subject:"\[time\-nuts\] Practical considerations making a lab standard with an LTE lite"


In message 20141123153744.biokf...@smtp16.mail.yandex.net, Charles Steinmetz 
writes:

First, mount the LTE in a cast aluminum box (not thin sheet metal, 
something with some heft). [...]

Charles' design has some good points, but I don't agree with it.

What you are trying to do is to low-pass filter any thermal signals
before they reach the LTE or OCXO.

Charles' design works great from the outside, but doesn't do anything
with respect to the thermal energy expended by the encapsulated
device themselves, which will cause convection in the inner box.

(For LTE and OCXO it is probably less of a problem that changing
power-disipation will have a outsized effect on the central
temperature.)

Here is a much simpler and likely cheaper way to do it:

Put the LTE or OCXO in a small box of your choice.  Even a cardboard
box is fine.  A little thermal insulation in the box is OK, but not
too much, the heat must be able to get out.

Find a medium sized cardboard box, something like a cubic feet or so.

Place it where you want your house-standard, with some kind of
thermal insulation under it, two layers of old rug will do fine.

Lay a floor of bricks inside the box.

Build a wall of bricks along the outside of the box.

Place the smaller box in the hole in the middle, cut the
corner of a brick to run the cables without too much leakage.

Use a floortile as roof, possibly with a layer of bricks on top.

Close the outher cardboard box with tape to minimize convection.

Congratulations, you now have a cheap and incredibly efficient
thermal low-pas filter, which will allow thermal energy to move in
both directions -- eventually.

The outher cardboard box is not optional, unless you replace it
with some other mostly air-tight barrier.

The little bit of insulation the outher cardboard adds are not a
bad idea either, for instance it reduces the effect of sunlight
hits the box at certain times of the day/year.

But you can substitute any geological building material you have
at hand for the bricks, because the trick is that geological building
materials have just the right thermal properties we are looking
for:  Decent but not too good thermal conductivity with healthy
dose of thermal mass.

Cinderblocks comes with convenient interior holes premade.

Aerated concrete blocks are also a candidate material but
don't make it too thick since it insulates quite well, and
paint the surface to bind the dust.

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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Re: [time-nuts] Practical considerations making a lab standard with an LTE lite


Dave wrote


But given the TCXOs sensitivity to temperature changes, I don't
know whether it might be preferable to mount the LTE lite in its own box
without any power supplies in it - perhaps with some thermally insulting
material around the LTE lite so the crystal doesn't experience any fast
temperature changes.


First, mount the LTE in a cast aluminum box (not thin sheet metal, 
something with some heft).  Use thermally insulating standoffs 
(teflon or nylon, with no metal through fasteners) to get the board 
in the middle of the volume of the box.  Use a box a bit larger than 
you'd first think, so there is at least 1 of air on all 6 sides of 
the LTE board.  Do NOT mount any part of the LTE board (connectors, 
etc.) directly to the box walls -- use pigtails for all 
connections.  Do NOT use any insulation between the LTE and the box 
walls other than the 1+ of air.


The mounting described above will add substantial thermal capacitance 
to the LTE board (good) without adding significant thermal resistance 
(bad).  For further discussions of this issue, search the list 
archives for thermal capacitance and thermal mass.


Now, mount the cast box (plus any thermal mass you add to it -- see 
below) so that IT is thermally isolated from the overall enclosure 
(or, if it sits out in the open, thermally isolated from anything 
solid).  The air space in the enclosure isolates the oscillator from 
the cast box and the box is sufficiently massive that its temperature 
cannot change nearly as fast as ambient.  The thermal mass of the 
cast box can be adjusted by adding thermal mass to it as desired.


The goal is for the box temperature to change only by changes in 
ambient AIR temperature, and the LTE board to change only by changes 
in the AIR temperature inside the cast box.  This integrates any 
changes to the LTE board temperature with a very long time constant, 
which allows the GPS discipline to track and cancel the temperature changes.


(If you mount an ovenized oscillator this same way, it integrates any 
changes to the OCXO temperature so that the oven control loop can 
track and cancel any changes to the crystal temperature.)


You can, of course, improve things even further by making sure the 
ambient air temperature surrounding the cast box changes slowly, or 
not at all.  But the technique described above can be counted on to 
reduce thermal effects in most OCXOs or GPSDOs to better (often much 
better) than the 1e-13 level unless the ambient temperature changes 
MUCH more and MUCH faster than any change we wouild consider normal 
for a living space.  This is true whether the cast box is mounted out 
in the open, or inside an overall enclosure with other electronics.


Best regards,

Charles



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Re: [time-nuts] Practical considerations making a lab standard with an LTE lite

2014-11-23 Thread Magnus Danielson

NIST did something similar for their WWWV site, where they used bottled 
water in its staple packaging to build a thermal mass. They measured how 
their atomic clocks and rig behaved before and after, and could see the 
difference. Very neat way of using off the (store)shelf components for a 
test.


Another aspect is to think about what kind of heating/coolling you have. 
If it can act more as a proportional system rather than bang-bang 
regulations, it won't produce as drastic swings for you.


Cheers,
Magnus

On 11/23/2014 02:32 PM, Poul-Henning Kamp wrote:


In message 20141123153744.biokf...@smtp16.mail.yandex.net, Charles Steinmetz
writes:


First, mount the LTE in a cast aluminum box (not thin sheet metal,
something with some heft). [...]


Charles' design has some good points, but I don't agree with it.

What you are trying to do is to low-pass filter any thermal signals
before they reach the LTE or OCXO.

Charles' design works great from the outside, but doesn't do anything
with respect to the thermal energy expended by the encapsulated
device themselves, which will cause convection in the inner box.

(For LTE and OCXO it is probably less of a problem that changing
power-disipation will have a outsized effect on the central
temperature.)

Here is a much simpler and likely cheaper way to do it:

Put the LTE or OCXO in a small box of your choice.  Even a cardboard
box is fine.  A little thermal insulation in the box is OK, but not
too much, the heat must be able to get out.

Find a medium sized cardboard box, something like a cubic feet or so.

Place it where you want your house-standard, with some kind of
thermal insulation under it, two layers of old rug will do fine.

Lay a floor of bricks inside the box.

Build a wall of bricks along the outside of the box.

Place the smaller box in the hole in the middle, cut the
corner of a brick to run the cables without too much leakage.

Use a floortile as roof, possibly with a layer of bricks on top.

Close the outher cardboard box with tape to minimize convection.

Congratulations, you now have a cheap and incredibly efficient
thermal low-pas filter, which will allow thermal energy to move in
both directions -- eventually.

The outher cardboard box is not optional, unless you replace it
with some other mostly air-tight barrier.

The little bit of insulation the outher cardboard adds are not a
bad idea either, for instance it reduces the effect of sunlight
hits the box at certain times of the day/year.

But you can substitute any geological building material you have
at hand for the bricks, because the trick is that geological building
materials have just the right thermal properties we are looking
for:  Decent but not too good thermal conductivity with healthy
dose of thermal mass.

Cinderblocks comes with convenient interior holes premade.

Aerated concrete blocks are also a candidate material but
don't make it too thick since it insulates quite well, and
paint the surface to bind the dust.


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Re: [time-nuts] Practical considerations making a lab standard with an LTE lite


All:
I am enjoying this thread.  These are all very interesting ideas.

Hoping to power up my first unit later today

I'm putting my LTE-Lite in the recommended HAMMOND box.  That takes care 
of the box with air.  I was then considering proportional heating of the 
surface of the box, like I did long ago with some GUNNPLEXERS -- seemed 
to work pretty well.   Then this whole assembly goes inside two or four 
inches of the foam insulation.


Now, the question becomes, to what temperature to heat it?  With a 
crystal, I'd plot /f/ vs. /T/, and look for minimum slope.  How to do 
that with LTE-Lite -- plot /efc/ vs /T/ and look for either center of 
range or minimum slope??


Thoughts?

Jim
wb4...@amsat.org

On 11/23/2014 9:03 AM, Magnus Danielson wrote:
NIST did something similar for their WWWV site, where they used 
bottled water in its staple packaging to build a thermal mass. They 
measured how their atomic clocks and rig behaved before and after, and 
could see the difference. Very neat way of using off the (store)shelf 
components for a test.


Another aspect is to think about what kind of heating/coolling you 
have. If it can act more as a proportional system rather than 
bang-bang regulations, it won't produce as drastic swings for you.


Cheers,
Magnus

On 11/23/2014 02:32 PM, Poul-Henning Kamp wrote:


In message 20141123153744.biokf...@smtp16.mail.yandex.net, Charles 
Steinmetz

writes:


First, mount the LTE in a cast aluminum box (not thin sheet metal,
something with some heft). [...]


Charles' design has some good points, but I don't agree with it.

What you are trying to do is to low-pass filter any thermal signals
before they reach the LTE or OCXO.

Charles' design works great from the outside, but doesn't do anything
with respect to the thermal energy expended by the encapsulated
device themselves, which will cause convection in the inner box.

(For LTE and OCXO it is probably less of a problem that changing
power-disipation will have a outsized effect on the central
temperature.)

Here is a much simpler and likely cheaper way to do it:

Put the LTE or OCXO in a small box of your choice.  Even a cardboard
box is fine.  A little thermal insulation in the box is OK, but not
too much, the heat must be able to get out.

Find a medium sized cardboard box, something like a cubic feet or so.

Place it where you want your house-standard, with some kind of
thermal insulation under it, two layers of old rug will do fine.

Lay a floor of bricks inside the box.

Build a wall of bricks along the outside of the box.

Place the smaller box in the hole in the middle, cut the
corner of a brick to run the cables without too much leakage.

Use a floortile as roof, possibly with a layer of bricks on top.

Close the outher cardboard box with tape to minimize convection.

Congratulations, you now have a cheap and incredibly efficient
thermal low-pas filter, which will allow thermal energy to move in
both directions -- eventually.

The outher cardboard box is not optional, unless you replace it
with some other mostly air-tight barrier.

The little bit of insulation the outher cardboard adds are not a
bad idea either, for instance it reduces the effect of sunlight
hits the box at certain times of the day/year.

But you can substitute any geological building material you have
at hand for the bricks, because the trick is that geological building
materials have just the right thermal properties we are looking
for:  Decent but not too good thermal conductivity with healthy
dose of thermal mass.

