Re: [time-nuts] PICTIC II
Moin Richard,
On Fri, 25 Jun 2010 23:11:39 -0800 (AKDT)
"Richard H McCorkle" wrote:
> Over the last 18 months I have developed a new diode switched
> interpolator based on the comments made on line and have thoroughly
> tested it. Some suggestions made improvements in the performance and
> some resulted in poorer performance
Would it be possible to put the schematics of the board in
PDF form onto your website? For all those poor souls that
dont have windows at home and cannot install ExpressPCB?
Thanks in advance
Attila Kinali
--
If you want to walk fast, walk alone.
If you want to walk far, walk together.
-- African proverb
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[time-nuts] yet another GPSDO design, or so
Moin,
I recently had a look at the data sheet of the LEA6-T GPS module
from ublox, which now features a second time pulse output that
is capable of delivering a 10MHz signal, synchronized to GPS.
After thinking quite some time quite some time about building
my own GPSDO and struggling with the question how to synchronize
a 10MHz signal to a 1Hz signal that has some substantial phase
noise, the new LEA6-T module seems like to make things a lot
easier. Although the LEA6 specs do not say anything about how
the timepulse output is generated or how it is synchronized
to GPS, i assume that it will either have some jumps or phase/frequency
noise due to oszillator and synchronization imperfections.
But, it should be possible to use the LEA6-T together with
some OCXO and a PLL setup to stabilize the OCXO to get a high
quality frequency standard.
Unfortunately, my knowledge in that field is rather limited, thus
before starting to make wrong design decisions i'd like to ask
for some advice here.
My basic idea is to feed the 10MHz output of the LEA6-T and
the 10MHz OCXO into a current output PFD, do some low-order
filtering of the output signal. Feed that into an ADC which
is read by a uC which in turn controls an DAC that sets over
some amplifier stage the EFC input of the OCXO.
As PFD i thought about using a ADF4002 from Analog, which
is actually an PLL, but allows to bypass the input dividers,
so that it can be used as pure current output PFD.
I'm not yet sure what kind of output filter i want to use.
I probably have to add at least one low noise opamp there,
to isolate the PFD output/filter from the ADC. I'm also
not sure what filter frequency i should use here. It will
have to be below 10MHz for sure, probably in the lower
kHz range, but how low is the question. The lower the easier
gets the ADC stage and the less work has to be done in the uC,
but using a low frequency filter either means using an active
filter (noise) or high value R or L (again noise, especially
the L might couple in 50Hz noise from the enviroment or show
microphone effects).
The ADC will be either a low-noise 16bit type or a 24bit
type. This will largely depend on the sample rate to be
used and the availabilty of the ADCs. Any good advices
on what to use here? Should there be some form of signal
conditioning done? If, what form of conditioning would
you advise me to use?
As a uC i thought about using a AT91SAM7 variant from Atmel.
I know these beasts (and their bugs) pretty well by now
and already have some code ready for those.
I thought about clocking the uC with a 40MHz crystal that
is synchronized to the 10MHz OCXO using a PLL. This would
allow me to generate quite precise+accurate digital signals.
Unfortunately, there doesnt seem to be VCXOs at 40MHz available
so that means that i'd have to build one by hand.
The loopfilter is going to end up in the uC as it is easier
to build such low frequency filters digitally than in analog.
I havent put much thought into how that filter should look
like, as this can be easily changed later.
The DAC will probably be a 16bit type (there does not seem
any higher resolution DAC with sane specs and still reasonable
availability). The amplifier for the DAC output will be a two
stage amplifier. One stage that adds an (adjustable) offset
and one stage that adds the (again adjustable) amplification.
This approach is choosen as the needed EFC range will probably
much lower than the full range. Hence the resolution of the
DAC can be enhanced by producing only values within that range.
The disadvantage here is that it requires calibration.
A rough guestimate is that the whole thing will probably cost
less than 500CHF (including PCB production, but excluding OCXO).
Yes, i know, i could get a Rb frequency standard for that money
on ebay. But where is the fun in that? ;-)
Beside whether this setup makes sense, the two biggest questions
i have are, what OCXO to use. Are the ISOTEMP 134-10 that are
available on ebay "good enough" for such an application?
Or shall i look for something better/different?
And the other is, how do i amplify and distribute the 10MHz
signal i get out of the OCXO to be used by other devices
with minimal phase noise?
Thanks for your help
Attila Kinali
--
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If you want to walk far, walk together.
-- African proverb
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Re: [time-nuts] yet another GPSDO design, or so
Moin, On Sat, 26 Jun 2010 12:38:29 -0600 Ed Palmer wrote: > Another GPS board with a 10 MHz output is the Navsync CW-12 module > (price ~US$85-90). Hmm.. i didn't know about this one. Both seem to be comparable from the specs, the LEA6-T being slightly better (well, the design is newer, so that's to be expected). As for the price. ublox is here, literally, sitting in the next town and i'm in the fortunate position to get a LEA-6T out of a bigger batch which makes it considerably cheaper than the CW-12. > I measured the 1 PPS output and found a Standard > Deviation of < 5 ns with a range of < 30 ns. The 10 MHz output is kept > on frequency by occasionally adjusting the period of the 10 MHz output > by one cycle of the CPU clock (~8.3 ns = 120 MHz). How often this > happens depends on the exact clock frequency of the particular unit. On > mine it happens about 200 times per second. Interesting information, thanks. I know that the LEA6 has a TXCO that can be adjusted and the timepulse output is generated from this source. What i dont know is whether the TXCO is adjusted tracking the GPS signal or whether it uses a similar "skip a cycle" technique like the CW-12. Maybe i should drop ublox a mail and ask about that. Attila Kinali -- If you want to walk fast, walk alone. If you want to walk far, walk together. -- African proverb ___ 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.
Re: [time-nuts] yet another GPSDO design, or so
Moin, On Sun, 27 Jun 2010 02:24:31 -0700 Said Jackson wrote: > The 4002 expects a tight phase lock on the two inputs to properly stay > locked, Why does the ADF4002 need that? Or do you mean by "locked" that the locked output of the ADF4002 does reflect the actual locked state? If you mean that, i dont think i will use that at oput. Maybe as a debugging help, but not for the control loop itself. As for the design, i wanted to rely on the ADF4002 haveing a linear phase difference response within [-2Pi,2Pi] and integrate over the phase error to average out the jitter introduced by GPS. > and your adc/dac will likely introduce too much phase lag and > cause oscillation. In fact when using the Analog Devices PLL simulator > one has to closely follow the component values of the loop filter that > the software suggests otherwise the system won't be stable, unless you do > a lot of manual math. The 4002 works well with loop bandwidths of 30 Hz > or more. The exact control of the loop parameters are exactly the reason why i want to use a uC implementing the control loop. Implementing such low frequency control loops is a lot easier in software (or rather digitally) than it is doing with analog electronics. And yes, i'm quite aware that i'd have to tweak the loop parameter for stability. But i dont expect this to be difficult as long as the analog part is operated in its linear range. Unless of course, there is something in the electronics i have not taken into account. Which is why i'm asking here for advice :-) > For a GPSDO you are looking for loop bandwidths of 0.001Hz or less, a > totally different world. Even if you use the 10 Mhz output rather than > the 1 pps. This is because your Isotemp Ocxo will be much more stable > than the gps for short time intervals, say 0.1s to 500 s Yes, i'm thinking about a 1/f in the range of 100s to several 1000s. > What would be easier to try is to replace the gps internal Tcxo with > an external ocxo, but you have to generate the frequency the gps is > using, such as 26 MHZ and do some soldering on the gps itself. Yes, that would be an idea. But it's not that easy. I dont know how the control loop in the LEA-6 works and whether they are actively changing the TCXO frequency. If they are, i would need to provide a VCO that is stabilized, either in form of an seperate OCXO or by locking/syncinc the VCO to my 10MHz OCXO. I have one open LEA4-S infront of me. That has crystal mounted marked with R4130 and that looks from the configuration (two of the 4 pads on GND, two connected to other components) that it is a simple quartz without any voltage control. The Atmel uC (probably a SAM7 OEM variant) has only one small crystal connected to it that looks like a 32kHz quartz. No other frequency source is on the uC side of the module. Although the LEA4 is two generations older than the LEA6, i expect it to be at least similar by design. > It would be very interesting to see just how good the uBlox lea-6t can > work with an ultra stable frequency source rather than a $5 tcxo.. Yes. But then i'd have to build two devices, one that uses a stock LEA6-T and one that uses a modified LEA6-T and measure both to have an indication how much improvement this brings :-) Attila Kinali -- If you want to walk fast, walk alone. If you want to walk far, walk together. -- African proverb ___ 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.
Re: [time-nuts] yet another GPSDO design, or so
Moin,
On Sat, 26 Jun 2010 21:14:02 EDT
ewkeh...@aol.com wrote:
> What you want is basically a Shera Board. That design has been around for
> quite some time and has served me very well.
Yes. The Shera Board and similar designs serve as an example for me.
> I have a total of six running
> including two controlling Rubidium. There are in my opinion a couple of
> problems: not every 4066 works on the design the 18 bit D/A is very hard to
> find and now expensive and the single step of the D/A is intended for a 1.7
> E-13 frequency step.
Yes. My goal is to update the venerable 4066 with something more
modern and have components that are easy to get trough farnell, digikey,
mouser, and all the other distributors. Yes, 16bit D/A seems to
be the maximum that is currently available. It crossed my mind
to build a 24bit R-2R D/A using discrete components, but this might
have actually a worse performance than a off the shelf 16bit D/A.
(temperature drifft, resistor values missmatch, EMI, etc)
Attila Kinali
--
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If you want to walk far, walk together.
-- African proverb
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Re: [time-nuts] Yet another GPSDO - locking to 10MHz
On Sun, 27 Jun 2010 20:59:51 -0400
"Robert Benward" wrote:
> All this talk about interpolation reminds me of a little neat chip by Analog
> Devices, AD9500. It's programmable digital delay, bit, with lops resolution
> with a loons full-scale range. I believe (from app notes) you can push it
> to 100us FS, giving 390ns resolution. I think the minimum jitter at the
> lowest FS was about lops. The AD9500 is cell and the 9501 is TTS.
Unfortunately, the AD9500 line is obsolete with no replacement.
Which means it will be quite soon not available anymore.
Attila Kinali
--
If you want to walk fast, walk alone.
If you want to walk far, walk together.
-- African proverb
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[time-nuts] hp10811-60111 on ebay
Moin, There are currently a few HP10811-60111 for 125USD on ebay (with only 5h left). Could anyone tell me whether this is a good buy or whether i should wait for another OCXO to apear? Thanks in advance Attila Kinali -- If you want to walk fast, walk alone. If you want to walk far, walk together. -- African proverb ___ 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.
