Re: [time-nuts] Last Call Group Buy Ublox LEA-6T

[Bert Kehren via time-nuts]

That is why we stay with Ublox 5T for saw tooth correction and 6M for what  
I call PLL applications where you can change the 1 pps to higher frequency 
to be  used in a PLL.
Maybe we will one of these days see 1 ns on ebay. I am sure NDA's prohibit  
the company from resale of chip
Bert Kehren
 
 
In a message dated 5/19/2016 8:00:59 P.M. Eastern Daylight Time,  
kb...@n1k.org writes:

Hi

Well, the first step is to talk to the outfits about you  weekly usage rate 
of the 
chip sets. In some cases anything under 10K chips  a day simply isn’t 
interesting to 
them. After that you sign their NDA and  they sign your NDA. After both of 
the
lawyer teams are happy that the right  signatures are in the right places, 
you 
get access to the basic info. From  there you go back and forth a bit about 
what
can or can’t be done.  

Next step is to get a spec on an actual chip set and the design data  for 
it. You then
are off to source this and that odd part needed to  complete the design. 
After that you
do a board layout. Almost inevitably  that’s an HDI board. Spend $5K or 
more on the first
panel of boards and  wait 30 to 60 days to get them (in one case it was 90 
days, they  goofed
twice in a row). 

Boards come in. Send them off to pick and  place for assembly.  Then you 
find out what 
you did or didn’t miss in  the spec and if your choice of odd parts to 
complete the design 
actually  work or not. Figure on a re-spin of the board as a real 
possibility.  

Assuming it passes a basic smoke test, off to see how it does as a  timing 
receiver. Maybe
it works. Maybe there are bugs. Maybe the bugs can  be fixed …. maybe they 
can’t. Likely
that part is a few months at least  before all the emails are sorted out 
and there is a decision. 

Off to  the next vendor and the same process on their chip set … then the 
next one  ….
then the next one …. then the next one.  Same process every time.  Same NDA’
s same
gag order as a result. Ultimately you can get a part that  will give you 
about +/- 1 ns 
without sawtooth correction and who knows how  much better with sawtooth. 
Since the 
sawtooth is part of the NDA stuff, I  can’t even tell you who that is… 
Here I’m simply
talking about resolution  and the range of the un-corrected pulse. 

Bob



> On  May 19, 2016, at 4:21 PM, David  wrote:
>  
> On Thu, 19 May 2016 15:30:05 -0400, you wrote:
> 
>>  ...
>> 
>>> You can see this phenomena with the LEA  modules quite clearly: 
>>> The LEA-4, -5, -6, -7 and -8 modules  all use an internal 48MHz clock. 
>>> Even though there were 2  complete overhauls of the system in this ~13 
year
>>>  timespan.
>> 
>> Which is why a lot of outfits have  abandoned uBlox and moved on to other
>> outfits that didn’t stall  out.
>> 
>> Bob
> 
> Could you give some  examples?  I have been reviewing the uBlox and
> other modules for  my own project but maybe there are better options
> that I have  missed.
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Re: [time-nuts] Last Call Group Buy Ublox LEA-6T

[Bob Camp]

Hi

Well, the first step is to talk to the outfits about you weekly usage rate of 
the 
chip sets. In some cases anything under 10K chips a day simply isn’t 
interesting to 
them. After that you sign their NDA and they sign your NDA. After both of the
lawyer teams are happy that the right signatures are in the right places, you 
get access to the basic info. From there you go back and forth a bit about what
can or can’t be done. 

Next step is to get a spec on an actual chip set and the design data for it. 
You then
are off to source this and that odd part needed to complete the design. After 
that you
do a board layout. Almost inevitably that’s an HDI board. Spend $5K or more on 
the first
panel of boards and wait 30 to 60 days to get them (in one case it was 90 days, 
they goofed
twice in a row). 

Boards come in. Send them off to pick and place for assembly.  Then you find 
out what 
you did or didn’t miss in the spec and if your choice of odd parts to complete 
the design 
actually work or not. Figure on a re-spin of the board as a real possibility. 

Assuming it passes a basic smoke test, off to see how it does as a timing 
receiver. Maybe
it works. Maybe there are bugs. Maybe the bugs can be fixed …. maybe they 
can’t. Likely
that part is a few months at least before all the emails are sorted out and 
there is a decision. 