Cinderblocks comes with convenient interior holes premade.

Aerated concrete blocks are also a candidate material but
don't make it too thick since it insulates quite well, and
paint the surface to bind the dust.


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Re: [time-nuts] Practical considerations making a lab standard with an LTE lite


Dave wrote:


It would be great if there was a circuit published which can give 50 Ohn
output impedance from a 12-15 power supply,  which

a) Doesn't load the TCXO
b) Doesn't degrade the phase noise.


WRT loading the TCXO, someone should establish quantitatively how 
high the load impedance must be to avoid significant negative 
effects.  Said mentioned 1M ohm, which is the other common lab 
instrument input impedance besides 50 ohms, but I would be very 
surprised to find that the load resistance really needs to be that 
high.  Why does this matter?  The lower the impedance you load the 
oscillator with, the more power you get out of it; therefore, the 
lower the power gain that is necessary to develop an output signal 
you can use to feed the external world -- and, consequently, the less 
noise you are forced to add to the signal during amplification.


I would recommend testing the LTE with a 1M ohm load resistance to 
establish a baseline.


1)  Measure and record the outout voltage.

2)  Measure and record the levels of the first few harmonics in 
relation to the carrier.


3)  Get a qualitative feel for the levels of higher harmonics.

Then, start reducing the load impedance (I would start with 10k ohms, 
then move to 1k ohms), paying attention to:


a)  The output voltage

b)  The levels of the first few harmonics in relation to the carrier, and

c)  The levels of higher harmonics, if they increase faster than the 
first few as the load resistance decreases.


When you get to the point where the output voltage drops to 1/2 of 
the 1M ohm voltage, you have reached the output impedance of the LTE 
board (matched source and load impedances).  As a general matter, it 
would not be useful to use a load impedance lower than this.  If you 
reach this point without a significant increase in the output 
harmonics, great -- use this impedance as the input resistance of 
your buffer amplifier.  If, however, the harmonics increase faster 
(with decreasing load resistance) and become objectionable before you 
reach the 1/2 voltage point, you must decide how much distortion is 
acceptable and use the load resistance that produces this level of 
harmonics.  In this case, you trade off distortion and noise.


So, the first step is for someone to do the experiment and find out 
how low the input resistance of the buffer amp can be as a practical 
matter.  Then, a buffer amp topology can be chosen for best 
performance with this input resistance.


Also, determine how many oscillator-frequency outputs you need 
(including outputs that will feed dividers, multipliers, or other 
circuitry internal to the buffer box).  This will also influence the 
optimum choice of buffer amp topology.


Best regards,

Charles


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Re: [time-nuts] Practical considerations making a lab standard with an LTE lite

Hi

If you have a basement in your house / building 

—and —

it’s dry and reasonably draft free (no garage doors opening up from time to 
time)

— and —

At least one side / corner is well buried in the ground 

— and —

You can get at that corner / side.

Move your thermal baffle gizmo up against that wall, move it into that corner. 
There is a lot more mass in the foundation of a building than anything you 
would want to lug around for a project. You still need to handle the issues on 
at least half the surface, that should be less trouble than doing the whole 
thing. 

There is another subtle advantage to this approach. The standard is out of the 
way. It’s not in the middle of the lab. It does not get bumped. It does not get 
sparked (unless you have full ESD protection in the lab …). It’s less likely to 
have random power cycle events due to cords being accidentally pulled. Even 
second order stuff related to ground loops from connecting and disconnecting 
cables may be reduced.  “Just leave it alone” is much easier to do when the 
gizmo is surrounded by a pile of bricks.

With a GPSDO, you don’t care (much) about the environmental  swings from week 
to week or month to month. The GPS will take care of that. What you care about 
are the hour to hour or minute to minute  movements. Those are the ones that 
the filter on an OCXO based unit will struggle with.  Hotter in the summer / 
colder in the winter is not as big a deal as “cold when I come  in / hot after 
I turn everything on”. 

One practical hint if you do try this: 

Put a cheap plastic bag around the gizmo and tape it up. It discourages the bug 
colonies. I have empirical evidence that this is a good idea ...

Bob

 On Nov 23, 2014, at 9:03 AM, Magnus Danielson mag...@rubidium.dyndns.org 
 wrote:
 
 NIST did something similar for their WWWV site, where they used bottled water 
 in its staple packaging to build a thermal mass. They measured how their 
 atomic clocks and rig behaved before and after, and could see the difference. 
 Very neat way of using off the (store)shelf components for a test.
 
 Another aspect is to think about what kind of heating/coolling you have. If 
 it can act more as a proportional system rather than bang-bang regulations, 
 it won't produce as drastic swings for you.
 
 Cheers,
 Magnus
 
 On 11/23/2014 02:32 PM, Poul-Henning Kamp wrote:
 
 In message 20141123153744.biokf...@smtp16.mail.yandex.net, Charles 
 Steinmetz
 writes:
 
 First, mount the LTE in a cast aluminum box (not thin sheet metal,
 something with some heft). [...]
 
 Charles' design has some good points, but I don't agree with it.
 
 What you are trying to do is to low-pass filter any thermal signals
 before they reach the LTE or OCXO.
 
 Charles' design works great from the outside, but doesn't do anything
 with respect to the thermal energy expended by the encapsulated
 device themselves, which will cause convection in the inner box.
 
 (For LTE and OCXO it is probably less of a problem that changing
 power-disipation will have a outsized effect on the central
 temperature.)
 
 Here is a much simpler and likely cheaper way to do it:
 
 Put the LTE or OCXO in a small box of your choice.  Even a cardboard
 box is fine.  A little thermal insulation in the box is OK, but not
 too much, the heat must be able to get out.
 
 Find a medium sized cardboard box, something like a cubic feet or so.
 
 Place it where you want your house-standard, with some kind of
 thermal insulation under it, two layers of old rug will do fine.
 
 Lay a floor of bricks inside the box.
 
 Build a wall of bricks along the outside of the box.
 
 Place the smaller box in the hole in the middle, cut the
 corner of a brick to run the cables without too much leakage.
 
 Use a floortile as roof, possibly with a layer of bricks on top.
 
 Close the outher cardboard box with tape to minimize convection.
 
 Congratulations, you now have a cheap and incredibly efficient
 thermal low-pas filter, which will allow thermal energy to move in
 both directions -- eventually.
 
 The outher cardboard box is not optional, unless you replace it
 with some other mostly air-tight barrier.
 
 The little bit of insulation the outher cardboard adds are not a
 bad idea either, for instance it reduces the effect of sunlight
 hits the box at certain times of the day/year.
 
 But you can substitute any geological building material you have
 at hand for the bricks, because the trick is that geological building
 materials have just the right thermal properties we are looking
 for:  Decent but not too good thermal conductivity with healthy
 dose of thermal mass.
 
 Cinderblocks comes with convenient interior holes premade.
 
 Aerated concrete blocks are also a candidate material but
 don't make it too thick since it insulates quite well, and
 paint the surface to bind the dust.
 
 ___
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Re: [time-nuts] Practical considerations making a lab standard with an LTE lite


In message c9e99c83-aaa9-4d50-9729-b86a79af2...@n1k.org, Bob Camp writes:

At least one side / corner is well buried in the ground 

But be aware that such a corner may be dry only when empty.

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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Re: [time-nuts] Practical considerations making a lab standard with an LTE lite


In message 20141123174632.kvk4s...@smtp18.mail.yandex.net, Charles Steinmetz 
writes:

And good luck fitting a cubic foot box with a surround of bricks into 
a 3U rack cabinet, or any other relocatable (much less,semi-portable)
enclosure.

I didn't say it doesn't work, I said that I don't agree with it ;-)

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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Re: [time-nuts] Practical considerations making a lab standard with an LTE lite

Hi

What you have in the LTE is a TCXO rather than a bare crystal or an OCXO. It’s 
got a compensation circuit that corrects the FT curve of the crystal. The net 
result is likely a 5th or higher order curve when you plot frequency over 
temperature. Every TCXO off that production line will have a different curve. 
You would need a full characterization of that curve for your specific TCXO to 
pick an optimum point. 

With a GPSDO, taking care of the long term drift is not what you are after. The 
GPS does that. If the GPSDO is TCXO based, the the loop filter is going to be 
pretty fast. That is *not* a knock on the LTE part, it’s just physics. An OCXO 
part is a different beast. Each has their strong points. Don’t try to run the 
OCXO off batteries for a week … With a fast filter, temperature variations at 
the “per hour” level are not likely an issue.

Once you get to the point that drafts are worked out, and that temperature 
change is slowed down, you are done. No need for anything more complex.

Bob

 On Nov 23, 2014, at 9:30 AM, Jim Sanford wb4...@wb4gcs.org wrote:
 
 All:
 I am enjoying this thread.  These are all very interesting ideas.
 
 Hoping to power up my first unit later today
 
 I'm putting my LTE-Lite in the recommended HAMMOND box.  That takes care of 
 the box with air.  I was then considering proportional heating of the surface 
 of the box, like I did long ago with some GUNNPLEXERS -- seemed to work 
 pretty well.   Then this whole assembly goes inside two or four inches of the 
 foam insulation.
 
 Now, the question becomes, to what temperature to heat it?  With a crystal, 
 I'd plot /f/ vs. /T/, and look for minimum slope.  How to do that with 
 LTE-Lite -- plot /efc/ vs /T/ and look for either center of range or minimum 
 slope??
 
 Thoughts?
 
 Jim
 wb4...@amsat.org
 
 On 11/23/2014 9:03 AM, Magnus Danielson wrote:
 NIST did something similar for their WWWV site, where they used bottled 
 water in its staple packaging to build a thermal mass. They measured how 
 their atomic clocks and rig behaved before and after, and could see the 
 difference. Very neat way of using off the (store)shelf components for a 
 test.
 
 Another aspect is to think about what kind of heating/coolling you have. If 
 it can act more as a proportional system rather than bang-bang regulations, 
 it won't produce as drastic swings for you.
 
 Cheers,
 Magnus
 
 On 11/23/2014 02:32 PM, Poul-Henning Kamp wrote:
 
 In message 20141123153744.biokf...@smtp16.mail.yandex.net, Charles 
 Steinmetz
 writes:
 
 First, mount the LTE in a cast aluminum box (not thin sheet metal,
 something with some heft). [...]
 