Re: [time-nuts] hp10811-60111 on ebay
On Wed, 30 Jun 2010 00:17:53 +1200
Steve Rooke wrote:
> So it goes without saying that you really don't know what you have
> unless you can test it in some way. It's OK looking at a table of what
> someone else has tested for their 10811 but that doesn't mean yours is
> exactly the same.
And now the big question is, how do i test such an
oscillator? I dont have any high precision counter
avilable at all. And i dont want to spend the money
for a measurement service (for the same money, i
could buy a good oscillator new). Or is there
anyone new Switzerland who has such equipment who
would measure oscillators for me?
Attila Kinali
--
If you want to walk fast, walk alone.
If you want to walk far, walk together.
-- African proverb
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Re: [time-nuts] hp10811-60111 on ebay
On Tue, 29 Jun 2010 07:57:19 EDT
ewkeh...@aol.com wrote:
> Personally I am happy with my Datum and HP 10811's but I think there are
> many later model Osc. out there that may give them a run for the money.
What other, later model oscillators are out there that i could afford?
And trough which channels can i get hold of those?
Attila Kinali
--
If you want to walk fast, walk alone.
If you want to walk far, walk together.
-- African proverb
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Re: [time-nuts] yet another GPSDO design, or so
On Tue, 29 Jun 2010 21:32:10 +1200
Bruce Griffiths wrote:
> Its possible to build a 24 bit resolution D/A using a synchronously
> filtered PWM circuit.
> A pair of PWM outputs and a few relatively low precision resistors and
> capacitors together with a low noise low drift reference are required.
> The technique takes advantage of the fact that the required EFC voltage
> changes slowly and isnt updated at a highg rate.
> The synchronous filter technique eliminates the very long time constant
> RC filters required with an asynchronously filtered PWM waveform.
I've thought about that, but i'm afraid that this will add too
much phase noise trough EFC noise. Though, i have not calculated
how much noise this would generate.
Attila Kinali
--
If you want to walk fast, walk alone.
If you want to walk far, walk together.
-- African proverb
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Re: [time-nuts] hp10811-60111 on ebay
On Tue, 29 Jun 2010 13:32:33 + "Paramithiotti, Luciano Paolo S" wrote: > > "If you want to walk far, walk together" so, the best solution > is to buy a surplus ocxo calibrated. May be some frquency standard > hobbist have one for you. The 10811 sometime is sold with a small board > with a frequency divider to 1MHz and a trimmer to fine tuning it. The callibration itself is not important. That's what i have the GPS vor. As Steve said, the important thing is the ADEV. > I remember you the 10811 need a Ps voltage of 12 and 24 vdc. The power supply will be designed according to the needs of the circuit :-) > If you buy a new one You willnot receive it calibrated because the DC > external control is not included. > Where do you live? May be some ham close tu you can help you. I live in Switzerland. Attila Kinali -- If you want to walk fast, walk alone. If you want to walk far, walk together. -- African proverb ___ 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.
Re: [time-nuts] hp10811-60111 on ebay
On Wed, 30 Jun 2010 02:10:03 +1200 Steve Rooke wrote: > I seem to remember some discussions on a lost cost test instrument, > which would give "good enough: results, on this list very recently. I think i remember this one as well :-) > That would be the sort of gadget which would allow you to compare what > ocxo devices you have. If you have a dedicated spectrum analyser that > would allow you to look directly at phase-nose. There are a number of > ways to determine such "quality" measurements and not all of them > require a hefty outlay in test equipment. I wonder what you are trying > to achieve with your search for a good ocxo as this may indicate what > path is best for you. My goal is to build a GPSDO and to learn as much as possible in the process. And while i'm at it, i'd like to get a precission/accuracy that comes close to what can commercially bought, if possible even better ;-) And as most of the parameters of the GPSDO are dictated by the quality of the OCXO, i'd like to get some that are of good quality. Or at least worth the money i pay for them. Attila Kinali -- If you want to walk fast, walk alone. If you want to walk far, walk together. -- African proverb ___ 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.
Re: [time-nuts] yet another GPSDO design, or so
On Tue, 29 Jun 2010 09:17:39 -0700 (PDT) Stanley Reynolds wrote: > If we lower the size of each step to over lap more would this > lower the error ? Software would adjust both converters at the > cross over point so neither would change it's full range at this point. > Two 12 bit converters would form one 18 or 20 bit converter. Yes, you can do that. With good D/A converters, the non-linearity is within 1-2LSB, so if a full range of the fine D/A is more than, lets say 4LSB of the coarse D/A you can minimize the step in control voltage, when you switch from one fine D/A range to the next. But it will be always there, you cannot get completely rid of it. There are two things that make this step problematic: 1) If it happens automatically, it will result in problems when doing long term measurements using that GPSDO as reference. When doing the switch manually triggered (ie the GPSDO says that it needs to adjust the coarse D/A and does so only after the user presses a button), then unattended operation over long periods is not possible anymore. 2) Each adjustment of the coarse D/A is a non-linear operation. It is basically a step function excitation of the control loop. With such a non-linear element within the control loop, the software has to take either precautions during the period of the non linearity or the control loop has to be able to cope with such steps, without starting to oscillate. > I guess taken to the extreme we could interweave any number of > converters so hopefully the errors would average out :-) 64 times > 12 bit converters making a 20 bit converter each with an equal > contribution at each step. Actually, the less components you have, the better. Not only do more components add more non-linearity (it is very difficult to average multiple components if they arent R's and C's), the whole circuitry involved produces also noise. Attila Kinali -- If you want to walk fast, walk alone. If you want to walk far, walk together. -- African proverb ___ 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.
Re: [time-nuts] yet another GPSDO design, or so
On Tue, 29 Jun 2010 12:54:52 -0400 "Bob Camp" wrote: > Some of the TI (Burr Brown) 16 bit parts are 1/4 lsb DNL on > 98% of the > transitions. Most of the time you have a "coarse" DAC that's at 18 bits. > Some of the errors are predictable and you can take them out with a simple > training process. You won't easily get 24 bits, but 20 is very achievable. > > 20 bits is a nice round million to one factor. A 1 ppm EFC becomes a 1 ppb > step if everything is perfectly linear. Even with a 4:1 slope ratio it's > still quite small. With a more restricted EFC of 2.5x10^-8 you are at > 1x10^-13 with the 4:1 slope ratio. What currently puzzles me with such high bit D/A solutions is, how to stabilize the output voltage. Given a 20 bit D/A working over e.g. an 5V range (0-5V), 1LSB becomes 4.7uV. With 24 bit it's already at 300nV. This is getting awfully near to the noise voltages that a low noise circuit has. Not to talk that designing a power supply with a noise of less than 1uV is very daunting task. Attila Kinali -- If you want to walk fast, walk alone. If you want to walk far, walk together. -- African proverb ___ 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.
Re: [time-nuts] yet another GPSDO design, or so
On Tue, 29 Jun 2010 14:07:17 EDT ewkeh...@aol.com wrote: > > > just bought four AD 1861 on ebay with shipping was $11 each. Will see > > > hat I get, but they are out there and 18 bit will cover in my opinion > > > most > > Any one interested should hold off for a day buying. I have contacted the > > seller asked how many he has and what a quantity price would be. To much > > interest and the price will go up. I think the market for audio equipment > > replacement is shrinking and there will be more reasonable offers out > > there > > for this device, because repair of the audio equipment is prohibitive > This seller has 95 AD1861 in stock. Is there a reason why they would not > work for all applications. No I do not get a cut. 95 would justify to do a > new design but I am convinced there will be plenty more. I don't think this is such a good deal. The AD5680 which seems to have the better characteristics for a GPSDO application is available for 6.8USD/piece at digikey. If going for an audio DAC, i'd go for a 24bit one like the AD1853 which costa about 13USD/pi...@digikey. But please note that these audio DACs are not necessarily the right DACs for a GPSDO application. They have a high linearity, yes, but the have quite a bit of drift and other nastynes, which is ok for a audio application where voltage differences over time are not so important, but differential non-linearity is very important. Of course, time dependent non-linearities can be compensated by a the control loop, but it will add to the phase noise. Attila Kinali -- If you want to walk fast, walk alone. If you want to walk far, walk together. -- African proverb ___ 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.
[time-nuts] pc clock crystal long term variations
Moin,
I just had a little bit too much time at hand and had a look at
the ntp loopstats of one of my machine. Specifically at the ppm value.
After filtering out all items, where the ntp loop isnt running with
a poll intervall of 2^10, i got a more or less nice curve (see ntp.png).
The noise seen is quite expected, takeing into account that the
references used are behind an ADSL connection. The jumps are
exactly at the dates when the machine was rebooted.
What surprises me though is the stability of the crystal.
In the months between reboots, there is less than +-1ppm variation,
rather in the range of +-0.2ppm (i havent made any stasticial
sound analysis, so take the values with a grain of salt).
Especially when comparing to the +-40ppm jumps on reboots.
The machine is a 16y old DEC PC, which has been used as a desktop
before it came into my hands, and has been permanently running for
the last ~5 years.
So, the question is: are the ntp loopstats a valid way to judge
a crystal or am i looking at a GIGO-System? And why doesnt the
crystal relax back into it's old ppm value, but stays where it
is after a reboot/power cylce?
Attila Kinali
--
Why does it take years to find the answers to
the questions one should have asked long ago?
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Re: [time-nuts] pc clock crystal long term variations
On Sun, 08 Aug 2010 21:40:35 + "Poul-Henning Kamp" wrote: > DEC used way better crystals than the average PC-HW producers, so > I am not very surprised. Not sure if this was just general good > engineering or a panicy reaction to all the trouble the alphas > gave them. > > They had a few machines that could slot either x86 of alpha CPU > boards, and they were built from very high quality parts. This machine is a quite "cheap" dual P-II 266 system. No way to fit in Alpha CPUs. Though, there were Alpha machines in the same case. I guess they must have used very expensive crystals back then :-) > >And why doesnt the > >crystal relax back into it's old ppm value, but stays where it > >is after a reboot/power cylce? > > You kernel tries to measure/estimate the crystal frequency at boot, > it does not get the same value on every boot. Do mean the BogoMIPS callculation of linux? I don't know of any other timing dependend loop in there. > Check your syslog/dmesg for the frequency estimate and you can see > this clearly. I will try to fit the BogoMIPS data over the ntp loopstats and see what that yields. Thanks Attila Kinali -- If you want to walk fast, walk alone. If you want to walk far, walk together. -- African proverb ___ 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.
