Re: [time-nuts] EFOS Maser turns 34!
Re: EFOS Maser turns 34!
In a hydrogen maser the hydrogen atoms have to be confined in a storage-bulb within which the oscillating RF magnetic field is all in-phase. The storage-bulb has to be made from fused quartz for mechanical stability and for very low dielectric loss. The bulb has to be very thin walled, say 1mm to keep the dielectric loading and the dielectric loss acceptably small. For an active maser the product of the loaded Q-factor of the cavity and the "filling factor" of the storage bulb has to exceed a certain minimum value. The filling factor is a function of the shape of the storage bulb. Now fused quart is very difficult stuff and it can only be worked white hot "in the flame" and very few people can do it. It is much more difficult to work than ordinary glass blowing. You can't expect a storage-bulb to be made very exactly to an engineering drawing. As a result the cavity has to be machined to suit the given storage-bulb. The guys at Oscilloquartz told me that after making a lot of EFOS masers they eventually got their quartz bulb maker to make the bulbs interchangeable between cavities but you can't expect such accuracy if you want to make a one-off maser. The first time I had bulbs made the wall thickness was far too great. The quartz people said thay had no way of measuring the wall thickness. I said I can weigh the bulb and thus deduce the average thickness, indeed it was obvious just holding it the hand that it was too heavy.
It turns out that the resonant frequency of the cavity is much more critically dependent on its diameter than on its length. So it would be best to be able to mount the bulb in the cavity and to measure the resonant frequency with the cavity still in the lathe to avoid having to recentre the cavity each time one needs to take off a few thou (mils to you in the US). The loaded Q should be about 35,000 and the resonance is so narrow that one has to off-set tune the cavity so that it is on-tune when it is in vacuum and when it is at the chosen working temperature (40°C is a common choice). For an aluminium cavity the resonant frequency shifts about one bandwidth per °C of temperature change.
These are matters that need to be understood if one contemplates making one's own H-maser.
John P
In message 8EE9C792-A2F6-402D-9D07-F8929F656CA1@gmail.com, John Ponsonby writ
es:
It turns out that the resonant frequency of the cavity is
much more critically dependent on its diameter than on its length.
Copper has a quite high temperature expansion, so could you servo
that via the cavity temperature ?
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
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FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
-----Original Message-----
From: time-nuts [mailto:time-nuts-bounces@febo.com] On Behalf Of John
Ponsonby
... It turns out that the resonant frequency of the cavity is much more
critically dependent on its diameter than on its length. So it would be best
to be able to mount the bulb in the cavity and to measure the resonant
frequency with the cavity still in the lathe...
This reminds me of an anecdote about the construction of the first NH3 maser in Charles Townes's book ("How the Laser Happened.") They were having trouble with the irregularities in the cavity associated with the entrance and exit apertures for the ammonia gas. They found it was better to get rid of the gas ports altogether and open the cavity completely at the ends, essentially replacing it with a long pipe relative to the resonant frequency at K band.
Is that an option at 1420 MHz? Or would the cavity pipe and storage cylinder have to be so long that it would be even more expensive to build (and to shield)?
-- john, KE5FX
Miles Design LLC
Hi,
the thought of being able to work on building a H Maser has always accompanied me in recent years.
I fully understand the many difficulties of this project and also the necessity of a work team.
Maybe a Passive Maser would be easiest to implement, but I do not know in detail the processes
of construction of the physical part of the interrogation.
Honestly, I would love to spend My next ten years on a project like this, but...
my curiosity is to know of there are other people with these mental disorders on earth.
If you want to answer me.
Luciano
www.timeok.it
You could try a cavity like the one in;http://tf.nist.gov/general/pdf/156.pdf
This avoids the requirement for a fused quartz storage bulb.
Bruce
On Sunday, 8 January 2017 11:33 PM, timeok <timeok@timeok.it> wrote:
Hi,
the thought of being able to work on building a H Maser has always accompanied me in recent years.
I fully understand the many difficulties of this project and also the necessity of a work team.
Maybe a Passive Maser would be easiest to implement, but I do not know in detail the processes
of construction of the physical part of the interrogation.
Honestly, I would love to spend My next ten years on a project like this, but...
my curiosity is to know of there are other people with these mental disorders on earth.
If you want to answer me.
Luciano
www.timeok.it
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.