 Charles' design has some good points, but I don't agree with it.
 
 What you are trying to do is to low-pass filter any thermal signals
 before they reach the LTE or OCXO.
 
 Charles' design works great from the outside, but doesn't do anything
 with respect to the thermal energy expended by the encapsulated
 device themselves, which will cause convection in the inner box.
 
 (For LTE and OCXO it is probably less of a problem that changing
 power-disipation will have a outsized effect on the central
 temperature.)
 
 Here is a much simpler and likely cheaper way to do it:
 
 Put the LTE or OCXO in a small box of your choice.  Even a cardboard
 box is fine.  A little thermal insulation in the box is OK, but not
 too much, the heat must be able to get out.
 
 Find a medium sized cardboard box, something like a cubic feet or so.
 
 Place it where you want your house-standard, with some kind of
 thermal insulation under it, two layers of old rug will do fine.
 
 Lay a floor of bricks inside the box.
 
 Build a wall of bricks along the outside of the box.
 
 Place the smaller box in the hole in the middle, cut the
 corner of a brick to run the cables without too much leakage.
 
 Use a floortile as roof, possibly with a layer of bricks on top.
 
 Close the outher cardboard box with tape to minimize convection.
 
 Congratulations, you now have a cheap and incredibly efficient
 thermal low-pas filter, which will allow thermal energy to move in
 both directions -- eventually.
 
 The outher cardboard box is not optional, unless you replace it
 with some other mostly air-tight barrier.
 
 The little bit of insulation the outher cardboard adds are not a
 bad idea either, for instance it reduces the effect of sunlight
 hits the box at certain times of the day/year.
 
 But you can substitute any geological building material you have
 at hand for the bricks, because the trick is that geological building
 materials have just the right thermal properties we are looking
 for:  Decent but not too good thermal conductivity with healthy
 dose of thermal mass.
 
 Cinderblocks comes with convenient interior holes premade.
 
 Aerated concrete blocks are also a candidate material but
 don't make it too thick since it insulates quite well, and
 paint the surface to bind the dust.

Re: [time-nuts] Practical considerations making a lab standard with an LTE lite

2014-11-23 Thread paul swed

I am scratching my head here.
From what I see the LTE is a good unit but does swim around a bit. The
conclusion I might get from this thread is that lots of insulation will fix
that.
I suspect not.
The LTE in use down  at 2.8 e-10 according to its output.
I have put it in a small cardboard box with free standing air and some
Styrofoam.
Because thats what turned up in the basement.
I have added heat to it. It sits on top the Lucent box thats on. :-)

It still swims around. It moves forward and backwards stays steady. Random.
Certainly not terrible. I just think as neat as bricks may be it would not
help allot.
The top of the thread is excellant about checking the TCXO output Z.
Regards
Paul
WB8TSL






On Sun, Nov 23, 2014 at 9:55 AM, Poul-Henning Kamp p...@phk.freebsd.dk
wrote:

 
 In message 20141123174632.kvk4s...@smtp18.mail.yandex.net, Charles
 Steinmetz
 writes:

 And good luck fitting a cubic foot box with a surround of bricks into
 a 3U rack cabinet, or any other relocatable (much less,semi-portable)
 enclosure.

 I didn't say it doesn't work, I said that I don't agree with it ;-)

 --
 Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
 p...@freebsd.org | TCP/IP since RFC 956
 FreeBSD committer   | BSD since 4.3-tahoe
 Never attribute to malice what can adequately be explained by incompetence.
 ___
 time-nuts mailing list -- time-nuts@febo.com
 To unsubscribe, go to
 https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
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Re: [time-nuts] Practical considerations making a lab standard with an LTE lite

Hi

Yup, that’s another good reason for the plastic bag :)

If moisture might be an issue in your area,  cover up the corner for a while in 
the rainy season to check for that problem before the project begins. Depending 
on the bag is not a real good idea. 

Bob

 On Nov 23, 2014, at 9:50 AM, Poul-Henning Kamp p...@phk.freebsd.dk wrote:
 
 
 In message c9e99c83-aaa9-4d50-9729-b86a79af2...@n1k.org, Bob Camp writes:
 
 At least one side / corner is well buried in the ground 
 
 But be aware that such a corner may be dry only when empty.
 
 -- 
 Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
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Re: [time-nuts] Practical considerations making a lab standard with an LTE lite

2014-11-23 Thread Dr. David Kirkby (Kirkby Microwave Ltd)


Poul-Henning wrote:


Charles' design works great from the outside, but doesn't do anything
with respect to the thermal energy expended by the encapsulated
device themselves, which will cause convection in the inner box.


I have been using the technique for 30+ years, including with many 
OCXOs (which, obviously, generate significant heat) and have never 
observed any problems of that nature at the 1e-13 level.  I did 
consider the possibility when I first started doing it, and tested 
two potential fixes:  (i) putting a fan inside the box to homogenize 
the internal temperature, and (ii) filling the air space inside the 
box with irregular solid shapes to break up the convection 
pattern.  I tested both methods extensively with instrumented 
sources, in many variations (fan speeds and orientations, mass and 
porosity of passive internal shapes), and did not find any difference 
at the 1e-13 level.  I have occasionally used an internal fan just on 
theoretical grounds, but I have never measured any practical difference.


Thinking about it, this does not seem too surprising -- one would 
expect any convection to settle into a stable pattern and thus not to 
cause any temperature changes over time (once it is warm and 
settled).  Whether this explains my results or some other effect 
predominates (for example, convection may move enough air in the 
limited space to achieve substantial isothermy), I have confirmed to 
my satisfaction that it is simply not a factor in practice at the 
levels we are concerned with.


If you test the cast aluminum box method and find that your results 
do not accord with mine, please publish them and we can discuss what 
might account for the observed differences and how the method could 
be improved.  Until then, you are just posting speculative musings on 
the subject based on no data, which does not seem helpful.


And good luck fitting a cubic foot box with a surround of bricks into 
a 3U rack cabinet, or any other relocatable (much less, 
semi-portable) enclosure.


Best regards,

Charles



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Re: [time-nuts] Practical considerations making a lab standard with an LTE lite

2014-11-23 Thread Tom Van Baak

The short-term performance is 10x worse if you don't shield the TCXO from air, 
even if the ambient air is still. I suggested Said sell the product with some 
sort of engineered shield in place. Instead each of us will solve the problem 
in our own way; which is ok for a dev kit.

For plots and photos showing performance with, and without, and with insulation 
see:
http://leapsecond.com/pages/LTE-Lite/
The difference is dramatic, especially if you are used to working with OCXO 
where this sort of effect does not occur.

The insulation may be found in convenient rolls at many local stores. I used 
TP, which for this application is an acronym for Thermal Paper.

/tvb
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Re: [time-nuts] Practical considerations making a lab standard with an LTE lite

On 23 Nov 2014 14:45, Bob Camp kb...@n1k.org wrote:

 Hi

 If you have a basement in your house / building

I do not.

 —and —

 it’s dry and reasonably draft free (no garage doors opening up from time
to time)

My lab is a room which is part of the garage! Just about everything is
against me with this method,  BUT you do give me an idea...

You got me thinking about the possibility of actually mounting the TCXO
burried in the ground!   The temperature of that is not going to change
very rapidly.

FWIW, I know a guy that did work as an air conditioning engineer,, but now
works for a company selling geothermal heating.  He installs  ground source
heat pumps for the geothermal energy.  He says that they actually work
quite poorly in many cases. In a couple of years the temperature of the
ground falls as the heat is extracted faster than it replenishes.  So the
efficiency falls off. I don't think that the TCXO would heat the ground
faster than it dissipates away.

Of course there would be some practical issues burying the TCXO, but those
would not be insurmountable ones. I have no idea what depth might be
needed.

My wife thinks thinks I am a nutcase - that would only confirm it to her!

Dave, G8WRB
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Re: [time-nuts] Practical considerations making a lab standard with an LTE lite

2014-11-23 Thread Dr. David Kirkby (Kirkby Microwave Ltd)


In message canx10hb0kdrnaayzgvm1gkduj7gklth0acdxczg894hxbus...@mail.gmail.com
, Dr. David Kirkby (Kirkby Microwave Ltd) writes:

He installs  ground source
heat pumps for the geothermal energy.  He says that they actually work
quite poorly in many cases.

There is a BIG difference between geothermal and ground heating.

Geothermal means you drill at least 50m (Iceland) or more likely
half a kilometer down, in order to harvest water at near boiling
point from the Earths geological heat-sources (mostly uranium decay).

Extracting more energy than available just means the temperature
drops temporarily.  It will increase again once you reduce the
pump rate.

Horizontal ground heat means that you are harvesting sunshine
accumulated in the top one meter of the soil.  Much of the energy
is harvested from freezing the water around the pipe thus pulling
out the relatively high melting energy of water.

If you extract more energy than you deposit sunshine, you end
up freezing a larger and larger volume of water/soil around
the pipe and your compressor will eat a lot of electricity.

In practice it looks like this:


http://ing.dk/artikel/varmepumpe-mareridt-jordslange-var-dybfrossen-i-maj-113176

(The two pictures show the same pipe, with and without frozen ground.)

Finally there is vertial ground heat where you drill down only about
40-80 meter, tapping heat mostly from ground water resources.Most
places the ground water doesn't move fast enough to deliver the amounts
of energy extracted, and over time the source returns unusably low
temperature and must be abandonned.  Typically after 25-30 years.

-- 
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p...@freebsd.org | TCP/IP since RFC 956
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Re: [time-nuts] Practical considerations making a lab standard with an LTE lite

On 23 Nov 2014 17:49, Poul-Henning Kamp p...@phk.freebsd.dk wrote:

 
 In message 
canx10hb0kdrnaayzgvm1gkduj7gklth0acdxczg894hxbus...@mail.gmail.com
 , Dr. David Kirkby (Kirkby Microwave Ltd) writes:

 He installs  ground source
 heat pumps for the geothermal energy.  He says that they actually work
 quite poorly in many cases.

 There is a BIG difference between geothermal and ground heating.

 Geothermal means you drill at least 50m (Iceland) or more likely
 half a kilometer down, in order to harvest water at near boiling
 point from the Earths geological heat-sources (mostly uranium decay).

