In message 000001c701a5$5f076420$0202fea9@athlon, "Ulrich Bangert" writes:

This is because rubidium vapour standards are not primary standards.

They don't have a "correct" frequency, only a very stable frequency.

The actual resonance frequency of a rubidium standard depends amongst
other things on the partial pressures inside the physics package.

--
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phk@FreeBSD.ORG        | TCP/IP since RFC 956
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Never attribute to malice what can adequately be explained by incompetence.

Hi Poul-Henning,

We are well aware of these facts! But if THAT were the reason to correct
for with different thumbwheel settings would not EVERY rubidium standard
in the world desperately need this kind of correction feature?

Both my FRK-L and my LPRO need only C-field correction to get the
nominal 10.0000000 MHz out of it. Or has HP not been able to build the
physics packages more 'repeatable'?

Cheers
Ulrich

In message 000101c701a8$24687ef0$0202fea9@athlon, "Ulrich Bangert" writes:

Yes, and they do.

They are factory adjusted.

--
Poul-Henning Kamp      | UNIX since Zilog Zeus 3.20
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Never attribute to malice what can adequately be explained by incompetence.

From: "Poul-Henning Kamp" phk@phk.freebsd.dk
Subject: Re: [time-nuts] Frequency processing scheme of HP5065 vapour rubidium standard
Date: Mon, 06 Nov 2006 13:21:50 +0000
Message-ID: 4604.1162819310@critter.freebsd.dk

Other issues includes the exact frequency pulling of the cavity wall, cavity
tuning and the mixture of buffert gas which to some degree compensates the
wall pulling.

Cheers,
Magnus

At 2:33 PM +0100 11/6/06, Ulrich Bangert wrote:

Ulrich,

We have a 13 year old rubidium standard at my place of work that
drifted by about 1.5E-9 over its lifetime. This is within factory
specifications, but beyond the range of the C-field adjustment
trimpot.

The rubidium vapor method does not generate anything like an exact
frequency; it can vary quite a bit depending on the lamp, the gas,
etc. The unit I was testing has a fixed resistor that is factory
selected to set the C-field control in the middle of its range when
the device is new. I could bring the C-field control back into range
by changing that resistor if desired. That's apparently standard
procedure for these devices.

--

--David Forbes, Tucson, AZ
http://www.cathodecorner.com/

Hi folks,

please be assured that I do not want to argue away the existence of
these dependencies!

amongst

Agreed! But you are talking about things that happen INSIDE the physics
package, don't you? Ok, let us assume that there WERE big differences in
the physics packages that need to be compensated for. In THIS case the
tunable synthesizer would indeed make sense and even more the printed
synthesizer settings on the physics packages! If this were the only
information available, i would immediatly agree to you!

However, when i look into the circuit drawings of my FRK-L it is beyond
any question that it uses a FIXED FREQUENCY SYNTHESIZER unlike the
HP5060 which uses the described tuneable synthesizer. And that arises
the question how Ball/Efratom/Datum/Irvine manage to do it with a fixed
frequency synthesizer (even exchange of the physics package) when HP
needs a tunable synthesizer.

IMHO this can only be possible with one of the two following conditions
given:

1. The Ball/Efratom/Datum/Irvine physics packages do have tighter
   frequency specifications than the HP ones (some orders of magnitude)

2. There is analogue way to pull the atomic resonance to a kind of
   'setpoint'.

I screwed quite a bit to get my FRK running ok. The lamp temperature was
not ok and the plasma excitation frequency was also. I know there are
lots of parameters having a subtle but measurable influence on the
atomic resonance. Efratom even specified the coefficient for atmospheric
pressure, but all of this are very SUBTLE and easily compensated for
with the C-field which gives a total +/-10E-9 freqency control range.
+/-10E-9 makes about +/-0.7 Hz absolute at the rubidium's resonance
frequency.

The HP tuneable synthesizer is tuned in app. 1 Hz steps (!) and allows
for offsets up to a stunning 1 KHz!

Cheers
Ulrich

Ulrich Bangert wrote:

Ulrich, one thing that hasn't been mentioned is that back in the ancient
days, before leap seconds, UTC was "corrected" by applying a frequency
offset that changed annually.  IIRC, it was typically something like
300x10e-10.

I think the main use of the adjustable synthesizer was to allow you to
dial in that offset.

