cesium clocks..
Bruce Griffiths wrote:
Chuck Harris wrote:
This is a chicken vs egg sort of problem. When I took apart the oven
on my 5065A rubidium, it looked to me as though the enamel insulated
nichrome wire developed a short about 50% into the coil, and wiped out
the transistor. It also heated the rubidium lamp hot enough to reflow
the solder on its circuit board and thoroughly char the PCB's epoxy.
I am not sure how the quartz ovens are wound (I suspect they are the
same), but with the rubidium ovens, the nichrome wire is wound as a
bifilar loop. This is done for two reasons, 1) to cancel the magnetic
fields, and 2) to make the start and finish wires of the winding happen
at the end of the oven where the terminals are.
-Chuck Harris
An Ayrton-Perry style winding will also have low magnetic field.
There are no doubt hundreds of ways of achieving the same result,
but HP used a single layer bifilar winding of enameled nichrome wire
that was shorted on the far end.
When I replaced the oven winding on my Rubidium, I used a shielded coaxial
winding that was also shorted on the far end.
-Chuck Harris
From: Bruce Griffiths bruce.griffiths@xtra.co.nz
Subject: Re: [time-nuts] Home built cesium clocks???
Date: Sun, 29 Jun 2008 01:52:36 +1200
Message-ID: 48664224.5070004@xtra.co.nz
swingbyte wrote:
G'day fellow time-nuts.
I was just going through some old projects and found my old home-made
mass spectrometer. This was a project based on a design from either
Scientific American or The Amateur Scientist back in the '60s. I was
wondering if anyone here had heard of a similar project for a cesium
clock? Although my home built mass-spec wasn't in the same league as a
bought one, it did work and did get me a HD in physics! How hard is it
to make a cesium clock? Just thinking about it and wondering what is
actually inside the physics package.
Tim.
Not a great deal:
A Caesium oven
A mechanical collimator for the Caesium beam
A pair of state selection magnets
A Caesium detector
A pair of Microwave cavities
The microwave cavities should have a phase-stable distribution inbetween them
and also a stable physical distance.
Getter to capture stray atoms.
C coil.
The physical package should be magnetically shielded.
Also, an ion pump.
A variation would optically pump the cesium beam rather than using the original
state selection magnets. I have not heard of any commercial cesiums using that
technique, it is only used in a few lab cesiums.
Masspectrometers seems to be the most popular detection method too, but
optical detection is again used in a few lab cesiums.
The physical package is along with the RF chain the most problematic parts.
The rest is no big magic, but needs to be done with care.
Cheers,
Magnus
The heater winding for my 5061A crystal oven doesn't seem to be bifilar
wound, but it's a little difficult to tell. Since the heater works, I
don't want to risk poking around too much. However, one lead comes in
at one end, the other lead is at the other end.
BTW, my oven failed again, this time because I was lazy the first time
I fixed it. There was a fairly crispy resistor I didn't have a
replacement for. It seemed OK, so I left it in place. Of course, it
just failed. I had to open everything up again and replace it. While I
was in there, just to make everyone happy, I rerouted the power and
heater return lines that I had moved outside the foam back inside,
replacing them with some nice, Teflon-insulated, fine-gauge wire I had.
Bill Ezell
They said 'Windows or better'
so I used Linux.
Chuck Harris wrote:
Bruce Griffiths wrote:
Chuck Harris wrote:
This is a chicken vs egg sort of problem. When I took apart the oven
on my 5065A rubidium, it looked to me as though the enamel insulated
nichrome wire developed a short about 50% into the coil, and wiped out
the transistor. It also heated the rubidium lamp hot enough to reflow
the solder on its circuit board and thoroughly char the PCB's epoxy.
I am not sure how the quartz ovens are wound (I suspect they are the
same), but with the rubidium ovens, the nichrome wire is wound as a
bifilar loop. This is done for two reasons, 1) to cancel the magnetic
fields, and 2) to make the start and finish wires of the winding happen
at the end of the oven where the terminals are.
-Chuck Harris
An Ayrton-Perry style winding will also have low magnetic field.
There are no doubt hundreds of ways of achieving the same result,
but HP used a single layer bifilar winding of enameled nichrome wire
that was shorted on the far end.
When I replaced the oven winding on my Rubidium, I used a shielded coaxial
winding that was also shorted on the far end.
-Chuck Harris
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and follow the instructions there.
References
Some references also mention some "flip coil" in between microwave
cavities. Does anyone knows what it is?
