Thinking outside the box a super reference
Hoi Rick,
On Sat, 5 Nov 2016 07:17:21 -0700
"Richard (Rick) Karlquist" richard@karlquist.com wrote:
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.
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:
Hoi Rick,
On Sat, 5 Nov 2016 07:17:21 -0700
"Richard (Rick) Karlquist" richard@karlquist.com wrote:
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.
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
Attila, PHK, et al --
Rb maser proposal, including some photos. 3 PDF's, 175 pages of weekend reading:
https://archive.org/details/NASA_NTRS_Archive_19720025867
https://archive.org/details/NASA_NTRS_Archive_19730017775
https://archive.org/details/NASA_NTRS_Archive_19750006044
/tvb
On 11/05/2016 03:16 PM, Attila Kinali wrote:
On Sat, 05 Nov 2016 12:25:35 +0000
"Poul-Henning Kamp" phk@phk.freebsd.dk wrote:
Active maser like the hydrogen would be possible naturally, but would
require the resonator.
I don't think they are.
They are. It took a while, but they have been a thing since '64.
Though all of them have been using vapor cells.
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.
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.
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:
On Thu, 3 Nov 2016 16:37:06 -0400
Ruslan Nabioullin rnabioullin@gmail.com 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:
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 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:
Attila, PHK, et al --
Rb maser proposal, including some photos. 3 PDF's, 175 pages of weekend reading:
https://archive.org/details/NASA_NTRS_Archive_19720025867
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.
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.
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.
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:
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.
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.
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
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
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:
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.
Ah.. neat! That's a nice way to avoid any stray field!
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.
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:
On 11/03/2016 06:10 PM, Attila Kinali 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 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?
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.
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?
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.
Or for
lower-budget and/or higher-MTBF setups, the same for a rubidium standard
and OCXO standards, resp.)
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)
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.
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.