Off to the next vendor and the same process on their chip set … then the next 
one ….
then the next one …. then the next one.  Same process every time. Same NDA’s 
same
gag order as a result. Ultimately you can get a part that will give you about 
+/- 1 ns 
without sawtooth correction and who knows how much better with sawtooth. Since 
the 
sawtooth is part of the NDA stuff, I can’t even tell you who that is… Here I’m 
simply
talking about resolution and the range of the un-corrected pulse. 

Bob



> On May 19, 2016, at 4:21 PM, David  wrote:
> 
> On Thu, 19 May 2016 15:30:05 -0400, you wrote:
> 
>> ...
>> 
>>> You can see this phenomena with the LEA modules quite clearly: 
>>> The LEA-4, -5, -6, -7 and -8 modules all use an internal 48MHz clock. 
>>> Even though there were 2 complete overhauls of the system in this ~13 year
>>> timespan.
>> 
>> Which is why a lot of outfits have abandoned uBlox and moved on to other
>> outfits that didn’t stall out.
>> 
>> Bob
> 
> Could you give some examples?  I have been reviewing the uBlox and
> other modules for my own project but maybe there are better options
> that I have missed.
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Re: [time-nuts] Last Call Group Buy Ublox LEA-6T

[David]

On Thu, 19 May 2016 15:30:05 -0400, you wrote:

>...
>
>> You can see this phenomena with the LEA modules quite clearly: 
>> The LEA-4, -5, -6, -7 and -8 modules all use an internal 48MHz clock. 
>> Even though there were 2 complete overhauls of the system in this ~13 year
>> timespan.
>
>Which is why a lot of outfits have abandoned uBlox and moved on to other
>outfits that didn’t stall out.
>
>Bob

Could you give some examples?  I have been reviewing the uBlox and
other modules for my own project but maybe there are better options
that I have missed.
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Re: [time-nuts] Last Call Group Buy Ublox LEA-6T

[David]

On Thu, 19 May 2016 19:17:17 +0200, you wrote:

>...
>
>The node size of microcontrollers is also kind of stuck, mostly due
>to power consumption constraints. If you want a transistor to switch
>off well and not just becomming a high valued resistor, you have to make
>it big. Hence most microcontrollers have a process node size between 130nm
>and 250nm. Few use 90nm (i'm only aware of the high end STM32 uC). Low power
>microcontrollers can even use larger node sizes (350nm and larger).
>
>...
>
>Attila Kinali

I thought this was do to the need to support NOR Flash or EEPROM,
mixed signal logic like converters, and relatively high interface
voltages.
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Re: [time-nuts] Last Call Group Buy Ublox LEA-6T

[Bob Camp]

Hi

> On May 19, 2016, at 1:17 PM, Attila Kinali  wrote:
> 
> On Thu, 19 May 2016 09:08:40 -0400
> Bert Kehren via time-nuts  wrote:
> 
>> Today GPS receivers are getting better by the year due to the fact that in  
>> order to save silicon the chips are getting smaller and the clock frequency 
>> goes  up reducing saw tooth excursion. If it was not for hanging bridge 
>> filtering it  on the input of a GPSDO would be simple without info from the 
>> receiver
> 
> This assumptions do not hold true. GPS timing receivers are almost always
> just standard receivers with special firmware and slightly modified hardware.
> The normal GPS receivers are optimized for low power consumption as they
> are integrated into mobile devices. As such, the clock frequency with which
> the baseband processor runs will hardly change, as the frequency is the
> biggest knob with which the power consumption can be tuned. 
> 
> The node size of microcontrollers is also kind of stuck, mostly due
> to power consumption constraints. If you want a transistor to switch
> off well and not just becomming a high valued resistor, you have to make
> it big. Hence most microcontrollers have a process node size between 130nm
> and 250nm. Few use 90nm (i'm only aware of the high end STM32 uC). Low power
> microcontrollers can even use larger node sizes (350nm and larger).
> 
> You can see this phenomena with the LEA modules quite clearly: 
> The LEA-4, -5, -6, -7 and -8 modules all use an internal 48MHz clock. 
> Even though there were 2 complete overhauls of the system in this ~13 year
> timespan.

Which is why a lot of outfits have abandoned uBlox and moved on to other
outfits that didn’t stall out.

Bob

> 
>   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] HP5065A environmental sensitivities

[Bob Camp]

Hi

> On May 19, 2016, at 12:46 PM, Attila Kinali  wrote:
> 
> On Thu, 19 May 2016 07:40:15 -0400
> Bob Camp  wrote:
> 
>> One advantage of doing all the compensation off of a single sensor is that 
>> *if* there are cross effects and *if* you can characterize them, you can 
>> correct them out. Put another way, if the pressure reading changes by 
>> 0.01% per C, having a reasonable idea of the temperature of the sensor lets
>> you take care of that. 
> 
> But munching everything into a single system makes the thing mathematically
> intractable. Seperating the values, compensating them for induced errors
> first and then using them is much easier and less error prone.

