cesium clocks..
Poul,
That is the reason I wanted FE5440A
First of all it is a military device. CBTs are replaced before
expiring their operating life so that F18 (or any, i don't know the
details) do not loose communication in mid air.
All of FE5440a ebay tubes still have some cesium left. Then, early
models have their primary loop without any sinthesizor: 14.59+ MHz
OCXO multiplied by 630.
The simplest possible frequency plan. Synthesizing useful output
frequency comes in the secondary loop.
Since I do have experience with FPGAs it is an easy part for me.
Microwave PCB is a bit more difficult, but doable. I do not expect
too much trouble.
I was in London last november, but the main interest for my daughter
was Natural History Museum..... For an 11yr old it is understandible.
Don't know when I'll make another visit. It is terribly expensive town.
Last week I actually spent to "get something to work"
FE5440a came from ebay not working with some pieces burnt and
missing. Also I paid it too much (2500 USD).
I saw some HP's going for 600, but since I already had 6 FE5440a tubes......
But now it is all working, and I learned a lot in the process, so I
do not consider that effort a waste.
Predrag
At 12:22 29.6.2008, you wrote:
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.
--
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.
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Predrag Dukic wrote:
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
Pedrag
The easiest way given your AOMs may be to use a combined optical and electrical method without dual frequency pumping - slightly less efficient but no need for a 9GHz AOM.
Bruce
From: Predrag Dukic stijena@tapko.de
Subject: Re: [time-nuts] Home built cesium clocks???
Date: Sun, 29 Jun 2008 12:10:46 +0200
Message-ID: 7.0.1.0.1.20080629120421.01ebecc8@tapko.de
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.
A YIG oscillator or similar should be considered. The FPGA would be great
for the state handling, but be sure to externally reclock the signal
before use to remove the FPGA jitter.
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.
In the article he referenced, the AOM only needs to handle 250,1 MHz.
Only if you intend to achieve 100% pumping and detection ratios you need
a full set of frequencies. Notice the important note on relation between
laser linewidth and S/N relationship. Luckilly those are limitations
outside of the cavity.
The interesting aspect with an optically pumped cesium is that one of the
common failuremodes, the contamination of the masspectrometer is removed.
The detection is off-axis from the beam. Wonder if an open oven could not
be installed there. That would allow for a ping-pong mode of operation,
which the optical pumping itself fits very nicely too. It would cancel
some of the systematic shifts due to assymetries in the microwave
assembly which to the best of my knowledge is hard to compensate normally.
Maybe state of art designs have found a way to handle it properly.
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.
Surely. It could be hairpulling too.
Cheers,
Magnus
Magnus Danielson wrote:
From: Predrag Dukic stijena@tapko.de
Subject: Re: [time-nuts] Home built cesium clocks???
Date: Sun, 29 Jun 2008 12:10:46 +0200
Message-ID: 7.0.1.0.1.20080629120421.01ebecc8@tapko.de
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.
A YIG oscillator or similar should be considered. The FPGA would be great
for the state handling, but be sure to externally reclock the signal
before use to remove the FPGA jitter.
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.
In the article he referenced, the AOM only needs to handle 250,1 MHz.
Only if you intend to achieve 100% pumping and detection ratios you need
a full set of frequencies. Notice the important note on relation between
laser linewidth and S/N relationship. Luckilly those are limitations
outside of the cavity.
The interesting aspect with an optically pumped cesium is that one of the
common failuremodes, the contamination of the masspectrometer is removed.
The detection is off-axis from the beam. Wonder if an open oven could not
be installed there. That would allow for a ping-pong mode of operation,
which the optical pumping itself fits very nicely too. It would cancel
some of the systematic shifts due to assymetries in the microwave
assembly which to the best of my knowledge is hard to compensate normally.
Maybe state of art designs have found a way to handle it properly.
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.
Surely. It could be hairpulling too.
Cheers,
Magnus
Even PTB's CSF2 caesium fountain doesn't require a 9 GHz AOM:
http://tycho.usno.navy.mil/ptti/ptti2005/paper29.pdf
If one starts with a low noise 9GHz oscillator and divides down to a
suitable PLL loop frequency using regenerative multipliers then SRD
multipliers arent required.
Alternatively if you can still find a suitable NTL multiplier they are
somewhat quieter than SRDs.