Sorry.  What he installs is pipes in the ground in residential or
industrial sites. Basically he says they work initially,  but performance
drops dramatically over a couple of years.

 If you extract more energy than you deposit sunshine, you end
 up freezing a larger and larger volume of water/soil around
 the pipe and your compressor will eat a lot of electricity.

That is what he was saying.

Dave.
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Re: [time-nuts] Practical considerations making a lab standard with an LTE lite


In message canx10hcaob-5gysbr7sdxwl7dyh7qubmhxwmi9xdrcf3mdm...@mail.gmail.com
, Dr. David Kirkby (Kirkby Microwave Ltd) writes:

 Geothermal means you drill at least 50m (Iceland) or more likely
 half a kilometer down, in order to harvest water at near boiling
 point from the Earths geological heat-sources (mostly uranium decay).

Sorry.  What he installs is pipes in the ground in residential or
industrial sites. Basically he says they work initially,  but performance
drops dramatically over a couple of years.

That is not geothermal then, and yes, a LOT of those systems are
badly underdimensioned.

I've been researching this topic intensively because my new house
will be heated that way.

My conclusion, based on reading a lot of reports, is that there
is no credible way to predict the performance.  The wetter your
soil the better, but that's about it.

I'm going to overprovision by a factor two to be on the safe side,
afterall it only costs EUR7 for each extra meter of pipe.

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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Re: [time-nuts] Practical considerations making a lab standard with an LTE lite

2014-11-23 Thread Alexander Pummer

Schomandl -- the company which made the first indirect synthesizers in 
the sixties in the past century -- used buried crystal oscillators as 
standard frequency source, 12meter deep in the companies yard in the 
Belfort Strasse in Munich, Bavaria Germany, ...Rohde Schwarz also had 
buried oscillators. I have one in California, where, the temperature at 
10m deep is 15,784C° around the year, and measuring the frequency off 
set between wwvb's harmonic and the buried oscillator originally tuned 
to cca 3MHz, to the natural serial resonance of the crystal, by counting 
the beat -- to a harmonic of wwvb, cca 4217Hz , 364 358 801 pulses per 
day, as of Nov 2014, counter resets by wwvb daily, daily changes max ± 8 
pulses, are to see, but a yearly decrement of 15 to 8 pulses per year, 
less per year in the last time is observable the system down thereis 
running since 1991.

73
KJ6UHN
Alex


On 11/23/2014 8:46 AM, Dr. David Kirkby (Kirkby Microwave Ltd) wrote:

On 23 Nov 2014 14:45, Bob Camp kb...@n1k.org wrote:

Hi

If you have a basement in your house / building

I do not.


—and —
it’s dry and reasonably draft free (no garage doors opening up from time

to time)

My lab is a room which is part of the garage! Just about everything is
against me with this method,  BUT you do give me an idea...

You got me thinking about the possibility of actually mounting the TCXO
burried in the ground!   The temperature of that is not going to change
very rapidly.

FWIW, I know a guy that did work as an air conditioning engineer,, but now
works for a company selling geothermal heating.  He installs  ground source
heat pumps for the geothermal energy.  He says that they actually work
quite poorly in many cases. In a couple of years the temperature of the
ground falls as the heat is extracted faster than it replenishes.  So the
efficiency falls off. I don't think that the TCXO would heat the ground
faster than it dissipates away.

Of course there would be some practical issues burying the TCXO, but those
would not be insurmountable ones. I have no idea what depth might be
needed.

My wife thinks thinks I am a nutcase - that would only confirm it to her!

Dave, G8WRB
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Re: [time-nuts] Practical considerations making a lab standard with an LTE lite

I've read about die-hard microwave hams burying their master oscillators 
for a long time . . . .


On 11/23/2014 11:46 AM, Dr. David Kirkby (Kirkby Microwave Ltd) wrote:

On 23 Nov 2014 14:45, Bob Camp kb...@n1k.org wrote:

Hi

If you have a basement in your house / building

I do not.


—and —
it’s dry and reasonably draft free (no garage doors opening up from time

to time)

My lab is a room which is part of the garage! Just about everything is
against me with this method,  BUT you do give me an idea...

You got me thinking about the possibility of actually mounting the TCXO
burried in the ground!   The temperature of that is not going to change
very rapidly.

FWIW, I know a guy that did work as an air conditioning engineer,, but now
works for a company selling geothermal heating.  He installs  ground source
heat pumps for the geothermal energy.  He says that they actually work
quite poorly in many cases. In a couple of years the temperature of the
ground falls as the heat is extracted faster than it replenishes.  So the
efficiency falls off. I don't think that the TCXO would heat the ground
faster than it dissipates away.

Of course there would be some practical issues burying the TCXO, but those
would not be insurmountable ones. I have no idea what depth might be
needed.

My wife thinks thinks I am a nutcase - that would only confirm it to her!

Dave, G8WRB
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Re: [time-nuts] Practical considerations making a lab standard with an LTE lite


Interesting comment about the geothermal.

I have to take continuing education courses in order to maintain my PE; 
one was in geothermal.


Intuitively, great for cooling, even (especially!) in Florida. 
Intuitively, not so hot for heating, especially in PA, and especially 
with the price of natural gas plummeting.


The guy who services our conventional AC and gas furnace was not very 
enthused, when I told him I was considering geothermal for the next 
cooling unit.  He got a little more enthused when he found out I already 
have more pipe in the ground than I'd need (ft per ton of cooling 
capacity) and a several thousand gallon in-ground tank. Still not 
excited about it.  I really appreciate your new data point.


Shortly, I'll post response to all replies to my original post on this 
topic.  For now, the bury it option might actually have use here.


Jim

On 11/23/2014 11:46 AM, Dr. David Kirkby (Kirkby Microwave Ltd) wrote:

On 23 Nov 2014 14:45, Bob Camp kb...@n1k.org wrote:

Hi

If you have a basement in your house / building

I do not.


—and —
it’s dry and reasonably draft free (no garage doors opening up from time

to time)

My lab is a room which is part of the garage! Just about everything is
against me with this method,  BUT you do give me an idea...

You got me thinking about the possibility of actually mounting the TCXO
burried in the ground!   The temperature of that is not going to change
very rapidly.

FWIW, I know a guy that did work as an air conditioning engineer,, but now
works for a company selling geothermal heating.  He installs  ground source
heat pumps for the geothermal energy.  He says that they actually work
quite poorly in many cases. In a couple of years the temperature of the
ground falls as the heat is extracted faster than it replenishes.  So the
efficiency falls off. I don't think that the TCXO would heat the ground
faster than it dissipates away.

Of course there would be some practical issues burying the TCXO, but those
would not be insurmountable ones. I have no idea what depth might be
needed.

My wife thinks thinks I am a nutcase - that would only confirm it to her!

Dave, G8WRB
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Re: [time-nuts] Practical considerations making a lab standard with an LTE lite

2014-11-23 Thread Dave Martindale

Did you use one-ply, two-ply, or three-ply TP?

More seriously, your LTE-Lite differs in a couple of respects from the
batch of production ones, or at least my example.  Your TCXO seems to be
in a metal package (shiny gold colour) and open to the air, if I'm
interpreting the photo on your LTE-Lite page correctly (and also the photo
that Said posted in his divide-by-two document).  The production units have
the TCXO in a solid black package, probably black epoxy, with a blob of RTV
rubber on top.  So the production units are probably already somewhat
better shielded against drafts.

(Thanks for doing the tests, particularly for those of us who can't do
these tests ourselves.  I can only watch the 1 PPS of the LTE-Lite wander
with respect to the 1 PPS from my old Thunderbolt (Piezo oscillator), and
look at the worst-case variation, but I have no way of knowing how much of
the drift is due to each GPSDO).

- Dave

On Sun, Nov 23, 2014 at 11:24 AM, Tom Van Baak t...@leapsecond.com wrote:

 The short-term performance is 10x worse if you don't shield the TCXO from
 air, even if the ambient air is still. I suggested Said sell the product
 with some sort of engineered shield in place. Instead each of us will solve
 the problem in our own way; which is ok for a dev kit.

 For plots and photos showing performance with, and without, and with
 insulation see:
 http://leapsecond.com/pages/LTE-Lite/
 The difference is dramatic, especially if you are used to working with
 OCXO where this sort of effect does not occur.

 The insulation may be found in convenient rolls at many local stores. I
 used TP, which for this application is an acronym for Thermal Paper.

 /tvb
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Re: [time-nuts] Practical considerations making a lab standard with an LTE lite


All:

I appreciate all the responses to my post earlier today.  Very informative.

First:  DownEast Microwave sells a nice kit for distributing 10 MHz.  
Specs are on their website, but basically, one in, four out -- each 
individually buffered and filtered.


Second:  I will use the 20 MHz from the LTE-Lite to lock a 100Mhz TCXO 
which will be the LO for a high performance 2meter amateur software 
defined radio.  (OpenHPSDR.org for info on the SDR)  I may multiply it 
to help with some of the microwave LOs.  It will also use the 20 Mhz to 
lock a 1GHz TXCO to be multiplied for microwave LOs.


Third:  I will have three of the LTE-Light units.  The first will feed 
some LOs as described above, and the synthesized 10 MHz output will be 
my lab frequency standard.  The lab is in a cinder block room off the 
basement, with 2 of foam insulation under 2 inches of concrete which is 
the floor for a covered porch above.  I'd never thought of it, but the 
put it on the floor next to a brick wall idea fits here.  Actually, I 
can put it next to 2 buried brick walls, and will surround it with 
cinder block on the remaining sides.  Can probably cover it with a few 
12x12 paver stones.  NOW, this involves drilling a hole through cinder 
block and drywall between the office/ham shack and the lab.  Would 
rather not, but have to anyway.  I have been informed that the fan 
noise from the ham shack gigabit ethernet switch will become politically 
unacceptable in about 72 hours.  (Office/ham shack share a guest 
bedroom.)  I would like to get 1E-10 or 1E-11 accuracy out of this 
setup.  Thanks for this suggestion!


Fourth:  The second unit will be in a building at the base of my antenna 
tower, about 350 feet from the house.  This building is above ground, 
and will be allowed to swing from 45F to 80F over the course of the 
year.  Hence my interest in insulating and heating.  I might consider 
putting something in the ground here, the problem would be access for 
servicing  I would like to get 1E-10 or 1E-11 accuracy out of this 
unit.  Considered shipping 10 MHz in coax out from the house, would 
rather not, and would like some redundancy, anyway.