Re: [time-nuts] Hydrogen Maser KIT! Update #1
On Mon, 03 Nov 2014 00:39:24 +0100
Magnus Danielson wrote:
> It is worth knowing that active masers have a span for how the hydrogen
> in-flux will make it oscillate or not. Too little or too high, and the
> oscillation will die off. It may be one of the things to tune up if you
> got an older one which needs a bit of good old Love, Tender and Care.
BTW: I always ment to ask, what makes H-Masers stop when there is
too much hydrogen? I can understand too little H causes the system
not having enough atoms to probe (or not getting enough energy into
the system for active masers), but i don't understand the "too many" case.
Attila Kinali
--
I pity people who can't find laughter or at least some bit of amusement in
the little doings of the day. I believe I could find something ridiculous
even in the saddest moment, if necessary. It has nothing to do with being
superficial. It's a matter of joy in life.
-- Sophie Scholl
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Re: [time-nuts] Hydrogen Maser KIT! Update #1
On Sun, 02 Nov 2014 21:49:34 -0500
Chuck Harris wrote:
> They cleaned the vessel very well first with acetone and second,
> probably a little distilled water to etch the glass slightly,
Distilled water etches glass? Really?
Attila Kinali
--
I pity people who can't find laughter or at least some bit of amusement in
the little doings of the day. I believe I could find something ridiculous
even in the saddest moment, if necessary. It has nothing to do with being
superficial. It's a matter of joy in life.
-- Sophie Scholl
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Re: [time-nuts] AOL Email Issues
On Tue, 4 Nov 2014 12:12:34 -0500
"John C. Roos via time-nuts" wrote:
> Why must this be so hard? Would there be some huge cost
> involved in getting a more forgiving server setup that does not
> throw out all but the most primitive text. The FMT-nuts is a good
> example of something that works well and accepts photos and graphics.
Because it's not that easy. I have been managing smaller and larger
mailinglists with a similar setup as this one here for over a decade.
I had quite a bit of trouble myself with different email providers.
Most of these issues are actually not because the mailinglist setup
is broken, but because the receipients email provider does something
weird, non-standard or even violating standards in order to "protect"
themselves against spam. The whole yahoo thing is a good example of that.
AOL is also one of those known to break stuff from time to time.
Often, it's just a small thing that makes them to throw up on you,
like having a dash ("-") in your hostname (which is completly valid, btw).
Unfortunately, these big email providers do not care about mailinglists.
The reaction, when you report problems with them, varies from just ignoring
you (AoL, hotmail), to outright tell you that you are an idiot for even
considering to talk to them (yahoo). So you cannot resolve those issues
and are faced with a rat race to "fix" them (which sometimes
is impossible) or just tell your users to use a different email provider.
Yes, the one who suffers most from this are the users of the mailinglist.
And i can asure you, that none of the mailinglists admin wants to upset
any of their users, but please keep in mind that these mailinglists are
run in the free time of those admins, as a service to other people who
share the same hobby and interests.
The best you can do, is to report such issues to the mailinglist admin,
whos email address you can usually find in the header of the mail.
Attila Kinali
--
I pity people who can't find laughter or at least some bit of amusement in
the little doings of the day. I believe I could find something ridiculous
even in the saddest moment, if necessary. It has nothing to do with being
superficial. It's a matter of joy in life.
-- Sophie Scholl
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Re: [time-nuts] NPR Story I heard this morning
On Mon, 3 Nov 2014 11:54:41 -0800
Peter Monta wrote:
> Sorry if this is a bit off-topic. I'd like a simple, clear explanation for
> the layman that drills down on exactly how the current definitional scheme
> can be realized to arbitrary precision. For example, assume that we must
> go off-earth at some point to get a better timescale. How fuzzy is the
> solar potential ("soloid")?
It will be done as usual: As soon as they can reliably measure an systematic
effect that is impossible to cancel out, they will redefine or ammend the
definition of the second to account for this issue.
And going by the presentations given at EFTF this year, there is quite
some interest in precision gravity measurements in the time/frequency
community. And yes, they use the same basic phyiscs as their atomic clocks :-)
(one apporach is to let Cs atoms fall down a tube and measure their
acceleration using doppler shift of the hyperfine transitions line)
Attila Kinali
--
I pity people who can't find laughter or at least some bit of amusement in
the little doings of the day. I believe I could find something ridiculous
even in the saddest moment, if necessary. It has nothing to do with being
superficial. It's a matter of joy in life.
-- Sophie Scholl
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Re: [time-nuts] NPR Story I heard this morning
On Tue, 4 Nov 2014 11:04:58 -0800 Peter Monta wrote: > Let me rephrase what I'm after. The geoidal uncertainty sets a hard limit > on clock comparison performance on the Earth's surface (for widely-spaced > clocks). At some point, as Chris Albertson noted, the clocks will measure > the potential and not the other way around. (It should be possible to > express this geoidal uncertainty as an Allan variance and include it in > graphs with the legend "Earth surface performance limit".) Actually, currently the limit of clock comparison is not the geoid uncertainties, but the comparison itself. Common view GPS does not cut it at all. TWSTFT might be enough, if more second/third order effects are compensated for and the orbit is measured with a higher precision [1,2]. For "short" distances (up to 1000km or so), temperature and delay-variation compensated fibers seem to be the way to go [3,4]. Also, frequency transfer down to very low numbers seems to be easier (depending on system and distance in the range of 1e-12 to 1e-16) than accurate time transfer (around a couple 100ps seems to be the limit for any non-trival distance, at the moment) [1] "Two-way Satellite Time and Frequency Transfer:Overview, Recent Developments and Application", by Wu et al, 2014 [2] "Practical Evaluation of Relativistic Effects in Two-Way Satellite Time and Frequency Transfer", by Shemar, Delva, Lamb, 2014 [3] "Optical Frequency Transfer with a 1284 km Coherent Fiber Link", by Calonico et al, 2014 [4] "Novel Techniques for Optical Fiber Links beyond Current Practice", by Calosso et al, 2014 And these are just a few of the presentation given at EFTF this year on that topic. Attila Kinali -- I pity people who can't find laughter or at least some bit of amusement in the little doings of the day. I believe I could find something ridiculous even in the saddest moment, if necessary. It has nothing to do with being superficial. It's a matter of joy in life. -- Sophie Scholl ___ 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.
Re: [time-nuts] FYI: Galileo satellite recovered and transmitting navigation signals
On Fri, 5 Dec 2014 21:16:14 -0500
Bob Camp wrote:
> Running one locked to each system is really the only approach that makes
> sense. There inevitably are minor differences in systems and trying to
> average things out is not the best way to do it.
Might or might not be. At least for GPS and Galileo there is an agreement
to synchronize the clocks and have a field in the message data that specifies
the difference between UTC(GPS) and UTC(Galileo).
There was some discussion at last EFTF about how they are going to measure
the time difference accurately. Apparently the GPS people were not impressed
by Galileos plan to have a physical realization of UTC(Galileo). They seem to
have run into problems in the past and have thus switched to a paper clock.
Attila Kinali
--
I pity people who can't find laughter or at least some bit of amusement in
the little doings of the day. I believe I could find something ridiculous
even in the saddest moment, if necessary. It has nothing to do with being
superficial. It's a matter of joy in life.
-- Sophie Scholl
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Re: [time-nuts] FYI: Galileo satellite recovered and transmitting navigation signals
On Sat, 06 Dec 2014 14:47:54 +0100
Magnus Danielson wrote:
> Also, GPS L2C and L5 signals is already there.
AFAIK there is no satellite with L5 capabilities in space yet.
Also L2C is still marked as unhealthy.
Attila Kinali
--
I pity people who can't find laughter or at least some bit of amusement in
the little doings of the day. I believe I could find something ridiculous
even in the saddest moment, if necessary. It has nothing to do with being
superficial. It's a matter of joy in life.
-- Sophie Scholl
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Re: [time-nuts] FYI: Galileo satellite recovered and transmitting navigation signals
On Sat, 6 Dec 2014 12:49:53 +0100
Azelio Boriani wrote:
> The 2014 EFTF abstracts are available here: (55MB ZIP file)
> <http://www.eftf-2014.ch/media/EFTF-2014-USB-DRIVE_20140624.zip>
The papers are also online, but only available to those who were
at the conference.
Attila Kinali
--
I pity people who can't find laughter or at least some bit of amusement in
the little doings of the day. I believe I could find something ridiculous
even in the saddest moment, if necessary. It has nothing to do with being
superficial. It's a matter of joy in life.
-- Sophie Scholl
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Re: [time-nuts] FYI: Galileo satellite recovered and transmitting navigation signals
On Sat, 6 Dec 2014 12:35:16 -0200
Edesio Costa e Silva wrote:
> According to <http://www.defense.gov/releases/release.aspx?releaseid=1>
> the L2C and L5 signals are now available.
Oh.must have missed that.
Thanks!
Attila Kinali
--
I pity people who can't find laughter or at least some bit of amusement in
the little doings of the day. I believe I could find something ridiculous
even in the saddest moment, if necessary. It has nothing to do with being
superficial. It's a matter of joy in life.
-- Sophie Scholl
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Re: [time-nuts] New Years Eve TV countdown
On Thu, 01 Jan 2015 02:08:04 -0800
Rex wrote:
> TV doesn't seem to care about time sync much these days. It also depends
> a lot on the path getting to you,
Oh, they do. Just ask Magnus :-)
The thing is, that video delay in digital systems is hard to keep down
with all the intermediate processing steps. Video is processed in groups
of pictures (GOP) that can be anything from a single frame to several hundred.
AFAIK DVB based systems are around 8 to 30 or so. Which makes already
up to a second delay at the recording point. And every time you need to
process a complete GOP at once, it adds another second.
> One thing annoys me though. Many channels don't care much about start
> and stop times. If I program something to record using the schedule,
> often I miss the end of it. They frequently go over the half-hour or
> hour mark by a minute or two. Occasionally they complicate it more by
> starting a show a little early too. That irks me.
That's what we have VPS for, or PDC for digital systems[1].
[1] http://en.wikipedia.org/wiki/Programme_Delivery_Control
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] Current state of optical clocks and the definition of the second
Hi, I just stumbled over this [1] nice article by Fritz Riehle that might be of interest to others as well. Attila Kinali [1] "Towards a Re-definition of the Second Based on Optical Atomic Clocks", by Fritz Riehle, 2015 http://arxiv.org/abs/1501.02068 -- 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 ___ 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.
