Bob Camp wrote:

Figure 7 on the FE5680 page (also on the data sheet) indicates that you
may need somewhat less than 3hours to achieve  ADEV ~1E-13.
0.01C stability should be adequate.however its not necessary to control
the room temperature to this stability if the FE5680 is in an enclosure
with a sufficiently high time constant whilst having a sufficiently low
thermal resistance so as to avoid overheating the FE5680.

Bruce

The cheap Datum LPRO-101s coming out of China appear to be capable of great
performance, no problems at all getting into the 1E-13s at t=1000 seconds.

(This plot shouldn't be taken seriously beyond t=1000s, and the flattening
effect at t=700s might be the Thunderbolt's fault.  I haven't run my
LPRO-101 long enough to see what it will do at 10000 seconds, but at some
point the ADEV curve can be expected to turn upward for real.)

-- john, KE5FX

Hi

I agree that if you simply bolt the rubidium to an old engine block and toss a blanket over it, you might get some pretty good thermal stability in the "hour to couple hours" time period. That's certainly a better approach than putting some kind of DC heater (and it's varying magnetic field) near the rubidium.

I'm still wondering if they do indeed hit 1x10-13 (as in almost 1x10-14) or not. I suspect not. I'm sure that they do indeed get into the 1x10-13's, just not sure they get to the bottom of that region.

Bob

On Dec 22, 2009, at 8:26 PM, Bruce Griffiths wrote:

Bob

Some isothermal radiation (thermal) shields between the blanket and the
top of the Rubidium source may also be required.

Unless you have a hydrogen maser you will need to use 3 rubidium sources
each with its own engine block in order to determine AVAR (using the 3
cornered hat technique).
FEI claim that their rubidium sources are actually quieter than typical
caesium sources so using a caesium reference isn't as effective for
measuring the short term (< 1day) stability.

Bruce

Bob Camp wrote:

That's what I've found, even with no special effort to heat-sink the LPRO's
baseplate.  You need a better-than-average cesium standard to benchmark the
medium-term stability of one of these.  Not bad for $79...

-- john, KE5FX

sheesh! How about a right-sized water jug?
Don

----- Original Message -----
From: "Bob Camp" lists@cq.nu
To: "Discussion of precise time and frequency measurement"
time-nuts@febo.com
Sent: Tuesday, December 22, 2009 8:23 PM
Subject: Re: [time-nuts] Cheap Rubidium

Hi

Well the intent is indeed to set up a number of them, and run clean up OCXO's after them. I'm guessing at least 4 setups and possibly eight or ten.

Bob

On Dec 22, 2009, at 11:12 PM, Bruce Griffiths wrote:

Hi

Water might work. It would take quite a bit of it.

Here's my "wild guess" level math:

1. The basement moves 0.1 to 1 C short term / over a day.

2. I want to get to < 0.01

That takes the time constant out to >= 10X the time I'm interested in.

3. The time period of interest is 3 to 30 hours.

That gets to a time constant of at least 10 days.

At the same time you have >10 watts coming out of the gizmo. You can't put the thermal mass inside a vacuum  bottle.

I suspect that some combination of thermal mass and active stabilization will be needed.

So much fun ....

Bob

On Dec 23, 2009, at 2:18 AM, Don Latham wrote:

Try an insulated water cooled metal block for the baseplate heatsink
The water can be recirculated and heated/cooled as required.

With a recirculating system and say 25W dissipation with no temperature
control you will only need about 5 cubic meters (5 tons) of water to
maintain a temperature rise of less than 0.01C for 3 hours. Assuming
that the 25W rubidium dissipation is the only significant source of
heating for the water.
That means you need a well insulated swimming pool in your basement.

Controlling the temperature of a smaller amount of recirculating water
is probably a simpler proposition.

Bob Camp wrote:

Bob,

I don't know why you would want 4 Rb's running, not to mention 8 or ten of them.  I don't see the need for a follow up OCXO either.  If you had such a good OCXO, it would not make much sense to also have the Rb.