Predrag Dukic
PS: I will make one myself one day. For the moment I am tinkering
with one FE5440a, and have also 6 (six) spare tubes.
First step is to replace the original electronics, and then I will
start fighting with the rest. Vacuum chamber is waiting....
At 15:52 28.6.2008, you wrote:
swingbyte wrote:
G'day fellow time-nuts.
I was just going through some old projects and found my old home-made
mass spectrometer. This was a project based on a design from either
Scientific American or The Amateur Scientist back in the '60s. I was
wondering if anyone here had heard of a similar project for a cesium
clock? Although my home built mass-spec wasn't in the same league as a
bought one, it did work and did get me a HD in physics! How hard is it
to make a cesium clock? Just thinking about it and wondering what is
actually inside the physics package.
Tim.
Not a great deal:
A Caesium oven
A mechanical collimator for the Caesium beam
A pair of state selection magnets
A Caesium detector
A pair of Microwave cavities
Bruce
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and follow the instructions there.
Microwave components are now cheap and easy to fabricate (thanks to
millions of GSMs GPSs and sat receivers).
Optical pumping/detection is difficult because optical frequencies
(hundreds of THz) have to be accurate and stable within 100khz (1
MHz at worst).
Cesium itself is also difficult part: It has to be extremely pure (N6
or better), and filling it without contamination....could be tricky.
Predrag Dukic
At 17:14 28.6.2008, you wrote:
From: Bruce Griffiths bruce.griffiths@xtra.co.nz
Subject: Re: [time-nuts] Home built cesium clocks???
Date: Sun, 29 Jun 2008 01:52:36 +1200
Message-ID: 48664224.5070004@xtra.co.nz
swingbyte wrote:
G'day fellow time-nuts.
I was just going through some old projects and found my old home-made
mass spectrometer. This was a project based on a design from either
Scientific American or The Amateur Scientist back in the '60s. I was
wondering if anyone here had heard of a similar project for a cesium
clock? Although my home built mass-spec wasn't in the same league as a
bought one, it did work and did get me a HD in physics! How hard is it
to make a cesium clock? Just thinking about it and wondering what is
actually inside the physics package.
Tim.
Not a great deal:
A Caesium oven
A mechanical collimator for the Caesium beam
A pair of state selection magnets
A Caesium detector
A pair of Microwave cavities
The microwave cavities should have a phase-stable distribution inbetween them
and also a stable physical distance.
Getter to capture stray atoms.
C coil.
The physical package should be magnetically shielded.
Also, an ion pump.
A variation would optically pump the cesium beam rather than using
the original
state selection magnets. I have not heard of any commercial cesiums using that
technique, it is only used in a few lab cesiums.
Masspectrometers seems to be the most popular detection method too, but
optical detection is again used in a few lab cesiums.
The physical package is along with the RF chain the most problematic parts.
The rest is no big magic, but needs to be done with care.
Cheers,
Magnus
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To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Predrag Dukic wrote:
Microwave components are now cheap and easy to fabricate (thanks to
millions of GSMs GPSs and sat receivers).
Optical pumping/detection is difficult because optical frequencies
(hundreds of THz) have to be accurate and stable within 100khz (1
MHz at worst).
Cesium itself is also difficult part: It has to be extremely pure (N6
or better), and filling it without contamination....could be tricky.
Predrag Dukic
Pedrag
It would appear that constructing one's own hydrogen maser would be
easier since purifying the hydrogen via a heated nickel or palladium
leak is much simpler.
Also the vacuum hardware is simpler and there is no need for a caesium
detector etc.
The biggest hurdle may be coating the storage bulb.
Bruce
Bruce,
I need a primary standard, and hydrogen maser is not defined as such.
I am working at the University of Split, Croatia,
and I want to apply for Croatia's reference time and frequency
reference laboratory.
At the moment that status is unassigned, because noone in the whole
country thinks that is important or that it pays off in any way.
Every user that needs precise time or frequency relies on GPS, so it
is not possible to find budget for anything like this.
This is my personal initiative, and my own money....
I can use some equipment from other University labs, but that is all.
Predrag
At 00:27 29.6.2008, you wrote:
Predrag Dukic wrote:
Microwave components are now cheap and easy to fabricate (thanks to
millions of GSMs GPSs and sat receivers).
Optical pumping/detection is difficult because optical frequencies
(hundreds of THz) have to be accurate and stable within 100khz (1
MHz at worst).