Re: [time-nuts] GPS 1PPS ultimate accuracy
Ciao Andrea, On Mon, 12 Jan 2015 11:59:26 +0100 Andrea Baldoni wrote: > The sampling interval could come from a (long time based on a) sawtooth > uncorrected PPS from a cheap GPS, a sawtooth corrected from a good one > (perhaps > the Lucent GPSDO), or a computer using NTP. The GNSS Timing AppNote for the LEA6-T receiver[1] will give you an idea what jitter you get with GPS. Please be aware that these measurements were done with an antenna located at a _good_ position (ontop of a 4 story building with no other high buildings around). Unless you have a simlarly good location you will have worse performance. Said Jackson reported some time ago that he got around 1us of jitter for a GPS receiver (i presume it was either a LEA5-T or a LEA6-T) behind a window. After he averaged the position for a long time (several days) manually and stored that in the receiver he got much better performance (sorry i cannot find the mail at the moment, you have to look for it in the archives yourself). NTP will give you a jitter in the range of 1-100ms, depending on your internet connection and its conguestion. On a local network based NTP system, you can expect jitter in the range of 10-100us IIRC. > Each of these sources should reach a goal stability (say, 1 part in 10^13) > after averaging them on a different (and very high I suppose) number of > seconds (averaging them for an infinity number of seconds should give the > stability of the underlying reference clock, but I'm willing to stop > sooner...). > I know there's no reason to go 1E-13 when the Milliren couldn't go that far, > but the DUT may be also something else like a FE-5680A). To get to 1e-13 with GPS (assuming 1-10ns jitter) you need somewhere around 10k to 100k seconds. At these time scales, the temperature dependent deviation of your OCXO is likely to dominate your measurement. I would rather do a two step measurement. If you have a FE-5680A measure its drift with a tau in the 100ks-200ks region. Then use the FE-5680A as refrence to measure the drift of the OCXO in 10s-1000s timescales. If you do both continuously, you can apply some math and get out pretty good numbers (see three cornered hat method) Additional to GPS jitter you also have the deviation of GPS time in respect to TAI/UTC. This has been in recent years below 5ns (GPS vs UTC(USNO)). But because GPS time is steered to be close to UTC it will oscillate slightly around it. How much, i do not know. (But then the deviation between the different UTC realizations is larger) [2] > The sawtooth uncorrected GPS receiver may never yeld a good stability in the > short term, but in the long one it should as well because the internal clock > jitter would average results. It would average out if and only if the sawtooth correction would be completely independent of anything else. But it isn't. This results in effects where the cycle to cycle jitter is quite low, but there is a large offset in the sawtooth correction. This is know as "hanging bridges" in the GNSS world. > By the way, the stability of the TAI is known or, because it's > the reference one, it has zero deviation for definition (so you can reach > its ultimate stability through GPS really only at the infinity...)? There is an uncertainty number attached to TAI, but i dont know any numbers from the top of my head. I'm sure it is mentioned in the BIPM report somewhere. Attila Kinali [1] http://www.u-blox.com/images/downloads/Product_Docs/Timing_AppNote_%28GPS.G6-X-11007%29.pdf [2] "GPS time and its steering to UTC(USNO)", presentatin by Edward Powers, 2009 http://www.gps.gov/multimedia/presentations/2009/09/ICG/powers.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 ___ 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.
Re: [time-nuts] Current state of optical clocks and the definition of the second
On Mon, 12 Jan 2015 13:34:03 +0100 Attila Kinali wrote: > I just stumbled over this [1] nice article by Fritz Riehle that might be > of interest to others as well. And while we are at it: "2e-18 total uncertainty in an atomic clock", by T.L. Nicholson et.al., 2015 http://arxiv.org/abs/1412.8261 -- 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 ___ 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.
Re: [time-nuts] FOSDEM 2015 has a time-track
Moin moin,
On Wed, 07 Jan 2015 08:06:20 +
Poul-Henning Kamp wrote:
> FOSDEM is an Open-Source gathering once a year in Bruxelles, and
> this year there is a track dedicated to time:
>
> https://fosdem.org/2015/schedule/track/time/
>
> Those of you of an european persuassion may find it relevant...
I'll be at FOSDEM, Friday to Monday. Do any of the present time-nuts care
for a meetup (like some drinks or dinner)?
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] Current state of optical clocks and the definition of the second
On Mon, 12 Jan 2015 20:09:45 + Gregory Maxwell wrote: > On Mon, Jan 12, 2015 at 12:34 PM, Attila Kinali wrote: > > I just stumbled over this [1] nice article by Fritz Riehle that might be > > of interest to others as well. > > I've seen less discussion of non-atomic stable optical oscillators. > Most (all?) of these optical atomic standards are passive atomic > clocks and need a free running oscillator. The local oscillator is considered a solved problem in research. If you need something low noise and stable you either go to Oscilloquartz or to Wenzel and get one of ther OCXO. The only place where you have to be carefull is the Dick Effect, but that's well understood and people usually acount for it. One exception here is space qualified oscillators. For those you go to the JPL and ask them to help you. > Seems that the state of the art in stabilized lasers has improved a > lot lately, e.g. there are commercial available 1550nm devices which > have a <=3Hz line-width: http://stablelasers.com/products.html (well > on a short term basis, the medium term performance is not so > impressive) Laser stabilization, especially for quantum metrology is still an actively researched field. Current state of the art is IIRC 0.3Hz linewidth (sorry, cannot find the reference at the moment). Mid- and long term stability depends highly on the reference used. Current research is fucused mainly on special, low vibration structures made out of low expansion glass or silicon. And these cavities are usually put into a temperature controlled chamber in vacuum. > Considering the rarity and extreme cost of H-masers, or just really > exceptional quarts oscillators; might it be the case that optical LOs > start looking interesting for applications which just need stability > (or being steered by other sources; e.g. GPSDL)? Well, an 8607 costs more than a Rb-standard. Yes, the 8607 has lower close in phase noise and up to several 1000s it rivals the Rb, but handling it is much more difficult than handling an Rb. Also, if you want to buy one of those exceptionally low noise/high stable 8607's (those that go down into the 10^-14 range) you'd have to sell your car. But, if you buy a H-maser from SpectraTime, you get a 8607 for free ;-) There used to be quite some literature on how to build low noise quartz oscillators. Most of those books are out of print today. With two notable exceptions: "Discrete Oscillator Design: Linear, Nonlinear, Transient, and Noise Domains" by Randall Rhea, 2010 and "Understanding Quartz Crystals and Oscillators", by Ramon Cerda, 2014 I had a look at the book by Rhea, it looks quite well written and contains a lot of real world information, but is a bit weak on the more theoretical part (description of oscillation, noise sources,...) and thus on the on the why things are done that way. I didn't had the chance to buy Cerdas book yet. The UFFC has some of the older books online. You need to be registered to access them, though. There is also a lot of knowledge on quartz crystalls hidden in old papers, but going trough them is some serious work. On the topic of opto-electronic oscillators, those are technologically nice, but they are rather bulky. That's why they are mostly used in research projects for atomic clocks. Also getting them to do low phase noise is not that easy, and unlike quartz oscillators, there is not much literature about that. > (They can be down-converted to microwave frequencies using an optical > comb; a mode-locked laser whos pulses are phase locked to an incoming > beam.) That is actually the current trend. There was a paper by NIST last year on downconverting the beat frequency of an optical comb down to RF using a frequency divider chain. They managed to get noise measures that rival that of a good quartz oscillator at 5MHz. Ie at higher frequencies, it is actually better than what a quartz oscillator can deliver. (for some reason i have not archived that paper and google fails me) > Certainly just the local oscillator is _closer_ to something a > time-nut might experiment with than a complete optical atomic standard > (if still not quite in reach). Well, building a CPT based Rb vapor cell frequency standard should be feasible. Yes, it's not a primary standard, but should do the job for most :-) >From what i've read, using one of the MOT cells like those of Sachser Laser [1] one might even be able to build a primary standard. But my understanding of MOT is relatively weak and i cannot say how difficult it actually would be. But it would be definitly a fun project to try :-) But i agree, building one of those ion or neutral atomic standards is pretty much out of question on a hobby budget. Heck, even an optical frequency comb is difficult to build, at best. And buying them.. i think buying a good Rb is still cheape
Re: [time-nuts] FOSDEM 2015 has a time-track
On Tue, 13 Jan 2015 01:57:56 -0800 "Tom Van Baak" wrote: > I was told some of the time slots of https://fosdem.org/2015/schedule/track/ > time/ > might be tentative Well, it's FOSDEM. It's not a professionally organised conference. And as presentations often take longer than their time slot, the schedule tends to shift around quite a bit. > but we'll all get together after the last talk, whenever it is. So far > everyone I've heard from has the evening open. > Time nuts -- if you're within a couple hundred km of Brussels it should be > worth it -- Sunday, 2015-02-01. If you are new to FOSDEM, don't miss the social event on friday evening. 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 ___ 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.
Re: [time-nuts] Current state of optical clocks and the definition of the second
On Tue, 13 Jan 2015 17:46:01 + "Dr. David Kirkby (Kirkby Microwave Ltd)" wrote: > Of course I'm not suggesting a HeNe would provide the stability of > cutting edge research laser optical clock, but they are easily within > the budget of a hobbyist and could be a bit of fun to try to measure > their stability/phase noise. The tricky bit would be getting 470 THz > down to 10 MHz, but a cheap and quick experiment would prove whether > it is a total waste of time or not. Actually, you can get better than that, and cheaper. If you use a standard laser diode, these have a linewidth of around 20-100MHz. If you provide them the slightest feedback, they go down to 1MHz easily (ie just by adding some window glass infront of the laser, that reflects a tiny bit back). Using a more sophisticated scheme with a grating and you get into the range of 1-100kHz, which is pretty darn good, and enough for vapor cells with their broad lines. Wieman wrote a couple of papers on how to build such laser system [1-3]. Also worth a look are the two papers by Libbrecht [4,5]. For those who need some theory for calculation or as background [6] will be a good start. It also contains a lot of usefull references. That said. For just doing something like CPT, you don't need to narrow the linewidth of a standard laser diode. Eg the CSAC uses just a standard VCSEL without any additional optics. The disadvantage is, that your only means to control the laser wavelength is temperature and current. Also, you will see mode jumps within the range you are interested in. Attila Kinali [1] "Using diode lasers for atomic physics", by Wieman, Holberg, 1990 http://web.mit.edu/kimt/www/nice_readings/wieman-diode-lasers.pdf [2] "A narrow-band tunable diode laser system with grating feedback, and a saturated absorption spectrometer for Cs and Rb", by MacAdam, Steinbach, Wieman, 1992 http://fisica.usach.cl/~iolivare/MacAdamSteinbachWieman92.pdf [3] "Inexpensive laser cooling and trapping experiment for undergraduate laboratories", by Wieman, Flowers, Gilbert, 1994 http://ajp.aapt.org/resource/1/ajpias/v63/i4/p317_s1 [4] "Teaching physics with 670nm diode lasers - construction of stabilized lasers and lithium cells", by Libbrecht, et al, 1995 http://ajp.aapt.org/resource/1/ajpias/v63/i8/p729_s1 [5] "Teaching physics with 670nm diode lasers - experiments with fabry-perot cavities", by Boyd, Bliss, Libbrecht, 1996 http://www.its.caltech.edu/~atomic/publist/cavity.pdf [6] "Mode stability of external cavity diode lasers", by Saliba, Junker, Turner, Scholten, 2009 http://www.opticsinfobase.org/ao/abstract.cfm?uri=ao-48-35-6692 -- 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 ___ 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.