I believe that in later versions of the 5065A, the thumbwheel setting
was removed because after leap seconds came along the need to adjust the
frequency annually went away.  My 5065A is a very late one and I don't
think it has those thumbwheels (but I'm not going to take it out of the
rack to find out...).

John

From: John Ackermann N8UR jra@febo.com
Subject: Re: [time-nuts] Frequency processing scheme of HP5065 vapour rubidium standard
Date: Mon, 06 Nov 2006 11:11:56 -0500
Message-ID: 454F5ECC.80304@febo.com

This makes sense. I think John nailed it.

Cheers,
Magnus

John,

Agreed! And that is what the manual says its good for!

However, the question remains why different physics packages need
DIFFERENT thumbwheel settings in order to achieve the SAME time scale.

73 de Ulrich, DF6JB

--- Ulrich Bangert df6jb@ulrich-bangert.de wrote:

I've read the answer last week on the forum... (sorry
i don't remember who gave the answer...)

It's simple: The technology used on cesiums CAN NOT be
applioed on Rubidiums. With Cesium, high end
techniologies like fountains or beans can be used, and
if i understand well, with these technologies, PURE
CESIUM is used, so there is NOTHING that can affect or
"pull" the resonance of cesium from it's natural
resonance. (9 192 631 770 Hz).

With rubidium, buffer gases must be used, and these
gasses "pull away" the resonance away from Rubidium's
natural resonance. And that is the source of all our
problems with rubidium: Buffer gas/rubidium
evaporation/absorption will affect the frequency
"pulling", thus the drift in Rubidiums. This also
explins why two rubidiums clocks wiill have different
settings (Rb/buffer mixture tolerances). With Cesium,
no pulling, with rubidium, some pulling. That's why
Rubidiums aren't primary standards. If we could build
a Rb (or ANY OTHER element) atomic clock with the same
technology that we use with Cs (total element purity),
there wouldn't be any pulling over time and Rb's would
be considered primary standards.

Hope this explanation will help!

73 de Normand Martel VE2UM

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The offsets were determined by BIH for UTC as ;
1960, 1961  -150 x10-10
1962-1963  -130 x10-10
1964-1965  -150x10-10
1966-1971 -300x10-10
and in 1972  -0-
"the offset in clock rate was chosen to keep the UTC clock in reasonable
agreement with ET" (Chapter 1 - NBS Monograph 140)

Ulrich Bangert wrote:

--- Bill Hawkins bill@iaxs.net wrote:

...Oops, Beams!!!

BTW, beans make me fart, and farts are bad timekeepers
(frequency is unstable, poor S/N ratio, very high
jitter and drifts way too much. Sorry, no Allan
deviation!)

Have a good day!

73 de Normand Martel VE2UM

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What about the Rubidium Fountain?

See first article in the Autumn 2005 report at link below.

http://www.npl.co.uk/publications/news/time/

Rob Kimberley

-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of Normand Martel
Sent: 07 November 2006 00:29
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Frequency processing scheme of HP5065
vapourrubidium standard

--- Ulrich Bangert df6jb@ulrich-bangert.de wrote:

I've read the answer last week on the forum... (sorry i don't remember who
gave the answer...)

It's simple: The technology used on cesiums CAN NOT be applioed on
Rubidiums. With Cesium, high end techniologies like fountains or beans can
be used, and if i understand well, with these technologies, PURE CESIUM is
used, so there is NOTHING that can affect or "pull" the resonance of cesium
from it's natural resonance. (9 192 631 770 Hz).

With rubidium, buffer gases must be used, and these gasses "pull away" the
resonance away from Rubidium's natural resonance. And that is the source of
all our problems with rubidium: Buffer gas/rubidium evaporation/absorption
will affect the frequency "pulling", thus the drift in Rubidiums. This also
explins why two rubidiums clocks wiill have different settings (Rb/buffer
mixture tolerances). With Cesium, no pulling, with rubidium, some pulling.
That's why Rubidiums aren't primary standards. If we could build a Rb (or
ANY OTHER element) atomic clock with the same technology that we use with Cs
(total element purity), there wouldn't be any pulling over time and Rb's
would be considered primary standards.

Hope this explanation will help!

73 de Normand Martel VE2UM

Sponsored Link

$200,000 mortgage for $660/mo - 30/15 yr fixed, reduce debt, home equity -
Click now for info http://yahoo.ratemarketplace.com

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Seems very interesing!!!