Having all the outputs from a single sensor or multiple sensor makes the math 
no harder or easier. If the pressure sensor moves 0.01% per C with a separate
pressure sensor and a separate temperature sensor …. the math is the same as
if it comes off a single device. You have the same effect to train out and the 
same
math to do it.


> 
> Also, composite sensors have higher uncertainties and drift
> then single sensors.

That’s often the difference between a $10,000 sensor and a $1 sensor rather
than an integrated part. 

> Even more so: the integrated temperature sensors
> are intended for use with the main sensor as a compensation tool.

Which is one of the reasons they work for that purpose. 

> The specs
> of the temperature sensor are good enough if the drift/hysteresis of the
> temperature sensor is less than the one of the main sensor. That you can
> read out the temperature sensors value is more a goody for those applications
> when a temperature sensor is needed but not high accuracy/precision required.

Again, a delta between a $10,000 sensor and a $1 sensor is indeed that you can 
likely read the Fluke / Hart setup to a lot higher level of accuracy. 

> 
> What is usually a good approach is to use the temperature sensors on
> barometric and hygrometric sensors only for their temperature compensation.
> At most, use the temperature sensor for cross checking and detecting faults.
> 
> For real temperature measurements, I would use a wirewond Pt sensor
> on a 24bit ADC with a stable reference.

I would prefer a set of at least three SPRT’s each with their own readout and 
to calibrate
them each with an independent triple point cell. That most certainly would do a 
*much* better
job of producing accurate temperature. Of course, that’s not going to fit into 
a modest $10K 
budget. 

> 
> Temperature effects are by far the largest effects we have to deal with.
> Having a stable and reliable measurement system for temperature is not
> only worthwhile, but actually a requirement before you start compensating
> anything else

But is +/- 0.0001 K  good enough or do we need +/- 0.01 K. Oddly enough, it 
turns out
that you can do a really good job compensating most frequency sources with a 
much more 
modest *relative* accuracy. It also turns out that gradients will get you 
*long* before anything 
much below 0.1C applies. 

> 
>> Things like sensor drift and sensor hysteresis … that’s not quite so easy to
>> take care of. The only hope there is that they are small enough to be
>> neglected. The same issue with hysteresis is actually a big limit on
>> humidity compensation of some devices. They adsorb water vapor at a very
>> different rate than they desorb. 
>> Modeling that can be really messy. 
> 
> Hysteresis can be properly modeled and compensated. The problem is, that
> the math behind it becomes nasty very quickly. Often just using a simple
> second order diff equation system and letting a Kalman filter estimate
> the parameters is easier than modeling a full memory system... under the
> condition that one can excite the system reliably and isolate/estimate
> the other effects well enough.

It’s generally not the math that is the issue…..Try modeling a humidity effect 
that takes < 1 minute
to adsorb and a couple of months do desorb. Hysteresis in OCXO’s can turn out 
to be dependent
on rate, range, starting point, and air flow direction. Something over a 
thousand independent 
test profiles (six directions, eight rates, ten ranges, ten starting points ..) 
 may be needed to fully train it out. 

Bob

> 
>   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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[time-nuts] FE-5680A GPS discipline board on sale now

[Nick Sayer via time-nuts]

This is a mash-up of my breakout board and GPSDO. You give it 30+W 18-24 VDC in 
(hack up a surplus laptop power supply) and it supplies up to 2A @ 15 VDC and 
500 mA @ 5 VDC. In my testing I see around 25 mV p-p of ripple on the 15V rail. 
The 5V rail is a bit noisier at around 35 mV. Functionally, the discipline 
system is the same as the latest OH300 units - it has the phase discriminator 
that Jim Harman recommended, but now there’s a JFET that acts to make the phase 
ramp more linear (useful if you want to gather stats). The firmware has 4 modes 
of operation - an initial FLL, followed by a PLL with TC 100s, 1/2 hr and 2 
hours. Once it’s in the 2 hour mode, the EFC value often goes for hours without 
changing (I’m throwing away the bottom two bits of EFC resolution).

