Re: [time-nuts] H-maser drift

[Mike Cook]

Thanks for that input John. 

> Le 21 nov. 2017 à 21:26, John Ponsonby  a écrit :
> .
> 7. The RF discharge generates UV. This shines up the beam path and 
> illuminates the bulb coating in the region where the incoming atoms first 
> make contact with the bulb coating. This UV undoubtledly damages the FEP120 
> coating. The deterioration of the coating may be one of the causes of long 
> term drift.

Your excellent contribution addresses an issue of long term drift but Dana 
Whitlow’s question in a previous post which I repeat here related to a short 
term issue.

«  On the day of eye passage over the site ( of the eye of a hurricane) the 
frequency suddenly decreased by a few parts in 10^14, held about constant for 
roughly a week,then
resumed almost its original value and drift rate thereafter. « 

Maybe you could shine some light on that reported temporary frequency offset. 


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

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Re: [time-nuts] H-maser drift

[David Smith]

Yes,



Thank you John. Enjoyable reading and informative.



Dave W6TE



Sent from Mail for Windows 10




From: time-nuts  on behalf of John Ponsonby 

Sent: Tuesday, November 21, 2017 12:26:35 PM
To: time-nuts@febo.com
Subject: Re: [time-nuts] H-maser drift

There seem to be a lot of misunderstandings about H-masers. To set the record 
straight note:
1. The flow of hydrogen is generally controlled using a palladium membrane, 
though a palladium-silver alloy is to be preferred because it is less likely to 
crack. Only hydrogen will diffuse through the palladium-silver membrane, so as 
well as being a temperature controlled regulator it is also a filter. Indeed it 
is an isotopic filter through which even deuterium doesn’t pass. The protons 
are thought to migrate through the membrane and recombine on the output surface 
first into atoms and then into H2 molecules. I used thin walled 
palladium-silver tubes which had roughly the dimensions of a match stick. 
Hydrogen on the inside was at about twice atmospheric pressure with output into 
“vacuum” on the outside. Control is by heating with a large current flowing 
along the rather low resistance tube. Russian H-masers use nickel tubes rather 
than the more expensive palladium-silver. Such a “palladium leak” requires only 
a few seconds on Turn-On to settle to a steady flow.
2. Hydrogen from the "palladium leak” passes to a “dissociator" which is a 
small bulb made of heavily boronated glass, e.g. Pyrex, in which the H2 
molecules are dissociated into H atoms by a non-contacting RF discharge. Atomic 
hydrogen recombines very readily on any metal surface so the discharge is 
either by magnetic or electric field acting through the glass wall. Metals are 
charactersised by having conduction bands full of free electrons. Boron is an 
electron acceptor, so Pyrex is very unlike a metal and it has a low surface 
recombination rate. Not as low as FEP120 (See 5. below) but one can’t line a 
discharge bulb with it.
3. The very high Q RF cavity (loaded Q ≈ 36000), which is tuned very exactly to 
the hydrogen frequency of 1,420,405,751Hz, operates in the TE011 mode in which 
the oscillating RF magnetic field is toroidal, going up the middle and down the 
outer part of the cavity. The resonant frequency is much more sensitively 
dependent on the cavity diameter than on its length.
4. Inside the cavity is the "storage bulb" which is made not of glass but of 
fused quartz. It is typically about 1mm thick. Fused quartz is chosen for its 
exceptionally low RF loss tangent. But of course it has a dielectric constant 
which results in its loading the cavity which is thus a little smaller than one 
first thinks. Since it is very difficult to manufacture quartz bulbs to normal 
engineering tolerances it is not possible to calculate how much the cavity will 
be loaded. So it is not unusual to manufacture the cavity to match the given 
storage bulb.
5. The inside of the storage bulb is coated typically with a layer of FEP120, a 
Dupont product akin to Teflon. An H atom can make of the order of 10,000 
bounces off its surface without change of quantum state. Also H atoms won’t 
stick to the coating. (Non-stick frying pans are coated with FEP120 and what is 
true for an egg is true for an atom.)
6. The shape of the storage bulb should be chosen to maximize the “filling 
factor”. This is defined as: η’=Vb^2b/Vcc  Here the numerator is the 
product of the storage bulb volume Vb times the square of the mean of the z 
component of the RF magnetic field Hz averaged over the internal volume of the 
bulb b, and the denominator is the product of the cavity volume Vc times the 
mean of the square of the magnitude of the RF magnetic field Ha averaged over 
the entire volume of the cavity c. A spherical bulb is non-optimal though may 
early masers had spherical storage bulbs.
7. The RF discharge generates UV. This shines up the beam path and illuminates 
the bulb coating in the region where the incoming atoms first make contact with 
the bulb coating. This UV undoubtledly damages the FEP120 coating. The 
deterioration of the coating may be one of the causes of long term drift.
Cheers
John P

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Re: [time-nuts] H-maser drift

[Dana Whitlow]

Thank you John.  That was most informative.

dana


On Tue, Nov 21, 2017 at 2:26 PM, John Ponsonby 
wrote:

