Re: [time-nuts] OXCO insulation

[Bill Hawkins]

I've lost track of who said what in this thread, but someone cautioned
against
over-insulating the oven. The quest for the best insulation is not
necessary or
desired.

If you use aerogel and your oven controller has the least bit of
overshoot, it
will take a long time for the overshoot to dissipate, during which time
your
controller has no control over the slowly decreasing temperature.
Indeed, the PID
algorithm could drive the output to the heater all the way to zero while
the
temperature comes back to and slightly below the setpoint. This is
guaranteed
to produce another overshoot as the temperature continues to drop while
the
controller raises the output from zero.

You need to have enough heat leakage to keep the heater running at a
reasonable
value. If you want to do something different, try using coarse and fine
heaters.
The coarse heater and control provide fast warmup to a small deadband
where the
fine heater takes over. Commercial ovens don't add the expense of a
coarse heater
because they assume that warmups will be infrequent. The user can wait
for some
warmup time before using the device. OTOH, fast warmup may be bad for
the crystal.

One other thing to consider when designing an oven: put the temperature
sensor
as close as possible to the crystal. Distance delays the sensing of
crystal temp,
called dead time. Dead time will cause the controller to oscillate at
lower gain,
so the gain has to be reduced. This reduces the ability of the
controller to
respond to external temperature changes, called load disturbances.

Hope this was of some use.

Bill Hawkins

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Re: [time-nuts] OXCO insulation

[Howard Davidson]

Try polyimide foam. Rated to 300 c.
http://www.professionalplastics.com/POLYIMIDEFOAM

 
hld 

Howard L. Davidson 
hl...@att.net 





>
> From: Dave M 
>To: brian.ing...@systematicsw.ab.ca; Discussion of precise time and frequency 
>measurement  
>Sent: Tuesday, February 24, 2015 4:32 PM
>Subject: Re: [time-nuts] OXCO insulation
> 
>
>Ok, there has been a couple replies suggesting aerogel.  I've read a bit 
>about it, and understand that it's extremely light and effective, but quite 
>difficult for a hobbyist to make.  Also, probably very expensive.  Is there 
>a source for very small quantities of it?  Is is flexible enough to wrap 
>around a cubical or cylindrical object without destroying it?
>I've considered fiberglass as a cheap, available insulation, and will 
>probably be what I use to repair my oscillators.
>
>I'm very leery of trying to use Great Stuff household foam insulation.  I 
>just don't want to risk having another failure because of it.
>
>Cheers,
>Dave M
>
>
>Brian Inglis wrote:
>> On 2015-02-22 17:42, Charles Steinmetz wrote:
>>> Brian wrote:
>>>
 Thought of trying aerogel insulation?
 Dust free varieties avoid handling issues.
>>>
>>> Be careful not to over-insulate the oven -- it depends on a certain
>>> amount of heat flow to ambient to balance the heater.  The stability
>>> of the heater control loop depends on having the correct amount of
>>> thermal resistance from oven to ambient (also, on the thermal
>>> resistance being distributed similarly to the original scheme).
>>
>> R-value for commercial aerogel insulation is about double rigid
>> polyurethane insulation, so half the thickness would be about right.
>
>
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Re: [time-nuts] OXCO insulation

[DaveH]

This looks interesting:

http://www.buyaerogel.com/product/spaceloft/

The whole site has aerogel products for reasonable prices. Note the caution
for spaceloft:

Note: Product is dusty; gloves, eye protection, and dust mask
recommended for handling. 


Dave


> -Original Message-
> From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf 
> Of Dave M
> Sent: Tuesday, February 24, 2015 16:32
> To: brian.ing...@systematicsw.ab.ca; Discussion of precise 
> time and frequency measurement
> Subject: Re: [time-nuts] OXCO insulation
> 
> Ok, there has been a couple replies suggesting aerogel.  I've 
> read a bit 
> about it, and understand that it's extremely light and 
> effective, but quite 
> difficult for a hobbyist to make.  Also, probably very 
> expensive.  Is there 
> a source for very small quantities of it?  Is is flexible 
> enough to wrap 
> around a cubical or cylindrical object without destroying it?
> I've considered fiberglass as a cheap, available insulation, and will 
> probably be what I use to repair my oscillators.
> 
> I'm very leery of trying to use Great Stuff household foam 
> insulation.  I 
> just don't want to risk having another failure because of it.
> 
> Cheers,
> Dave M
> 
> 
> Brian Inglis wrote:
> > On 2015-02-22 17:42, Charles Steinmetz wrote:
> >> Brian wrote:
> >>
> >>> Thought of trying aerogel insulation?
> >>> Dust free varieties avoid handling issues.
> >>
> >> Be careful not to over-insulate the oven -- it depends on a certain
> >> amount of heat flow to ambient to balance the heater.  The 
> stability
> >> of the heater control loop depends on having the correct amount of
> >> thermal resistance from oven to ambient (also, on the thermal
> >> resistance being distributed similarly to the original scheme).
> >
> > R-value for commercial aerogel insulation is about double rigid
> > polyurethane insulation, so half the thickness would be about right.
> 
> 
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Re: [time-nuts] OXCO insulation

[Jim Lux]

On 2/24/15 4:32 PM, Dave M wrote:

Ok, there has been a couple replies suggesting aerogel.  I've read a bit
about it, and understand that it's extremely light and effective, but
quite difficult for a hobbyist to make.  Also, probably very expensive.
Is there a source for very small quantities of it?  Is is flexible
enough to wrap around a cubical or cylindrical object without destroying
it?


No.. you cut it into pieces at least the stuff I've seen.


www.aerogel.com/


http://www.buyaerogel.com/  appears to be a more retail-ey site and they 
have a flexible aerogel "thermal wrap".. about a square foot 6mm (1/4"?) 
thick for $25.  Dust free as opposed to:


here's another choice
http://www.buyaerogel.com/product/spaceloft-10-mm-cut-to-size/
10mm thick, minimum purchase is 5ft x 58" so it's a pretty big investment

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Re: [time-nuts] Looking for advice to get a submillisecond setup

[Chris Albertson]

The tower could create multipath reflections, and electrical equipment
> on a roof, such as elevator motors, could add noise.
> On top of the tower or further away south west would reduce reflections.
>

This might be a very small problem if the goal were nanosecond level
timing.  But the goal here is "sub millisecond" so the tower is a
non-issue.  All you need is a view of most of the sky. don't worry about
"noise" either.  NTP will NEVER notice effects smaller than a microsecond

Chris Albertson
Redondo Beach, California
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Re: [time-nuts] OXCO insulation

[Dave M]

Ok, there has been a couple replies suggesting aerogel.  I've read a bit 
about it, and understand that it's extremely light and effective, but quite 
difficult for a hobbyist to make.  Also, probably very expensive.  Is there 
a source for very small quantities of it?  Is is flexible enough to wrap 
around a cubical or cylindrical object without destroying it?
I've considered fiberglass as a cheap, available insulation, and will 
probably be what I use to repair my oscillators.


I'm very leery of trying to use Great Stuff household foam insulation.  I 
just don't want to risk having another failure because of it.


Cheers,
Dave M


Brian Inglis wrote:

On 2015-02-22 17:42, Charles Steinmetz wrote:

Brian wrote:


Thought of trying aerogel insulation?
Dust free varieties avoid handling issues.


Be careful not to over-insulate the oven -- it depends on a certain
amount of heat flow to ambient to balance the heater.  The stability
of the heater control loop depends on having the correct amount of
thermal resistance from oven to ambient (also, on the thermal
resistance being distributed similarly to the original scheme).


R-value for commercial aerogel insulation is about double rigid
polyurethane insulation, so half the thickness would be about right.



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Re: [time-nuts] homebrew counter new board test result

[Charles Steinmetz]

Attila wrote:

I think the proper solution here would be to use a high speed 
comparator instead (with hysteresis).


See below for three possibilities, in addition to the Wenzel-style 
squarer I posted previously.


Circuit A is the simplest of these (and, in my view, best, because it 
minimizes noise).  It is DC-coupled (although, if the input may have 
a DC offset, you should add a 10n coupling cap before R2).  The 
LT1719 uses separate supplies for the front end and the output, so 
you can run the input on split +/- 5v supplies and still have 
whatever logic level you want.  The down side is that you need +5v 
and -5v supplies, which you may not already have.  Still, I think it 
is better to add these supplies than to try to do the whole 
conversion with only a 3v supply, because (i) these comparators work 
better on 5v than on 3v, and (ii) with 3v supplies you have to be 
very careful with the input level so as not to exceed the allowable 
input voltage.


Circuit B uses the simple-to-apply LT1720 in an AC-coupled 
circuit.  Again, it uses a 5v supply (but no -5v supply) for the 
reasons given above.  Use your favorite 5v to 3v logic converter, or 
just put a 220 ohm (series) and 330 ohm (shunt) resistive divider on 
the output to drive 3v logic.


Circuit C allows using the LT1720 with the existing 3v supply, at the 
cost of adding an input transformer.  This connection keeps the input 
voltage within the comparator's allowable input voltage range.


Any of these should work better than a logic gate.

Best regards,

Charles

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Re: [time-nuts] Looking for advice to get a submillisecond setup

[Brian Inglis]

On 2015-02-24 03:48, Matt wrote:

Thanks for all the advice received on and off list.
My main doubt was about the quality of cheap receivers but you cleared
that doubt. To answer a few questions, the antenna would be put on top
of the building on top right corner of
http://referentiel.nouvelobs.com/file/2458497.jpg (the only square
with some kind of roof) in Paris. So I am confident we can receive a
good signal here. I don't think the tower could be a problem.


The tower could create multipath reflections, and electrical equipment
on a roof, such as elevator motors, could add noise.
On top of the tower or further away south west would reduce reflections.
--
Take care. Thanks, Brian Inglis
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Re: [time-nuts] OXCO insulation

[Jim Lux]

On 2/23/15 9:35 PM, Brian Inglis wrote:

On 2015-02-22 17:42, Charles Steinmetz wrote:

Brian wrote:


Thought of trying aerogel insulation?
Dust free varieties avoid handling issues.


Be careful not to over-insulate the oven -- it depends on a certain
amount of heat flow to ambient to balance the heater.  The stability
of the heater control loop depends on having the correct amount of
thermal resistance from oven to ambient (also, on the thermal
resistance being distributed similarly to the original scheme).


R-value for commercial aerogel insulation is about double rigid
polyurethane insulation, so half the thickness would be about right.


What about fiberglass or rockwool

extruded foam polystyrene is about R-5 per inch
Fiberglass is about R-3.2/inch, mineral wool is a bit better at R-4 to 
R-4.3/inch

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Re: [time-nuts] homebrew counter new board test result

[Attila Kinali]

On Tue, 24 Feb 2015 14:43:10 +0800
Li Ang  wrote:

> I saw people talking about using 74AC to square the signal, what's the
> difference between 74LVC and 74AC? 74AC is not easy to get.

These are different families of chip production. You can see the 74HCxx as
the grandfather, 74ACxx as the father and the 74LVCxx as the son.

IIRC the AC (Advanced CMOS) was introduced in the 80s. The process
which they were produced got superseeded and also the voltage levels
went down. The LVC (Low Voltage CMOS) and LVX families are the current
choice for logic gates. The main difference is that the node size (those nm
measures people boast with, when they talk about chips these days) went
down and with that the threshold voltage of the FETs and the maximum
voltage the chips can withstand. Of course there are differences in the
timing specs as well.

TI's Logic Guide[1] and their Logic Migration Guide[2] contain
additional information.


Attila Kinali


[1] http://www.ti.com/lit/sg/sdyu001aa/sdyu001aa.pdf
[2] http://www.ti.com/lit/ml/scyb032/scyb032.pdf

-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
 -- Miss Matheson, The Diamond Age, Neil Stephenson
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Re: [time-nuts] homebrew counter new board test result

[Attila Kinali]

On Mon, 23 Feb 2015 21:10:30 +0800
"Li Ang" <379...@qq.com> wrote:

Thanks for the update!

>  It looks like that the jitter of MC100LVELT22 is much bigger at slow slew 
> rate.

Yes. You should not use a logic gates with analog input signals.
Using a 74LVC14 helps due to its Schmitt-Trigger input. I think
the proper solution here would be to use a high speed comparator
instead (with hysteresis).

Do you have an Idea why the ADEV diverges between 10s and 100s?
Are those temperature effects on the different input configurations?
Or is it an artefact of the measurement?

Attila Kinali

-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
 -- Miss Matheson, The Diamond Age, Neil Stephenson
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Re: [time-nuts] homebrew counter new board test result

[Li Ang]

Hi Magnus,
The C channel is the SMA on the back of the PCB. The input of 74LVC2G14
is set to 0.5vcc with 1k resistor and AC coupled with 100nF.
Today I compared the performance 74LVC2G04, 74LVC2G17, 74LVC2G14.
http://www.qsl.net/b/bi7lnq//freqcntv4.1/test/20150224/  .
I saw people talking about using 74AC to square the signal, what's the
difference between 74LVC and 74AC? 74AC is not easy to get.

Thanks

Li Ang

2015-02-24 5:36 GMT+08:00 Magnus Danielson :

> Dear Li Ang,
>
> Nice to have you back reporting on your progress!
>
> Now, you have some pretty impressive performance going on there. Looks
> like a nice little unit too.
>
> Is the C-channel the SMA on the back of the PCB?
>
> How did you wire up the 74LVC2G14?
>
> While it is tempting to use both channels in it, don't if you want to keep
> cross-talk between channels low.
>
> Cheers,
> Magnus
>
>
> On 02/23/2015 02:10 PM, Li Ang wrote:
>
>> Hi,
>> I'm back. I have been testing my new borad for days.
>> Compared to previous version, this board makes the PCB track of
>> signals far from each other and replaces LDO for TDC with LP5907.
>> CH_A: simple resistor bias and ac couple "front end", CH_B:
>> CH_A+MC100LVELT22 LVPECL , CH_C: CH_A+74LVC2G14 .
>> At first, the result is worse than previous board. Using CH_B as the
>> REF and DUT source, the stdev of the phase measurement is about 160ps. The
>> old board can reach about 70ps. CH_A and CH_C are way much better than
>> CH_B. That bothers me for days.
>> Today, I use the 74LVC2G14 to square the signal from MV89A, and do
>> the same test. For all three channel, the stdevs are about 37ps. The spec
>> of TDC_GP22 is 35ps. And now the performance looks a little bit better than
>> the previous board.  It looks like that the jitter of MC100LVELT22 is much
>> bigger at slow slew rate.
>> It seems that next step is to play with the front end.
>>
>>
>> The raw data is uploaded to http://www.qsl.net/b/bi7lnq/
>> freqcntv4.1/test/20150222/
>> The pic of this version is uploaded to http://www.qsl.net/b/bi7lnq/
>> freqcntv4.1/pic/ ‍
>>
>>
>>
>>
>> Regards
>> Li Ang
>>
>>
>>
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Re: [time-nuts] OXCO insulation

[paul swed]

I agree with Andy's comment and here is why. It may not be perfect but is
readily available and stable at the temperatures we operate at. Most of the
stuff I have run into even in HP seems to deteriorate over time. Granted
none of it was intended for 20 plus years.
I sure have cleaned out some ugly gunky sticky stuff. The last was a HP
3801 oven.
Regards
Paul
WB8TSL

On Mon, Feb 23, 2015 at 5:48 PM, Andy Bardagjy 
wrote:

