016 06:53:45 -0700
jimlux jimlux@earthlink.net wrote:

Yes, they fullfill the "constant field" condition, but not the "properly
oriented" condition. The field in these cells has still a quite considerable
curl. One can of course minimize that by building a larger one, but
then there are smaller structures with similar properties, when one does
not need the the wideband property of those TEM cells.

		Attila Kinali

--
Malek's Law:
Any simple idea will be worded in the most complicated way.

On 11/5/2016 12:18 AM, Poul-Henning Kamp wrote:

I probably am not remembering the story exactly, but
I do definitely remember it had to do with unexplained
helium, which they tried to blame Kusters company for.
He said there was a simple explanation, namely radon
gas emitting alpha particles that turn into helium
and helium can diffuse into "sealed" containers.
He basically told them that if they dropped the issue,
it wouldn't be necessary for him to publicize the fact
that their plant was full of radon.  It was really
funny when Jack himself told it.

Rick

Hoi Rick,

On Sat, 5 Nov 2016 07:17:21 -0700
"Richard (Rick) Karlquist" richard@karlquist.com wrote:

I don't get what you mean with "danger of leaking into the CBT cavity"?
When signal leakage into the cavity is a problem, shouldn't that also
exist for the signal after the mixer? And what does this leaking actually
mean? The 9192.63177 is supposed to end up in the cavity anyways.

		Attila Kinali

--
Malek's Law:
Any simple idea will be worded in the most complicated way.

One of the main limiting factors in the 5061 was
microwave leakage.  An excellent Italian engineer
named DiMarchi mastered the so called "top cover
effect", where removing the top cover changed the
frequency.  He had a small business going refurbishing
5061's by cleaning up the waveguide gasketing, etc.
If any 9192.63177 reaches the beam at one end or
the other, it will upset the phase balance.  In
the 5071, phase balance is the main limiting factor
in accuracy.  They go to extreme measures to make
the cavity absolutely symmetrical using fabrication
techniques analogous to "self aligning" IC masking.
In the 5071, the only place 9192 shows up is in the
microwave module that is directly attached to the
coax to waveguide transition into the cavity.
There are no frequencies anywhere that are sub
harmonics of 9192.  Incidentally, there are no
frequencies anywhere that are coherent with
50 Hz, 60 Hz, etc line frequencies.  Nothing
is by accident when Len Cutler is involved.

In terms of basic synthesizer architecture, the
mix from 9280 to 9192 using 87 is described by
the technical term "free lunch" :-)  We pick
up two decades of resolution.  Furthermore, we
don't have to filter out 9280 or 9367 because
they are ignored by the CBT.  One of the reasons
for going up from 12 to 87 was to get these
spurs safely removed from anything that would
interact quantum mechanically with the cesium
line tail.  With the increased accuracy, 12
was no longer high enough.

Rick

On 11/5/2016 7:39 AM, Attila Kinali wrote:

On 11/05/2016 03:16 PM, Attila Kinali wrote:

Hydrogren maser is really a development out of the beam device, through
the intermediary step of a beam device who's beam is extended with a
"bounce box" to increase the time between the two Ramsey interegation
zones. The quick decorrelation due to the wall-bounces for many atoms
made this impractical except for the hydrogen, and the hydrogen maser is
a refined variant of it.

In the end of the day, many of the classicial atomic clocks and the
choice of elements for them is really dependent on what is "practical".

Cheers,
Magnus

On 11/03/2016 06:10 PM, Attila Kinali wrote:

If it's so relatively straightforward, then why not establish such a
project instead of reinventing the wheel by attempting to perform atomic
standard R&D and fabrication on a shoestring?  It should be much more
practical, even considering the fact that one will obtain diminishing
returns on the ensemble's n, and furthermore should be extremely
successful---apparently only a single Russian company holds a global
monopoly on this product, apart from custom-fabricated setups in
national metrology labs, and numerous people would benefit (why purchase
an exorbitantly-expensive and short-lifespan cesium standard when one
can fuse a redundant ensemble of rubidium standards?  Or for
lower-budget and/or higher-MTBF setups, the same for a rubidium standard
and OCXO standards, resp.)

Another project, much simpler in comparison but even more useful, would
be a rack-mount standard for an OCXO or rubidium physics package, which
should consist of just a chassis, power supply, thermal structure, and a
monitoring subsystem with interfaces (LEDs, an LCD display, and
RS-232/USB/GPIB/Ethernet).  The used market is flooded with cheap
physics packages, yet actual standards are uncommon and expensive.

-Ruslan

In message FFC6EFF7EA124D6392339DADF8A5CD10@pc52, "Tom Van Baak" writes:

Interesting!

As is this:

https://arxiv.org/abs/physics/0508227

--
Poul-Henning Kamp      | UNIX since Zilog Zeus 3.20
phk@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.

FWIW we have the remains of this experiment somewhere in the basement - but
no time or resources to really play with it...
http://lib.tkk.fi/Diss/2010/isbn9789526035024/article4.pdf
Fig 3 is a fairly clear overview of the two cells and loops, one for
stabilizing the laser wavelength, and one for the 3 GHz
sidebands/clock-transition.
For hobby tinkering I would expect the Rb-cells and the optical isolator to
be hard/expensive to source. Otherwise the electronics needed looks
DIY-able.