> There seem to be a lot of misunderstandings about H-masers. To set the
> record straight note:
> 1. The flow of hydrogen is generally controlled using a palladium
> membrane, though a palladium-silver alloy is to be preferred because it is
> less likely to crack. Only hydrogen will diffuse through the
> palladium-silver membrane, so as well as being a temperature controlled
> regulator it is also a filter. Indeed it is an isotopic filter through
> which even deuterium doesn’t pass. The protons are thought to migrate
> through the membrane and recombine on the output surface first into atoms
> and then into H2 molecules. I used thin walled palladium-silver tubes which
> had roughly the dimensions of a match stick. Hydrogen on the inside was at
> about twice atmospheric pressure with output into “vacuum” on the outside.
> Control is by heating with a large current flowing along the rather low
> resistance tube. Russian H-masers use nickel tubes rather than the more
> expensive palladium-silver. Such a “palladium leak” requires only a few
> seconds on Turn-On to settle to a steady flow.
> 2. Hydrogen from the "palladium leak” passes to a “dissociator" which is a
> small bulb made of heavily boronated glass, e.g. Pyrex, in which the H2
> molecules are dissociated into H atoms by a non-contacting RF discharge.
> Atomic hydrogen recombines very readily on any metal surface so the
> discharge is either by magnetic or electric field acting through the glass
> wall. Metals are charactersised by having conduction bands full of free
> electrons. Boron is an electron acceptor, so Pyrex is very unlike a metal
> and it has a low surface recombination rate. Not as low as FEP120 (See 5.
> below) but one can’t line a discharge bulb with it.
> 3. The very high Q RF cavity (loaded Q ≈ 36000), which is tuned very
> exactly to the hydrogen frequency of 1,420,405,751Hz, operates in the TE011
> mode in which the oscillating RF magnetic field is toroidal, going up the
> middle and down the outer part of the cavity. The resonant frequency is
> much more sensitively dependent on the cavity diameter than on its length.
> 4. Inside the cavity is the "storage bulb" which is made not of glass but
> of fused quartz. It is typically about 1mm thick. Fused quartz is chosen
> for its exceptionally low RF loss tangent. But of course it has a
> dielectric constant which results in its loading the cavity which is thus a
> little smaller than one first thinks. Since it is very difficult to
> manufacture quartz bulbs to normal engineering tolerances it is not
> possible to calculate how much the cavity will be loaded. So it is not
> unusual to manufacture the cavity to match the given storage bulb.
> 5. The inside of the storage bulb is coated typically with a layer of
> FEP120, a Dupont product akin to Teflon. An H atom can make of the order of
> 10,000 bounces off its surface without change of quantum state. Also H
> atoms won’t stick to the coating. (Non-stick frying pans are coated with
> FEP120 and what is true for an egg is true for an atom.)
> 6. The shape of the storage bulb should be chosen to maximize the “filling
> factor”. This is defined as: η’=Vb^2b/Vcc  Here the numerator is
> the product of the storage bulb volume Vb times the square of the mean of
> the z component of the RF magnetic field Hz averaged over the internal
> volume of the bulb b, and the denominator is the product of the cavity
> volume Vc times the mean of the square of the magnitude of the RF magnetic
> field Ha averaged over the entire volume of the cavity c. A spherical bulb
> is non-optimal though may early masers had spherical storage bulbs.
> 7. The RF discharge generates UV. This shines up the beam path and
> illuminates the bulb coating in the region where the incoming atoms first
> make contact with the bulb coating. This UV undoubtledly damages the FEP120
> coating. The deterioration of the coating may be one of the causes of long
> term drift.
> Cheers
> John P
>
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Re: [time-nuts] HP5065A C-field mods and optical unit mods

[Poul-Henning Kamp]

In message <1159987519.5777361.1511296831...@webmail.xtra.co.nz>, Bruce Griffit
hs writes:

>What is the effect of the C-field coil dimension tempco?

I have not been able to measure it.

The C-coil is located thermally close to the temperature controlled
parts of the physics package.

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
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Never attribute to malice what can adequately be explained by incompetence.
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Re: [time-nuts] HP5065A C-field mods and optical unit mods

[Bruce Griffiths]

What is the effect of the C-field coil dimension tempco?

At some point this will surely dominate overthe coil current tempco.

Bruce

> 
> On 22 November 2017 at 09:16 Charles Steinmetz  
> wrote:
> 
> Luciano wrote:
> 
> > > 
> > what you refer is the resistance relation referred to the LM299 
> > source around 14VDc but you have to consider
> > the tuning range of the pot, in the original HP5065A is 2E10-9.
> > Of course, it depends on the setting value of the variable 
> > resistance, but you have to consider a possible variation of 20PPM/c on 
> > 2E10-9.
> > 
> > > 
> No, you don't. The tempco that matters is the aggregate tempco of the
> series string. Only a very small portion of the string voltage appears
> across the pot, so a 20ppm tempco of that small part will cause a much
> smaller change in overall tempco of the series string.
> 
> Perhaps Corby will tell us what value the pot is, and then you can
> calculate the aggregate tempco of the string at various pot settings and
> see for yourself.
> 
> Charles
> 
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Re: [time-nuts] H-maser drift