Fifth:  I get that the /efc/ vs. /temp/ relationship is very complex and 
accept that trying to characterize it is not worth the effort.  Thanks 
for this bit of information.


Sixth:  My third LTE-Lite will drive a 10MHz reference for a mobile 
(rover) microwave setup, providing the reference for a bunch of GHz 
LOs.  This station will see motion, and temperature variation. Ultra low 
power will not be a concern, so heaters are acceptable. I would be happy 
with 1E-9 accuracy out of this unit.  That translates into 10Hz 
frequency error at 10 GHz.  This kind of frequency accuracy has been 
demonstrated to provide 3+db improvement in the ability to detect weak 
signals -- very significant for microwave weak signal work.


Finally:
I have pondered all the suggestions about measuring output impedance, 
etc.  For now, I have decided to default to Said's expertise with the 
units and will use one of his suggested circuits as buffers.  Hopefully, 
these will be  on a board inside the HAMMOND box with the LTE-Lite.  
That buffer will drive one of the MMICs to provide additional power to 
drive a filter and then output to the distribution amplifier.  I will 
continue to look for a better idea from one of you smarter than me.


Thanks again for all the insight and ideas.  You guys type and I learn.

73,
Jim
wb4...@amsat.org

On 11/23/2014 4:46 AM, Dr. David Kirkby (Kirkby Microwave Ltd) wrote:

I would like to make a unit with multiple 10 MHz 50 Ohm outputs to feed my
various bits of test equipment.  I am thinking about some practical
considerations.

1) It would be great if there was a circuit published which can give 50 Ohn
output impedance from a 12-15 power supply,  which

a) Doesn't load the TCXO
b) Doesn't degrade the phase noise.
c) Powered the LTE lite.

Ideally one for both 10  20 MHz crystals.

Better still if there was a PCB available.

2) How should I mount the components?

My preference would be a metal box with
* IEC mains socket
* antenna input socket
* 9-pin D for reading dats
* 15  BNC's outputs

With a power amplifier to provide the output for 15 sockets, some
ventilation possibly requiring a small amount of forced air cooling would
be needed. But given the TCXOs sensitivity to temperature changes, I don't
know whether it might be preferable to mount the LTE lite in its own box
without any power supplies in it - perhaps with some thermally insulting
material around the LTE lite so the crystal doesn't experience any fast
temperature changes. Then have the power hungry bits completely separately.

I don't have a particularly big lab, so wherever I mount the LTE lite, the
temperature is going to change with the air conditioning unit blows hot or
cold

There are fairly large temperature changes when I am not using the lab, as
I don't run the air conditioning unit

Re: [time-nuts] Practical considerations making a lab standard with an LTE lite

2014-11-23 Thread S. Jackson via time-nuts

Hi guys,
 
this is the kind of lively discussion I was hoping for! I enjoyed  this.
 
Some comments (these are my opinions only):
 
* Thanks much for Tom publishing the plots, and spending a lot(!) of time  
evaluating and helping improve the units significantly. Tom's unit was a  
pre-production unit. We added RTV (some units black, some a combo) to the TCXO 
 production units based on his suggestion of the successful TP  
modification. The RTV will help keep airflow away, but additional shielding 
will  help 
even more.
 
* There is a point where thermally stabilizing the unit does not help  
anymore. I suspect that point is reached shortly before burying the unit 50  
meters underground :) At the point of diminishing marginal returns the GPS  and 
loop noise will be larger than the thermally induced phase offsets. Also  
local heating from the GPS receiver (which is not constant) will swamp 
external  thermal effects at some point. For us in our lab, the point of 
diminishing  returns is reached when we simply slide the unit into its ESD 
packaging, 
then  put some pink ESD padding on top of it. With that simple  shielding 
we can get ADEV at 5x to 8x its rated 1ppb performance out of most  units.
 
* Temperature changes are typically not the problem with TCXOs, simple  
airflow and convection turbulence is what causes most of the phase drift  
problems. As shown by Tom simply putting a layer of TP on top of the unit made 
a  
huge difference in stability by keeping convective flow away from the TCXO, 
 while it probably did nothing for temperature insulation. These convective 
flows  are very fast and high-frequency so inside the GPS loop time 
constant, whereas  temp changes are usually easy to low-pass dampen to the 
point 
that the  GPS loop will hide them.
 
* Actively heating the units' enclosure to some stable temperature is  
counter-productive in my opinion for two reasons: first higher temperatures  
cause convective airflow inside the enclosure. We want as little convective 
flow  as possible. Second CMOS slows down at higher temperatures, and noise 
levels go  up with temperature. As mentioned before temperature changes (other 
than instant  changes such as when the sun almost sudden hits the enclosure) 
usually are  easily low-pass filtered to be slower than the GPS loop time 
constant which is  below a couple 100 seconds, so keeping the enclosure at 
some high temperature is  probably going to make things worse. There are other 
items to consider such as  the AT-cut TCXO crystal probably has its most 
stable operating point at  around 25C, and the lifetime MTBF of electronics 
typically gets cut in  half with every 10C Degree increase in temperature.
 
* The 10MHz units have a different RF output than the 20MHz units. The  
20MHz units have a 50 Ohms series-terminated and buffered RF output, while the  
10MHz units have the TCXO output drive the MMCX connector directly without  
series impedance matching. Both drive the line with 3.0V CMOS levels. This 
means  the cable on the 10MHz unit should be kept as short as possible, and 
that  impedance matching for maximum power-transfer is not required nor 
desired. The  suggestion that Charles made for checking the impedance by 
progressively loading  the output more and more is valid for Sine Wave outputs, 
but 
not for CMOS  outputs as implemented on the LTE Lite. One issue is that the 
TCXO is driving a  1.8V CMOS input through a capacitive voltage divider, 
and if you load  the TCXO so much that its output voltage goes to 1/2 the 
no-load voltage then  the input of the processor will likely not get enough 
voltage range to  operate properly.
 
I mentioned 1M Ohms input impedance simply for convenience as it is a  
standard input impedance as Charles mentions. You can significantly reduce that 
 
impedance since the 10MHz TCXO can drive a handful of mA no problem, and 
the  20MHz buffered output can drive 20mA or more. This means a 1K Ohms load 
is also  no issue as it would load the output only with 3mA, however(!) the 
more you load  the CMOS output the more heating will happen in the 3.0V 
linear regulator close  to the TCXO and inside the 10MHz DIP-14 TCXO. This will 
cause load-induced  instability.
 
The best input for the LTE-Lite output is simply a 3.3V or 5V powered CMOS  
gate. No input termination resistance required. Cable lengths should  be 
kept short (less than a foot) to prevent ringing and loading the TCXO output  
for more than a couple of nanoseconds as the edges traverse into the  coax. 
I like to put a weak pull-down of 470K to 1M on those CMOS gate  inputs so 
the input does not float when its not connected to anything. There is  
absolutely no need to load down the output with 100 Ohms, 1K, or even 10K. For  
CMOS inputs, the only thing that makes a difference in phase noise seems to be 
 the rise/fall time and voltage swing. The faster swing and higher  voltage 
the better. Loading down the output will reduce this

Re: [time-nuts] Practical considerations making a lab standard with an LTE lite

2014-11-23 Thread Dr. David Kirkby (Kirkby Microwave Ltd)

Hi

If your target frequency error is in the  1x10^-10 to the “hopefully 1x10^-11” 
range, You should consider your very requirements carefully. I tossed up some 
frequency plots of the KS boxes and of the Z3801 a while back. They are OCXO 
based boxes running in a very good thermal environment.   Their OCXO’s ADEV is 
roughly 1x10^-12 at 1 to 10 seconds. That compares directly to the TCXO’s 
apparent ADEV posted by Tom earlier at 5x10^-11 in the 1 to 10 second region.  

The OCXO based parts (with a very loose interpretation of 1x10^-11 frequency 
accuracy) do not hit  +/- 1x10^-11 frequency accuracy. If the plots are to far 
back to dig up, I can re-post them. They will hit a  1x10^-10 frequency 
accuracy limit without any quibbling over the definition of the spec. The 
frequency accuracy of a TCXO based part is not going to measure up to an OCXO 
based part. That’s not because the TCXO part is in some way flawed, it’s just 
the way things work on a GPSDO. 

If you are going with a TCXO, concrete bunker construction is not needed. With 
an OCXO based part, it just might help a bit. This may be a bit counter 
intuitive. It’s a function of where the (much better) ADEV of the OCXO 
intersects the (constant slope) ADEV of the GPS receiver. The control loop on 
the OCXO based part will be running at a *much* longer time constant. If the 
OCXO ADEV is 10X better, it will be 10X longer. If it’s 100X better it will be 
100X longer.  In both cases (TCXO and OCXO) the ADEV at 1 or even 10 seconds 
will not be improved by thermal this or that , once drafts are eliminated. The 
filter will still track where it needs to track. If the OCXO is running a 
filter out at a thousand seconds, you will *will* see slow thermal variations. 
The TCXO based part’s output running at (say) 10 seconds will not see the same 
variations, they will be corrected out by the GPS before they hit the output. 

—

Why tie these things together? 

Where you wind up depends very much on where you are headed. Starting with the 
right gear for the application will matter in the end. Putting a lot of effort 
into a project without considering the ultimate goal may not be as economical 
as it could otherwise be. 



Bob


 On Nov 23, 2014, at 3:04 PM, Jim Sanford wb4...@wb4gcs.org wrote:
 
 All:
 
 I appreciate all the responses to my post earlier today.  Very informative.
 
 First:  DownEast Microwave sells a nice kit for distributing 10 MHz.  Specs 
 are on their website, but basically, one in, four out -- each individually 
 buffered and filtered.
 
 Second:  I will use the 20 MHz from the LTE-Lite to lock a 100Mhz TCXO which 
 will be the LO for a high performance 2meter amateur software defined radio.  
 (OpenHPSDR.org for info on the SDR)  I may multiply it to help with some of 
 the microwave LOs.  It will also use the 20 Mhz to lock a 1GHz TXCO to be 
 multiplied for microwave LOs.
 