Anders

Neither Rb cells nor isolators are difficult to source.They are both catalog items. However if using a cavity it may need to be tailored to the available cells.Walk-off isolators using double refraction are somewhat more convenient than those requiring a strong magnetic field.
Bruce

On Sunday, 6 November 2016 10:10 PM, Anders Wallin <anders.e.e.wallin@gmail.com> wrote:

FWIW we have the remains of this experiment somewhere in the basement - but
no time or resources to really play with it...
http://lib.tkk.fi/Diss/2010/isbn9789526035024/article4.pdf
Fig 3 is a fairly clear overview of the two cells and loops, one for
stabilizing the laser wavelength, and one for the 3 GHz
sidebands/clock-transition.
For hobby tinkering I would expect the Rb-cells and the optical isolator to
be hard/expensive to source. Otherwise the electronics needed looks
DIY-able.

Anders

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and follow the instructions there.

Hoi Rick,

Thanks for the detailed explanation!

On Sat, 5 Nov 2016 08:32:58 -0700
"Richard (Rick) Karlquist" richard@karlquist.com wrote:

Ah.. neat! That's a nice way to avoid any stray field!

Interesting. I guess the choice not to sync to line frequency
was to avoid any kind of offset that would cause and instead
let the system "average" the line noise?

		Attila Kinali

--
Malek's Law:
Any simple idea will be worded in the most complicated way.

Hoi Ruslan,

On Sat, 5 Nov 2016 14:30:18 -0400
Ruslan Nabioullin rnabioullin@gmail.com wrote:

Could it be that you didn't see my small note on "paper clock"?
A paper clock is a virtual clock, one which only exists as list of
numbers in a computer. One that comes only into existence after the fact.
You create it by measuring all the clocks against each other, run your
ensemble algorithm on it and then you have a list that shows how each
clock deviated from the ensemble time.

This is the prefered over steering a clock for many reasons, but sometimes
a real physical realization of an ensemble clock is needed.

But even if you have a lot of atomic clocks, and a paper clock is all
you need, building an ensemble is not an easy task and there are lots
of little traps that one can fall into. One that is easy to see is, if
your clocks have a common source of instability, that is the same for all,
then this instability will not average out. The most common of these
instabilities is temperature variations, which affects especially Rb vapor
cells. Easy to keep stable you say? How about atmospheric pressure?
Humidity? Magnetic fields? The second trap most people fall into is
that adding and removing a clock from the ensemble causes a jump in
phase unless you do special adjustments. How to do them is definitely
not obvious.

I recommend reading at least Monographie 1994-1[1]. If you are interested
in building your own time scale, I can recommend you reading the papers
by Patrizia Tavella and Judah Levine in general. They give good overviews
of what the state of the art and its problems is and how to possibly
improve it.

Measuring the phase differences between the clocks is the easiest part
of it. Be it with some SDR setup that does everything in digital, or
with an almost completely analog DMDT setup. For a hobbyist grade system,
where ps to 100fs level of synchronization is sufficient, I would go
with a simple high-speed ADC based system that does everything in
an FPGA. The paper by Sherman and Jördens[2] tells you what you need
to do. And the book "Understanding Digital Signal Processing" by Loyds
contains all the information you need to actually implement it.

They do not hold a monopoly on this kind of thing. It is more like
that the economics of such a product are that you will probably not
make any money from developing it. Beside the national labs that have
to produce a physical representation of UTC for one reason or other,
there are very few people who actually need something like this.
For most people a single GPS stabilized Rb standard is way better than
they require. Heck, I know of one guy who lost the GPS on his Rb-GPSDO
and didn't bother to replace it because "it wont lose more than a couple
of ms per year anyways".

And for those who need a physical realization of an clock ensemble, the
requirements can differ wastly. To the point that a single product might
not be able to fullfill the requirements of more than one or two labs.
Hence a lot of national labs build there own, from a time difference
measurement system and a phase/frequency microstepper, with some
computer inbetween that implements the algorithm (usually their own algorithm).

Besides, as I wrote before, creating a real-time realization of an
ensemble clock is not trivial at all. Neither phyisically/electronically
nor algorithmically. Do not underestimate the number of problems you
might run into when trying to do that.

A small annectode regarding this:
At an EFTF a couple of years ago, there was a presentation on the current
state of the GPS system, how they were doing things and how they planned
to improve it. The topic of the local GPS-time timescale got mentioned
and they said that they switched from a physical representation to a pure
paper clock some years ago. Apparently, the problems a physical representation
created were not easy to overcome and it didn't give much added value
over a paper clock. They also mentioned, due to the experience they had,
that they cannot understand why Galileo insists on having a phyical
representation.
And these are probably the two time labs with the largest available budget.

I think you got your MTBF backwards. Adding more clock decreases MTBF.
The more components you have, the more likely it is that anyone of
those will fail. For a nice and easy to understand description of this,
google for MTBF on RAID systems.

If you insist on doing a fault-tolerant ensemble algorithm, then I welcome
you to a nice field of research, where basically nothing exists yet.
(There exist faul-tolerant clock syncrhonization systems, but none of
them have been analyzed with ensembles in mind and often have very low
synchornization capabilities)

What do you mean by a "rack-mount standard"? A simple oscillator
in a rack-mount chassis with some electronics around it? What makes
this different from all the contraptions we usually build?

		Attila Kinali

[1] "Time Scales", BIPM Monographie 1994-1, by Thomas, Woldf and Tavella
http://www.bipm.org/utils/common/pdf/monographies-misc/Monographie1994-1.pdf

[2] "Oscillator metrology with software defined Radio",
by Sherman and Jördens, 2016

--
Malek's Law:
Any simple idea will be worded in the most complicated way.