You could put an oil bath together for a better thermal mass.  Use a mineral oil much like Johnson&Johnson Baby oil.

You would probably want at least two gallons (if not more) per Rb and make sure you have a heat sink on the Rb to help spread the heat in to the oil.  If you have a big enough tube then you could have all four in the same pot.

You would want to stir the oil constantly at a slow rate.  A small 2 1/2 or 3 " 12 volt computer fan, suspended in the oil, would be good for that.  You can adjust it's speed by varying the voltage to the fan.  The Johnson&Johnson Baby type mineral Oil would not hurt the electronics, but it would be messy in some
respects.

Bill....WB6BNQ

Bob Camp wrote:

I meant to say TUB not tube in the third paragraph.

WB6BNQ wrote:

Hi

If you can achieve <= 1x10^-13 at 10,000 to 100,000 seconds, that's quite a
bit better than any OCXO has a right to be doing. Yes I know that there is
one in the entire universe that gets close.

Even if you just do < 1x10^-12 at 1,000 seconds, that's better than a whole
lot of OCXO's will do at that tau.

The place where the OCXO does come in is < 100 seconds. Between 1 and 100
seconds you can get a number of OCXO's that will run <2x10^-12 over the
entire range. You can fine a lot more that will do < 1x10-12 over that range
than you can find that will do < 1x10^-12 at 1,000 seconds. The rubidium is
struggling to get to 1x10^-11 at 1 second and may or may not get to 1x10^-12
at 100 seconds.

To get the "best", you need both the medium term of the rubidium and the
short term of a good OCXO.

Once the rubidium starts to "turn up" from it's floor, you may need GPS. Of
course it takes GPS quite a while to get to well below 1.0x10-13 unless you
are comparing two GPS's to each other.

The reason for needing more than one is that you really won't know what's
going on unless you compare them to each other. That assumes you don't have
an active hydrogen maser running full time in the basement (I don't ...).
Three is a nice number, four is reasonable if one is running as an offset
oscillator chain for beat note frequency measurements.

Past four it's just experimenting with this and that. If you need 10 samples
at 100,000 seconds it can take a while just to see what you have done...

So much fun ...

Bob

-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of WB6BNQ
Sent: Wednesday, December 23, 2009 8:08 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Cheap Rubidium

Bob,

I don't know why you would want 4 Rb's running, not to mention 8 or ten of
them.  I don't see the need for a follow up OCXO either.  If you had such a
good OCXO, it would not make much sense to also have the Rb.

You could put an oil bath together for a better thermal mass.  Use a mineral
oil much like Johnson&Johnson Baby oil.

You would probably want at least two gallons (if not more) per Rb and make
sure you have a heat sink on the Rb to help spread the heat in to the oil.
If you have a big enough tube then you could have all four in the same pot.

You would want to stir the oil constantly at a slow rate.  A small 2 1/2 or
3 " 12 volt computer fan, suspended in the oil, would be good for that.  You
can adjust it's speed by varying the voltage to the fan.  The
Johnson&Johnson Baby type mineral Oil would not hurt the electronics, but it
would be messy in some
respects.

Bill....WB6BNQ

Bob Camp wrote:

the thermal mass inside a vacuum  bottle.

will be needed.

time-nuts@febo.com

toss a blanket over it, you might get some pretty good thermal stability in
the "hour to couple hours" time period. That's certainly a better approach
than putting some kind of DC heater (and it's varying magnetic field) near
the rubidium.

1x10-14) or not. I suspect not. I'm sure that they do indeed get into the
1x10-13's, just not sure they get to the bottom of that region.

term stability is 1.4/sqrt(Tau) x 10-11.  Since I never doubt anything I see
on a data sheet, this immediately tells me I should get 1.4x10-12 at 100
seconds, and I only have to wait for 10,000 seconds to get to 1.4x10-13.

would need a room that's stable to much better than 0.1 C over a 3 hour
period to get there. I suspect that 0.01C might not be good enough ...

very stable temperature environment to see how close they get / what the
floor is?  I've run through a lot of data on the web, but I haven't really
found what I'm looking for.