It has a mini-DIN-4 diagnostic jack that has a buffered GPS PPS output and two 
TTL serial streams (log and NMEA), an SMA antenna jack (the module has an 
internal antenna, but an external one is recommended), a 2.1mm barrel connector 
for power and two JST jacks with independently buffered 5V square wave outputs. 
The board is the same width as the 5680A. It comes with rubber feet so it can 
rest on the table next to the oscillator, or you can remove them and mount it 
on 4 grounded screw holes in the corners. The three LEDs have light pipes to 
make them stick out from the edge of the board.

If you’ve got a 5680A and your biggest complaint about it is that it’s not 
actually *accurate* by itself, then this is a good solution.

http://www.tindie.com/products/nsayer/fe-5680a-gps-discipline-module/
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Re: [time-nuts] Last Call Group Buy Ublox LEA-6T

[Attila Kinali]

On Thu, 19 May 2016 09:08:40 -0400
Bert Kehren via time-nuts  wrote:

> Today GPS receivers are getting better by the year due to the fact that in  
> order to save silicon the chips are getting smaller and the clock frequency 
> goes  up reducing saw tooth excursion. If it was not for hanging bridge 
> filtering it  on the input of a GPSDO would be simple without info from the 
> receiver

This assumptions do not hold true. GPS timing receivers are almost always
just standard receivers with special firmware and slightly modified hardware.
The normal GPS receivers are optimized for low power consumption as they
are integrated into mobile devices. As such, the clock frequency with which
the baseband processor runs will hardly change, as the frequency is the
biggest knob with which the power consumption can be tuned. 

The node size of microcontrollers is also kind of stuck, mostly due
to power consumption constraints. If you want a transistor to switch
off well and not just becomming a high valued resistor, you have to make
it big. Hence most microcontrollers have a process node size between 130nm
and 250nm. Few use 90nm (i'm only aware of the high end STM32 uC). Low power
microcontrollers can even use larger node sizes (350nm and larger).

You can see this phenomena with the LEA modules quite clearly: 
The LEA-4, -5, -6, -7 and -8 modules all use an internal 48MHz clock. 
Even though there were 2 complete overhauls of the system in this ~13 year
timespan.

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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[time-nuts] QST Review of Bodnar GPSDO

[David]

The June 2016 issue of QST includes a brief two page review of the
Bodnar GPSDO distributed by Force 12 in the US and manufactured by
Bodnar Electronics in England.

http://www.leobodnar.com/shop/index.php?main_page=product_info_id=234
http://www.force12inc.com/products/gps-locked-precision-frequency-reference-low-jitter-gps-clock-450-hz-to-800-mhz-output-custom-low-phase-noise-xtal-version.html
http://www.force12inc.com/products/gps-locked-precision-frequency-reference-low-jitter-gps-clock-450-hz-to-800-mhz-output.html
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Re: [time-nuts] HP5065A environmental sensitivities

[Attila Kinali]

On Thu, 19 May 2016 07:40:15 -0400
Bob Camp  wrote:

> One advantage of doing all the compensation off of a single sensor is that 
> *if* there are cross effects and *if* you can characterize them, you can 
> correct them out. Put another way, if the pressure reading changes by 
> 0.01% per C, having a reasonable idea of the temperature of the sensor lets
> you take care of that. 

But munching everything into a single system makes the thing mathematically
intractable. Seperating the values, compensating them for induced errors
first and then using them is much easier and less errorprone.

Also, composite sensors have higher uncertainties and drift
then single sensors. Even more so: the integrated temperature sensors
are intended for use with the main sensor as a compensation tool. The specs
of the temperature sensor are good enough if the drift/hysteresis of the
temperature sensor is less than the one of the main sensor. That you can
read out the temperature sensors value is more a goody for those applications
when a temperature sensor is needed but not high accuracy/precision required.

What is usually a good approach is to use the temperature sensors on
barometric and hygrometric sensors only for their temperature compensation.
At most, use the temperature sensor for cross checking and detecting faults.

For real temperature measurements, I would use a wirewond Pt sensor
on a 24bit ADC with a stable reference.

Temperature effects are by far the largest effects we have to deal with.
Having a stable and reliable measurement system for temperature is not
only worthwhile, but actually a requirement before you start compensating
anything else.

> Things like sensor drift and sensor hysteresis … that’s not quite so easy to
> take care of. The only hope there is that they are small enough to be
> neglected. The same issue with hysteresis is actually a big limit on
> humidity compensation of some devices. They adsorb water vapor at a very
> different rate than they desorb. 
> Modeling that can be really messy. 

Hysteresis can be properly modeled and compensated. The problem is, that
the math behind it becomes nasty very quickly. Often just using a simple
second order diff equation system and letting a Kalman filter estimate
the parameters is easier than modeling a full memory system... under the
condition that one can excite the system reliably and isolate/estimate
the other effects well enough.