Hi
I guess the question then would be:
Is a H Maser that runs 6.6 x 10^-12 at 1 second worth the trouble?
With 100 KHz / C temperature coefficients running around, getting
good stability in a real world setting at 1 day will be “interesting”.
Just for reference: The MH-2010 data sheet shows 1.5x10^-13 at
1 second for the “cheap” version and 8x10^-14 at one second for
the low noise version. Data showing the 5065 Rb at 1x10^-12 at
1 second is running around on various web sites.
The NIST paper suggests that they made several prototypes before
they got one good one working. That’s a lot of “fun and games” with
ceramic machine lathes and Rb magnetometers…..
The punch line being - would the same effort / cost / many years of time be more
fruitful (ADEV wise) doing a large package Rb (like a 5065) ? Based on
the number of people making them in volume over the years, Rb’s appear to
be the easier item to debug, design, and build.
Bob
On Jan 8, 2017, at 6:01 AM, Bruce Griffiths bruce.griffiths@xtra.co.nz wrote:
You could try a cavity like the one in;http://tf.nist.gov/general/pdf/156.pdf
This avoids the requirement for a fused quartz storage bulb.
Bruce
On Sunday, 8 January 2017 11:33 PM, timeok <timeok@timeok.it> wrote:
Hi,
the thought of being able to work on building a H Maser has always accompanied me in recent years.
I fully understand the many difficulties of this project and also the necessity of a work team.
Maybe a Passive Maser would be easiest to implement, but I do not know in detail the processes
of construction of the physical part of the interrogation.
Honestly, I would love to spend My next ten years on a project like this, but...
my curiosity is to know of there are other people with these mental disorders on earth.
If you want to answer me.
Luciano
www.timeok.it
On 8 January 2017 at 15:22, Bob Camp kb8tq@n1k.org wrote:
Hi
I guess the question then would be:
Is a H Maser that runs 6.6 x 10^-12 at 1 second worth the trouble?
With 100 KHz / C temperature coefficients running around, getting
good stability in a real world setting at 1 day will be “interesting”.
Just for reference: The MH-2010 data sheet shows 1.5x10^-13 at
1 second for the “cheap” version and 8x10^-14 at one second for
the low noise version. Data showing the 5065 Rb at 1x10^-12 at
1 second is running around on various web sites.
The NIST paper suggests that they made several prototypes before
they got one good one working. That’s a lot of “fun and games” with
ceramic machine lathes and Rb magnetometers…..
The punch line being - would the same effort / cost / many years of time
be more
fruitful (ADEV wise) doing a large package Rb (like a 5065) ? Based on
the number of people making them in volume over the years, Rb’s appear to
be the easier item to debug, design, and build.
Bob
If you build a H2 maser, you would learn a lot more than building a bunch
of rubidiums. That sounds a good enough reason to me.
I've been contemplating buying one of the older HP 5061A or 5061B cesium
frequency standards from eBay. Almost all are sold as "for spares or
repair", and are probably not going to be economically viable to get
working due to the fact the tubes are probably useless. But I'd sure learn
a lot from playing around inside one of the older ones.
Dave
Hi
On Jan 8, 2017, at 11:21 AM, Dr. David Kirkby (Kirkby Microwave Ltd) drkirkby@kirkbymicrowave.co.uk wrote:
On 8 January 2017 at 15:22, Bob Camp kb8tq@n1k.org wrote:
Hi
I guess the question then would be:
Is a H Maser that runs 6.6 x 10^-12 at 1 second worth the trouble?
With 100 KHz / C temperature coefficients running around, getting
good stability in a real world setting at 1 day will be “interesting”.
Just for reference: The MH-2010 data sheet shows 1.5x10^-13 at
1 second for the “cheap” version and 8x10^-14 at one second for
the low noise version. Data showing the 5065 Rb at 1x10^-12 at
1 second is running around on various web sites.
The NIST paper suggests that they made several prototypes before
they got one good one working. That’s a lot of “fun and games” with
ceramic machine lathes and Rb magnetometers…..
The punch line being - would the same effort / cost / many years of time
be more
fruitful (ADEV wise) doing a large package Rb (like a 5065) ? Based on
the number of people making them in volume over the years, Rb’s appear to
be the easier item to debug, design, and build.