you may need somewhat less than 3hours to achieve  ADEV ~1E-13.

control the room temperature to this stability if the FE5680 is in an
enclosure with a sufficiently high time constant whilst having a
sufficiently low thermal resistance so as to avoid overheating the FE5680.

https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts

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Hi

So if I want to set up 4 uncorrelated systems, that would require 20 tons of
water split into 4 tubs. Each tub would be roughly 3' x 4' x 15'. Of course
if they are all in the same basement, I still have a correlation problem. My
guess is that no matter what I do, any system that controls all the systems
the same way will run into correlation.

Oils, silicon fluids, and the like mostly hold less heat than water so the
tubs would get bigger. Maybe a few tons of mercury...

Active heat control and a rational heat sink is sounding like a better
approach...

Bob

-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of Bruce Griffiths
Sent: Wednesday, December 23, 2009 8:01 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Cheap Rubidium

Try an insulated water cooled metal block for the baseplate heatsink
The water can be recirculated and heated/cooled as required.

With a recirculating system and say 25W dissipation with no temperature
control you will only need about 5 cubic meters (5 tons) of water to
maintain a temperature rise of less than 0.01C for 3 hours. Assuming
that the 25W rubidium dissipation is the only significant source of
heating for the water.
That means you need a well insulated swimming pool in your basement.

Controlling the temperature of a smaller amount of recirculating water
is probably a simpler proposition.

Bob Camp wrote:

the thermal mass inside a vacuum  bottle.

will be needed.

measurement"time-nuts@febo.com

toss a blanket over it, you might get some pretty good thermal stability in
the "hour to couple hours" time period. That's certainly a better approach
than putting some kind of DC heater (and it's varying magnetic field) near
the rubidium.

or not. I suspect not. I'm sure that they do indeed get into the 1x10-13's,
just not sure they get to the bottom of that region.

term stability is 1.4/sqrt(Tau) x 10-11.  Since I never doubt anything I see
on a data sheet, this immediately tells me I should get 1.4x10-12 at 100
seconds, and I only have to wait for 10,000 seconds to get to 1.4x10-13.

need a room that's stable to much better than 0.1 C over a 3 hour period
to get there. I suspect that 0.01C might not be good enough ...

very stable temperature environment to see how close they get / what the
floor is?  I've run through a lot of data on the web, but I haven't really
found what I'm looking for.

may need somewhat less than 3hours to achieve  ADEV ~1E-13.

the room temperature to this stability if the FE5680 is in an enclosure with
a sufficiently high time constant whilst having a sufficiently low thermal
resistance so as to avoid overheating the FE5680.

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and follow the instructions there.

Bob Camp wrote:

Try about 145 tons of mercury per rubidium source as the specific heat
of mercury is about 1/29 that of water.
The redeeeming feature is that it will only occupy about 2.14x the volume.
The specific of some oils may be as large as 1/2 that of water however
the density is around 10-20% lower.

Distributed heating using wire wound or printed heaters perhaps, but to
reduce the associated magnetic field bifilar winding should be considered.
The major limitation is that the 25W or so dissipated by the rubidium
source has to be transferred to ambient without raising the rubidium
temperature too much.
This limits the maximum thermal resistance between the baseplate and
ambient that can be safely used.

Bruce

Hi

Well so much for my plans to corner the mercury market and ultimately become
a super fund site...

I had the conversation about "heater blankets" back a while ago. Apparently
the magic printed circuit board like heaters have a much lower magnetic
signature than a twisted pair of heater wire. I didn't dig into it at the
time, and simply accepted it as being true. I'm hoping I can get away with
twisted pair heater wire....

Bob

-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of Bruce Griffiths
Sent: Wednesday, December 23, 2009 2:58 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Cheap Rubidium

Bob Camp wrote:

of

course

My

systems

Try about 145 tons of mercury per rubidium source as the specific heat
of mercury is about 1/29 that of water.
The redeeeming feature is that it will only occupy about 2.14x the volume.
The specific of some oils may be as large as 1/2 that of water however
the density is around 10-20% lower.

