As I understand it, not only the intensity of the ambient H-field but its
orientation is critical.  Sounds like you either pulled the 1,0 -> 0,0
transition frequency too far for the control loop to compensate, or the
static field was no longer oriented properly with respect to the cavity's TE
mode axis.

The impression I got from my reading on the subjecct is that tuning an
H-maser isn't something you can do incrementally.  It's not a conventional
RF tank circuit -- there's a list of factors as long as your arm that have
to be just right, or you will get nothing at all for your trouble.  Getting
those factors right seems to require a graduate-level understanding of both
the materials and the math.  Ars longa, vita brevis.

I imagine the cavity has to be pretty stout not to either collapse from
barometric pressure or flex excessively.

It would be great if you could upload these to the Manuals page at
www.ko4bb.com.  I've looked over the Symmetricom maser's manual but it's
pretty terse.

The current edition is $70 at Amazon, not too bad by textbook standards.
It's a good book, but often more valuable as a pointer for further reading
than as a practical, up-to-date handbook.  Seems like a good overview of
vacuum technology.

The book you really want to start with is Major's "The Quantum Beat," IMHO.

(Shrug) PLLs are PLLs.  I don't see a role for a PC in the cavity tuning or
oscillator disciplining loops, but that's a very small part of the overall
control picture.  Most of the actual software work would involve UI design
for monitoring (and ideally graphing) the dozens of operating parameters
over time.  It would probably make the most sense to use either analog or
microcontroller-based controls for the realtime (RF) loops, and use Labview
or another instrumentation package to monitor everything.

There are also various high-latency thermal loops that could be controlled
as well as monitored by Labview-like software on the PC.

-- john, KE5FX

That would be great. If the files are really big (over 100MB) and if your internet access is not truly broadband, you may find it more convenient to put them on a CD/DVD and snail mail them to me if you prefer.

Either way is fine with me

Didier KO4BB

Sent from my BlackBerry Wireless thingy while I do other things...

-----Original Message-----
From: "John Miles" jmiles@pop.net
Sender: time-nuts-bounces@febo.com
Date: Sun, 29 Aug 2010 16:39:42
To: Discussion of precise time and frequency measurementtime-nuts@febo.com
Reply-To: Discussion of precise time and frequency measurement
time-nuts@febo.com
Subject: Re: [time-nuts] Homebrew H Maser

As I understand it, not only the intensity of the ambient H-field but its
orientation is critical.  Sounds like you either pulled the 1,0 -> 0,0
transition frequency too far for the control loop to compensate, or the
static field was no longer oriented properly with respect to the cavity's TE
mode axis.

The impression I got from my reading on the subjecct is that tuning an
H-maser isn't something you can do incrementally.  It's not a conventional
RF tank circuit -- there's a list of factors as long as your arm that have
to be just right, or you will get nothing at all for your trouble.  Getting
those factors right seems to require a graduate-level understanding of both
the materials and the math.  Ars longa, vita brevis.

I imagine the cavity has to be pretty stout not to either collapse from
barometric pressure or flex excessively.

It would be great if you could upload these to the Manuals page at
www.ko4bb.com.  I've looked over the Symmetricom maser's manual but it's
pretty terse.

The current edition is $70 at Amazon, not too bad by textbook standards.
It's a good book, but often more valuable as a pointer for further reading
than as a practical, up-to-date handbook.  Seems like a good overview of
vacuum technology.

The book you really want to start with is Major's "The Quantum Beat," IMHO.

(Shrug) PLLs are PLLs.  I don't see a role for a PC in the cavity tuning or
oscillator disciplining loops, but that's a very small part of the overall
control picture.  Most of the actual software work would involve UI design
for monitoring (and ideally graphing) the dozens of operating parameters
over time.  It would probably make the most sense to use either analog or
microcontroller-based controls for the realtime (RF) loops, and use Labview
or another instrumentation package to monitor everything.

There are also various high-latency thermal loops that could be controlled
as well as monitored by Labview-like software on the PC.

-- john, KE5FX

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.

Yes and no.

I watched while a cryogenic MASER experiment was done at Harvard.

First off, a H MASER built at Smithsonian Astrophysical Observatory, was
set up and a GPS set up as a comparison. This was late 1980s.

That MASER was used as a reference for a synthesizer which was swept a
Hertz two around the 1421 MHz frequency to excite the cavity. The cavity
was peaked with a reflectometer using a narrow sweep and then H was added.
Parameters were adjusted while the cavity microwave field monitored.

The RF field was pulsed, as I remember, and they watched as the RF decayed
in a damped exponential. You could see what was happening to the gain of
the medium, the decay took longer, and parameters were slowly adjusted to
the point where there was enough gain to oscillate and thing "took off".

Fun stuff, if you have lots of time.

Best,

-J0ohn

==========

On Sun, Aug 29, 2010 at 7:56 PM, Didier Juges didier@cox.net wrote:

Try the old DjVu Solo 3.1 program that you can download from here:
http://djvu.org/resources/
I've seen it turn 100M page scans into 100K files.  If you want to turn the
DjVu into a PDF, use the Print command to a PDF driver, such as GhostScript,
or Acrobat.

--
http://blog.softwaresafety.net/
http://www.designer-iii.com/
http://www.wearablesmartsensors.com/

On Sun, 29 Aug 2010 13:27:13 -0700
Corby Dawson cdelect@juno.com wrote:

Hmm.. i'd guess that the oscillation went outside the cavity's resonant
range. Other than shifting the resonance frequency and spreading the
hyperfine lines, it should not have any other effect. But i might
be very well wrong.

The thermal length constant of Al is 23e-6/K, which means that per
°C you get a pulling of about 23ppm of the frequency. Guestimating
that more than 20°C of heating should not be done to keep the whole
thing in a easy to handle range. Then we would have a maximum pulling
range of +/-230ppm, which means +/-10um precission on a 10cm diameter.
This is still a very thight tollerance. Not impossible, but not that
easy either.

I couldn't find anything telling me that it is difficult to do
when i did a quick search. If i understood it correctly, the collimator
for a H-maser is nothing else than a tight and straight pipe from the
H beam source to the state selector magnet. Did i misunderstand something
here?

I would very much like to read those. Even if i dont build a maser.
As John suggested, it would be IMHO best to put them on Didier's site
as others might be interested as well.

		Attila Kinali

--
If you want to walk fast, walk alone.
If you want to walk far, walk together.
-- African proverb