Bob
If you build a H2 maser, you would learn a lot more than building a bunch
of rubidiums. That sounds a good enough reason to me.
I’m not sure I agree with that. Both have their own issues. Much of the learning
in both cases involves fiddly mechanical and machining details. Working each
out by a lot of trial and error would be useful for that particular standard. It’s hard
to see how it would be useful for much else …. Yes, there is a bunch of obscure
physics involved in each, but again it’s very use specific stuff.
Bob
I've been contemplating buying one of the older HP 5061A or 5061B cesium
frequency standards from eBay. Almost all are sold as "for spares or
repair", and are probably not going to be economically viable to get
working due to the fact the tubes are probably useless. But I'd sure learn
a lot from playing around inside one of the older ones.
Dave
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and follow the instructions there.
Bob, I think you're missing the point here. This is not the quest for
utimate standards of accuracy/precision/resolution, it Is not about
economic viability, or even attainability, let alone being "worth the
trouble.".
It is about a fun project. Fun even if it comes to nothing. Is that
difficult to understand?
On Sunday, January 8, 2017, Bob Camp kb8tq@n1k.org wrote:
Hi
On Jan 8, 2017, at 11:21 AM, Dr. David Kirkby (Kirkby Microwave Ltd) <
On 8 January 2017 at 15:22, Bob Camp <kb8tq@n1k.org javascript:;>
wrote:
Hi
I guess the question then would be:
Is a H Maser that runs 6.6 x 10^-12 at 1 second worth the trouble?
With 100 KHz / C temperature coefficients running around, getting
good stability in a real world setting at 1 day will be “interesting”.
Just for reference: The MH-2010 data sheet shows 1.5x10^-13 at
1 second for the “cheap” version and 8x10^-14 at one second for
the low noise version. Data showing the 5065 Rb at 1x10^-12 at
1 second is running around on various web sites.
The NIST paper suggests that they made several prototypes before
they got one good one working. That’s a lot of “fun and games” with
ceramic machine lathes and Rb magnetometers…..
The punch line being - would the same effort / cost / many years of time
be more
fruitful (ADEV wise) doing a large package Rb (like a 5065) ? Based on
the number of people making them in volume over the years, Rb’s appear
to
be the easier item to debug, design, and build.
Bob
If you build a H2 maser, you would learn a lot more than building a bunch
of rubidiums. That sounds a good enough reason to me.
I’m not sure I agree with that. Both have their own issues. Much of the
learning
in both cases involves fiddly mechanical and machining details. Working
each
out by a lot of trial and error would be useful for that particular
standard. It’s hard
to see how it would be useful for much else …. Yes, there is a bunch of
obscure
physics involved in each, but again it’s very use specific stuff.
Bob
I've been contemplating buying one of the older HP 5061A or 5061B cesium
frequency standards from eBay. Almost all are sold as "for spares or
repair", and are probably not going to be economically viable to get
working due to the fact the tubes are probably useless. But I'd sure
learn
a lot from playing around inside one of the older ones.
Dave
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If you gaze long into an abyss, your coffee will get cold.
Hi
On Jan 8, 2017, at 11:57 AM, William H. Fite omniryx@gmail.com wrote:
Bob, I think you're missing the point here. This is not the quest for
utimate standards of accuracy/precision/resolution, it Is not about
economic viability, or even attainability, let alone being "worth the
trouble.".
It is about a fun project. Fun even if it comes to nothing. Is that
difficult to understand?
You are talking about a project that will take many years and likely
more money than the price of a new home. If that is “fun money”, then
fine. For most people that sort of commitment is a bit outside the range
of do it for fun.
Even as a “fun project”, I question the bang for the buck. If cost and time
are no object, why not do an optical ion standard or a Cesium fountain?
I would suggest that both are more cool than than a maser and likely
have a lot more fun aspects to them. You then would have something
truly unique and not simply a more expensive / poorer performing example
of something you could have bought.
Having been down this road before, there is a lot of physics involved
in any of these standards. You may not quite do the work to earn ( possibly
another) Phd in Physics, but if you do it alone, the learning will be close.
I’m by no means saying don’t do it. That is very much up to the individual
to decide. What I’m saying is that to have any chance of completing the
project, you need to face up to the costs (both money and time) up front.
If you don’t, this will simply become an exercise in thrashing around.
Bob