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] GENIUS by Stephen Hawking (PBS TV), with 5071A cesium clocks

[jmfranke]

Well done Tom! As always, you represented the Time-Nuts community in a most 
professional manner. 

John  WA4WDL
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Re: [time-nuts] Last Call Group Buy Ublox LEA-6T

[Bert Kehren via time-nuts]

Today GPS receivers are getting better by the year due to the fact that in  
order to save silicon the chips are getting smaller and the clock frequency 
goes  up reducing saw tooth excursion. If it was not for hanging bridge 
filtering it  on the input of a GPSDO would be simple without info from the 
receiver. Back to  the Motorola days the receiver was a larger contributor to 
the timing error now  it is external to the receiver but removing receiver 
error, depending on the  application does make sense. We have done tests of 
different units using a  Cesium and a HP5372A and the Tbolt stand out with 100 
psec +- 500.  That is  short term 278 samples speaking only for the unit 
performance, long term other  factors external to the unit degrades time by a 
factor 100.
Back to ublox if you use a T the question is why. If it is GPSDO it can use 
 the saw tooth data in the software I am sure commercial units do it. 
Richard MCC  was working on his GPSDO incorporating that info. For pure time 
application if  you want hardware correction a programmable timing element 
makes 
sense specially  since the cost has come down. DS1124 250 psec. does the 
job and less than $ 5  works for us. Micrel  at 10 psec will take two, again 
does it make sense?  Since we are frequency nuts not time nuts DS1124 is our 
choice. Chips with  larger steps are obsolete and would be significantly 
more expensive since it  takes more esilicon. 
In our GPSDO performance tests we found no difference between using Tbolt  
and M6.It does incorporate an adjustable GPS filter on the input.
Bert Kehren
 
 
In a message dated 5/18/2016 8:00:34 P.M. Eastern Daylight Time,  
csteinm...@yandex.com writes:

Bert  wrote:

> Our first tests are with a 500 ps
> DS  chip  because I did have them, but  200 ps will work with a T5 or 6. 
We
>  are  also considering using two Micrel SY 89295UTG in series with 10  ps
> resolution,  but with the limitation of a single frequency GPS  receiver 
and
> ionosphere delay  variations one has to ask does it  make sense?

Think first about what the GPS engine has to work with --  nothing but 
the timing generated by its current GPS timing solution.   It seems very 
doubtful that sub-nS accuracy is possible.  This  provisional conclusion 
is supported if we look at commercial GPSDOs using  single-frequency GPS 
engines and sawtooth correction (or using local  oscillators that divide 
evenly by 100nS, like the Tbolt).  The best  commercial units seem to 
place the PPS within 5nS or so on a routine  basis.

So, even 500pS appears to be considerably better than necessary,  given 
the limitations imposed by the timing engine, atmospheric  dispersion, 
and the GPS system.

Best  regards,

Charles


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Re: [time-nuts] HP5065A environmental sensitivities

[Bob Camp]

Hi

One advantage of doing all the compensation off of a single sensor is that 
*if* there are cross effects and *if* you can characterize them, you can 
correct them out. Put another way, if the pressure reading changes by 
0.01% per C, having a reasonable idea of the temperature of the sensor lets
you take care of that. 

Things like sensor drift and sensor hysteresis … that’s not quite so easy to
take care of. The only hope there is that they are small enough to be neglected.
The same issue with hysteresis is actually a big limit on humidity compensation
of some devices. They adsorb water vapor at a very different rate than they 
desorb. 
Modeling that can be really messy. 