[John Ponsonby]

There seem to be a lot of misunderstandings about H-masers. To set the record 
straight note:
1. The flow of hydrogen is generally controlled using a palladium membrane, 
though a palladium-silver alloy is to be preferred because it is less likely to 
crack. Only hydrogen will diffuse through the palladium-silver membrane, so as 
well as being a temperature controlled regulator it is also a filter. Indeed it 
is an isotopic filter through which even deuterium doesn’t pass. The protons 
are thought to migrate through the membrane and recombine on the output surface 
first into atoms and then into H2 molecules. I used thin walled 
palladium-silver tubes which had roughly the dimensions of a match stick. 
Hydrogen on the inside was at about twice atmospheric pressure with output into 
“vacuum” on the outside. Control is by heating with a large current flowing 
along the rather low resistance tube. Russian H-masers use nickel tubes rather 
than the more expensive palladium-silver. Such a “palladium leak” requires only 
a few seconds on Turn-On to settle to a steady flow.  
2. Hydrogen from the "palladium leak” passes to a “dissociator" which is a 
small bulb made of heavily boronated glass, e.g. Pyrex, in which the H2 
molecules are dissociated into H atoms by a non-contacting RF discharge. Atomic 
hydrogen recombines very readily on any metal surface so the discharge is 
either by magnetic or electric field acting through the glass wall. Metals are 
charactersised by having conduction bands full of free electrons. Boron is an 
electron acceptor, so Pyrex is very unlike a metal and it has a low surface 
recombination rate. Not as low as FEP120 (See 5. below) but one can’t line a 
discharge bulb with it.
3. The very high Q RF cavity (loaded Q ≈ 36000), which is tuned very exactly to 
the hydrogen frequency of 1,420,405,751Hz, operates in the TE011 mode in which 
the oscillating RF magnetic field is toroidal, going up the middle and down the 
outer part of the cavity. The resonant frequency is much more sensitively 
dependent on the cavity diameter than on its length.
4. Inside the cavity is the "storage bulb" which is made not of glass but of 
fused quartz. It is typically about 1mm thick. Fused quartz is chosen for its 
exceptionally low RF loss tangent. But of course it has a dielectric constant 
which results in its loading the cavity which is thus a little smaller than one 
first thinks. Since it is very difficult to manufacture quartz bulbs to normal 
engineering tolerances it is not possible to calculate how much the cavity will 
be loaded. So it is not unusual to manufacture the cavity to match the given 
storage bulb. 
5. The inside of the storage bulb is coated typically with a layer of FEP120, a 
Dupont product akin to Teflon. An H atom can make of the order of 10,000 
bounces off its surface without change of quantum state. Also H atoms won’t 
stick to the coating. (Non-stick frying pans are coated with FEP120 and what is 
true for an egg is true for an atom.)
6. The shape of the storage bulb should be chosen to maximize the “filling 
factor”. This is defined as: η’=Vb^2b/Vcc  Here the numerator is the 
product of the storage bulb volume Vb times the square of the mean of the z 
component of the RF magnetic field Hz averaged over the internal volume of the 
bulb b, and the denominator is the product of the cavity volume Vc times the 
mean of the square of the magnitude of the RF magnetic field Ha averaged over 
the entire volume of the cavity c. A spherical bulb is non-optimal though may 
early masers had spherical storage bulbs.
7. The RF discharge generates UV. This shines up the beam path and illuminates 
the bulb coating in the region where the incoming atoms first make contact with 
the bulb coating. This UV undoubtledly damages the FEP120 coating. The 
deterioration of the coating may be one of the causes of long term drift.
Cheers
John P
 
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Re: [time-nuts] HP5065A C-field mods and optical unit mods

[Charles Steinmetz]

Luciano wrote:


what you refer is the resistance relation referred to the LM299 source 
around 14VDc but you have to consider
the tuning range of the pot, in the original HP5065A is 2E10-9.
Of course, it depends on the setting value of the variable resistance, but 
you have to consider a possible variation of 20PPM/c on 2E10-9.


No, you don't.  The tempco that matters is the aggregate tempco of the 
series string.  Only a very small portion of the string voltage appears 
across the pot, so a 20ppm tempco of that small part will cause a much 
smaller change in overall tempco of the series string.


Perhaps Corby will tell us what value the pot is, and then you can 
calculate the aggregate tempco of the string at various pot settings and 
see for yourself.


Charles


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[time-nuts] Programmed Test Sources PTS-x10

[GandalfG8--- via time-nuts]

The Programmed Test Sources PTS-x10 manual is available from  Mediafire
 
http://www.mediafire.com/file/ak193b371mbb3vc/PTS_X10.pdf
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Re: [time-nuts] H-Maser drift (was: Why discipline Rubidium oscillator?)

[Ole Petter Rønningen]

Hi, Dana.

> What does 'EFOS' mean?  I hadn't heard the term before.

EFOS was a series of masers made by Oscilloquartz in Switzerland, there is a 
little information on my website www.efos3.com under «about».

