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 tvb@leapsecond.com wrote:

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

insulation see:

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

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 ….. errrr …. 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

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

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

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

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

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.

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:

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