Re: [time-nuts] Current state of optical clocks and the definition of the second
On Tue, 13 Jan 2015 19:37:05 +0100 Attila Kinali wrote: > If you use a standard laser diode, these have a linewidth of > around 20-100MHz. If you provide them the slightest feedback, > they go down to 1MHz easily (ie just by adding some window glass > infront of the laser, that reflects a tiny bit back). > Using a more sophisticated scheme with a grating and you get into > the range of 1-100kHz, which is pretty darn good, and enough for > vapor cells with their broad lines. Wieman wrote a couple of papers > on how to build such laser system [1-3]. Also worth a look are the two > papers by Libbrecht [4,5]. For those who need some theory for > calculation or as background [6] will be a good start. It also > contains a lot of usefull references. Oh.. i forgot to mention. The DIY holographcy community is full of people who build their own narrow linewidth, stabilized lasers. They have also quite a few, hands-on descriptions on how to build grating based external cavity diode lasers. Especially W's website[1] and blog[2]. Attila Kinali [1] http://redlum.xohp.pagesperso-orange.fr/argonlaser.html [2] https://hololaser.wordpress.com/ -- 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 ___ 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.
Re: [time-nuts] Current state of optical clocks and the definition of the second
On Tue, 13 Jan 2015 17:46:01 + "Dr. David Kirkby (Kirkby Microwave Ltd)" wrote: > I had a brief read. Equation 1 made me wonder what could be achieved > with a cheap HeNe laser. It should be fairly easy to mix a couple of > HeNe lasers on a photodiode and look at the difference frequency > between them, so gaining insight into their stability. A quick check > on Wikipedia > > https://en.wikipedia.org/wiki/Helium%E2%80%93neon_laser > > indicates a spectral width of 0.002 nm. > > The common 632.8 nm laser has a frequency of 4.7 x 10^14 Hz, or 470 THz. Oops.. i just reread the part of the paper an realized that i answered in a completely meaningless way. Sorry about that. For the real answer: You can use a HeNe laser to provide with a stable wavelength, but as with all lasers, the linewidth and stability are determined by the cavity, not by the atomic transition. The width of the atomic transition is much wider than the cavity free spectral range. Usually, these lasers have a 2-10cm long cavity, which results in a free spectral range of 60GHz to 3Ghz. The exact wavelength depends on the length of the cavity. Which means that any temperature change will shift the laser wavelength around. And we are not yet talking about possible mode hops. All this together will lead to laser wavelengths of different HeNe laser tubes that are so far apart that a simple diode detection of the beat frequency will not work (the beat frequency could be in the several 10GHz and/or wander around very quickly). When stable lasers are needed, they are locked to something that does not change. For example a vapor cell (DAVLL) or to a high stability fabry-perot cavity (Pound-Drever-Hall). Both, the vapor cell or the cavity are temperature stabilized. Locked also means that the laser is steered, ie the wavelength of the laser is controlled electronically using the feedback of the reference element. Long story short, a simple HeNe laser will not give you anything stable, without some additional stabilization. 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 ___ 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.
Re: [time-nuts] Maser on a chip
On Sun, 18 Jan 2015 22:59:57 +
Mark Sims wrote:
> http://www.princeton.edu/main/news/archive/S42/13/37M75/index.xml
> Not much detail there... but there is an article in Science.
This maser is basically a variation of the quantum cascade laser,
using tunable quantum dots instead of hetero structures to define
the electron levels (think "particle in a box" where the box
can be electrically tuned).
>From the text it seems like that this is only a first demonstrator,
that the technology works. They drove the maser externally and measured
its response to it.
They got an output frequency of 7880MHz and a line width of 34kHz.
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] question Alan deviation measured with Timelab and counters
On Mon, 19 Jan 2015 08:59:58 -0500
Bob Camp wrote:
> The most basic way to do phase noise in the basement is with a single mixer
> setup running into some sort of audio FFT device. A sound card can be used or
> an audio spectrum analyzer. Parts are < $100 to get one setup once you can do
> the audio measurements.
2-3 years ago, i got a presentation of an italian amateur radio on
how to measure phase noise of osciallators using this technique in quite
detail. Only draw back is that the presentation is in italian. If someone
wants this presentation, please contact me off list.
Attila Kinali
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Re: [time-nuts] Maser on a chip
On Sun, 18 Jan 2015 22:59:57 +
Mark Sims wrote:
> http://www.princeton.edu/main/news/archive/S42/13/37M75/index.xml
> Not much detail there... but there is an article in Science.
It looks like the supplemantary material[1] of the paper isnt behind a pay wall.
Attila Kinali
[1] http://www.sciencemag.org/content/347/6219/285/suppl/DC1
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[time-nuts] Clock stability and its measures
Hi, I have been tasked to give a talk on clock stability and its measures next thursday. Most of the stuff is pretty clear (and the rest can be easily looked up in Rubiolas book, various app notes and papers). But I would like to make sure I did not forget anything important. The types of stability measures we have are: * deviations * Allan deviation * modified Allan deviation * time deviation * Hadamard deviation * noise spectrum * single sided power spectral density * jitter * cycle-to-cycle jitter * period jitter * time interval error Are there any other measures? Or anything important I should make sure to mention? Also, if someone has a presentation where I could steal some stuff from, I would appreciate that as well. 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 ___ 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.
Re: [time-nuts] question Alan deviation measured with Timelab and counters
Moin Magnus,
On Wed, 21 Jan 2015 07:07:54 +0100
Magnus Danielson wrote:
> For oscillators, they should have been turned on long enough such that
> any drift is negligible. Alternatively you process out the quadratic
> trend out of it. The later should be accompanied by some quality measure
> of how much remaining systematics there is (see Jim Barnes PTTI paper on
> Drift Estimators).
Do you mean "The measurement of linear frequency drift in oscillators",
http://tf.nist.gov/timefreq/general/tn1337/Tn264.pdf ?
Attila Kinali
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Re: [time-nuts] Good references on holdover?
On Fri, 6 Feb 2015 10:21:08 +0100 Javier Serrano wrote: > We would like to start working on holdover performance for White > Rabbit [1]. This is a new domain for us. Our main use case is a WR > switch losing its reference because someone disconnects a fiber. We > can have redundancy, but it will take some time for a switch to change > over to another reference. During this time, the oscillator in that > switch will be free-running. We want to minimize the phase drift > during that interval, which we think should be a couple of seconds > maximum. We have never worked on holdover, and I am wondering if we > can do something smarter than the obvious feeding of some constant > voltage to the VCXO, based on averaging during the locked state. Does > anybody know of any good references on holdover? I think you are looking for something like [1]. I think [2] could be also of help, although it's not as good as the Nicholls paper. Zhou's paper [3] seems to be very similar to what Nicholls did (i have not fully read it yet). HTH Attila Kinali [1] "Adaptive OXCO Drift Correction Algorithm", by Nicholls and Carlton, 2004 http://dx.doi.org/10.1109/FREQ.2004.1418510 [2] "A Frequency Model for OCXO for Holdover Mode of DP-PLL", by Hwang, Shin, Han, Kim, 2000 http://dx.doi.org/10.1109/SICE.2000.889649 [3] "Adaptive Correction Method for an OCXO and Investagion of Analytical Cummulative Time Eror Upperbound", by Zhou, Kunz, Schwartz, 2011 http://www.sce.carleton.ca/faculty/schwartz/abstracts/HuiPaperschwartz.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 ___ 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.
Re: [time-nuts] D term (was no subject)
On Mon, 26 Jan 2015 20:15:12 +
"Poul-Henning Kamp" wrote:
> The basic math of PID has been around for about 100 years. The invention
> of the servo (and synchro/resolver) is what makes its day...
If anyone wants to dive into control theory I recommend reading the
book "Feedback control of dynamic systems" by Franklin, Powell and Emami-Naeini.
It's very accessible, requires only little more than high school math and
is geared to an engineering approach (ie lots of real world examples and
how to solve them)
Attila Kinali
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Re: [time-nuts] T.I. questions
On Fri, 06 Feb 2015 19:29:46 +0100
Magnus Danielson wrote:
> Since then interpolation of single-shot events have been investigated,
> and is now down to 200 fs in the best counter I know of (and have).
Which counter is that? I'm only aware of an experimental TDC that does
500fs. Namely the SAW filter based TDC by Petr Panek[1,2], which he presented at
EFTS 2013. (I don't have that paper at hand and cannot look it up due
to broken german internet).
Attila Kinali
[1] "Time-Interval Measurement Based on SAW Filter Excitation", Panek, 2007
[2] "Time interval measurement device based on surface acoustic wave
filter excitation, providing 1ps precision and stability", Panek, Prochazka,
2007
http://link.aip.org/link/RSINAK/v78/i9/p094701/s1
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Re: [time-nuts] GPS active antenna delay ?
On Sat, 7 Feb 2015 10:07:44 -0800 Tom McDermott wrote: > While compensating for cable delay is relatively straight forward by > measuring the length and compensating for > the velocity factor, a question is: how much amplifier / filter group delay > is to be expected within the antenna itself? The usual way is to calibrate the whole setup, including antenna, LNA, cable and receiver. Ie. you drive to the national lab, set up your whole system, then measure the timing difference of your GPS receiver to the one of the lab, drive back home, and apply the correction. > Looking through GPS SAW filter datasheets seems to show none with group > delay specifications. Not surprising. Group delay is not considered of any importance in most RF designs. > googling leads to some research papers with delays of about: > > L1 - 20 MHz wide SAW filter has about 15 nsec of group delay > L1 - 2 MHz wide SAW filter has about 65 nsec of group delay > L1 - LC filter - can't find anything, but suspect it's probably just a few > nanoseconds. I would be very much interested in those papers. Could you list their titles and authors at least? > I'm not sure a consumer grade antenna even has a SAW filter, it may simply > be an LC filter. Unlikely. LC filters are not sharp enough and difficult to build reliably at those frequencies. I would rather assume that there are no filters at all (beside the antenna characteristics). 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 ___ 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.
Re: [time-nuts] D term (was no subject)
On Fri, 06 Feb 2015 21:20:39 + "Poul-Henning Kamp" wrote: > >If anyone wants to dive into control theory I recommend reading the > >book "Feedback control of dynamic systems" by Franklin, Powell and > >Emami-Naeini. > > And if you are more of a historical bent, the MIT Radiation Lab > series is the motherlode. And here the link to the pdf's in case anyone is looking: https://www.jlab.org/ir/MITSeries.html 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 ___ 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.
[time-nuts] Wavecres SIA-3000 and DTS-2070 schematics (was: T.I. questions)
On Fri, 06 Feb 2015 20:55:56 +0100
Magnus Danielson wrote:
> The Wavecres SIA-3000 has a single-shot resolution of 200 fs, but the
> trigger jitter. Later models only went to 300 fs as far as I know. The
> DTS-2070C has a resolution of 800 fs.
Hmm... does anyone have the schematics (or any other description
of the inner working) of those two? My google skills fail me.
Attila Kinali
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Re: [time-nuts] Wavecres SIA-3000 and DTS-2070 schematics
Moin Magnus,
On Mon, 09 Feb 2015 12:37:04 +0100
Magnus Danielson wrote:
> > Hmm... does anyone have the schematics (or any other description
> > of the inner working) of those two? My google skills fail me.
>
> I've made sure to dump a lot of documentations on Didiers site.
Thats the first place i looked. But i apperantly missed the patent file
there. The rest of the Wavecrest related documents don't seem to be
very interesting.
> There is a set of interesting patents to be read.
I will dig for those. Thanks!
Attila Kinali
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Re: [time-nuts] Wavecres SIA-3000 and DTS-2070 schematics (was: T.I. questions)
On Mon, 9 Feb 2015 11:31:54 -0500
"Mike Feher" wrote:
> I have two DTS2070s. The only manual I can find now is one for the DTS-2079.
> No schematics, but, a whole lot of other info. Can email it to you if you
> would like. Regards - Mike
Thanks. If it's the same users manual as can be found on didiers site, then
i already have it :-)
Attila Kinali
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Re: [time-nuts] question Alan deviation measured with Timelab and counters
On Tue, 20 Jan 2015 08:39:13 +0100
Attila Kinali wrote:
> 2-3 years ago, i got a presentation of an italian amateur radio on
> how to measure phase noise of osciallators using this technique in quite
> detail. Only draw back is that the presentation is in italian. If someone
> wants this presentation, please contact me off list.
Azelio Boriani was so kind to translate the presentation.
You can find the original pdfs and the Azelio's translations
at http://attila.kinali.ch/phase_noise_measurement/
Attila Kinali
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[time-nuts] Event based Kalman Filter for Clock Synchronization
Hi, As usual, while looking for something completely different i stumbled over this interesting paper[1]. I know a few people here are dealing with clock synchronization where the synchronization is not really continious (think NTP) and i think for those this might be worth to have a look at. That said, I hardly know anything about Kalman Filters (or adapative control in general). So I would appreciate if someone who knows this stuff could give his oppinion on the paper. Attila Kinali PS: If the paywall is a problem, contact me off list [1] "An Event-Based Kalman Filter for Clock Synchronization", by Giada Giorgi. 2015 http://dx.doi.org/10.1109/TIM.2014.2340631 -- 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 ___ 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.
Re: [time-nuts] GPS active antenna delay ?
On Tue, 17 Feb 2015 18:33:24 -0800
Tom McDermott wrote:
> Hi Dave - agree that VNA is one good way to measure the delay. If required
> accuracy is less than about
> 0.5 nsec, then Tx antenna to Rx antenna mutual impedance starts to become
> an issue. Above about
> 1 nsec error probably most of these can be ignored. No access to a vector
> VNA that works at 1.5 GHz.
> unfortunately.
You could try tinyVNA[1]. I have used it once, it has some quirks
(it's half hobby, half commercial project and that shows) but works
otherwise. I have no idea how accurate it is.
Attila Kinali
[1] http://miniradiosolutions.com/minivna-tiny
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Re: [time-nuts] GPS active antenna delay ?
On Wed, 18 Feb 2015 07:24:32 -0800 Jim Lux wrote: > > [1] http://miniradiosolutions.com/minivna-tiny > > > > > And tough to find any substantive information on the hardware design. I > poked around for a few minutes, but all I was able to find was software > user manuals, but no hardware description. > > I assume that it's the usual 2 port, 1 direction thing.. A DDS for the > RF source, and some sort of dual channel detector with directional > couplers or a bridge on the output port When i had one on my desk, i opened it up, but apparently i forgot to take pictures. From what i remember, i think it works either similar to the VNWA design done by DG8SAQ[1,2] or by N2PK[3]. The tinyVNA can only do S11 and S12, lacking the additional source at the second port. Attila Kinali [1] http://sdr-kits.net/DG8SAQ/VNWA/baier_VNWA10_QEX.pdf [2] http://sdr-kits.net/DG8SAQ/VNWA/QEX-Letters.pdf [3] http://n2pk.com/VNA/n2pk_vna_pt_1_ver_c.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 ___ 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.
Re: [time-nuts] GPS active antenna delay ?
On Thu, 19 Feb 2015 10:51:04 +0100
Attila Kinali wrote:
> When i had one on my desk, i opened it up, but apparently i forgot to take
> pictures. From what i remember, i think it works either similar to the
> VNWA design done by DG8SAQ[1,2] or by N2PK[3]. The tinyVNA can only do
> S11 and S12, lacking the additional source at the second port.
Correction, a little bit of googling brought up [1] (sorry, mostly german).
The discussion contains top[2], bottom[3] pictures and the block diagram[4]
Attila Kinali
[1] http://www.mikrocontroller.net/topic/351273
[2] http://www.mikrocontroller.net/attachment/238726/image.jpg
[3] http://www.mikrocontroller.net/attachment/238727/image.jpg
[4] http://www.mikrocontroller.net/attachment/243812/vna_scm_col_v3.jpg
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Re: [time-nuts] Looking for advice to get a submillisecond setup
On Thu, 19 Feb 2015 18:11:08 +0100 Matt wrote: > My university would like to have a <1ms precise source of time to do > some networking experiments (measure one way propagation delays > etc...). So I wandered on the internet to find the best choice with a > budget of ~1000€ (~1100 American dollars). > I've been overwhelmed by the number of possibilities (atomic > clocks/GPS signal etc...) and as no price appear on the seller > websites, it's difficult to rule out options. Can you say a little bit more about your setup? There are many choices about how to get time accurately and precisely to a computer, but which one is the "best" depends highly on your setup and location (and what your requirements are, of course). 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 ___ 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.
Re: [time-nuts] homebrew counter new board test result
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
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Re: [time-nuts] homebrew counter new board test result
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
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Re: [time-nuts] OXCO insulation
On Tue, 24 Feb 2015 22:44:30 -0600
"Bill Hawkins" wrote:
> 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.
Actually, you should put the temp sensor close to the heater, not the crystal.
The delay between the actuator (heater) and the feedback (temperature sensor)
defines the dead time. The presence of a crystal somewhere in the system is
of no importance to the oven controller, it's just additional thermal weight.
Attila Kinali
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Re: [time-nuts] OXCO insulation
On Wed, 25 Feb 2015 10:16:58 +0100 Attila Kinali wrote: > Actually, you should put the temp sensor close to the heater, not the crystal. > The delay between the actuator (heater) and the feedback (temperature sensor) > defines the dead time. The presence of a crystal somewhere in the system is > of no importance to the oven controller, it's just additional thermal weight. Bob Camp just reminded me of Rick Karlquist's papers on this topic: "A low Profile High-Performance Crystal Oscillator for Timekeeping Applications", by Karlquist, Cutler, Ingman, Johnson, Parisek, 1997 http://www.karlquist.com/osc.pdf "The Theory of Zero-Gradient Crystal Ovens", by Karlquist, Cutler, Ingman, Johnson, Parisek, 1997 http://www.karlquist.com/oven.pdf More can be found on his homepage: http://www.karlquist.com/ A bit more theoretic, but maybe also of interest: "OCXO Design Using Composite Heating of the Crystal Resonator", by Abramson, 1994 http://dx.doi.org/10.1109/58.279145 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 ___ 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.
[time-nuts] Witch Navigator Project
Hi, I just stumbled over a nice OSS GNSS receiver in FPGA project done by the Czech Technical University. They use two MAX2120 DVB-S tuners together with 8bit 22Msps ADCs and an Spartan6 FPGA. You can find the project homepage at http://www.witchnav.cz/ 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 ___ 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.
Re: [time-nuts] homebrew counter new board test result
On Wed, 25 Feb 2015 01:44:40 -0800
Hal Murray wrote:
> The Schmitt trigger mostly avoids glitches on the output. Does it do
> anything to reduce timing noise if the input signal is clean enough that it
> doesn't make any glitches?
A Schmitt Trigger avoids glitches at the input, not the output.
It does prevent the input circuitry in the gate to switch back and forth
between 0 and 1, or, even worse, from going metastable.
This by itself might improve timing, if you have problems due to low
slew rate. But as Magnus wrote, in general does not improve things.
Attila Kinali
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Re: [time-nuts] new tdc from Texas
On Thu, 05 Mar 2015 01:27:23 +
Angus wrote:
> I've not seen any mention of anything other than the TDC1000.
>
> I was a bit surprised that they went down the less-integrated route
> and separated the TDC, but it turns out that for a lot of the sort of
> things they designed it for, a uC provides good enough timing itself,
> and no extra TDC is needed at all.
I think the main application TI intended it for is for ultrasonic
flow meeters (like [1]). There you have quite small and bounded
start-stop delays. With this they can get into the growing electronics
for low energy building market.
In contrast to that, the Acam devices seem to be general purpose TDCs
Attila Kinali
[1] http://www.shk-profi.de/imgs/52579203_0d4dd378d4.jpg
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Re: [time-nuts] AVAR <-> S_Y conversion
Servus!
On Thu, 05 Mar 2015 14:35:51 +0100
Wolfgang Wallner wrote:
> For the random walk noise the expected line is off by a factor of
> exactly 2 from the calculated plot, and I don't know how to explain this
> behavior.
I'm probably the wrong one to answer, as I have never done any noise
simulation or even read up the relevant papers, but...
A factor of 2 sounds like the difference you would get between one sided
and two sided noise PSD's.
Attila Kinali
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Re: [time-nuts] new tdc from Texas
On Thu, 05 Mar 2015 09:39:44 -0500
Ben Gamari wrote:
> Is this just a function of the ring oscillator
> duty cycle being much smaller?
There has been some development on how to do ring oscillators for
TDC applications in recent years. Driven to a large part by the need
for better (longer measure time, higher resolution, better linearity)
TDCs for all digital PLLs (ADPLL).