The manuals for those masers are also available, lots of good info for the 
interested: 
http://www.leapsecond.com/museum/efos/

> I do hear mixed reports about where the conversion to atomic H
> occurs, and consider the jury to still be out on that question.

Well, I think that jury is in.. :) plenty of information in old papers on that 
part.

Ole

> I had thought that the volume of the storage bulb was much
> smaller in out maser, perhaps in the pint to quart range.  For a
> frequency of ~1420 MHz, I guess it would take a cavity that is
> operating in a somewhat higher than fundamental mode if the
> volume is in the gallon regime as you suggest.  But with the
> narrow gain profile width of this transition, I supposed there'd
> be no risk of the thing running in the wrong mode.
> 
> Dana
> 
> 
> On Tue, Nov 21, 2017 at 8:14 AM, Ole Petter Ronningen > wrote:
> 
>>> On Tue, Nov 21, 2017 at 2:50 PM, Attila Kinali  wrote:
>>> 
>>> [...] The advantage of the platinum valve
>>> system is that it "generates" single atom Hydrogen, as required
>>> by the maser.
>> 
>> 
>> Picking nits here.. It was my understanding that the splitting of molecular
>> hydrogen into atomic hydrogen happens using RF in the dissociator - not in
>> the platinum leak valve. Is my understanding incorrect?
>> 
>> 
>>> Within the cavity there is a small glass bulb that keeps the atoms
>>> in the right position of the cavity field.
>> 
>> 
>> 4.5 liters in EFOS type masers - so not *that* small. I believe other
>> masers are the same order of magnitude.
>> 
>> 
>>> Yes, IIRC normal numbers are several 10s to 100s of wall collisions
>>> before the atom loses its state due to wall colisions and without
>>> contributing to the signal.
>>> 
>> 
>> Lifetime ~1 second I think
>> 
>> 
 I've long wondered what causes the slow frequency drift, typically
>>> amounting
 to about 3E-14 over a time span of several months.
>>> 
>>> Mostly changes in the wall coating leading to a different wall collision
>>> shift and mechanical changes of the cavity dimension (think air pressure
>>> and creep) leading to a different cavity pulling. To a lesser extend
>>> it's the changes in the quality of the vacuum and number of Hydrogen
>> atoms
>>> in the cavity.
>> 
>> 
>> Also aging of electronic components - coarse tuning of the cavity is done
>> by temperature, and any drift if the temperature-sensor/amplifiers etc will
>> result in drift. At least for EFOS type masers.
>> 
>> Ole
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Re: [time-nuts] Why discipline Rubidium oscillator?

[Bob kb8tq]

Hi

Cesiums (that may be on their last legs or maybe not) are pretty common 
in the market. Prices vary, but generally are < $4,000. Bought new they are
in the $70,000 range.  Masers show up much less often. Price wise … that
depends. The cheapest working unit I have heard of was in the $30,000 range.
New, you see some with $150,000 price tags on them. 

Fountain standards for the commercial market have been a “real soon now” 
sort of thing since the 1980’s. I have yet to see anybody selling one (as 
opposed 
to building it in a lab and using it). Yes, there always has been a lot of 
talk. 
There don’t seem to be any shipments….

State of the art Ion standards are something you lock up a building full of 
very 
smart people for a good chunk of their career to come up with. Unless you have 
a budget funded by a rich uncle (or something similar)… don’t go there. 

That sounds very discouraging. Actually it’s not. There is no real need to have
a “best in the world” fountain or ion standard. One that simply works probably 
would be fine by any of us. The same is true of the Maser. Putting in a few 
years
of work to get one up and running might be an ok thing if the price was right. 

=

The bigger point is: what do you do / what can you do with this stuff? 

As you scale up the standard, the bench that goes around it probably scales
as well. The counter that was fine back when you only had a partially working 
OCXO as a standard may not be “good enough” with your maser. Watching
the second tick on your WWVB clock may no longer be “interesting” you may
want to plot signals from far away stars ….

It just keeps getting worse !!!

Bob

> On Nov 20, 2017, at 9:43 PM, Dana Whitlow  wrote:
> 
> As far as I knew, the highest level steps *actually on the market* are
> the Cesium beam clocks and the active hydrogen masers.  Are any
> of the newer technologies available for purchase today?
> 
> Dana
> 
> 
> On Mon, Nov 20, 2017 at 6:13 PM, Hal Murray  wrote:
> 
>>> aren’t too many steps after that
>> 
>> Your imagination is broken.
>> 
>> There are lots more steps.  Most of them are very expensive.
>> 
>> 
>> --
>> These are my opinions.  I hate spam.
>> 
>> 
>> 
>> 
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Re: [time-nuts] H-Maser drift (was: Why discipline Rubidium oscillator?)

[Bert Kehren via time-nuts]

Corby can most likely answer some of these questions, since he also has a  
maser and does maintain it. He is right now most likely still asleep, 
California  time.
Bert Kehren
 
 
In a message dated 11/21/2017 9:25:30 A.M. Eastern Standard Time,  
att...@kinali.ch writes:

On Tue,  21 Nov 2017 15:14:59 +0100
Ole Petter Ronningen   wrote:

> > [...] The advantage of  the platinum valve
> > system is that it "generates" single atom  Hydrogen, as required
> > by the maser.
> 
> Picking nits  here.. It was my understanding that the splitting of 
molecular
>  hydrogen into atomic hydrogen happens using RF in the dissociator - not  
in
> the platinum leak valve. Is my understanding incorrect?