Distributed heating using wire wound or printed heaters perhaps, but to
reduce the associated magnetic field bifilar winding should be considered.
The major limitation is that the 25W or so dissipated by the rubidium
source has to be transferred to ambient without raising the rubidium
temperature too much.
This limits the maximum thermal resistance between the baseplate and
ambient that can be safely used.

Bruce

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Typical (Cassini, MGS, etc., data from Sami Asmar) UltraStableOscillator (USO) specs as used in spaceflight do about 1E-13 at tau =10 to 1000 seconds, 3E-13 at 1 second.  Today, you can probably do maybe an order of magnitude better.  These are state of the art oscillators in a vacuum envelope with double ovens, etc.

Lux, Jim (337C) said the following on 12/23/2009 03:17 PM:

As far as I know, the best OCXO you can get commercially today is an
Oscilloquartz 8607 option 008 BVA
(www.oscilloquartz.ch/file/pdf/8607.pdf), which is spec'd at 1.2x10e-13
at 1 second and 8x10e-14 from 3 to 30 seconds.  TVB's page at
http://www.leapsecond.com/pages/8607-drift shows it's in the 13s out to
10K seconds.  The spec sheet says the aging may be <3x10e-12/day after
30 days operation (there's one option for best aging, and another for
best short term stability; it's not clear whether you can get both in
the same package).

John

What they do for space applications where they care (gravity science experiments are a good example) is make a whole batch of crystals and their packages and then burn them in and look for the noise and aging properties and pick the ones they want. Each crystal will have a different turnover temperature, so that factors into the selection as well.

There's a paper from Greg Weaver at APL about USO performance.  It shows a daily drift rate of about 1E-11 for the GRACE USOs, and Figure 3 shows measured performance from 1 to 1000 seconds for 3 USOs. The Cassini USO has performance like John mentions (6E-14 at 10 seconds).  The New Horizons USOs have drifts of 1E-11/day and ADEV<1E-13 from 10-100 seconds.  Lots of other interesting stuff from Greg and his colleagues in the paper as well:
http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA503333&Location=U2&doc=GetTRDoc.pdf

Hi

At least at the 1 second point, I believe that the main issue with getting an order of magnitude better than the 3x10^-13 point is the lack of funding for a decent crystal package for 25+ mm diameter  blanks.

I doubt I'm going to solve that one in the basement ....

Bob

On Dec 23, 2009, at 3:17 PM, Lux, Jim (337C) wrote:

Bruce Griffiths wrote:

This seems exceedingly unhealthy.... 145 tons of mercury in pools in the
basement. Not that I don't deal with mercury at home, but fairly well
contained and giving me readings in mm Hg as I go to work or come home.

Mineral oil seems more healthy. Not to speak of active systems.

Merry Christmas.

Cheers,
Magnus

Magnus Danielson wrote:

At your location, at present, it wouldnt be a significant problem as
long as the basement was unheated.
Also good ventilation would help, together with a thin layer of oil on
top of the mercury.
The biggest obstacle would be the cost of the Mercury.

Bruce

Bruce,

Bruce Griffiths wrote:

Depends. But having 3 dm snow on the ground helps to keep the ground
around the house warmer, as it will insulate against the cold of the
open sky. -12.8 C is the lowest so far. Since winter is reoccuring, we
build the houses accordingly.

Mmm. Yes, didn't think about covering the baths with fluids.

Actually, it could be an obstcle just obtaining in those amounts it here
within EC, so it would involve some form of approval of some form of
excempt since it is mercury is a ROS element.

Cheers,
Magnus

Magnus Danielson wrote:

Guidline price is around $US600/flask (1 flask = 34.5kg).
Thus cost for 145 ton would be around $US2.5million.

The Canadians have a liquid mercury mirror telescope about 6m in diameter.
Whilst this doesn't use 145 tons of mercury the surface area would be of
the same order.

