bob91343@yahoo.com said:

How good is your crystal?

Junk crystals are good thermometers.  Ballpark is 1 ppm/degree-C
If you are running ntpd, turn on loopstats and measure the temperature...
http://www.megapathdsl.net/~hmurray/ntp/slope.gif

I've been watching a 3 MHz ovenized crystal.  It was something like 4 for $25
from ebay.  It's a 2 in sq can, over an inch high.  It's got a few ppb of
noise over minutes/hours and a few more ppb of drift/wander over days/months.
It took several weeks to stabilize after power on.

--
These are my opinions.  I hate spam.

----- Original Message -----
From: "Hal Murray" hmurray@megapathdsl.net
To: "Bob Albert" bob91343@yahoo.com; "Discussion of precise time and
frequency measurement" time-nuts@febo.com
Cc: hmurray@megapathdsl.net
Sent: Sunday, March 02, 2014 2:45 AM
Subject: Re: [time-nuts] Another "atomic" clock question

bob91343@yahoo.com said:

How good is your crystal?

Junk crystals are good thermometers.  Ballpark is 1 ppm/degree-C
If you are running ntpd, turn on loopstats and measure the temperature...
http://www.megapathdsl.net/~hmurray/ntp/slope.gif

I've been watching a 3 MHz ovenized crystal.  It was something like 4 for
$25
from ebay.  It's a 2 in sq can, over an inch high.  It's got a few ppb of
noise over minutes/hours and a few more ppb of drift/wander over
days/months.
It took several weeks to stabilize after power on.

--

Is that 3 MHz OCXO one from Ridge? If so, I opened one up and was surprised
to find it did not have any foam insulation.

Tom

So does this mean I can epoxy a sandstone power resister to a junk
crystal and keep the frequency exactly perfect by varying the power in
the resister?

--

Chris Albertson
Redondo Beach, California

Nigel,

Thank you for your comments.  I see the situation a bit more clearly now, and will do some searches on Trimble and GPSDO and so on.  Right now I am interested in seeing what my options are, and deciding which way to go.

Yes this can become an obsession but I keep reminding myself that it's a hobby and isn't stopping me from eating or sleeping or breathing.  I do have fun with it.  Recently I bored a couple of visitors showing how my counter and signal generator drifted during warmup but eventually settled within about 10 ppb of one another, within about a half hour.  (Both units have 24/7 ovens.)  The generator actually accounts for nearly all the drift.  The counter is a venerable HP 5245L with 500 MHz plugin.

Bob

On Sunday, March 2, 2014 10:33 AM, Tom Miller tmiller11147@verizon.net wrote:

----- Original Message -----
From: "Hal Murray" hmurray@megapathdsl.net
To: "Bob Albert" bob91343@yahoo.com; "Discussion of precise time and
frequency measurement" time-nuts@febo.com
Cc: hmurray@megapathdsl.net
Sent: Sunday, March 02, 2014 2:45 AM
Subject: Re: [time-nuts] Another "atomic" clock question

bob91343@yahoo.com said:

How good is your crystal?

Junk crystals are good thermometers.  Ballpark is 1 ppm/degree-C
If you are running ntpd, turn on loopstats and measure the temperature...
  http://www.megapathdsl.net/~hmurray/ntp/slope.gif

I've been watching a 3 MHz ovenized crystal.  It was something like 4 for
$25
from ebay.  It's a 2 in sq can, over an inch high.  It's got a few ppb of
noise over minutes/hours and a few more ppb of drift/wander over
days/months.
It took several weeks to stabilize after power on.

--

Is that 3 MHz OCXO one from Ridge? If so, I opened one up and was surprised
to find it did not have any foam insulation.

Tom

time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

HI

If that is what you currently have for references, then you probably need a “lab standard” to drive things. Having one reference for all the gear makes things much easier. You don’t have to mess with a lot of “which one’s right today” sort of decisions.

That would make the GPSDO pretty much a slam dunk decision. You get both the reference and the calibration all in one box.

Bob

On Mar 2, 2014, at 2:56 PM, Bob Albert bob91343@yahoo.com wrote:

Hi

As long as your resistor keeps the temperature to within a micro degree it will do pretty well.

Bob

On Mar 2, 2014, at 2:09 PM, Chris Albertson albertson.chris@gmail.com wrote:

On 3/2/14 11:09 AM, Chris Albertson wrote:

Yes.. but you have to hold temperature to 0.001 degree, which is
somewhat challenging<grin>

A lot of SAW devices have tempcos that look like a parabola that fits in
a box that is 100 degrees wide, and 100 ppm high.

On 3/2/14 12:21 PM, Bob Camp wrote:

Oh, you were looking for 1E-12.. I was thinking 1E-9 would be good enough.

The other issue is that the phase noise might be pretty bad with a cheap
crystal, if it's not particularly high Q.  Probably not what you want
to use if you're multiplying it up for the carrier on your 240GHz
narrowband transmitter.

Hi

The gotcha is that there are second order temperature effects. If you are going to run the crystal very far off turn, you need to keep it more stable than you might think.

Bob

On Mar 2, 2014, at 3:40 PM, Jim Lux jimlux@earthlink.net wrote:

On 02/03/14 21:45, Bob Camp wrote:

"hysteresis", "memory effect", "restart of frequency drift"

Yeah, it puts a limit on how good a TCXO can track-and-compensate.