Good  question. I don't know. I've only read a dozen or so papers on
maser  construction. I have never owned or operated one. Much less
taken appart  and studied its construction.

> > Within the cavity there is a  small glass bulb that keeps the atoms
> > in the right position of  the cavity field.
> 
> 4.5 liters in EFOS type masers - so not  *that* small. I believe other
> masers are the same order of  magnitude.

Hehe.. Yes. It's "small" compared to the cavity. Depending  on the
exact cavity construction, the storage space can be as small as
a  tenth of the total cavity volume.


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
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Re: [time-nuts] H-Maser drift (was: Why discipline Rubidium oscillator?)

[Attila Kinali]

On Tue, 21 Nov 2017 14:50:48 +0100
Attila Kinali  wrote:

> The source for the Hydrogen atoms is usually a heated platinum
> valve (a heated plate of platinum that is thin enough that the
> Hydrogen will leak through). 

Several people pointed out that the valve is made of paladium
and not of platinum. Sorry about that. And thanks to everyone
who corrected me.


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
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Re: [time-nuts] H-Maser drift (was: Why discipline Rubidium oscillator?)

[Dana Whitlow]

Hi Ole,

What does 'EFOS' mean?  I hadn't heard the term before.

I think I've heard the one-second lifetime figure before.

I do hear mixed reports about where the conversion to atomic H
occurs, and consider the jury to still be out on that question.

I had thought that the volume of the storage bulb was much
smaller in out maser, perhaps in the pint to quart range.  For a
frequency of ~1420 MHz, I guess it would take a cavity that is
operating in a somewhat higher than fundamental mode if the
volume is in the gallon regime as you suggest.  But with the
narrow gain profile width of this transition, I supposed there'd
be no risk of the thing running in the wrong mode.

Dana


On Tue, Nov 21, 2017 at 8:14 AM, Ole Petter Ronningen  wrote:

> On Tue, Nov 21, 2017 at 2:50 PM, Attila Kinali  wrote:
>
> > [...] The advantage of the platinum valve
> > system is that it "generates" single atom Hydrogen, as required
> > by the maser.
>
>
> Picking nits here.. It was my understanding that the splitting of molecular
> hydrogen into atomic hydrogen happens using RF in the dissociator - not in
> the platinum leak valve. Is my understanding incorrect?
>
>
> > Within the cavity there is a small glass bulb that keeps the atoms
> > in the right position of the cavity field.
>
>
> 4.5 liters in EFOS type masers - so not *that* small. I believe other
> masers are the same order of magnitude.
>
>
> > Yes, IIRC normal numbers are several 10s to 100s of wall collisions
> > before the atom loses its state due to wall colisions and without
> > contributing to the signal.
> >
>
> Lifetime ~1 second I think
>
>
> > > I've long wondered what causes the slow frequency drift, typically
> > amounting
> > > to about 3E-14 over a time span of several months.
> >
> > Mostly changes in the wall coating leading to a different wall collision
> > shift and mechanical changes of the cavity dimension (think air pressure
> > and creep) leading to a different cavity pulling. To a lesser extend
> > it's the changes in the quality of the vacuum and number of Hydrogen
> atoms
> > in the cavity.
>
>
> Also aging of electronic components - coarse tuning of the cavity is done
> by temperature, and any drift if the temperature-sensor/amplifiers etc will
> result in drift. At least for EFOS type masers.
>
> Ole
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Re: [time-nuts] H-Maser drift (was: Why discipline Rubidium oscillator?)

[Attila Kinali]

On Tue, 21 Nov 2017 15:31:25 +0100
Ole Petter Ronningen  wrote:

> > Hehe.. Yes. It's "small" compared to the cavity. Depending on the
> > exact cavity construction, the storage space can be as small as
> > a tenth of the total cavity volume.
> 
> Thats interesting, I would think a small volume would result in increased
> spin exchange - do you have any papers detailing the tradeoffs with
> big/small storage bulbs?

I would have to go through my collection to find those that mention
anything on it.

The tradeoff is bascially, that you want to have an as large volume
as possible to minimize wall and atom-atom collisions. But there is
only a certain volume within the cavity, where the field has the
right orientation. The higher the mode of the cavity, the smaller
the volume (relative to the cavity size). Higher cavity modes are
used to shrink the overall cavity size, without the need of loading,
which introduces losses. 

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
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Re: [time-nuts] H-Maser drift (was: Why discipline Rubidium oscillator?)

[Ole Petter Ronningen]

>
>
> > 4.5 liters in EFOS type masers - so not *that* small. I believe other
> > masers are the same order of magnitude.
>
> Hehe.. Yes. It's "small" compared to the cavity. Depending on the
> exact cavity construction, the storage space can be as small as
> a tenth of the total cavity volume.