I haven't read it completely yet, but Straayers dissertation [1]
gives a nice overview of a couple of methods on how to enhance
ring oscillators for the use as a TDC.
I also find [2] quite nice. They use delay lines to both store pulses
and to stretch them. This enables them to work similar to a
pipeline ADC. (I haven't read the paper completely either, so
i might have misunderstood some stuff)
Attila Kinali
[1] "Noise Shaping Techniques for Analog and Time to Digital Converters
Using Voltage Controlled Oscillators", by Straayer, 2008
http://cppsim.org/Publications/Theses/straayer_phdthesis.pdf
[2] "A 9 bit, 1.12ps Resolution 2.5b/Stage Pipelined Time-to-Digital
Converter in 65nm CMOS using Time-Register", by Kim, Yu, Cho, 2014
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[time-nuts] How does NTP's local clock estimation work in detail?
Moin,
I am a little bit stuck here. I am trying to work out the math behind
a synchronization of clocks problem. It shouldn't be too difficult,
but every couple of minutes I'm getting stuck at some details and it
takes me always a lot of time to get around it. I'm pretty sure that
what I am doing is similar to what NTP does locally after it got an
estimate on it's time difference. I tried to look up what NTP does
but I got lost in the huge amount of papers/presentations.
Could someone point me to some papers that explain what NTP
does locally? If possible in compact form.
Thanks in advance
Attila Kinali
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Re: [time-nuts] How does NTP's local clock estimation work in detail?
On Fri, 6 Mar 2015 17:23:14 +0100 Attila Kinali wrote: > Could someone point me to some papers that explain what NTP > does locally? If possible in compact form. I just send this of into a different direction, but i think it is usefull for some people here as well: ---schnipp--- > Did you find your answer yet? I would be interested too. Yes, Magnus hint with the book[1] was very good. Its chapter 4 gives a nice overview of how it is done, but does not go too much into the details. The other chapters cover a lot of the real world issues that NTP in a nice and concentrated form. For the details the book referes to [2] which covers the algorithm for NTPv3 and [3] which covers NTPv4. There seem some typographical problems with [3] though, which make me unsure about the formulas, without really checking them, but [4] contains them without the typographical problems. The book also mentiones [5], but i have not had the time to have a look at it yet [1] "Computer Network Time Synchronization", 2nd ed, by David L. Mills, 2010 [2] "Improved Algorithms for Synchronizing Computer Network Clocks", by David Mills, 1995 http://www.eecis.udel.edu/~mills/database/papers/tune.pdf [3] "Clock discipline algorithms for the network time protocol version 4", by Mills, 1997 http://www.eecis.udel.edu/~mills/database/reports/allan/secureb.pdf [4] "Adaptive Hybrid Clock Discipline Algorithm for the Network Time Protocol", by Mills, 1998 http://www.eecis.udel.edu/~mills/database/papers/allan.pdf [5] "An Algorithm to Synchronize the Time of a Computer to Universal Time", by Levine, 1995 ---schnapp Attila Kinali -- < _av500_> phd is easy < _av500_> getting dsl is hard ___ 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.
Re: [time-nuts] Motorola Oncore UT+ firmware upgrade & backup power questions
On Sat, 14 Mar 2015 12:56:05 +0100
Mike Cook wrote:
> Anyway. Using a CR2032 is OK, at least with my hardware and you get backup
> for at least 4 years.
A CR2032 is a quite huge coin cell. An NVRAM module does not use much
power once Vcc goes to zero. In todays low power modules it's in the order
of 100nA max specified. You can assume it to be somewhere in the range
of 10nA (probably package leakage limited) and 1uA (something has gone
wrong or very old module). Compare that to the ~240mAh capacity a CR2032
has (terminal voltage at 2.0V). Even assumeing a 1uA current, this will
give you 27 years retention. The limit with coin cells is usually their
self-discharge which is often specified in the 1%/year range, but in
reality gives you a battery lifetime of 10 to 20 years.
Attila Kinali
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Re: [time-nuts] Motorola Oncore UT+ firmware upgrade & backup power questions
On Sun, 15 Mar 2015 03:27:06 -0700 Hal Murray wrote: > att...@kinali.ch said: > > A CR2032 is a quite huge coin cell. An NVRAM module does not use much power > > once Vcc goes to zero. In todays low power modules it's in the order of > > 100nA max specified. You can assume it to be somewhere in the range of 10nA > > (probably package leakage limited) and 1uA (something has gone wrong or very > > old module). ... > > GPS also needs the time, so add on a 32KHz clock. Oops.. right. I totally forgot that. Then it's somewhere in the range of 0.2uA (modern RTC's with NVRAM) to 10uA (really old ones). RTCs do not use that much current as one might think. I "recently" did a MSP430FR5736 based system that had its RTC running and was powered by two SR48 coin cells (~80mAh). Total expected lifetime was 1.5y with all the stuff it had to do. IIRC minimum current consumption we measured was 2.6uA(+/-0.5uA measurement accuracy, total of the whole device). Attila Kinali -- < _av500_> phd is easy < _av500_> getting dsl is hard ___ 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.
Re: [time-nuts] Motorola Oncore UT+ firmware upgrade & backup power questions
On Sun, 15 Mar 2015 11:05:53 -0400 paul swed wrote: > I agree with Atilla from what I have seen. Its actually somewhat difficult > to measure this level of current. It's not that difficult. You just need a good DMM. Standard ones will not work as they have resolution limits in the range of 10-100uA. A semi-decent Fluke handheld gets you already to 0.5uA. If you get a reall DMM, then you will start worrying about the surface currents on your device (FR4 has a quite low surface resistance of 10-100Mohm, depending on humidity and whether you have any finger prints on it) and anything you have in your setup (finger prints, small residues of oily stuff, dirt,...) The bigger problem is, that you have to make sure you have no floating inputs anywhere (inputs are not clearly 0 or 1, will have more input leakage current, additionally to the "shot trough" they cause inside the chip). If you use diodes for decoupling parts of circuitry, you need those with extremely low reverse current (in the low nA) and those will have high forward voltages (>1V, the ones we used had iirc 2V). etc pp Ultra low power electronics is probably as messy a field as ultra low noise electronics. > But all is not lost. Even if the unit is > drawing 1-10ua because something is going wrong. Simply add a battery > holder and 2 X AAA or AA or ... Please be aware that AA and AAA cells have a much higher self discharge than coin cells. A CR2032 is usually of LiMnO2 chemistry, while AA/AAA's are usually ZnMnO2. Also coin cells are optimized for long life times, with very little current drawn, while most AA/AAA are not, or not as much. Ie, i wouldn't expect an AAA cell, and much less an AA cell to last 10 years. Attila Kinali -- < _av500_> phd is easy < _av500_> getting dsl is hard ___ 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.
[time-nuts] Harmonics suppression in ring oscillators
Hi, I stumbled over something that does not seem to be properly documented anywhere. A ring oscillator (like any delay line oscillator) has an infinte number of poles (on the complex plane), which are on a straight line (disregarding the effect that the transistor acts like a first order low pass filter, as f_t is usually a lot higher than the oscillation frequency). This means that a ring oscillator will always excite more than just one mode and oscillate on multiple frequencies. While for (optical/electrical) delay line oscillators, the way to go is to add a frequency selective element, this is not done for ring oscillators. So, how do people keep ring oscillators from oscillating at higher modes? So far, my google skills have failed me to turn up any answer. 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 ___ 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.
Re: [time-nuts] Fwd: Harmonics suppression in ring oscillators
On Tue, 17 Mar 2015 07:52:07 -0700 Alex Pummer wrote: > Hi Attila, just think how all ring/delay line oscillators working: a > status change is traveling trough a delay, and after its arrival at the > next active component it will release a new status change, which will > travel and arrive at the next active component, and after once it will > get back to the "begin of the loop". Basically time which required to > travel between the active devices will determine the frequiency, and > --as it now obvious -- the status change can not release new status > change at the following active component before arriving to that next > active component , therefore self the oscillator can not run at higher > frequency that as it determinated by the delays. Of course depending on > the wave form at the output of the system you could see many other > spectral components Actually, no. If you argue digitally, then you can prove that any odd number of transitions is a valid state of the ring oscillator. There is nothing that a "status change" will latch on until it comes around again. E.g. consider a ring of 9 inverters. The output state of each inverter could be: 0-1-1-1-0-0-1-1-0- I.e. we have 3 transitions in here, and oscillate at 2 times the fundamental frequency. You can even show that something like 0-1-0-1-0-1-0-1-0- is valid, where the oscillator would oscillate at 4 times the fundamental frequency. If you argue analog (the circuit is better described in the analog domain than in the digital), then you can have even higher modes, as long as the Barkhausen Criterion is fullfiled, which are infintely many, if you disregard the unity gain frequency. Even if you take the limited gain bandwidth product into account, the number of possible harmonics is quite high, especially for longer ring oscillator chains. As i wrote, for delay line oscillators, they usually use frequency dependent components (aka filters) to select one harmonic mode and suppress all others. But for ring oscillators, i have not seen any description where any frequency dependent component was used. All they talk about is a chain of inverters. Attila Kinali -- < _av500_> phd is easy < _av500_> getting dsl is hard ___ 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.
Re: [time-nuts] Harmonics suppression in ring oscillators
On Tue, 17 Mar 2015 22:04:49 +0100 Florian Teply wrote: > funnily I stumbled across that very question just a few weeks ago while > doing my very first ring oscillator designs myself. Good, I am not alone.. I felt stupid not being able to find something this basic. > The explanation I have come to is essentially the following: In > principle, you're right, a ring oscillator CAN oscillate at a number of > frequencies. Given the way the ring oscillator works, the list of > possible fundamental frequencies (not considering the spectrum due to > the rectangular waveform with some duty cycle) is essentially given by > (1+2k)/(2*n*td), with n being the number of stages (odd integer), td > being the time delay of one stage (assuming all stages are identical), > and k being any integer between 0 and (n-1)/2. Hm.. so only odd harmonics? What prevents the even harmonics? > The trick here is to have one element in the chain that can be used to > create a steady internal state from which oscillation can be started > predictably. In the 11 stage ring oscillator mentioned above, that > might be a NAND or NOR gate together with 10 inverters. With one input > of that NAND or NOR being tied to the output of the chain and the other > one being tied to a reset input, which can be used to enable or disable > oscillation. A steady state would be reached within 11 gate delays in > the sample oscillator mentioned above after DISABLING oscillation. One > oscillation is reenabled, it will ONLY oscillate at 1/(22*td). Ok, so you are saying, that if you start the ring oscillator in the right way, you get only the fundamental mode. What prevents higher modes from apearing during runtime? What happens if a particle passes trough the oscillator and switches one of the transistors? > Does that answer your question? Most likely it answered one and turned > up three more ;-) Oh.. I have many questions! Too many actually ^^; Is there any good literature on ring oscillators? I have not been able to find anything substantial yet. It's just papers and books that highlight one particluar feature, but nothing else. BTW: Depending on how this project goes, we might work toghether with IHP on it. So I might potentially come over to Frankfurt 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 ___ 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.