 Third:  I will have three of the LTE-Light units.  The first will feed some 
 LOs as described above, and the synthesized 10 MHz output will be my lab 
 frequency standard.  The lab is in a cinder block room off the basement, with 
 2 of foam insulation under 2 inches of concrete which is the floor for a 
 covered porch above.  I'd never thought of it, but the put it on the floor 
 next to a brick wall idea fits here.  Actually, I can put it next to 2 
 buried brick walls, and will surround it with cinder block on the remaining 
 sides.  Can probably cover it with a few 12x12 paver stones.  NOW, this 
 involves drilling a hole through cinder block and drywall between the 
 office/ham shack and the lab.  Would rather not, but have to anyway.  I have 
 been informed that the fan noise from the ham shack gigabit ethernet switch 
 will become politically unacceptable in about 72 hours.  (Office/ham shack 
 share a guest bedroom.)  I would like to get 1E-10 or 1E-11 accuracy out of 
 this setup.  Thanks for
  this suggestion!
 
 Fourth:  The second unit will be in a building at the base of my antenna 
 tower, about 350 feet from the house.  This building is above ground, and 
 will be allowed to swing from 45F to 80F over the course of the year.  Hence 
 my interest in insulating and heating.  I might consider putting something in 
 the ground here, the problem would be access for servicing  I would like 
 to get 1E-10 or 1E-11 accuracy out of this unit.  Considered shipping 10 MHz 
 in coax out from the house, would rather not, and would like some redundancy, 
 anyway.
 
 Fifth:  I get that the /efc/ vs. /temp/ relationship is very complex and 
 accept that trying to characterize it is not worth the effort.  Thanks for 
 this bit of information.
 
 Sixth:  My third LTE-Lite will drive a 10MHz reference for a mobile (rover) 
 microwave setup, providing the reference for a bunch of GHz LOs.  This 
 station will see motion, and temperature variation. Ultra low power will not 
 be a concern, so heaters are acceptable. I would be happy with 1E-9 accuracy

Re: [time-nuts] Practical considerations making a lab standard with an LTE lite

On 23 Nov 2014 16:25, Tom Van Baak t...@leapsecond.com wrote:

 For plots and photos showing performance with, and without, and with
insulation see:
http://leapsecond.com/pages/LTE-Lite/
 The difference is dramatic, especially if you are used to working with
OCXO where this sort of effect does not occur.

Tom,

What plots are with and without the thermal paper?

I see several graphs, but don't know what is under what conditions.

The second graph shows something fairly significant happening at 300 s. Is
that where you removed the TP?

Dave
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Re: [time-nuts] Practical considerations making a lab standard with an LTE lite

Hi

Well the answer is obvious:)  

You simply need to turn on the air-conditioning full blast for more months of 
the summer in … ummm ….. e …. Denmark … hmmm…..

Heat only or cool only systems seem to be more practical when the heat sink is 
a flowing body of water or an ocean. Unfortunately those seem to also run up 
the price of adjacent real estate. 

Moving bodies of water also aren’t very good for stabilizing temperature on a 
frequency source. The same thing is true of a hole in the ground that goes 
above or below the level of ground water over the course of the year. If you 
drill a hole, there is indeed a wrong depth to pick. It might be interesting to 
see how deep you need to go for stable ground water temps. Around here the top 
layer of ground water was rain last week or last month.

Bob

 On Nov 23, 2014, at 1:07 PM, Poul-Henning Kamp p...@phk.freebsd.dk wrote:
 
 
 In message 
 canx10hcaob-5gysbr7sdxwl7dyh7qubmhxwmi9xdrcf3mdm...@mail.gmail.com
 , Dr. David Kirkby (Kirkby Microwave Ltd) writes:
 
 Geothermal means you drill at least 50m (Iceland) or more likely
 half a kilometer down, in order to harvest water at near boiling
 point from the Earths geological heat-sources (mostly uranium decay).
 
 Sorry.  What he installs is pipes in the ground in residential or
 industrial sites. Basically he says they work initially,  but performance
 drops dramatically over a couple of years.
 
 That is not geothermal then, and yes, a LOT of those systems are
 badly underdimensioned.
 
 I've been researching this topic intensively because my new house
 will be heated that way.
 
 My conclusion, based on reading a lot of reports, is that there
 is no credible way to predict the performance.  The wetter your
 soil the better, but that's about it.
 
 I'm going to overprovision by a factor two to be on the safe side,
 afterall it only costs EUR7 for each extra meter of pipe.
 
 -- 
 Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
 p...@freebsd.org | TCP/IP since RFC 956
 FreeBSD committer   | BSD since 4.3-tahoe
 Never attribute to malice what can adequately be explained by incompetence.
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Re: [time-nuts] Practical considerations making a lab standard with an LTE lite

Hi

There are two plots with activity changing at 300 seconds. The second plot 
(purple) is the removal of the paper at 300 seconds. The fourth plot (red) is 
the addition of the paper at 300 seconds. 

The last plot (green and blue) is ADEV with and without the paper. Blue is ADEV 
with paper. Green is ADEV without paper.

The second to last plot demonstrates the unit meeting 1x10^-9 (peak to peak) 
frequency stability with the paper over a 1,000 second test. It shows it doing 
about 5X worse on frequency stability over the same period without the paper. 
Yes, that’s all with 1 second averaging. Changing the averaging would impact 
each of the results. It should change their ratio. 

Again back to the basic question: frequency over what period? Go to a 24 hour 
average and the results should be terrific. In some systems, that’s a useful 
number (I guess….). I rarely see people set their counters to an 86,000 second 
gate time :)

Bob


 On Nov 23, 2014, at 4:42 PM, Dr. David Kirkby (Kirkby Microwave Ltd) 
 drkir...@kirkbymicrowave.co.uk wrote:
 
 On 23 Nov 2014 16:25, Tom Van Baak t...@leapsecond.com wrote:
 
 For plots and photos showing performance with, and without, and with
 insulation see:
 http://leapsecond.com/pages/LTE-Lite/
 The difference is dramatic, especially if you are used to working with
 OCXO where this sort of effect does not occur.
 
 Tom,
 
 What plots are with and without the thermal paper?
 
 I see several graphs, but don't know what is under what conditions.
 
 The second graph shows something fairly significant happening at 300 s. Is
 that where you removed the TP?
 
 Dave
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Re: [time-nuts] Practical considerations making a lab standard with an LTE lite

2014-11-23 Thread Said Jackson via time-nuts

Tom,

From the looks of the plots these may be from the first proto unit with early 
software no? Also was this with the indoor GPS antenna setup?

The production units with outdoor or windowed' antenna should have 
significantly improved average performance from the first unit and its early 
GPS and GPSDO firmware versions.

Bye,
Said

Sent From iPhone

 On Nov 23, 2014, at 14:18, Bob Camp kb...@n1k.org wrote:
 
 Hi
 
 There are two plots with activity changing at 300 seconds. The second plot 
 (purple) is the removal of the paper at 300 seconds. The fourth plot (red) is 
 the addition of the paper at 300 seconds. 
 
 The last plot (green and blue) is ADEV with and without the paper. Blue is 
 ADEV with paper. Green is ADEV without paper.
 
 The second to last plot demonstrates the unit meeting 1x10^-9 (peak to peak) 
 frequency stability with the paper over a 1,000 second test. It shows it 
 doing about 5X worse on frequency stability over the same period without the 
 paper. Yes, that’s all with 1 second averaging. Changing the averaging would 
 impact each of the results. It should change their ratio. 
 
 Again back to the basic question: frequency over what period? Go to a 24 hour 
 average and the results should be terrific. In some systems, that’s a useful 
 number (I guess….). I rarely see people set their counters to an 86,000 
 second gate time :)
 
 Bob
 
 
 On Nov 23, 2014, at 4:42 PM, Dr. David Kirkby (Kirkby Microwave Ltd) 
 drkir...@kirkbymicrowave.co.uk wrote:
 
 On 23 Nov 2014 16:25, Tom Van Baak t...@leapsecond.com wrote:
 
 For plots and photos showing performance with, and without, and with
 insulation see:
 http://leapsecond.com/pages/LTE-Lite/
 The difference is dramatic, especially if you are used to working with
 OCXO where this sort of effect does not occur.
 
 Tom,
 
 What plots are with and without the thermal paper?
 
 I see several graphs, but don't know what is under what conditions.
 
 The second graph shows something fairly significant happening at 300 s. Is
 that where you removed the TP?
 
 Dave
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Re: [time-nuts] Practical considerations making a lab standard with an LTE lite

Hi

A lot of these parts are designed for use in a system environment rather than 
sitting out on a bench. That’s as true of the KS boxes (forced air cooling) as 
it is of the LTE’s. In  90% (and likely   99.9%) of the places a TCXO gets 
used, it’s packed tight in with a bunch of other stuff. Not only is there no 
air movement, there might not be much air. A cell phone is a good example of 
this sort of assembly. Other battery powered portable gear fit this same 
general model, but possibly not to the same degree of “cram it in. 

Yes, we love our big rack mounted boxes full of this or that. They are useful. 
The TCXO guys would go broke quickly if that was the market they focused their 
main efforts on. Big Morion 2” x 2” x 1” OCXO’s, yes those are targeted more at 
big rack mount this or that. Different market focus for different products. 
It’s not a one size fits all world. 

Indeed, adapting a TCXO to a bench environment is something that you need to 
do. A nice fluffy cotton towel works quite well. Yes, that’s a 1970’s solution 
to the problem.  Most TCXO’s were bigger back then. The issue has been around 
“for a while”. It’s actually not a bad thing to keep handy when testing OCXO’s. 
If they don’t work you can always use it to cry into …:)

Bob
 
 On Nov 23, 2014, at 11:24 AM, Tom Van Baak t...@leapsecond.com wrote:
 
 The short-term performance is 10x worse if you don't shield the TCXO from 
 air, even if the ambient air is still. I suggested Said sell the product 
 with some sort of engineered shield in place. Instead each of us will solve 
 the problem in our own way; which is ok for a dev kit.
 
 For plots and photos showing performance with, and without, and with 
 insulation see:
 http://leapsecond.com/pages/LTE-Lite/
 The difference is dramatic, especially if you are used to working with OCXO 
 where this sort of effect does not occur.
 
 The insulation may be found in convenient rolls at many local stores. I used 
 TP, which for this application is an acronym for Thermal Paper.
 