Thats interesting, I would think a small volume would result in increased
spin exchange - do you have any papers detailing the tradeoffs with
big/small storage bulbs?
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Re: [time-nuts] H-Maser drift (was: Why discipline Rubidium oscillator?)

[Attila Kinali]

On Tue, 21 Nov 2017 15:14:59 +0100
Ole Petter Ronningen  wrote:

> > [...] The advantage of the platinum valve
> > system is that it "generates" single atom Hydrogen, as required
> > by the maser.
> 
> Picking nits here.. It was my understanding that the splitting of molecular
> hydrogen into atomic hydrogen happens using RF in the dissociator - not in
> the platinum leak valve. Is my understanding incorrect?

Good question. I don't know. I've only read a dozen or so papers on
maser construction. I have never owned or operated one. Much less
taken appart and studied its construction.

> > Within the cavity there is a small glass bulb that keeps the atoms
> > in the right position of the cavity field.
> 
> 4.5 liters in EFOS type masers - so not *that* small. I believe other
> masers are the same order of magnitude.

Hehe.. Yes. It's "small" compared to the cavity. Depending on the
exact cavity construction, the storage space can be as small as
a tenth of the total cavity volume.


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
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Re: [time-nuts] H-Maser drift (was: Why discipline Rubidium oscillator?)

[Ole Petter Ronningen]

On Tue, Nov 21, 2017 at 2:50 PM, Attila Kinali  wrote:

> [...] The advantage of the platinum valve
> system is that it "generates" single atom Hydrogen, as required
> by the maser.


Picking nits here.. It was my understanding that the splitting of molecular
hydrogen into atomic hydrogen happens using RF in the dissociator - not in
the platinum leak valve. Is my understanding incorrect?


> Within the cavity there is a small glass bulb that keeps the atoms
> in the right position of the cavity field.


4.5 liters in EFOS type masers - so not *that* small. I believe other
masers are the same order of magnitude.


> Yes, IIRC normal numbers are several 10s to 100s of wall collisions
> before the atom loses its state due to wall colisions and without
> contributing to the signal.
>

Lifetime ~1 second I think


> > I've long wondered what causes the slow frequency drift, typically
> amounting
> > to about 3E-14 over a time span of several months.
>
> Mostly changes in the wall coating leading to a different wall collision
> shift and mechanical changes of the cavity dimension (think air pressure
> and creep) leading to a different cavity pulling. To a lesser extend
> it's the changes in the quality of the vacuum and number of Hydrogen atoms
> in the cavity.


Also aging of electronic components - coarse tuning of the cavity is done
by temperature, and any drift if the temperature-sensor/amplifiers etc will
result in drift. At least for EFOS type masers.

Ole
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[time-nuts] H-Maser drift (was: Why discipline Rubidium oscillator?)

[Attila Kinali]

On Tue, 21 Nov 2017 04:24:51 -0600
Dana Whitlow  wrote:

> This is an active maser, meaning a self-sustaining oscillator whose gain
> medium
> was a volume of hydrogen atoms (at low pressure) maintained in a population-
> inverted state by squirting a thin stream of state-selected H atoms into a
> glass bulb,

They are not maintained in this state. Rather the Hydrogen atoms are
"used up" by emiting a photon at 1.4GHz. They are then "removed"
by leaking out of the opening of the bulb and pumped away.
The source for the Hydrogen atoms is usually a heated platinum
valve (a heated plate of platinum that is thin enough that the
Hydrogen will leak through). The advantage of the platinum valve
system is that it "generates" single atom Hydrogen, as required
by the maser. These atoms go through a specially formed magnet
that deflects the atoms that are in the wrong state (c.f. Stern-Gerlach
experiment). Those in the right state make it into the cavity.
Within the cavity there is a small glass bulb that keeps the atoms
in the right position of the cavity field. In order not to perturbe
the atoms too much, the bulb walls are coated with Teflon.

> The inside of the bulb was treated so that the collisions with the surface did
> not usually cause a quantum state change of the H atom involved.  I've read 
> that
> the average excited atom typically "survived" a large number of such wall
> collisions before being "consumed" by contributing a quantum of energy to
> the oscillating mode; this has always amazed me.

Yes, IIRC normal numbers are several 10s to 100s of wall collisions
before the atom loses its state due to wall colisions and without
contributing to the signal.

> So the primary frequency-determining mechanism is the collision-broadened
> line width of the gain mechanism. However, the cavity resonance exhibits a
> noticeable frequency-pulling effect, and our maser has a feedback loop that
> strives to keep the cavity tuned to the center of the medium's gain
> profile.
> But I think this loop is not a tight loop, ergo not completely successful.

The loop is quite tight. But there are multiple effects that prevent
perfect operation. Major problems are the low signal levels and the
shifts due wall colisions and cavity pulling.

> I've long wondered what causes the slow frequency drift, typically amounting
> to about 3E-14 over a time span of several months.

Mostly changes in the wall coating leading to a different wall collision
shift and mechanical changes of the cavity dimension (think air pressure
and creep) leading to a different cavity pulling. To a lesser extend
it's the changes in the quality of the vacuum and number of Hydrogen atoms
in the cavity.


