On Thu, 10 Nov 2016 11:20:37 +1100
Jim Palfreyman jim77742@gmail.com wrote:

Cryogenic sapphire or whispering gallery mode oscillators have been around
for quite some time. You basically have a piece of sapphire (aluminium oxide
in crystaline form)[1] in a cavity[2,3], cool everything down to liquid
helium temperatures and use this as an oscillator. There are two popular
configurations, one is to use the sapphire as resonant element like in
an LC or crystal oscillator, or more commonly, to use the sapphire as a
filter element in Pound locking scheme[4].

The short term stability of these oscillators is AFAIK unsurpassed
and flat up to 1000-10'000s, but exhibits drift at longer taus[5].

Their biggest problem is that they need a liquid helium cryo-cooler
which causes vibrations that need to be carefully filtered out.
This also makes them relatively large (fill between one and two 19" racks)

		Attila Kinali

[1] http://www.uliss-st.com/uploads/pics/tech2.jpg
[2] http://inspirehep.net/record/1244235/files/cavity.png
[3] http://www.uliss-st.com/uploads/media/imgmedias.jpg
[4] That's the (original) microwave variant of the Pound-Drever-Hall
locking scheme, see https://en.wikipedia.org/wiki/Pound%E2%80%93Drever%E2%80%93Hall_technique
[5] http://inspirehep.net/record/1409150/plots

Malek's Law:
Any simple idea will be worded in the most complicated way.

A lot of hype has been coming out of the left coast down
under for many years, with this being the latest example.
This technology tends to produce the world's most sensitive
microphone.  It's also a fairly sensitive thermometer, too,
which the helium bath tends to mask.  The prices asked
have tended to be fairly high.  Agilent (now Keysight) has made sapphire
resonators like this for use at room temperature on an
experimental basis.  They have a considerably better
design; I just happened to be talking to the designer
today, who is no longer with Keysight.  Last I heard
(2014) they were struggling with microphonics.  There
was also the well known problem of insufficient management
support for the technology.

Another issue is identifying the electronics that can
utilize this signal without degrading it.  And how to
measure this electronics to prove it isn't degrading
the signal.

Before the sapphire craze, HP/Agilent developed a
1 GHz dielectric resonator cavity (not a coaxial
resonator) that was huge.  The "puck" rivaled a
hockey puck.  I don't believe this ever got productized.
It was another big microphone of course.

Another HP experimental oscillator was a VCO that
covered an octave using around 100 varactor diodes.
It was called the "wagon wheel oscillator".  Again,
it was a hero experiment.  The total RF power was
enormous.

Just putting all this into perspective.

Rick

On 11/9/2016 4:20 PM, Jim Palfreyman wrote:

there was another sapphire oscillator company:

Industry News
http://www.microwavejournal.com/topics/3369-industry-news/ Test and
Measurement Channel
http://www.microwavejournal.com/topics/3449-test-and-measurement-channel

A Mobile Ultra-low Phase Noise Sapphire Oscillator

    Introduction to a low noise fixed-frequency X-band sapphire
    cavity oscillator

Poseidon Scientific Instruments Pty Ltd.
http://www.microwavejournal.com/authors/888-poseidon-scientific-instruments-pty-ltd
Fremantle WA  near Perth
January 1, 2002

http://www.microwavejournal.com/articles/3367-a-mobile-ultra-low-phase-noise-sapphire-oscillator

They were acquired, the produced shoe-box size  oscillators ready for
industrial/military application ...A self-confessed alternative guy from
Fremantle has sold the world-leading high technology firm he founded 24
years ago to global defense giant Raytheon.....

73

KJ6UHN

Alex

On 11/9/2016 4:48 PM, Attila Kinali wrote:

Dear Attila

You don't need a cryo-cooler, you can just use a cryostat if a break in
operation (when you top up the helium) is not a problem. We operated one of
the UWA CSOs like this as the flywheel for our Yb trapped ion frequency
standard.

A few other national standards labs use the CSOs - one for an ultra low
phase noise reference, another as the flywheel in their timescale
comprising fountains etc.

Cheers
Michael

On Thu., 10 Nov. 2016 at 11:48 am, Attila Kinali attila@kinali.ch wrote: