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SM

Scott McGrath

Tue, Mar 21, 2017 11:01 PM

Noted

However CSAC not subject to barometric effects as Rb units are

Content by Scott
Typos by Siri

On Mar 21, 2017, at 4:18 PM, jimlux jimlux@earthlink.net wrote:

On 3/21/17 12:51 PM, Scott McGrath wrote:
Or perhaps use the Symmetricom CSAC ...

Relatively expensive but might work

The CSAC is 8E-12 AVAR at 1000 seconds, comparable to a Rb.

See also http://tycho.usno.navy.mil/ptti/2011papers/Paper27.pdf
which shows a bit better performance (3E-12 @ 1000s), but the best performance appears to be at 10,000 seconds.

but don't you need better?
Attila wrote> You will need a stability 1e-14 @1d.

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Noted However CSAC not subject to barometric effects as Rb units are Content by Scott Typos by Siri > On Mar 21, 2017, at 4:18 PM, jimlux <jimlux@earthlink.net> wrote: > >> On 3/21/17 12:51 PM, Scott McGrath wrote: >> Or perhaps use the Symmetricom CSAC ... >> >> Relatively expensive but might work >> > > > The CSAC is 8E-12 AVAR at 1000 seconds, comparable to a Rb. > > > See also http://tycho.usno.navy.mil/ptti/2011papers/Paper27.pdf > which shows a bit better performance (3E-12 @ 1000s), but the best performance appears to be at 10,000 seconds. > > > but don't you need better? > Attila wrote> You will need a stability 1e-14 @1d. > _______________________________________________ > 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.

TV

Tom Van Baak

Tue, Mar 21, 2017 11:02 PM

Scott McGrath wrote:

Or perhaps use the Symmetricom CSAC ...

Chris Albertson wrote:

Get a weather balloon. Or there might already be an amateur group that
launches these. Balloons can go much higher than your local mountains.

You'll both be interested to hear that CSAC+balloon was proposed for the "Genius by Stephen Hawking" TV program and, yes, we were in touch with amateur high altitude balloon groups. The producer rightly thought that a small atomic clock going up in a helium balloon would make dramatic video for a time dilation demonstration. Symmetricom / Microsemi donated a SA.* series clock to the effort.

I got involved on the science and engineering side of the equation. Spent a month trying to make it work and in the end the balloon idea was dropped. Just too hard, and too uncertain, and would require many more months of R&D, and finger crossing. So that's why, instead, I drove six calibrated 5071A down to Tucson for a conventional mountain-valley time dilation experiment -- which I knew from prior experience would work, especially with 3x redundancy. http://leapsecond.com/great2016a/

Note that miniature Rb and Cs clocks (such as those sold by Microsemi) are very small, ultra light, and amazingly low power -- but their long-term stability (including environmental effects) is a hundred or even a thousand times worse than a 5071A/001. This is not to say CSAC are poor clocks. In fact they have a superb mass/power/size to adev ratio, and thus there are many unique applications for them. But they are not designed to be laboratory-quality frequency standards

/tvb

Scott McGrath wrote: > Or perhaps use the Symmetricom CSAC ... Chris Albertson wrote: > Get a weather balloon. Or there might already be an amateur group that > launches these. Balloons can go much higher than your local mountains. You'll both be interested to hear that CSAC+balloon was proposed for the "Genius by Stephen Hawking" TV program and, yes, we were in touch with amateur high altitude balloon groups. The producer rightly thought that a small atomic clock going up in a helium balloon would make dramatic video for a time dilation demonstration. Symmetricom / Microsemi donated a SA.* series clock to the effort. I got involved on the science and engineering side of the equation. Spent a month trying to make it work and in the end the balloon idea was dropped. Just too hard, and too uncertain, and would require many more months of R&D, and finger crossing. So that's why, instead, I drove six calibrated 5071A down to Tucson for a conventional mountain-valley time dilation experiment -- which I knew from prior experience would work, especially with 3x redundancy. http://leapsecond.com/great2016a/ Note that miniature Rb and Cs clocks (such as those sold by Microsemi) are very small, ultra light, and amazingly low power -- but their long-term stability (including environmental effects) is a hundred or even a thousand times worse than a 5071A/001. This is not to say CSAC are poor clocks. In fact they have a superb mass/power/size to adev ratio, and thus there are many unique applications for them. But they are not designed to be laboratory-quality frequency standards /tvb

BC

Bob Camp

Wed, Mar 22, 2017 12:25 AM

Hi

Ummm … errrr …. it’s a gas cell standard. I’d bet there is a pressure effect.

Bob

On Mar 21, 2017, at 7:01 PM, Scott McGrath scmcgrath@gmail.com wrote:

Noted

However CSAC not subject to barometric effects as Rb units are

Content by Scott
Typos by Siri

On Mar 21, 2017, at 4:18 PM, jimlux jimlux@earthlink.net wrote:

On 3/21/17 12:51 PM, Scott McGrath wrote:
Or perhaps use the Symmetricom CSAC ...

Relatively expensive but might work

The CSAC is 8E-12 AVAR at 1000 seconds, comparable to a Rb.

See also http://tycho.usno.navy.mil/ptti/2011papers/Paper27.pdf
which shows a bit better performance (3E-12 @ 1000s), but the best performance appears to be at 10,000 seconds.

but don't you need better?
Attila wrote> You will need a stability 1e-14 @1d.

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 Ummm … errrr …. it’s a gas cell standard. I’d bet there is a pressure effect. Bob > On Mar 21, 2017, at 7:01 PM, Scott McGrath <scmcgrath@gmail.com> wrote: > > Noted > > However CSAC not subject to barometric effects as Rb units are > > Content by Scott > Typos by Siri > >> On Mar 21, 2017, at 4:18 PM, jimlux <jimlux@earthlink.net> wrote: >> >>> On 3/21/17 12:51 PM, Scott McGrath wrote: >>> Or perhaps use the Symmetricom CSAC ... >>> >>> Relatively expensive but might work >>> >> >> >> The CSAC is 8E-12 AVAR at 1000 seconds, comparable to a Rb. >> >> >> See also http://tycho.usno.navy.mil/ptti/2011papers/Paper27.pdf >> which shows a bit better performance (3E-12 @ 1000s), but the best performance appears to be at 10,000 seconds. >> >> >> but don't you need better? >> Attila wrote> You will need a stability 1e-14 @1d. >> _______________________________________________ >> 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. > _______________________________________________ > 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.

TV

Tom Van Baak

Wed, Mar 22, 2017 2:03 AM

Yes, MAC and CSAC do show environmental sensitivity. But that should not be a surprise to anyone that works with precise time & frequency.

The factors include voltage, temperature, temperature gradient, pressure, humidity, acceleration, tilt (orientation), and who knows what else. Maybe even radiation? One looks for the coefficient of course, but also linearity, repeatability, hysteresis, and even interaction amongst factors. It's not an easy task to do this, nor can one assume each unit of a given make/model will be the same. I don't have comprehensive data or a nice report.

But attached is one of the first plots where I put a SA.32m in a home-brew vacuum chamber and pulled down to a few inches of Hg for a few hours to simulate the low pressure of a flight up to 50 or 90,000 ft. For a high altitude relativity experiment -- where you'd like your clock to remain stable to parts in e-13 and not accumulate too many stray ns -- it's not a good sign when your clock changes by 2e-11 (that's more than 1 ns per minute) just because of ambient pressure changes.

Of course some of you are thinking: use isolation, regulation, and live or even post-processed compensation mechanisms. If someone seriously wants to pursue the CSAC / balloon concept contact me off-list. A fair amount of work went into it before we pulled the plug. I watched enough HAB (high altitude balloon) videos to make me ill. For our precious nanoseconds, it is a very hostile environment up there.

Maybe let's take this thread off-list.

/tvb

Yes, MAC and CSAC do show environmental sensitivity. But that should not be a surprise to anyone that works with precise time & frequency. The factors include voltage, temperature, temperature gradient, pressure, humidity, acceleration, tilt (orientation), and who knows what else. Maybe even radiation? One looks for the *coefficient* of course, but also linearity, repeatability, hysteresis, and even interaction amongst factors. It's not an easy task to do this, nor can one assume each unit of a given make/model will be the same. I don't have comprehensive data or a nice report. But attached is one of the first plots where I put a SA.32m in a home-brew vacuum chamber and pulled down to a few inches of Hg for a few hours to simulate the low pressure of a flight up to 50 or 90,000 ft. For a high altitude relativity experiment -- where you'd like your clock to remain stable to parts in e-13 and not accumulate too many stray ns -- it's not a good sign when your clock changes by 2e-11 (that's more than 1 ns per minute) just because of ambient pressure changes. Of course some of you are thinking: use isolation, regulation, and live or even post-processed compensation mechanisms. If someone seriously wants to pursue the CSAC / balloon concept contact me off-list. A fair amount of work went into it before we pulled the plug. I watched enough HAB (high altitude balloon) videos to make me ill. For our precious nanoseconds, it is a very hostile environment up there. Maybe let's take this thread off-list. /tvb

CA

Chris Albertson

Wed, Mar 22, 2017 2:12 AM

"flight" there is the word. Why drive up a mountain? Take the clock
with you inside the pressurized cabin of a commercial airliner next time
you are on one of those 10 hour trans=pacific flights. You be taller then
any mountain and it is actually cheaper then a weather balloon.

Can you get a Rb clock past the TSA x-ray machine. Maybe if you ask
first. There must be a way to hand cary specialized equipment.

On Tue, Mar 21, 2017 at 7:03 PM, Tom Van Baak tvb@leapsecond.com wrote:

But attached is one of the first plots where I put a SA.32m in a home-brew
vacuum chamber and pulled down to a few inches of Hg for a few hours to
simulate the low pressure of a flight up to 50 or 90,000 ft. For a high
altitude relativity experiment -- where you'd like your clock to remain
stable to parts in e-13 and not accumulate too many stray ns -- it's not a
good sign when your clock changes by 2e-11 (that's more than 1 ns per
minute) just because of ambient pressure changes.

--

Chris Albertson
Redondo Beach, California

"flight" there is the word. Why drive up a mountain? Take the clock with you inside the pressurized cabin of a commercial airliner next time you are on one of those 10 hour trans=pacific flights. You be taller then any mountain and it is actually cheaper then a weather balloon. Can you get a Rb clock past the TSA x-ray machine. Maybe if you ask first. There must be a way to hand cary specialized equipment. On Tue, Mar 21, 2017 at 7:03 PM, Tom Van Baak <tvb@leapsecond.com> wrote: > > But attached is one of the first plots where I put a SA.32m in a home-brew > vacuum chamber and pulled down to a few inches of Hg for a few hours to > simulate the low pressure of a flight up to 50 or 90,000 ft. For a high > altitude relativity experiment -- where you'd like your clock to remain > stable to parts in e-13 and not accumulate too many stray ns -- it's not a > good sign when your clock changes by 2e-11 (that's more than 1 ns per > minute) just because of ambient pressure changes. > -- Chris Albertson Redondo Beach, California

J

jimlux

Wed, Mar 22, 2017 5:05 AM

On 3/21/17 5:25 PM, Bob Camp wrote:

Hi

Ummm … errrr …. it’s a gas cell standard. I’d bet there is a pressure effect.

But the gas cell, the laser, etc. is in a vacuum - that's the "wear out"
mechanism for a CSAC - the getter fills up, the pressure inside the
vacuum package increases, and the heater can't keep it hot.

I'm speculating here... I don't really know enough about the guts of the
CSAC to be sure.

On 3/21/17 5:25 PM, Bob Camp wrote: > Hi > > Ummm … errrr …. it’s a gas cell standard. I’d bet there is a pressure effect. > But the gas cell, the laser, etc. is in a vacuum - that's the "wear out" mechanism for a CSAC - the getter fills up, the pressure inside the vacuum package increases, and the heater can't keep it hot. I'm speculating here... I don't really know enough about the guts of the CSAC to be sure.

J

jimlux

Wed, Mar 22, 2017 5:08 AM

On 3/21/17 7:03 PM, Tom Van Baak wrote:

Yes, MAC and CSAC do show environmental sensitivity. But that should not be a surprise to anyone that works with precise time & frequency.

The factors include voltage, temperature, temperature gradient, pressure, humidity, acceleration, tilt (orientation), and who knows what else. Maybe even radiation? One looks for the coefficient of course, but also linearity, repeatability, hysteresis, and even interaction amongst factors. It's not an easy task to do this, nor can one assume each unit of a given make/model will be the same. I don't have comprehensive data or a nice report.

But attached is one of the first plots where I put a SA.32m in a home-brew vacuum chamber and pulled down to a few inches of Hg for a few hours to simulate the low pressure of a flight up to 50 or 90,000 ft. For a high altitude relativity experiment -- where you'd like your clock to remain stable to parts in e-13 and not accumulate too many stray ns -- it's not a good sign when your clock changes by 2e-11 (that's more than 1 ns per minute) just because of ambient pressure changes.

I wonder if the effect is due to vacuum, or something like thermal
gradients (no convective heat transfer in vacuo)

On 3/21/17 7:03 PM, Tom Van Baak wrote: > Yes, MAC and CSAC do show environmental sensitivity. But that should not be a surprise to anyone that works with precise time & frequency. > > The factors include voltage, temperature, temperature gradient, pressure, humidity, acceleration, tilt (orientation), and who knows what else. Maybe even radiation? One looks for the *coefficient* of course, but also linearity, repeatability, hysteresis, and even interaction amongst factors. It's not an easy task to do this, nor can one assume each unit of a given make/model will be the same. I don't have comprehensive data or a nice report. > > But attached is one of the first plots where I put a SA.32m in a home-brew vacuum chamber and pulled down to a few inches of Hg for a few hours to simulate the low pressure of a flight up to 50 or 90,000 ft. For a high altitude relativity experiment -- where you'd like your clock to remain stable to parts in e-13 and not accumulate too many stray ns -- it's not a good sign when your clock changes by 2e-11 (that's more than 1 ns per minute) just because of ambient pressure changes. > I wonder if the effect is due to vacuum, or something like thermal gradients (no convective heat transfer in vacuo)

MW

Michael Wouters

Wed, Mar 22, 2017 5:36 AM

Yes, that's what I was quoted by the Microsemi agent and the price on
Mouser is similar.
The $1568 version was EOL'ed in December 2016; the more expensive unit is
the '2nd generation'.

Cheers
Michael

On Wed, 22 Mar 2017 at 9:06 am, jimlux jimlux@earthlink.net wrote:

On 3/21/17 1:40 PM, Michael Wouters wrote:

These are less stable than a rubidium eg tau=10e-11@1000s and monthly
ageing of 9e-10.
The price of these has gone up too- they're now about US5000.

Really? That's a big increase. I bought some last year (well, in
December 2015) and they were $1568 ea.

It was a pain to buy them because Microsemi fell off JPL's approved
supplier list.

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Yes, that's what I was quoted by the Microsemi agent and the price on Mouser is similar. The $1568 version was EOL'ed in December 2016; the more expensive unit is the '2nd generation'. Cheers Michael On Wed, 22 Mar 2017 at 9:06 am, jimlux <jimlux@earthlink.net> wrote: > On 3/21/17 1:40 PM, Michael Wouters wrote: > > These are less stable than a rubidium eg tau=10e-11@1000s and monthly > > ageing of 9e-10. > > The price of these has gone up too- they're now about US5000. > > > > Really? That's a big increase. I bought some last year (well, in > December 2015) and they were $1568 ea. > > It was a pain to buy them because Microsemi fell off JPL's approved > supplier list. > > _______________________________________________ > 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. >

HB

Hugh Blemings

Wed, Mar 22, 2017 6:31 AM

Hi,

My profound thanks to Tom, Bob, Chris, Attila, Scott, Jim, Hal and
Michael for such thorough and thoughtful replies to my initial post.

I'm fortunate enough to know some of the local amateur high altitude
balloon crowd and had contemplated such an endeavour but note this
wouldn't be feasible due to the pressure and temperature sensitivities
of the Rb sources.

I had also thought the weight limitations might be a factor - an ardunio
and a battery one thing to slow if things go wrong, a Rb clock and other
bits a whole nother can of worms :)

I will still pick up one of the surplus Rb units and tinker with it, my
GPSDO and my TAPR TICC that arrived the other day.

Slightly more pedestrian (but equally fun :) construction projects ahead
I'm sure - keeping things stable in my garage in an Australian summer
may yet prove challenge enough ;)

Thanks again

vy 73
Hugh
VK3YYZ/AD5RV

Hi, My profound thanks to Tom, Bob, Chris, Attila, Scott, Jim, Hal and Michael for such thorough and thoughtful replies to my initial post. I'm fortunate enough to know some of the local amateur high altitude balloon crowd and had contemplated such an endeavour but note this wouldn't be feasible due to the pressure and temperature sensitivities of the Rb sources. I had also thought the weight limitations might be a factor - an ardunio and a battery one thing to slow if things go wrong, a Rb clock and other bits a whole nother can of worms :) I will still pick up one of the surplus Rb units and tinker with it, my GPSDO and my TAPR TICC that arrived the other day. Slightly more pedestrian (but equally fun :) construction projects ahead I'm sure - keeping things stable in my garage in an Australian summer may yet prove challenge enough ;) Thanks again vy 73 Hugh VK3YYZ/AD5RV

MW

Michael Wouters

Wed, Mar 22, 2017 7:04 AM

Dear Chris,

I believe IATA prohibits the carriage of any quantity of rubidium on
passenger aircraft.
You have to complete a "Dangerous Goods Declaration" and it then has
to go by cargo aircraft.

Cheers
Michael

On Wed, Mar 22, 2017 at 1:12 PM, Chris Albertson
albertson.chris@gmail.com wrote:

"flight" there is the word. Why drive up a mountain? Take the clock
with you inside the pressurized cabin of a commercial airliner next time
you are on one of those 10 hour trans=pacific flights. You be taller then
any mountain and it is actually cheaper then a weather balloon.

Can you get a Rb clock past the TSA x-ray machine. Maybe if you ask
first. There must be a way to hand cary specialized equipment.

On Tue, Mar 21, 2017 at 7:03 PM, Tom Van Baak tvb@leapsecond.com wrote:

But attached is one of the first plots where I put a SA.32m in a home-brew
vacuum chamber and pulled down to a few inches of Hg for a few hours to
simulate the low pressure of a flight up to 50 or 90,000 ft. For a high
altitude relativity experiment -- where you'd like your clock to remain
stable to parts in e-13 and not accumulate too many stray ns -- it's not a
good sign when your clock changes by 2e-11 (that's more than 1 ns per
minute) just because of ambient pressure changes.

--

Chris Albertson
Redondo Beach, California

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.

Dear Chris, I believe IATA prohibits the carriage of any quantity of rubidium on passenger aircraft. You have to complete a "Dangerous Goods Declaration" and it then has to go by cargo aircraft. Cheers Michael On Wed, Mar 22, 2017 at 1:12 PM, Chris Albertson <albertson.chris@gmail.com> wrote: > "flight" there is the word. Why drive up a mountain? Take the clock > with you inside the pressurized cabin of a commercial airliner next time > you are on one of those 10 hour trans=pacific flights. You be taller then > any mountain and it is actually cheaper then a weather balloon. > > Can you get a Rb clock past the TSA x-ray machine. Maybe if you ask > first. There must be a way to hand cary specialized equipment. > > > > On Tue, Mar 21, 2017 at 7:03 PM, Tom Van Baak <tvb@leapsecond.com> wrote: > >> >> But attached is one of the first plots where I put a SA.32m in a home-brew >> vacuum chamber and pulled down to a few inches of Hg for a few hours to >> simulate the low pressure of a flight up to 50 or 90,000 ft. For a high >> altitude relativity experiment -- where you'd like your clock to remain >> stable to parts in e-13 and not accumulate too many stray ns -- it's not a >> good sign when your clock changes by 2e-11 (that's more than 1 ns per >> minute) just because of ambient pressure changes. >> > -- > > Chris Albertson > Redondo Beach, California > _______________________________________________ > 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.

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Time Dilation tinkering