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
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[time-nuts] GNSS signals (was: Why discipline Rubidium oscillator?)

[Attila Kinali]

On Mon, 20 Nov 2017 20:50:17 -0800
Jerry Hancock  wrote:

> I read up on the GPS L1/L2 and I think there is an L5.

for your rainy Sunday reading:

http://www.navipedia.net/index.php/GPS_Signal_Plan
http://www.navipedia.net/index.php/Galileo_Signal_Plan
http://www.navipedia.net/index.php/GLONASS_Signal_Plan
http://www.navipedia.net/index.php/BeiDou_Signal_Plan

And because everyone likes large, colorful graphs:
http://www.insidegnss.com/auto/popupimage/GLONASS%20spectrum%200408.jpg

Yes, it's getting crowded.

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
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[time-nuts] Disciplining a Cs beam standard (was: Why discipline Rubidium oscillator?)

[Attila Kinali]

On Mon, 20 Nov 2017 20:18:18 -0500
Bob kb8tq  wrote:

> You can (or course) do a GPS disciplined Cs standard. That’s not easy to do, 
> but some are attempting it ….

It is actually quite easy. You measure the satellite carrier and code
phases relative to the output signal of the Cs, collect all the data,
wait a couple of weeks until the IGS final product becomes available,
then you calculate the frequency and phase difference and steer the
Cs accordingly using a control loop with a tau in the order of 3 weeks
at minimum (due to the delay in IGS data), rather 10 to 50 weeks.

Simple, right? :-)

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
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Re: [time-nuts] HP5065A C-field mods and optical unit mods

[tim...@timeok.it]

   Hi Charles,
   what you refer is the resistance relation referred to the LM299 source 
around 14VDc but you have to consider
   the tuning range of the pot, in the original HP5065A is 2E10-9.
   Of course, it depends on the setting value of the variable resistance, but 
you have to consider a possible variation of 20PPM/c on 2E10-9.
   Regards
   Luciano
   timeok


   Da "time-nuts" time-nuts-boun...@febo.com
   A time-nuts@febo.com
   Cc
   Data Tue, 21 Nov 2017 06:31:25 -0500
   Oggetto Re: [time-nuts] HP5065A C-field mods and optical unit mods
   Luciano wrote:

   > about the C field ten turn pot you write is a low TC pot. Normally a good 
Vishay pot is 20 PPM/C, This is in conflict with the 1PPM resistors ad voltage 
reference.

   In the schematic Corby posted, the potentiometer (used as a variable
   resistor) makes up a very small part of the total resistance of the
   series string, so the overall tempco is dominated by the tempcos of the
   fixed resistors (2.4k to 4.4k 1ppm/ C, depending on trim). The pot will
   increase the overall tempco a little bit, but not anywhere near 20ppm.

   Best regards,

   Charles


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Re: [time-nuts] HP5065A C-field mods and optical unit mods

[Charles Steinmetz]

Luciano wrote:


about the C field ten turn pot you write is a low TC pot. Normally a good 
Vishay  pot is 20 PPM/C, This is in conflict with the 1PPM resistors ad voltage 
reference.


In the schematic Corby posted, the potentiometer (used as a variable 
resistor) makes up a very small part of the total resistance of the 
series string, so the overall tempco is dominated by the tempcos of the 
fixed resistors (2.4k to 4.4k 1ppm/ C, depending on trim).  The pot will 
increase the overall tempco a little bit, but not anywhere near 20ppm.


Best regards,

Charles


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Re: [time-nuts] ***SPAM*** Re: Why discipline Rubidium oscillator?

[Dana Whitlow]

Oops, I should have mentioned:  The unit was a Symmetricom MHM-2010 (I hope
I got that right), except that it was built before the company was bought by
Symmetricom (which was later bought by Micro-Semi in turn).

This is an active maser, meaning a self-sustaining oscillator whose gain
medium
was a volume of hydrogen atoms (at low pressure) maintained in a population-
inverted state by squirting a thin stream of state-selected H atoms into a
glass
bulb, and simultaneously pumping on the bulb to maintain a low pressure.
The
inside of the bulb was treated so that the collisions with the surface did
not
usually cause a quantum state change of the H atom involved.  I've read that
the average excited atom typically "survived" a large number of such wall
collisions before being "consumed" by contributing a quantum of energy to
the oscillating mode; this has always amazed me.

So the primary frequency-determining mechanism is the collision-broadened
line width of the gain mechanism. However, the cavity resonance exhibits a
noticeable frequency-pulling effect, and our maser has a feedback loop that
strives to keep the cavity tuned to the center of the medium's gain
profile.
But I think this loop is not a tight loop, ergo not completely successful.

Anyway, a small amount of RF power (a fraction of a pW as I understand it)
is extracted from the cavity as the useful output.  This drives a frequency
synthesizer to make a useful standard frequency output.  The "divide ratio"
of that synthesizer is adjustable in fine steps, with one step being a
fractional
frequency change of about 7E-17.

I've long wondered what causes the slow frequency drift, typically amounting
to about 3E-14 over a time span of several months.

Dana


On Tue, Nov 21, 2017 at 1:39 AM, Mike Cook  wrote:

>
> > Le 20 nov. 2017 à 20:53, Dana Whitlow  a écrit :
> >
> >
> >
> > In my pre-retirement job I rode herd on an active Hydrogen maser
> system,and even
> > that has a clear drift tendency.  Generally a couple or three times per
> > year I had to make a frequency adjustment in the neighborhood of 3E-14.
> And still being
> > privy to its performance, I was amused to note that its drift tendency
> was
> > interrupted by the hurricane Maria.  On the day of eye passage over the
> site the frequencysuddenly
> > decreased by a few parts in 10^14, held about constant for roughly a
> week,then
> > resumed almost its original value and drift rate thereafter.  If anybody
> inthis group
> > can explain* that* behavior (that is, held for a week before resuming old
> > habits), I’d love to learn about it.
>
>   You don’t mention the make of the instrument, but I suspect the same
> basic technology is used by all.
> To quote from the Oscilloquartz page on their CH1-76A product:
> «  The quantum device is used as a frequency discriminator in an automatic
> frequency tuning system of a crystal oscillator. »
> They don’t however quote stability relative to air pressure. However…..
> It is known that atmospheric pressure changes can induce OCXO frequency
> changes due to deformation of the crystal envelope causing stray
> capacitance changes.
> As the eye of a hurricane has greatly reduced air pressure than normal, by
> as much as 15%, it could be related.
>
>
> >
> > Dana
> >
> >
> > On Mon, Nov 20, 2017 at 1:40 PM, Bob kb8tq  wrote:
> >
> >> Hi
> >>
> >> There is no direct relation for an Rb to 10 MYz. Cs beam tubes are what
> >> have a direct relation.
> >> Even then, the qualifier is “under standard conditions”. They are
> >> sensitive to magnetic field. Rb’s
> >> also are sensitive to magnetic field. Both can be tuned by varying the
> >> field. In the case of an Rb
> >> that also takes care of a multitude of other issues.
> >>
> >> In the case of Rb, there is a distribution of cells coming out of the
> >> manufacturing process. Some
> >> are pretty close to the “right” frequency. Others are way off (as in
> 100’s
> >> of KHz or more). All of them
> >> are capable of meeting the required specs. DDS techniques allow those
> >> cells to be used in a
> >> production part. That increases the yield and thus drops the production
> >> cost.
> >>
> >> Since you now magically have a DDS in the Rb, you can do all sorts of
> >> interesting things. If you
> >> suddenly need a 9.99900 MHz standard …. here it is … If you need to do
> >> temperature compensation
> >> via a lookup table … it just takes a bit of testing and some code to
> make
> >> it happen. Indeed, the DDS
> >> does also give you some issues. Without some sort of cleanup oscillator,
> >> you will have spurs and
> >> phase noise on the output.
> >>
> >> Lots of fun ….
> >>
> >> Bob
> >>
> >>
> >>> On Nov 20, 2017, at 1:34 PM, Jerry Hancock  wrote:
> >>>
> >>> I know this is going to sound dumb as I know many GPSDOs had rubidium
> >> oscillators in them.  I can see why, in that during holdover, they would
> >> tend to be more stable vs others, but given that there is a direct
> >> mathematical relationship betw

Re: [time-nuts] HP5065A C-field mods and optical unit mods

[tim...@timeok.it]

   Hi Corby,
   about the C field ten turn pot you write is a low TC pot. Normally a good 
Vishay  pot is 20 PPM/C, This is in conflict with the 1PPM resistors ad voltage 
reference.
   What kind of pot do you have used?
   http://www.mouser.com/ds/2/427/533534-768216.pdf
   Luciano
   timeok


   Da "time-nuts" time-nuts-boun...@febo.com
   A time-nuts@febo.com
   Cc
   Data Fri, 17 Nov 2017 12:37:57 -0800
   Oggetto [time-nuts] HP5065A C-field mods and optical unit mods
   Luciano,

   The TX and choke and filter caps were removed as I had envisioned I would
   have to re-mount the A1 and A7 in their location.
   However with some judicious movement of the mounting holes I was able to
   squeeze them in close
   to their original spots.

   The 5065 chassis was removed and inserted into a chassis from an HP
   8405A. (just used the side panels
   and the rear panel.)

   I'll post a schematic of the new C-field supply next week. It consists of
   two LM299AH in series feeding
   a string consisting of a 2.4K, 1k, 1K and a 1K low TC pot. A switch
   allows you to short out one or both of the 1K resistors as a coarse
   adjustment. All resistor are 1PPM.

   Fixing the 20Volt and the C-field temperature contributions allowed me to
   isolate the optical units changes
   due to temp.

   The resistor thermistor combo I mentioned would be taped to the optical
   unit and compensate it only.
   It would be in series with the C-field coil.
   Not needed in my unit but thought that others might want to try it rather
   than getting as complex as I have.

   Yes the active baro and temp circuit would be an alternative for a unit
   without my mods.

   attached are PIX of the enclosed optical unit and the front panel.

   Cheers,

   Corby
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