 /tvb
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Re: [time-nuts] Practical considerations making a lab standard with an LTE lite

Hi

Actually that was Bob trying to explain Tom’s plots simply from looking at 
them. I *think* I got it right, but it’s Tom’s data and his LTE part. Others 
have commented that Tom’s part looks different than theirs. 

Maybe Tom needs a Microsoft Windows Update on his GPSDO firmware :) For some 
reason the very thought of Microsoft getting involved in something like that 
makes me shudder…

Bob

 On Nov 23, 2014, at 5:33 PM, Said Jackson via time-nuts time-nuts@febo.com 
 wrote:
 
 Tom,
 
 From the looks of the plots these may be from the first proto unit with early 
 software no? Also was this with the indoor GPS antenna setup?
 
 The production units with outdoor or windowed' antenna should have 
 significantly improved average performance from the first unit and its early 
 GPS and GPSDO firmware versions.
 
 Bye,
 Said
 
 Sent From iPhone
 
 On Nov 23, 2014, at 14:18, Bob Camp kb...@n1k.org wrote:
 
 Hi
 
 There are two plots with activity changing at 300 seconds. The second plot 
 (purple) is the removal of the paper at 300 seconds. The fourth plot (red) 
 is the addition of the paper at 300 seconds. 
 
 The last plot (green and blue) is ADEV with and without the paper. Blue is 
 ADEV with paper. Green is ADEV without paper.
 
 The second to last plot demonstrates the unit meeting 1x10^-9 (peak to peak) 
 frequency stability with the paper over a 1,000 second test. It shows it 
 doing about 5X worse on frequency stability over the same period without the 
 paper. Yes, that’s all with 1 second averaging. Changing the averaging would 
 impact each of the results. It should change their ratio. 
 
 Again back to the basic question: frequency over what period? Go to a 24 
 hour average and the results should be terrific. In some systems, that’s a 
 useful number (I guess….). I rarely see people set their counters to an 
 86,000 second gate time :)
 
 Bob
 
 
 On Nov 23, 2014, at 4:42 PM, Dr. David Kirkby (Kirkby Microwave Ltd) 
 drkir...@kirkbymicrowave.co.uk wrote:
 
 On 23 Nov 2014 16:25, Tom Van Baak t...@leapsecond.com wrote:
 
 For plots and photos showing performance with, and without, and with
 insulation see:
 http://leapsecond.com/pages/LTE-Lite/
 The difference is dramatic, especially if you are used to working with
 OCXO where this sort of effect does not occur.
 
 Tom,
 
 What plots are with and without the thermal paper?
 
 I see several graphs, but don't know what is under what conditions.
 
 The second graph shows something fairly significant happening at 300 s. Is
 that where you removed the TP?
 
 Dave
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Re: [time-nuts] Practical considerations making a lab standard with an LTE lite

2014-11-23 Thread Alex Pummer

by us  in central California, we get 1kW/h square meter average around 
the year, the south even more, el Cajon will have today +29C° in the 
afternoon  as of 23 of November 2014

73
Alex
On 11/23/2014 9:49 AM, Poul-Henning Kamp wrote:


In message canx10hb0kdrnaayzgvm1gkduj7gklth0acdxczg894hxbus...@mail.gmail.com
, Dr. David Kirkby (Kirkby Microwave Ltd) writes:


He installs  ground source
heat pumps for the geothermal energy.  He says that they actually work
quite poorly in many cases.

There is a BIG difference between geothermal and ground heating.

Geothermal means you drill at least 50m (Iceland) or more likely
half a kilometer down, in order to harvest water at near boiling
point from the Earths geological heat-sources (mostly uranium decay).

Extracting more energy than available just means the temperature
drops temporarily.  It will increase again once you reduce the
pump rate.

Horizontal ground heat means that you are harvesting sunshine
accumulated in the top one meter of the soil.  Much of the energy
is harvested from freezing the water around the pipe thus pulling
out the relatively high melting energy of water.

If you extract more energy than you deposit sunshine, you end
up freezing a larger and larger volume of water/soil around
the pipe and your compressor will eat a lot of electricity.

In practice it looks like this:


http://ing.dk/artikel/varmepumpe-mareridt-jordslange-var-dybfrossen-i-maj-113176

(The two pictures show the same pipe, with and without frozen ground.)

Finally there is vertial ground heat where you drill down only about
40-80 meter, tapping heat mostly from ground water resources.Most
places the ground water doesn't move fast enough to deliver the amounts
of energy extracted, and over time the source returns unusably low
temperature and must be abandonned.  Typically after 25-30 years.



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Re: [time-nuts] Practical considerations making a lab standard with an LTE lite

2014-11-23 Thread Neville Michie

A Hint about avoiding convective cell heat transfer,
If you keep the spacing between two planes less than 5/16 then you will 
be unlikely to have convection cells forming. The stationary air is a good 
insulator
but thermal radiation will be the dominant heat transfer process.
This is true for double glazing, katharometers and generally all devices. 
The suppression of turbulent heat transfer may provide more insulation but also 
less noise and instability.
So it may be a good idea to use a relatively close fitting box with thick walls.
Cheers,
Neville Michie




On 23/11/2014, at 11:37 PM, Charles Steinmetz wrote:

 Dave wrote
 
 But given the TCXOs sensitivity to temperature changes, I don't
 know whether it might be preferable to mount the LTE lite in its own box
 without any power supplies in it - perhaps with some thermally insulting
 material around the LTE lite so the crystal doesn't experience any fast
 temperature changes.
 
 First, mount the LTE in a cast aluminum box (not thin sheet metal, something 
 with some heft).  Use thermally insulating standoffs (teflon or nylon, with 
 no metal through fasteners) to get the board in the middle of the volume of 
 the box.  Use a box a bit larger than you'd first think, so there is at least 
 1 of air on all 6 sides of the LTE board.  Do NOT mount any part of the LTE 
 board (connectors, etc.) directly to the box walls -- use pigtails for all 
 connections.  Do NOT use any insulation between the LTE and the box walls 
 other than the 1+ of air.
 
 The mounting described above will add substantial thermal capacitance to the 
 LTE board (good) without adding significant thermal resistance (bad).  For 
 further discussions of this issue, search the list archives for thermal 
 capacitance and thermal mass.
 
 Now, mount the cast box (plus any thermal mass you add to it -- see below) so 
 that IT is thermally isolated from the overall enclosure (or, if it sits out 
 in the open, thermally isolated from anything solid).  The air space in the 
 enclosure isolates the oscillator from the cast box and the box is 
 sufficiently massive that its temperature cannot change nearly as fast as 
 ambient.  The thermal mass of the cast box can be adjusted by adding thermal 
 mass to it as desired.
 
 The goal is for the box temperature to change only by changes in ambient AIR 
 temperature, and the LTE board to change only by changes in the AIR 
 temperature inside the cast box.  This integrates any changes to the LTE 
 board temperature with a very long time constant, which allows the GPS 
 discipline to track and cancel the temperature changes.
 
 (If you mount an ovenized oscillator this same way, it integrates any changes 
 to the OCXO temperature so that the oven control loop can track and cancel 
 any changes to the crystal temperature.)
 
 You can, of course, improve things even further by making sure the ambient 
 air temperature surrounding the cast box changes slowly, or not at all.  But 
 the technique described above can be counted on to reduce thermal effects in 
 most OCXOs or GPSDOs to better (often much better) than the 1e-13 level 
 unless the ambient temperature changes MUCH more and MUCH faster than any 
 change we wouild consider normal for a living space.  This is true whether 
 the cast box is mounted out in the open, or inside an overall enclosure with 
 other electronics.
 
 Best regards,
 
 Charles
 
 
 
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Re: [time-nuts] Practical considerations making a lab standard with an LTE lite

Hi

I believe that if you go back a few years in the archives, you will find a 
thread that ultimately stops with a swimming pool full of mercury. Needless to 
say, we’re been down this road once or twice before.

Bob

 On Nov 23, 2014, at 7:59 PM, Neville Michie namic...@gmail.com wrote:
 
 A Hint about avoiding convective cell heat transfer,
 If you keep the spacing between two planes less than 5/16 then you will 
 be unlikely to have convection cells forming. The stationary air is a good 
 insulator
 but thermal radiation will be the dominant heat transfer process.
 This is true for double glazing, katharometers and generally all devices. 
 The suppression of turbulent heat transfer may provide more insulation but 
 also 
 less noise and instability.
 So it may be a good idea to use a relatively close fitting box with thick 
 walls.
 Cheers,
 Neville Michie
 
 
 
 
 On 23/11/2014, at 11:37 PM, Charles Steinmetz wrote:
 
 Dave wrote
 
 But given the TCXOs sensitivity to temperature changes, I don't
 know whether it might be preferable to mount the LTE lite in its own box
 without any power supplies in it - perhaps with some thermally insulting
 material around the LTE lite so the crystal doesn't experience any fast
 temperature changes.
 
 First, mount the LTE in a cast aluminum box (not thin sheet metal, something 
 with some heft).  Use thermally insulating standoffs (teflon or nylon, with 
 no metal through fasteners) to get the board in the middle of the volume 
 of the box.  Use a box a bit larger than you'd first think, so there is at 
 least 1 of air on all 6 sides of the LTE board.  Do NOT mount any part of 
 the LTE board (connectors, etc.) directly to the box walls -- use pigtails 
 for all connections.  Do NOT use any insulation between the LTE and the box 
 walls other than the 1+ of air.
 
 The mounting described above will add substantial thermal capacitance to the 
 LTE board (good) without adding significant thermal resistance (bad).  For 
 further discussions of this issue, search the list archives for thermal 
 capacitance and thermal mass.
 
 Now, mount the cast box (plus any thermal mass you add to it -- see below) 
 so that IT is thermally isolated from the overall enclosure (or, if it sits 
 out in the open, thermally isolated from anything solid).  The air space in 
 the enclosure isolates the oscillator from the cast box and the box is 
 sufficiently massive that its temperature cannot change nearly as fast as 
 ambient.  The thermal mass of the cast box can be adjusted by adding thermal 
 mass to it as desired.
 
 The goal is for the box temperature to change only by changes in ambient AIR 
 temperature, and the LTE board to change only by changes in the AIR 
 temperature inside the cast box.  This integrates any changes to the LTE 
 board temperature with a very long time constant, which allows the GPS 
 discipline to track and cancel the temperature changes.
 