Bob

> On May 19, 2016, at 1:49 AM, Attila Kinali  wrote:
> 
> On Thu, 19 May 2016 06:33:38 +0200
> "Björn Gabrielsson"  wrote:
> 
> 
>> What are time-nuts using for monitoring the environment?
> 
> The Sensirion SHT21 has become the gold standard silicon based
> humidity sensor over the past years. Even though it's quite old
> (IIRC close to 10 years) it has performance metrics that still
> rival modern sensors. Its rather "large" package with the 1mm
> pitch makes it one of the easier to solder sensors as well.
> It's only drawback is its relatively large price of €6
> 
> As for barometric sensors, the ones by Measurment Specialities
> are quite good. The MS5607-02BA03 for example does a resolution
> of 2.4Pa with a long term stability of 100Pa/a.
> There is also the MS5611-01BA03 which offers 1.2Pa resolution,
> but also doubles the price and I am not so sure whether that
> tiny bit more resolution is more than just noise.
> 
> A little advice: If you want to measure pressure with high precision,
> you should think about temperature stabilizing the sensor.
> 
> The same is true for humidity, but does not work as well, as temperature
> stabilization (aka heating) changes the relative humidity and thus
> the measurement value depends quite a bit on how the air around the
> sensor flows.
> 
> Also, provide good and low noise power to the sensors. These are
> precision instruments with high resolution ADCs. To work properly
> they need a clean power source.
> 
>> I have been playing a little with the Bosch BME280 - doing air pressure,
>> temp and relative humidity in a small form factor. Easy to interface to
>> Raspberry Pi or Arduino.
> 
> The only Bosch sensor i've ever used was a BMA250 acceleration sensor.
> It worked reasonably well, but i've never evaluated it for precision
> or accuracy. But at least it looks like Bosch does not exagerate
> in their datasheets.
> 
> 
>   Attila Kinali
> -- 
> Reading can seriously damage your ignorance.
>   -- unknown
> ___
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Re: [time-nuts] HP5065A environmental sensitivities

[DG2OM]

Some answers to comments:

Magnus,
I don’t think I have made a closed loop. It works like UTC for poor man. I 
gathered data from different master clocks and from a weather station and 
produced a new software corrected time scale for my own.  But you are right. 
The correction is the best fit for this specific data-set and will be worse if 
applied to another. The ADEV plot should be clipped to trusted values - maybe 
50 sec. I intend to apply a hardware compensation. Therefore I was happy to 
find a barometric pressure sensor 144SC0811-Baro at an auction side some weeks 
ago for less than one tenth of the normal prize. Approximate 240 kOhm should be 
needed from the output of this module to the base of Q6B for compensation.

James,
when I made the correlation the best fit was obtained comparing a frequency 
difference data-set delayed 1 hour to the pressure measurements. But I have to 
dig into the data-set again – there might be an error calculating the MJD from 
Middle European Time.  As far as I understood from Corby´s measurements, the 
frequency reacts immediately to a pressure change without delay. For the 
compensation, a delay does not matter very much. Pressure changes are normally 
very slow.

Poul-Henning,
The measurement is made in normal environment. Temperature measurements of the 
Thunderbolt, which was two meter away, show daily variations of 1-2 degree C 
and an additional drop of 2 degree during the weekend. Humidity measurements 
are not made. Temperature effects as well as aging are still left in the 
residuals of my data. The aging of this specific instrument is nearly zero. The 
frequency was adjusted 6 month ago and the drift is less than 1E-12 during this 
time.

Bjørn,
I have the temperature measurements inside the Thunderbolt and temperature 
measurements from a temperature Data-logger placed inside the HP5065A. This 
datalogger has a temperature resolution of around 0.4 degC. 

Attila,
I know the SHT11 from the old days when a LPT-port could be controlled by the 
user.
It is a nice device. But I bought the 144SC0811 which can be used by adding 
only one resistor.

Corby,
It would be nice to see the results with temperature compensation. There are 
lots of sources producing temperature sensitivity. All have a different time 
constant. AS Poul-Henning found out, the rate of temperature change is the 
worst problem. In my eyes temperature compensation is much more complicated 
then compensation for barometric pressure.

Best regards
Wulf Oelschlägel
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Re: [time-nuts] GENIUS by Stephen Hawking (PBS TV), with 5071A cesium clocks

[Poul-Henning Kamp]

In message , "Bill Hawkins" writes:

>Meanwhile, here I am on the third floor of a retirement community,
>possibly living faster than those on the first floor.
>Not that it approaches a significant fraction of a second per year; it's
>the principle of the thing.

Dont knock it, mathematically speaking, your relative benefit of
difference will go asymptotically against infinity over time.

-- 
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] New Product Release - GPSDO Frequency Standard

[Bob Stewart]

HI Attila,

I use a fixed voltage (not fixed current) RC integrator to measure the phase 
between the 1PPS from the LEA to the 10MHz signal from the OCXO.  At the same 
time, I'm counting the pulses from the OCXO to make sure I'm locked to 10MHz, 
not 10MHz +/- something.  The dsPIC33FJ128MC802 has a 12-bit ADC which I use to 
measure the voltage on the integrator.  I use software to correct for the RC 
curve, as well as real-world aberrations caused by the various chips in my TIC 
chain.  I apply 2 corrections: one to flatten the RC curve, and the other is a 
sine-wave correction.  I hand picked a constant (kappa) to tune the RC 
correction and another constant for the two sine-wave corrections.  They're 
different for 0-180 and 180-360 degrees.