If i'm right, That could lead to rubidium based
primary standards...

Normand Martel

--- Rob Kimberley time.bandit@btinternet.com wrote:

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From: Normand Martel martelno@yahoo.com
Subject: Re: [time-nuts] Frequency processing scheme of HP5065 vapour rubidium standard
Date: Mon, 6 Nov 2006 16:28:47 -0800 (PST)
Message-ID: 20061107002847.49574.qmail@web50707.mail.yahoo.com

Wrong.

Rubidum beams and fountains is possible. Infact, recent research have shown
that Rubidium is better suited for fountains than Cesium is, so it outperforms
Cesium.

There is frequency pulling even in Cesium beams. Only a few beams handles the
phase error pulling by reverting the beam direction. Fountains have this
together with doppler reduction.

The Rubidium was found especially suited for the gas cell atomic standard.
The gas cell atomic standard is cheap, but the inherent wall shift is so large
that it prohibits repeatability of the same degree as the beam standards.
Later buffert gas mixtures and pressure was found to balance up the wall shift,
but it still prohibits the same repeatability in frequency.

Currently work on Cesium gas cells is being performed to reach chip scale
atomic clocks, but to the best of my knowledge they also suffer from wall
shift.

We could be measuring the SI second in Thallium, which according to those days
investigations proved even more suitable, but it was judged harder to acheive
the repeatability necessary in the technology of late 50s and early 60s so
Cesium was the winner. All to the best of my knowledge.

So, again, do not confuse the atomic standard measuring/realisation methods
with that of the various atoms, and the usual mappings. Certain combinations of
methods and atoms have proven especially suited for various purposes.

Toss in stuff like ion traps with all the fancy cooling stuff. Maybe we will go
for Mercury 199 ions and the laser combs on top of that.

Cheers,
Magnus

Magnus Danielson wrote:

In the 5071, nearly every error source has been beaten into
submission.  However, CBT phase shift is the last hold out.
Extraordinary proprietary measures are taken to make the microwave
cavity mechanically symmetrical to with tenths of thousands of
an inch, and with no systematic error.  I can't get into detail,
but you can believe no stone was left unturned.  The remaining random
error is typically a few parts in 10^13.  The systematic error
seems to be below 10^-14.

As Magnus said, the solution to this is beam reversal, however that
would be too complicated in a compact clock like the 5071.

Rick Karlquist

Hi Normand,

There are many factors which pull cesium too; and if
you want to get technical the actual frequency inside a
typical cesium standard, even at sea-level, isn't exactly
9 192 631 770 Hz anyway.

To see a very detailed list of pulling and corrections of
a cesium standard read something like this:

Accuracy evaluation of the primary frequency standard NIST-
http://www.tf.nist.gov/timefreq/general/pdf/1497.pdf

I think you will be very surprised as how complicated
it really is to make a good frequency standard. See also
this vintage, but more readable, less technical description:

HP 5062C Cesium Beam Frequency Reference, Theory of Operation
http://www.leapsecond.com/museum/hp5062c/theory.htm

Finally, if you'd like to read about current developments
in rubidium fountains, a good example is found here:

The USNO Rubidium Fountain Project
http://tycho.usno.navy.mil/clockdev/RubidiumFountain.html

For technical details google for rubidium fountain.

Still, optical clocks are the ones likely to succeed cesium
in the coming decade. It seems several times a year there
are new breakthroughs with optical clocks. For example:

Mercury Atomic Clock Keeps Time with Record Accuracy
http://www.nist.gov/public_affairs/releases/mercury_atomic_clock.htm

/tvb

Let me also repeat this posting from last week:

From: "Rick Karlquist" richard@karlquist.com
Subject: Re: [time-nuts] Frequency processing scheme of HP5065 vapour rubidium standard
Date: Tue, 7 Nov 2006 10:29:49 -0800 (PST)
Message-ID: 9313.192.25.240.225.1162924189.squirrel@webmail.sonic.net

I beleive you that no stone was left unturned, and then there is a few to turn.

What I have been thinking about is the possibility to electrically detune the
microwave cavity to introduce the necessary phase shift control. The key issue
with that would probably be how to detect the zero-phase shift in a separate
loop not involving external comparision. I haven't looked into the issue in
detail thought, it's not my field really.

However, I nevery fully understood what the issues with the RF path that was
solved/improved with the 5071 generation clocks. Maybe you could elaborate or
even point to some suitable document.