Bruce

Actually, couldn't you just squeeze your fish before you eat it? Should
have a lot of mercury in notime, according to the scaremongers.
Also, consider a heatsink buried about 10-15 feet deep. The temperature at
that depth in the ground does not vary very much at all. The trick to all
of this is to have a heatsink/source at a constant temp somewhere...
Merry Christams to all the nuts!
Don

Bruce Griffiths

--
Dr. Don Latham AJ7LL
Six Mile Systems LLP
17850 Six Mile Road
POB 134
Huson, MT, 59846
VOX 406-626-4304
www.lightningforensics.com
www.sixmilesystems.com

Hi

Actually burying a recirculating loop might work pretty well. The gotcha is that going much deeper than 18" would require significant amounts of blasting powder. I suspect the neighbors might object ....

Bob

On Dec 24, 2009, at 3:32 PM, Don Latham wrote:

Don Latham wrote:

Well, I don't like spoil a perfectly good dinner by squirting out half
the fish-weigth into a glas. Besides, I rarely eat fish.

Whatever mercury is there, it's not in collected in small droplets
awaiting the squeezing.

That would be quite a dig. I don't think I have that much before I hit
the rock anyware in the garden.

Cheers,
Magnus

Hi,

In most rural or semi-rural areas over here in Canterbury, New
Zealand, water is provided by a well on the domicile section. Wells
are drilled into the natural aquifer formed by volcanic ash which we
live on so it is relatively easy to create a bore hole and take
advantage of the naturally filtered water from quite a distance below
the surface. I wouldn't mind betting that this water comes out of the
ground at a very constant temperature season by season and the amount
needed to flow over the rb heatsink to hold it steady would not be so
great as to be able to be wasted back into the drains.

Ths would save all the messing about pumping water down into a bore
and pumping it back up again. Although I appreciate that not everone
is in the position to do this but some may already have a water supply
like this, even for garden irrigation. When I lived out in the sticks
I had reticulated water on the drip for the house uses but my own bore
for garden irrigation.

73
Steve

2009/12/25 Bob Camp lists@cq.nu:

--
Steve Rooke - ZL3TUV & G8KVD
A man with one clock knows what time it is;
A man with two clocks is never quite sure.

Hi

Around here when you drill a well, it's often unclear exactly how deep the water is really coming from. I think that anything that's safe to drink will be pretty constant temperature at the source. A typical well system here pumps the water into an above ground holding tank to keep the pump from running each time you wash your hands.  Since the pump is a non-trivial energy load that makes sense.

I suspect that the same thing would get you using a deep well for geo-thermal.

Bob

On Dec 26, 2009, at 5:52 AM, Steve Rooke wrote:

2009/12/27 Bob Camp lists@cq.nu:

Once the bore is drilled to below the water table, a pipe is lowered
down into the hole and attached to the pipe. Assuming that once the
water table is reached, there is still water below this point, the
water should be coming from the point level to where the end of the
pipe is, as this source has the highest pressure.

Indeed, well pumps do feed large storage containers for this purpose,
with some of them perched seeming precariously high up on towers to
obtain the pressure required. Living next door to a large concrete
storage tank full of water and standing on tall wooden trestles in a
land that is prone to earthquakes and volcanoes is quite interesting.

It is a trivial task to tap off some water coming straight from the
pump in these setups but would require the pump to basically cycle
continuously. You could put a smaller continuous duty pump T'd into
the well pipe for this cooling application but this starts to get
complicated and expensive.

Up in Rotorua in the North Island, the Earths crust is very thin there
and the extraction of geo-thermal energy is widely used. If you ever
come here it is a definite place to see and you will soon get used to
the very pungent smell of hydrogen sulphide in the air for the
duration of your visit. To see steam coming out of cracks in the road
and the storm drains is a sight to see. If you visit the Maori village
you are presented with a cemetery with steam coming out of the
monuments, quite a disturbing sight. Just don't fall into the boiling
pools there or you will be poached, as some visitors have discovered.

73,
Steve

--
Steve Rooke - ZL3TUV & G8KVD
A man with one clock knows what time it is;
A man with two clocks is never quite sure.