> Fiberglass seems like an obvious choice for high temperature insulation.
>
> Andy ◉ Bardagjy.com ◉ +1-404-964-1641
>
> > On Feb 23, 2015, at 12:51 AM, Dr. David Kirkby (Kirkby Microwave Ltd) <
> drkir...@kirkbymicrowave.co.uk> wrote:
> >
> >> On 22 Feb 2015 22:07, "Dave M"  wrote:
> >>
> >> Yes, I'm aware that the newer OXCOs don't have any insulation other than
> > air inside the package.  I failed to mention that in my post.  I am
> > primarily interested in the older OXCOs that have foam insulation inside.
> > I have a couple of them, including the crystal oven from an old HP 5245L
> > counter that needs new insulation.
> >
> > I don't know what is used, but clearly whatever is used *must* be stable
> > under heat for *long* periods of time.
> >
> > Domestic gas / oil / coal boilers must use insulation,  and whatever is
> > used would I assume be able to take heat for extended periods of time. I
> > wonder if you could get something like that.
> >
> > The trouble I see with other chemicals (spray foam etc), is you have no
> > idea if it will sustain heat for long periods of time.
> >
> > Dave.
> > ___
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[time-nuts] Importance or otherwise of counter rms jitter (one shot resolution)

[James via time-nuts]

Hi All,

At the risk of becoming a bore, while I'm searching out a good price on a high 
end counter I've been trying to determine how important various counter specs 
are to me for GPSDO testing.

The big headline one is the one shot resolution which for the three counters 
I'm considering are:

Keysight 53230A 20psec spec with 10-15 psecs measured
SR620 25 psec typical 50 psec max (according to spec sheet)
Tek fca 3100 (Pendulum CNT91) 50 psec max 30 psec measured.

It is obvious that the Keysight has the best spec but it also costs a lot more. 
The SR620 is the next best (but not by much on paper) and costs much less if 
bought second hand off ebay but quite a lot more if bought with warranty in the 
UK even second hand.

My question though, is that all these jitter values are probably too high for 
ADEV plots on a goodish oscillator so some sort of mixing arrangement will be 
needed.

Given that a mixer is to be used, isn't it the case that the one shot 
resolution becomes less important than the trigger jitter which depends on the 
counter noise (and signal noise) and the slew rate. On this measure the Tek 
fares much better:

Tek fca 3100 typical 200 uV max 500 uV
Keysight 53230A typical 350 uV max 500 uV
SR620 typical 350 uV

Is my thinking right - i.e. if I'm planning on using a mixer then the one shot 
resolution term is negligible compared to the dominant noise/slew rate term?

James



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Re: [time-nuts] Looking for advice to get a submillisecond setup

[Matt]

Thanks for all the advice received on and off list.
My main doubt was about the quality of cheap receivers but you cleared
that doubt. To answer a few questions, the antenna would be put on top
of the building on top right corner of
http://referentiel.nouvelobs.com/file/2458497.jpg (the only square
with some kind of roof) in Paris. So I am confident we can receive a
good signal here. I don't think the tower could be a problem.

Regards
Matt

2015-02-21 17:10 GMT+01:00 David C. Partridge :
> Symmetricon swallowed Navstar Systems Ltd. In 1993. So if there were any 
> information available, they would likely have it, but I fear it may be long 
> gone.
>
> I did find this reference in the time-nuts archive:
>
> 
>
> Which looks like the same animal ...
>
> HtH
> David Partridge
>
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Re: [time-nuts] OXCO insulation

[Brian Inglis]

On 2015-02-22 17:42, Charles Steinmetz wrote:

Brian wrote:


Thought of trying aerogel insulation?
Dust free varieties avoid handling issues.


Be careful not to over-insulate the oven -- it depends on a certain amount of 
heat flow to ambient to balance the heater.  The stability of the heater 
control loop depends on having the correct amount of thermal resistance from 
oven to ambient (also, on the thermal resistance being distributed similarly to 
the original scheme).


R-value for commercial aerogel insulation is about double rigid
polyurethane insulation, so half the thickness would be about right.

--
Take care. Thanks, Brian Inglis
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