Hi,
On that note we have Rick Karlquists article showing how he replaced the
traditional syntheis chain with an oscillator at the target frequency,
locked to the lower frequency. Benefit is in the phase-noise.
This was from the fine work on the 5071A.
This approach can be used for rubidiums too, if you care about phase
noise going into the cavity.
The traditional chain has essentially only one oscillator, but one leg
in the synthesis chain has a phase-modulation with the modulation
frequency for the sensing of the atomic reference.
Cheers,
Magnus
On 04/13/2017 01:19 AM, Bob kb8tq wrote:
Hi
There are papers from the mid 90’s talking about improving the GPS Rb’s. Those
parts are
as far as I know the best “production” Rb’s out there. The main comment seems
to be that
phase noise (in it’s various forms) is a major contributor to the stability of
the Rb’s….
Bob
On Apr 12, 2017, at 4:55 PM, Bert Kehren via time-nuts <time-nuts@febo.com>
wrote:
Looking back at the dialog I started on Rb’s and the repeated returns to
that subject allow me to make some comments, observations and
recommendations.. I stayed on purpose away from participating but learned a
lot. It also
resulted in some off list dialogs with members working on the subject off
list.
Rick’s discussion on why to use two frequencies was for me an eye opener
and gives me clear directions on how to proceed on frequency generation. The
single frequency project is dumped. Corby’s work on filters again
influences our future steps. Using a laser diode and its challenges again an
eye
opener and a challenge. We have time nuts that have working systems.
Let’s be honest, we have members with super knowledge but very few have
the appetite to do something with it in the form of hardware. Here is my
proposal that is based on walk before run.
FRK and M100 are next to the HP 5065A the most promising Rb’s in what we
like to do. They are easy to work on specially when you are 75/78 and in my
case have a macular hole.
Optical Filter. Corby actually did insert a filter in a M100 did however
not notice an improvement. When we discussed it come to find out he forgot
to change the time constant so the cell did not control the performance.
This was years ago and like many of us has his hands full with projects. He
decided to pass his M100/FRK to an other time nut and focus on HP and Maser.
We all benefit from these efforts.
Back to filter we have dissected a FRK and a M100 and are convinced that
there is a room for a filter, in case of the FRK, very easy. Corby used a
M100, in my opinion more of a challenge. Will not try it. After discussions
with Corby I now understand that the filter does not filter out a particular
wavelength but most the noise that Rb lamps produce as seen on optical
spectrum analyzers. It improves signal noise ratio after all that is what is
all about. Once we have completed our current projects we may do so.
We are also considering to review the frequency generation using Rick’s
postings as guidance. All this needs measuring capabilities which is what we
are working on. I am fortunate to have access to Corby’s Maser but Juerg
does not have that. We are working on a solution.
There are many FRK/M100’s out there some with low output lamps that would
be a natural for a Laser Diode replacement. The mechanical makeup begs for
a Laser solution. The two units have a cell in size only second to HP5065A
Going to laser would also allow to reduce cell temperature again
contributing to an improved signal noise ratio,
This is way off our expertise but it would be nice if some one would take
the ball and run with it. I am convinced from off list conversations that
$1000 is a reasonable goal.
There is no guarantee that we will do the filter depending what our
results will be on our present work so again maybe some one would carry that
ball.
Both can be a first step for future work. WALK
Bert Kehren
In a message dated 4/11/2017 12:02:09 P.M. Eastern Daylight Time,
att...@kinali.ch writes:
On Tue, 11 Apr 2017 07:31:01 +0000
Andre <an...@lanoe.net> wrote:
Has anyone else either built an atomic clock around a bare Rb lamp
module "core" or attempted
to make a hydrogen maser?
Building my own Rb vapor cell standard or H-maser is on my list
of Things-I-have-to-do-before-I-die :-)
If I had to do one of those now, I would go for a Rb vapor cell
with dual-resonance using an external cavity laser diode for pumping.
The electronics for such a thing are relatively easy, if you are not
afraid of Jiga-Hurts and using these pesky QFN packages. But it isn't
cheap either. There was a discussion started by Bert[1] where I ventured
a rough calculation what I think it wold cost. Though I think I have
understimated the cost of an ECLD (it's more like 1k-5k from what I have
read)
Attila Kinali
[1] search for "thinking outside the box" in the archives
--
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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