Bruce
One design for a tunable Littrow ECDL built using catalog parts plus a
little machining is:
http://optics.ph.unimelb.edu.au/atomopt/publications/littrow_rsi_vol72_p4477_2001.pdf
Bruce
Bruce,
Thank You for the links. The first one is out of my reach. Also I
need some time to digest their complex optical scheme and get a grasp
of what is happening there.
The second one is more interesting. I have gratings, piezo stacks,
and access to Universitie's machine shop. I only need the diode.
It is nice that it can be purchased from Thorlabs, but I'll try
ebay first. In few months, something will appear there.
In the meantime I'll start with electronics for a classic scheme.
One step at a time....
Thanks again.
Predrag
At 15:46 29.6.2008, you wrote:
One design for a tunable Littrow ECDL built using catalog parts plus a
little machining is:
http://optics.ph.unimelb.edu.au/atomopt/publications/littrow_rsi_vol72_p4477_2001.pdf
Bruce
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We dont get much info/comments about this
But what would an ammonia cell standard be able to do.
I mean frequency/time wise.
Maybe easier and simpler ?
comments ?
Luis Cupido.
ct1dmk.
(I understand the frequencies are much higher
but that is not a problem, at least for me).
From: Bruce Griffiths bruce.griffiths@xtra.co.nz
Subject: Re: [time-nuts] Home built cesium clocks???
Date: Mon, 30 Jun 2008 01:46:54 +1200
Message-ID: 4867924E.6040702@xtra.co.nz
One design for a tunable Littrow ECDL built using catalog parts plus a
little machining is:
http://optics.ph.unimelb.edu.au/atomopt/publications/littrow_rsi_vol72_p4477_2001.pdf
More on
http://optics.ph.unimelb.edu.au/atomopt/diodes.html
http://optics.ph.unimelb.edu.au/atomopt/atomopt_publications.html
Toptica has stabilisation schemes to narrow linewidth towards a few Hz:
http://www.toptica.com/page/applications_scientific_diode_lasers_coherence-control_narrow-linewidth_broad_linewidth_coherence-length.php
Combining that with the S/N dependence on linewidth observation should be
nice reduction of that S/N source. However, one must recall all the outer
noise-sources and not overoptimize that part.
Cheers,
Magnus
Now that is something I am interested in doing. I finally secured use of a
diffusion pump at a local university and expect to be making my first sealed
all-glass absorption cells this fall. The ammonia pressure needs to be
around 8-10 microns. I will be trying for a double pass cell giving a pass
length between 10 and 12 feet. The first ammonia atomic clock used a path
length of 33 feet. The cell was made from waveguide and did not hold a
charge due to leaks or the ammonia reacting with the gold plated waveguide.
I believe the best ammonia based standard was only good to 10 ^ -8 in
frequency stability.
John WA4WDL
----- Original Message -----
From: "Luis Cupido" cupido@mail.ua.pt
To: "Discussion of precise time and frequency measurement"
time-nuts@febo.com
Sent: Sunday, June 29, 2008 11:40 AM
Subject: [time-nuts] Home built Ammonia cell std !! / Home built
cesiumclocks???
We dont get much info/comments about this
But what would an ammonia cell standard be able to do.
I mean frequency/time wise.
Maybe easier and simpler ?
comments ?
Luis Cupido.
ct1dmk.
(I understand the frequencies are much higher
but that is not a problem, at least for me).
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.
From: "John Franke" jmfranke@cox.net
Subject: Re: [time-nuts] Home built Ammonia cell std !! / Home built cesiumclocks???
Date: Sun, 29 Jun 2008 12:20:28 -0400
Message-ID: 001e01c8da04$0b83a3c0$1e89a662@youre7075dc078
Now that is something I am interested in doing. I finally secured use of a
diffusion pump at a local university and expect to be making my first sealed
all-glass absorption cells this fall. The ammonia pressure needs to be
around 8-10 microns. I will be trying for a double pass cell giving a pass
length between 10 and 12 feet. The first ammonia atomic clock used a path
length of 33 feet. The cell was made from waveguide and did not hold a
charge due to leaks or the ammonia reacting with the gold plated waveguide.
I believe the best ammonia based standard was only good to 10 ^ -8 in
frequency stability.
More like 5E-11 both in cavity pulling and collision effects. Cavity
pulling was reduced in 1961 by means of automatic cavity tuning.
Recall that you do state-selection on the ammonia beam. An electrostatic
quadrapole configuration was used. Just like a Hydrogen maser.
Cheers,
Magnus