I agree fully. It would be far too complicated for such a clock. I know PTB did
this for some of their clocks, and I beleive NIST also did it. But those are
laboratory clocks with the emphasis on laboratory, i.e. far from commercial
clocks.

Cheers,
Magnus

Magnus Danielson wrote:

That paradigm assumes some auxiliary phase detector with better
symmetry that the CBT cavity.  The CBT cavity is as symmetrical
as anything else that could be made, so this doesn't seem to make
sense.  I can also tell you (having investigated this sort of thing)
that adding varactors to the cavity to tune it is a huge can of
worms that you want to avoid if at all possible.

For other info on the 5071 design process, see our papers from
1992 FCS.

Rick Karlquist

In message 9495.192.25.240.225.1162935068.squirrel@webmail.sonic.net, "Rick K
arlquist" writes:

Apart from being a can of worms, wouldn't it also be pointless ?

Every CBT will have to be corrected for relativistic height anyway
so wouldn't the tuning just turn into yet a C-field and not add
any actual improvement ?

If I have understood it right, the main thing about the RF part of
the cavity is stability and symmetry, more than precise dimensions ?

--
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.

Thanks! very interesting articles!!!

But something bugs me... In both fountains and single
ion mercury standards, lasers are used to COOL DOWN
atoms...

How is it possible? Lasers are energy sources, and (at
least for me), anything that is hit by a laser will
get warm, not cold!

Thanks for your attention..

Normand Matrel

--- Tom Van Baak tvb@leapsecond.com wrote:

http://tycho.usno.navy.mil/clockdev/RubidiumFountain.html

http://www.nist.gov/public_affairs/releases/mercury_atomic_clock.htm

http://tf.nist.gov/general/enc-re.htm#rubidiumoscillator

https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts

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From: Normand Martel martelno@yahoo.com
Subject: Re: [time-nuts] Frequency processing scheme of HP5065vapourrubidium standard
Date: Tue, 7 Nov 2006 17:25:19 -0800 (PST)
Message-ID: 20061108012519.4843.qmail@web50712.mail.yahoo.com

The short story is that you just push the atoms hard enougth with the pressure
of the photons. This have been used for many purposes and has infact been in
debate for a very long time. I even beleive the old greeks where into the
debate. Ah well. Basically you create an optical melass. Temperature is a
measure on the energy will to move around in Brownian motion. If you press hard
on something that wants to move around, that excess energy will be forced out
of that part of the system.

However, there is more happening in there which can't be explained by just the
pressure of the photons. It is the Sisyphys cooling effect, in which atoms too
much to the "left" (assuming a left-right scale of things) feels a pressure to
move "right" by the phase of the optical pumping. It is forced to climb the
hill continously.

Ion traps acheive about the same thing but using a different mechanism.

Above is very sloopy explanations, just to give you a very rought feel, but you
can get a better understandning than this. A good reading could be:
http://physics.nist.gov/News/Nobel/NobelLec.pdf

It's not every day that one has a reason to refer to a Nobel Lecture, but this
one felt relevant. :-)

Cheers,
MAgnus

Laser cooling is a very clever technique that uses slightly
off-tuned lasers. Start with:

http://en.wikipedia.org/wiki/Laser_cooling

http://tf.nist.gov/general/enc-l.htm#lasercooling

NIST Ion Storage Group
http://tf.nist.gov/ion/index.htm

/tvb

Please see the link below - gives quite a good explanation of laser cooling.
There are more detailed texts available at NIST in the US and NPL in the UK.

http://en.wikipedia.org/wiki/Laser_cooling

Rob K

-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of Normand Martel
Sent: 08 November 2006 01:25
To: Tom Van Baak; Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Frequency processing scheme of
HP5065vapourrubidiumstandard

Thanks! very interesting articles!!!

But something bugs me... In both fountains and single ion mercury standards,
lasers are used to COOL DOWN atoms...

How is it possible? Lasers are energy sources, and (at least for me),
anything that is hit by a laser will get warm, not cold!

Thanks for your attention..

Normand Matrel

--- Tom Van Baak tvb@leapsecond.com wrote:

http://tycho.usno.navy.mil/clockdev/RubidiumFountain.html

http://www.nist.gov/public_affairs/releases/mercury_atomic_clock.htm

http://tf.nist.gov/general/enc-re.htm#rubidiumoscillator

https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts

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