>From there, the computed phase is corrected for the sawtooth from the LEA, and 
>a somewhat modified PID controller controls the value of the DAC.  The DAC is 
>actually a 16-bit PWM in the dsPIC33 dithered to 20 bits.  From there it goes 
>through a 125 gate, low pass filter, and op-amp to the Trimble 34310-T OCXO.  
>The OCXO is sourced from China, and I hand select them for good ones.  The 
>rejection rate is pretty high.  I need to update the pictures in the brochure. 
> The production unit can be configured to accept 10Mhz and output EFC to an 
>external OCXO.  My engineer (Dan Kemppainen) has a 10811D (I think) buried in 
>30 pounds of sand, with a well located antenna.  He say's it's very stable.

I am currently working on software for temperature compensation.  I am on 
version 0.121 of my software.  The firmware in the unit can be updated through 
a USB port using the Microchip AN1094 bootloader.  I also have some plans for 
aging corrections, so that holdover will be better.  At the moment, the DAC is 
just frozen during holdover.  Owners will be invited to contribute to the 
software if they wish to and have a better solution than what I used.  System 
constants, such as the PID gains and surveyed position, are maintained across 
firmware updates and power outages.

When I said the PPS output from the unit comes directly from the receiver, I 
meant just that.  But that does not imply that my software doesn't compensate 
for the sawtooth in its own measurements for the 10Mhz/5MHz/1Mhz outputs.  I've 
been asked to add a PICDiv to the next build.  I don't know whether or not I 
can slew that exactly to phase 0.  It will be an interesting experiment to see 
if I can.

Tom actually made those plots from a pre-production unit I sent him last year.  
The refHM(J2) refers to his hydrogen maser.  The measurements were done on his 
Timepod.  I'm not sure which antenna he used.  I believe he said it was a 
precision surveying antenna.  

Hope that answers your questions.  I could send you a schematic if you like.

Bob

On Thu, 5/19/16, Attila Kinali  wrote:

 Subject: Re: [time-nuts] New Product Release - GPSDO Frequency Standard
 To: "Discussion of precise time and frequency measurement" 
 Date: Thursday, May 19, 2016, 12:14 AM
 
 Hoi Bob
 
 On Thu, 19 May 2016 01:11:32
 + (UTC)
 Bob Stewart 
 wrote:
 
  
 > It's time I got off the dime and did a
 product release of my GPSDO.
 > My mission
 in creating this unit was to provide a stable and
 accurate
 > frequency reference with
 10Mhz, 5Mhz, and 1Mhz outputs.  It does have
 > a PPS output, but that is directly from
 the Ublox receiver, and is not
 >
 corrected for sawtooth error.  More information can be
 found in the
 > brochure and quick start
 guide in the link below.
 
 Can you give a bit more information on how your
 GPSDO works on the inside?
 What OCXO do you
 use?
 What technique do you use to get the
 phase information from the LEA?
 How do you
 steer the OCXO?
 Do you use any active
 temperature compensation?
 What were your
 references for the ADEV and phase noise plots?
 
 
        
     Attila Kinali
 -- 
 Reading can seriously damage your ignorance.
         -- unknown
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Re: [time-nuts] GENIUS by Stephen Hawking (PBS TV), with 5071A cesium clocks

[Rex]

I just watched it on PBS. Nicely done recreation of your GREAT 
experiment, Tom. Good to see you had a couple personal appearances, and 
especially for the final results.


Looks like your SR620 counter had a hyperdrive undercarriage lighting 
option. :-)




On 5/17/2016 7:50 PM, Tom Van Baak wrote:

The TV show is tomorrow, Wednesday evening. 8/9 PM, or something like that.

Here are fresh web pages with background information, photos, and plots:

http://leapsecond.com/great2016a/

http://leapsecond.com/great2016a/photos.htm

I have no idea how minor my role is in the actual TV episode, but if nothing 
else, the above two pages will share some time nuts sort of details of the 
clock experiment itself. If you have any questions let me know.

/tvb

- Original Message -
From: "Tom Van Baak" 
To: "Discussion of precise time and frequency measurement" 
Sent: Friday, May 13, 2016 12:00 PM
Subject: [time-nuts] GENIUS by Stephen Hawking (PBS TV),with 5071A cesium clocks


Fellow time nuts,

Here in the US, a new six-part TV series on National Geographic / PBS starts next 
Wednesday, May 18th, 2016. The title is "Genius by Stephen Hawking" and episode 
1 is: Can We Time Travel?

Having not seen it yet, I can't make a promise of its "SNR" (Science to 
Nonsense Ratio). It might be quite educational, or at least, very entertaining. And I'm 
definitely going to watch it with my family.

So why do I mention this?

Well, I spent most of December 2015 and January 2016 working with the UK-based 
producers of the show -- in order to pull off another Einstein 100th 
anniversary, general relativity, cesium atomic clock, gravitational time 
dilation experiment. The location chosen was 9000+ foot Mt Lemmon, near Tucson, 
Arizona.

The Hawking series covers a wide variety of topics, and this atomic clock bit 
is just one very small part. They were inspired by the DIY experiment I did ( 
http://leapsecond.com/great2005/tour/ ) and they wanted to create and film 
something similar. So I offered to help. Scenes with (me? and) my 5071A cesium 
clocks and hp 53132A / SR620 time interval counters are in episode 1.

The PR link to the episode is:

http://www.pbs.org/genius-by-stephen-hawking/episodes/episode-1/

Attached is a photo. I will post lots of technical info, plots, photos and FAQ 
here next week:

http://leapsecond.com/great2016a/

/tvb
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Re: [time-nuts] HP5065A environmental sensitivities

[Attila Kinali]

On Thu, 19 May 2016 06:33:38 +0200
"Björn Gabrielsson"  wrote:


> What are time-nuts using for monitoring the environment?

The Sensirion SHT21 has become the gold standard silicon based
humidity sensor over the past years. Even though it's quite old
(IIRC close to 10 years) it has performance metrics that still
rival modern sensors. Its rather "large" package with the 1mm
pitch makes it one of the easier to solder sensors as well.
It's only drawback is its relatively large price of €6

As for barometric sensors, the ones by Measurment Specialities
are quite good. The MS5607-02BA03 for example does a resolution
of 2.4Pa with a long term stability of 100Pa/a.
There is also the MS5611-01BA03 which offers 1.2Pa resolution,
but also doubles the price and I am not so sure whether that
tiny bit more resolution is more than just noise.

A little advice: If you want to measure pressure with high precision,
you should think about temperature stabilizing the sensor.

The same is true for humidity, but does not work as well, as temperature
stabilization (aka heating) changes the relative humidity and thus
the measurement value depends quite a bit on how the air around the
sensor flows.

Also, provide good and low noise power to the sensors. These are
precision instruments with high resolution ADCs. To work properly
they need a clean power source.

> I have been playing a little with the Bosch BME280 - doing air pressure,
> temp and relative humidity in a small form factor. Easy to interface to
> Raspberry Pi or Arduino.

The only Bosch sensor i've ever used was a BMA250 acceleration sensor.
It worked reasonably well, but i've never evaluated it for precision
or accuracy. But at least it looks like Bosch does not exagerate
in their datasheets.


Attila Kinali
-- 
Reading can seriously damage your ignorance.
-- unknown
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Re: [time-nuts] GENIUS by Stephen Hawking (PBS TV), with 5071A cesium clocks

[Bill Hawkins]

Well, Tom, you did get an active part in the show, and Stephen Hawking
credited your worldwide reputation. Wow.

You even sounded as natural as the actors used to give emotional depth
to a science story.

What troubles me is that we have the instruments to detect a 20
nanosecond difference in atomic clocks, but we have no way of measuring
the effect on living cells. At least, not until we have devices that
will transport us near the speed of light.

Meanwhile, here I am on the third floor of a retirement community,
possibly living faster than those on the first floor.
Not that it approaches a significant fraction of a second per year; it's
the principle of the thing.

:-)

Bill Hawkins

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Re: [time-nuts] New Product Release - GPSDO Frequency Standard

[Attila Kinali]

Hoi Bob

On Thu, 19 May 2016 01:11:32 + (UTC)
Bob Stewart  wrote:

 
> It's time I got off the dime and did a product release of my GPSDO.
> My mission in creating this unit was to provide a stable and accurate
> frequency reference with 10Mhz, 5Mhz, and 1Mhz outputs.  It does have
> a PPS output, but that is directly from the Ublox receiver, and is not
> corrected for sawtooth error.  More information can be found in the
> brochure and quick start guide in the link below.

Can you give a bit more information on how your GPSDO works on the inside?
What OCXO do you use?
What technique do you use to get the phase information from the LEA?
How do you steer the OCXO?
Do you use any active temperature compensation?
What were your references for the ADEV and phase noise plots?


Attila Kinali
-- 
Reading can seriously damage your ignorance.
-- unknown
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