Cesium itself is also difficult part: It has to be extremely pure (N6
or better), and filling it without contamination....could be tricky.
Predrag Dukic
Pedrag
It would appear that constructing one's own hydrogen maser would be
easier since purifying the hydrogen via a heated nickel or palladium
leak is much simpler.
Also the vacuum hardware is simpler and there is no need for a caesium
detector etc.
The biggest hurdle may be coating the storage bulb.
Bruce
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and follow the instructions there.
Predrag Dukic wrote:
Bruce,
I need a primary standard, and hydrogen maser is not defined as such.
I am working at the University of Split, Croatia,
and I want to apply for Croatia's reference time and frequency
reference laboratory.
At the moment that status is unassigned, because noone in the whole
country thinks that is important or that it pays off in any way.
Every user that needs precise time or frequency relies on GPS, so it
is not possible to find budget for anything like this.
This is my personal initiative, and my own money....
I can use some equipment from other University labs, but that is all.
Predrag
Pedrag
In which case optical pumping and detection using external cavity diode
lasers (ECDLs) should be considered as this method greatly simplifies
the Caesium beam tube by eliminating the hot wire ionizer, electron
multiplier and state selection magnets. All optics can be external to
the beam tube as long as appropriate windows are provided. If necessary
you can build your own ECDL using either the Littrow or Littmann -
Metcalf configurations. Such ECDLs have been built using off the shelf
laser diodes without special AR coated endfaces. 100kHz stability isnt
too onerous with adequate temperature control and suitable low expansion
cavity spacers
http://tycho.usno.navy.mil/ptti/ptti2001/paper2.pdf
In principle it should be possible to lock the pump beam frequency to
the desired Caesium transition.
Bruce
Bruce,
I did my homework and collected everything from the internet I could
get. I have this one too.
If I go optical way, I still need 9+GHz electrical source, so I will
first recreate electronics. Using off the shelf DDS chips, or using FPGA.
Also I need 9 GHz AOM, so that I can split the same optical beam and
have two wavelengths 9ghz apart. That is a problem because I have
only 350 MHz AOM.
Multiple pass is difficult, it would take cca 27 passes to get 9
GHz. On the other side, I wouldn't need the last stages of SRD
multiplication to get 9 GHz microwave.
No doubt, I will have a lot of fun with the project.
Predrag
At 11:53 29.6.2008, you wrote:
Predrag Dukic wrote:
Bruce,
I need a primary standard, and hydrogen maser is not defined as such.
I am working at the University of Split, Croatia,
and I want to apply for Croatia's reference time and frequency
reference laboratory.
At the moment that status is unassigned, because noone in the whole
country thinks that is important or that it pays off in any way.
Every user that needs precise time or frequency relies on GPS, so it
is not possible to find budget for anything like this.
This is my personal initiative, and my own money....
I can use some equipment from other University labs, but that is all.
Predrag
Pedrag
In which case optical pumping and detection using external cavity diode
lasers (ECDLs) should be considered as this method greatly simplifies
the Caesium beam tube by eliminating the hot wire ionizer, electron
multiplier and state selection magnets. All optics can be external to
the beam tube as long as appropriate windows are provided. If necessary
you can build your own ECDL using either the Littrow or Littmann -
Metcalf configurations. Such ECDLs have been built using off the shelf
laser diodes without special AR coated endfaces. 100kHz stability isnt
too onerous with adequate temperature control and suitable low expansion
cavity spacers
http://tycho.usno.navy.mil/ptti/ptti2001/paper2.pdf
In principle it should be possible to lock the pump beam frequency to
the desired Caesium transition.
Bruce
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and follow the instructions there.
In message 7.0.1.0.1.20080629120421.01ebecc8@tapko.de, Predrag Dukic writes:
Bruce,
I did my homework and collected everything from the internet I could
get. I have this one too.
If I go optical way, I still need 9+GHz electrical source, so I will
first recreate electronics. Using off the shelf DDS chips, or using FPGA.
I would probably start out trying to get the thing to work, then
optimize later. For instance, I would start with an off-eBay HP
synthesizer, rather than fight with GHz frequency PCB layout.
No doubt, I will have a lot of fun with the project.
Ohh, absolutely.
Have you visited the Science Museum in London ? They have the original
Cesium beam frequency standard, spending a couple of hours with that
would probably help you determine what/where the really hard bits are.
Also, consider paying PTB a visit, they can probably be persuaded give
your a tour of their designs.
--
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FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.