 (If you mount an ovenized oscillator this same way, it integrates any 
 changes to the OCXO temperature so that the oven control loop can track and 
 cancel any changes to the crystal temperature.)
 
 You can, of course, improve things even further by making sure the ambient 
 air temperature surrounding the cast box changes slowly, or not at all.  But 
 the technique described above can be counted on to reduce thermal effects in 
 most OCXOs or GPSDOs to better (often much better) than the 1e-13 level 
 unless the ambient temperature changes MUCH more and MUCH faster than any 
 change we wouild consider normal for a living space.  This is true whether 
 the cast box is mounted out in the open, or inside an overall enclosure with 
 other electronics.
 
 Best regards,
 
 Charles
 
 
 
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Re: [time-nuts] Practical considerations making a lab standard with an LTE lite


Said wrote:


The 10MHz units have a different RF output than the 20MHz units. The
20MHz units have a 50 Ohms series-terminated and buffered RF output, 
while the

10MHz units have the TCXO output drive the MMCX connector directly without
series impedance matching. Both drive the line with 3.0V CMOS levels. This
means  the cable on the 10MHz unit should be kept as short as possible, and
that  impedance matching for maximum power-transfer is not required nor
desired. The  suggestion that Charles made for checking the impedance by
progressively loading  the output more and more is valid for Sine 
Wave outputs, but

not for CMOS outputs as implemented on the LTE Lite.


Absolutely correct -- I did not anticipate that anyone would make 
unbuffered logic levels available to the external world.


In that case, I'd put a logic-level line driver immediately at the 
unit (by immediately, I mean with a small breakout card that plugs 
directly onto the LTE's MMCX connector with no intervening 
cable).  For example, all 6 outputs of an HC14 or AC14 hex inverter 
connected in parallel, or a dedicated line driver chip like an 
HC365/366 or AC240/244/540/541.


The buffer should be inside the enclosure with the LTE, and I would 
also add a T-network filter to convert the logic-level square wave 
into a sine wave.  This would confine all of the fast logic 
transitions inside the shielded box, where they can do the least mischief.


For the T-network, I like 10uH/50.5pF/10uH, others like 
1.5uH/310pF/1.5uH.  Both draw ~ +/- 35mA from a 5v logic 
output.  Make sure your buffer can supply this current, and feed the 
T-network through 10nF and 50 ohms in series.  You'll get a 1Vrms 
(13dBm) sine wave into 50 ohms (675mVrms with 3v logic).  H3 is down 
40dBc with the 1.5uH network and 60dBc with the 10uH network.  [Note 
that the apparent source impedance is  50 ohms, so the open-circuit 
voltage is more than double.]


Best regards,

Charles



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Re: [time-nuts] Practical considerations making a lab standard with an LTE lite

2014-11-23 Thread Brooke Clarke

Hi Jim:

It turns out that ground water that's being pumped is very similar to pumping
oil. It's a limited resource.
There's a web page showing the GRACE satellite maps of California and that we
are running out of ground water.
This isn't the page, but gives the idea:
http://www.cnyo.org/2014/08/19/nasa-space-place-droughts-floods-and-the-earths-gravity-by-the-grace-of-nasa/

So depending on ground water as a stable heat sink may no longer be an option
as wells go dry.
It's been many years since the local water company has quit installing new
meters.

Mail_Attachment --
Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html
http://www.prc68.com/I/DietNutrition.html
Jim Lux wrote:

On 11/23/14, 11:15 AM, Alex Pummer wrote:

by us in central California, we get 1kW/h square meter average around
the year, the south even more, el Cajon will have today +29C° in the
afternoon as of 23 of November 2014

I suspect more like the insolation peaks at 1kW/square meter or a bit more, the average over a day is somewhat less.
At JPL we have a weather station on line that displays this and I don't recall seeing significantly more than 1000 W/m2.

The nominal average 1.362 kW/sq meter at solar max is at the top of the
atmosphere, and is normal to the incidence.

The surface insolation at the equator when the sun is directly overhead is
about 1.04 kW/sq meter.

I think you'd get pretty close to that at solar noon in the Summer in Southern California, which is 32-34 degrees
latitude, so at the solstice, the zenith angle is 10 degrees, and cos(10) is pretty close to 1.

You do pick up some additional insolation from diffuse and scattered radiation from clouds or haze, but I'm not sure
that makes up for the attenuation due to the same haze.

Some time ago, I calculated that in Los Angeles (34 degrees latitude), a horizontal flat plate gets about 8-9
kWh/m2/day in summer and about 1-2 kWh/m2/day in winter.. Tilting the collector would help a lot in the winter
(Zenith angle is 56 degrees instead of 10), but there's no making up for the short days.

Getting back to the time-nuts aspects, there are some charts around that show the temperature variation as a function
of depth, latitude, soil and season. I know that for DSN, they went through all kinds of gyrations to calculate (and
measure) this for the optical fiber timing links between the antennas and the masers. For small dissipated power (I
doubt your oscillator is going to be putting kilowatts into the soil) you don't have to go very deep (single digit
meters) before the diurnal variation is down in the 0.1 degree or smaller. Annual variations are bigger.

http://www.builditsolar.com/Projects/Cooling/EarthTemperatures.htm
has a bunch of charts for some unknown latitude (probably mid Atlantic states, since the data is from Virginia Tech).
They appear to use well water temperatures as the measurement technique.

A bit more googling found a paper by one G. Florides that refers to the Kasuda formula.. (the link is hard to cut and
paste.. I'm sure if you google Florides soil temperature you'll find it)

and gives this reference
Kasuda, T., and Archenbach, P.R. Earth Temperature and Thermal Diffusivity at Selected Stations in the United
States, ASHRAE Transactions, Vol. 71, Part 1, 1965.

Horizontal ground heat means that you are harvesting sunshine
accumulated in the top one meter of the soil. Much of the energy
is harvested from freezing the water around the pipe thus pulling
out the relatively high melting energy of water.

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Re: [time-nuts] Practical considerations making a lab standard with an LTE lite

2014-11-23 Thread Jim Lux


On 11/23/14, 5:46 PM, Brooke Clarke wrote:

Hi Jim:

It turns out that ground water that's being pumped is very similar to
pumping oil.  It's a limited resource.
There's a web page showing the GRACE satellite maps of California and
that we are running out of ground water.


Back east where that data is from, I suspect that's not a big an issue.

Water is many tens of meters down in most of California.

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Re: [time-nuts] Practical considerations making a lab standard with an LTE lite

2014-11-23 Thread Said Jackson via time-nuts

Charles,

Any buffer options added to the board would have caused either additive phase 
noise or added power consumption, and possibly yet another low noise LDO to be 
required.

On the 20MHz units there is already a strong buffer that can drive 50 Ohms 
terminations so adding a buffer in front of the coax connector on that version 
would have just added unnecessary phase and AM noise, parts count and cost, and 
power consumption, and would have resulted in a product with worse performance 
than we have now. That configuration is the normal one so we did not add 
unnecessary circuitry that would have decreased product performance.

On the 10MHz boards with external DIP-14 TCXO there is no buffer, and adding 
one would have required to possibly add yet another low noise supply regulator 
and possibly another MMCX connector. Since this is the optional 
configuration, we optimized for highest performance for the standard 
configuration.

Adding this many features to the board required some trade offs to be made, and 
we have to keep in mind the initial goal of the entire effort: to provide an 
easy way to evaluate the performance of our LTE Lite module - hence its called 
the LTE Lite Evaluation board. Everything else was a bonus.

But in the end it should be fairly trivial to put a 50 Ohms driver and low pass 
filter together using either a CMOS gate or a simple emitter follower. We also 
need to keep in mind that generating a Sine Wave output would have consumed 
200mW to 250mW additive power and thus would have more than doubled the total 
power consumption.

Lastly we have three outputs on the board so we would have required three 
additional buffers and their support circuitry, all that for a questionable 
improvement.

Or instead of adding a bunch of buffers one can use somewhat short cables and 
1M input impedance on the target hardware and that will work perfectly too 
without any changes..

Bye,
Said



Sent From iPhone

 On Nov 23, 2014, at 16:22, Charles Steinmetz csteinm...@yandex.com wrote:
 
 Said wrote:
 
 The 10MHz units have a different RF output than the 20MHz units. The
 20MHz units have a 50 Ohms series-terminated and buffered RF output, while 
 the
 10MHz units have the TCXO output drive the MMCX connector directly without
 series impedance matching. Both drive the line with 3.0V CMOS levels. This
 means  the cable on the 10MHz unit should be kept as short as possible, and
 that  impedance matching for maximum power-transfer is not required nor
 desired. The  suggestion that Charles made for checking the impedance by
 progressively loading  the output more and more is valid for Sine Wave 
 outputs, but
 not for CMOS outputs as implemented on the LTE Lite.
 
 Absolutely correct -- I did not anticipate that anyone would make unbuffered 
 logic levels available to the external world.
 
 In that case, I'd put a logic-level line driver immediately at the unit (by 
 immediately, I mean with a small breakout card that plugs directly onto the 
 LTE's MMCX connector with no intervening cable).  For example, all 6 outputs 
 of an HC14 or AC14 hex inverter connected in parallel, or a dedicated line 
 driver chip like an HC365/366 or AC240/244/540/541.
 
 The buffer should be inside the enclosure with the LTE, and I would also add 
 a T-network filter to convert the logic-level square wave into a sine wave.  
 This would confine all of the fast logic transitions inside the shielded box, 
 where they can do the least mischief.
 
 For the T-network, I like 10uH/50.5pF/10uH, others like 1.5uH/310pF/1.5uH.  
 Both draw ~ +/- 35mA from a 5v logic output.  Make sure your buffer can 
 supply this current, and feed the T-network through 10nF and 50 ohms in 
 series.  You'll get a 1Vrms (13dBm) sine wave into 50 ohms (675mVrms with 3v 
 logic).  H3 is down 40dBc with the 1.5uH network and 60dBc with the 10uH 
 network.  [Note that the apparent source impedance is  50 ohms, so the 
 open-circuit voltage is more than double.]
 
 Best regards,
 
 Charles
 
 
 
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Re: [time-nuts] Practical considerations making a lab standard with an LTE lite