I was also considering the use of XOs for temperature sensing, it has
the benefit that it is relatively easy to sense with resolution, but
after that frequency/phase measures is in, getting a good temperature
reading isn't as easy.

Is there a good temperature-sensing set of modes in AT-cut crystals, as
I know being used in SC-cut crystals?

Cheers,
Magnus

On 3/2/14 1:00 PM, Magnus Danielson wrote:

There's the scheme which measures the temperature by comparing
fundamental and third overtone modes of a crystal.

But if you want to measure temperature, a SAW might be one way.  You mix
the output of a SAW oscillator with a more stable bulk oscillator, and
count the difference frequency.

Back in the 80s, I worked at a place that made tons of sensors for all
sorts of things which either measured a SAW resonator, or measured the
difference between two SAW resonators that were back to back (so their
temperatures were the same).  The sensor depended on what you did to the
SAW: bend it, deposit mass on it, etc.

HI

On Mar 2, 2014, at 4:00 PM, Magnus Danielson magnus@rubidium.dyndns.org wrote:

In addition to those there is actually a “temperature rate of change” dependent frequency change coefficient. It varies with the angle of cut and the temperature.

As Jim mentions in another post, you can run on the fundamental and the third (or 5th or 7th) and get a thermometer out of the delta between the two modes. The gotcha is that a change in load impedance will shift the frequencies unequally. That will give you an apparent temperature change.

Bob

Hi Bob,

On 02/03/14 23:16, Bob Camp wrote:

Indeed. I expect it to be individual to each particular crystal.

I already know about the fundamental and third trick, my question was if
it could be done to AT-cut as well. I interpret your statement as yes,
it does. I don't trust it to be perfect, but reasonable. Ideas for means
to handle shift would be welcome.

I don't have SC-cut crystals lying around, only complete OCXOs.
It would be fun to build a simple double-mode oscillator around an AT
lying around.

Cheers,
Magnus

On Mar 2, 2014, at 5:29 PM, Magnus Danielson magnus@rubidium.dyndns.org wrote:

There is a body of information that suggests that it’s related to the cut, the same way as the AT (or SC) frequency temperature performance is. It also relates to the mounting, which will vary from part to part.

It was originally proposed by a very nice guy from Ft. Monmouth for use with AT cut resonators. I believe the paper is in the FCS proceedings from the mid 1980’s. The DOD kept rights to the technique and licensed it to a couple of oscillator companies.

Bob

Hmm.  SC cut, perhaps? (see the third reference down..

R. L. Filler and J. R. Vig, “Resonators for the microcomputer
compensated crystal oscillator,” 43rd Ann. Symp. Freq. Contr., pp. 8-
15, 1989.

there's also

The microcomputer compensated crystal oscillator (MCXO)

Bloch, M. ; Frequency Electron. Inc., Mitchel Field, NY, USA ; Meirs,
M. ; Ho, J.
The MCXO uses a novel technique to achieve temperature compensation
without the use of ovens or conventional temperature-compensating
components. The crystal oscillator in the MCXO, which is free to vary
with temperature, operates on two modes simultaneously-the fundamental
and the third overtone. Several advantages accrue because this method of
temperature compensation does not resort to frequency pulling. The
authors presents the details of how the MCXO operates and the details of
the performance of the delivered systems
Published in:
Frequency Control, 1989., Proceedings of the 43rd Annual Symposium on
Date of Conference:
31 May-2 Jun 1989

Page(s):
16 - 19
Meeting Date :
31 May 1989-02 Jun 1989
INSPEC Accession Number:
3685419

Conference Location :
Denver, CO
Digital Object Identifier :
10.1109/FREQ.1989.68853

But then,

Yoonkee Kim (from Ft Monmouth)
has a paper (DTIC ADA484423)
Aging of Dual Mode Resonator for Microcomputer Compensated Crystal
Oscillator
Abstract— A Microcomputer Compensated Crystal Oscillator (MCXO) utilizes
the dual c-mode excitation (fundamental mode and 3rd overtone (OT)) of
an SC-cut resonator for self- temperature sensing and compensation. The
long-term stability of the MCXO depends primarily on the aging of the
dual mode resonator. When two modes age differently in time, the aging
MCXO’s output frequency curve would shift with a tilt over its operating
temperature range

Hi

I believe the paper was by Stan Shadowski. I’m certain I’ve mis-spelled his last name, which is indeed a very poor move on my part. I would not be surprised if there are several co-authors.

I don’t have the UFC indexes here at home so I have no quick way to look it up.

Bob

On Mar 2, 2014, at 7:40 PM, Jim Lux jimlux@earthlink.net wrote:

Sure. In fact you can loosely phase lock it to GPS that way. Your xtal doesn't need to have an EFC pin. You are using external temperature as a replacement for EFC. Call it TFC (temperature frequency control) instead. You can't get much simpler than that. Make sure to use a plain XO (not a TCXO or OCXO).

I used a resistor heater to bust hanging-bridges: http://leapsecond.com/pages/vp/heater.htm

/tvb

Tom,

That's a pretty interesting idea.  It makes me wonder if it would be worth it to switch perhaps a 1/2W heat source (random number) off and on over the XO in the UT+ say every minute or so.

Bob