Re: [time-nuts] Harmonics suppression in ring oscillators
On Wed, 18 Mar 2015 21:19:55 +0100 Florian Teply wrote: > > Good, I am not alone.. I felt stupid not being able to find something > > this basic. > > > Maybe we are stupid not being able to find something this basic, but > then we're stupid together, so at least we have company ;-) :-) > > Hm.. so only odd harmonics? What prevents the even harmonics? > > Now you got me thinking... > > Based on my train of thought of yesterday, the prevention of even > harmonics is caused by the need of an odd number of stages. Now as I > rethink about it I'm no longer sure that there couldn't possibly any > even harmonic. From what it seems to me now, it doesn't even need to > have an odd number of stages, it just happens to need to have an odd > number of INVERTING stages for it to self-start oscillation reliably. Yes, I have seen reports of ring oscillators with even number of inverters. But all of them said that they needed to kick the oscillator to reliably start it. And yes, if you look at an inverter as an analog amplifier with a negative amplification that is non-linearly dependent on its input, then it is not clear at all, why there aren't any harmonics, both odd or even. My only guess is, that the R_DS_on of the transistors, together with the C_GS of the next stage form a first order low-pass filter that dampens the higher modes, such that the Barkhausen Criteria is violated. I would like to do a simulation of this to get some understanding, but i'm lacking the right simulation software and data of real transistors. (the disadvantage of being in an theoretical computer science group) > > Ok, so you are saying, that if you start the ring oscillator > > in the right way, you get only the fundamental mode. What prevents > > higher modes from apearing during runtime? What happens if a particle > > passes trough the oscillator and switches one of the transistors? > > > Well, assuming that we are talking about sane environments (which your > mentioning of particle strikes basically renders null and void, > pointing to either high energy physics or space applications which can > not be considered sane in this context due to their posssibility to > switch logic states in circuits), all possible causes of introduction of > higher order oscillation are excluded by definition ;-) > Joking aside, the case that one cell is switched should be covered > above. Well.. SEUs are common enough on earth that, if you are talking about high reliability, you need to take them into account. Of course if you are going into space, then it's a rather common event. The goal of what I am doing here is to have a clocking system that can withstand arbitrary faults and self-stabilize again after a number of nodes (not necessarily all) regain their composure and start working correctly again. Part of that is asking all those "what if..." questions that usually get discarded because they have low probability or because people think that the system will stabilize again in that case... maybe. > Hmm, I'm already mentally sorting the list of past and potential > project partners to see where this might lead. In any case, should you > come close to Frankfurt (or Berlin for that matter), notify me so we can > have a beer together. If it's on my boss, even better ;-) I definitly will :-) 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 ___ 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.
Re: [time-nuts] Harmonics suppression in ring oscillators
Moin,
On Thu, 19 Mar 2015 21:50:03 +0100
Florian Teply wrote:
> My guess would be slightly different: the fundamental mode of
> oscillation could be considered the lowest energy state of all
> oscillation modes. Assuming that the system wants to minimize energy,
> this would be the mode to choose if it can't get into a steady state.
> But here we are back in wild guess land, and I'm not even sure that the
> concept of minimum energy states has any meaning in this context.
That argumentation would work if all oscillation modes would have
a single, global energy source with a rate(power) limit.
An example for this are, e.g. lasers. There, the one mode with
the highest gain will suck up all energy from the other modes.
And the pump source replenishes the energy at a fixed, limted rate.
But in a ring oscillator, the energy is provided for each element
seperately and replenished as needed. Ie there is no competition
for energy between the different modes (all switching edges walk
around with the same speed and there are never two edges at the
same gate).
Hmm... maybe the assumption that all edges walk around at the
same speed is wrong?
Attila Kinali
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Re: [time-nuts] Obscure HP T/F instruments in ebay.fr
On Thu, 19 Mar 2015 15:44:07 + "Poul-Henning Kamp" wrote: > > In message , "Tom Van Baak" writes: > > >That is the most stunning collection of old hp gear I've ever seen. > >Given the content, location, and timing it looks to me like it's > >from http://hpmemoryproject.org > >See also http://hpmemoryproject.org/mm_tributes/ > >Can anyone confirm? > > No idea, but that would be a plausible explanation. If that is the case, then this stuff belongs to a museum and not on ebay. IMHO. BTW: i think if time-nuts are bidding on that stuff, it would be a good idea to kind of coordinate who wants what. Otherwise we just drive the price high for no reason. 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 ___ 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.
Re: [time-nuts] Comparing the BeagleBone Black & Raspberry Pi as NTP servers
On Sat, 21 Mar 2015 16:23:30 - "David J Taylor" wrote: > I've just put up my first draft of a comparison of these two popular devices > as NTP servers: > > http://www.satsignal.eu/ntp/BBB-vs-RPi.html > > Comments welcomed - I know it's an imperfect test! Something is wrong here. I would expect the BBB to perform at least as well as the rpi (after all, the BBB has an ethernet MAC with IEEE1588 support, while the rpi is basically a glorified USB controller with attached graphics card). You are most likely running services on the BBB (network services, local services, cron jobs,...) that cause the high, and spikey cpu load, which in turn destroys your ntp performance. Also, compare your results to [1], where Dan Drown uses the capture/compare unit of the AM3359 to timestamp the PPS and use this for ntp. In [2] he tries to measure the temperature dependence of the BBB oscillator (not be best way, but...). Attila Kinali [1] http://blog.dan.drown.org/beaglebone-black-timer-capture-driver/ [2] http://blog.dan.drown.org/tcxo-beaglebone-black/ -- < _av500_> phd is easy < _av500_> getting dsl is hard ___ 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.
Re: [time-nuts] Comparing the BeagleBone Black & Raspberry Pi asNTP servers
On Sun, 22 Mar 2015 09:29:56 -0400 Mike George wrote: > On this page: > > http://elinux.org/Beagleboard:BeagleBoneBlack_Debian#BBW.2FBBB_.28All_Revs.29 > > they list an alternative console only image: > > https://rcn-ee.com/rootfs/bb.org/release/2015-03-01/console/bone-debian-7.8-console-armhf-2015-03-01-2gb.img.xz > > It might be easier starting with that if you don't intend to use graphics. Alternatively, use an embedded buildsystem (e.g. buildroot[1]) so that the image contains only what is really required, and nothing else. There are also several, "preconfigured" buildroot forks for the BBB (e.g. [2]). If you need help with that, send me an email off-list. Attila Kinali [1] http://buildroot.net [2] https://github.com/fhunleth/buildroot-bbb -- < _av500_> phd is easy < _av500_> getting dsl is hard ___ 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.
Re: [time-nuts] Harmonics suppression in ring oscillators
On Fri, 20 Mar 2015 21:26:44 -0700
Hal Murray wrote:
> dmend...@gmail.com said:
> > You mean in a coaxial cable in a loop? It would be very fun... more points
> > if you use a directional coupler to put the pulse in the loop. Anyhow I
> > doubt it would settle to 1 :)
>
> I was thinking of an amplifier in there someplace so the pulse wouldn't decay
> simply due to the cable loss.
This is the description of how a delay line oscillator works.
While it is similar to a ring oscillator, there are certain things
that do not work exactly the same way. Rubiolas book[1, chapter 5]
contains a nice description of delay line oscillators and their
performance.
Attila Kinali
[1] "Phase Noise and Frequency Stability in Oscillators",
by Enrico Rubiola, 2008
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Re: [time-nuts] Harmonics suppression in ring oscillators
On Tue, 17 Mar 2015 11:28:59 +0100
Attila Kinali wrote:
> So, how do people keep ring oscillators from oscillating at higher modes?
>
> So far, my google skills have failed me to turn up any answer.
Ok, sofar i've dug up two papers (and a comment on one) that explicitly
deal with harmonics generation in ring oscillators. One is by Sasaki [1]
and quite old the other is current enough that it seems applicable today.
Sasaki[1] argues, that process variations between transistors
will prevent harmonics in small rings (see also comments in [2]),
but cannot be prevented reliably in large rings.
Bushan and Ketchen[3] on the other hand say nothing about harmonics in long
or short rings, but say that the proper startup sequence will inject
only a single edge into the ring.
Attila Kinali
[1] "Higher Harmonic Generation in CMOS/SOS Ring Oscillators",
by Nobuo Sasaki, 1982
http://dx.doi.org/10.1109/T-ED.1982.20696
[2] "Comments on 'Higher harmonic generation in CMOS/SOS ring oscillators'",
by T.W. Huston, 1983
http://dx.doi.org/10.1109/T-ED.1983.21244
[3] "Generation, Elimination and Utilization of Harmonics in Ring Oscillators",
by Manjul Bushan, Mark B. Ketchen, 2010
http://dx.doi.org/10.1109/ICMTS.2010.5466847
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Re: [time-nuts] Comparing the BeagleBone Black & Raspberry Pi as NTP servers
On Sun, 22 Mar 2015 14:14:01 - "David J Taylor" wrote: > Yes, my posting was at least in part for help with resolving the much higher > CPU load seen on a default BBB installation than on an RPi setup. If you > could provide a list of services and cron jobs to be disabled, and a brief > guide to doing so (as I'm a beginner with Linux) that would be appreciated. Sorry, I cannot. I don't have a BBB to test the image and tell you what it runs. But i can at least guide you trough the steps to figure out what's going on. If you run `ps aux` you will get a list of what processes are active. This is the low level view. The high level view is aquired using `systemctl list-units` You can stop the units you don't need using `systemctl stop ` You can find more information on how to deal with systemd on https://wiki.archlinux.org/index.php/systemd Do not get confused by this being an Arch Linux wiki, it applies to Debian as well. BTW: As Graham wrote Debian is in kind of a transition, though nobody has really decided where it will be going (there are too many people who opose the systemd switch). But unlike what he wrote, there is no mix of init systems. It's either systemd, or it isn't. You cannot have both at the same time. The default image of BBB runs systemd. The second place where to look at are your cron jobs. They can be found in: /etc/crontab /etc/cron.d /etc/cron.hourly /var/spool/cron/crontabs/ The first one (/etc/crontab) is the system wide, old school table that contains all jobs. On a regular debian system, you should have only 4 entries, the monthly, weekly, daily and hourly job scripts. If you have only these, don't touch it. They are necessary. The second one (/etc/cron.d/) is a directory that contains files of the same format as /etc/crontab for specific installed packages. Edit them as you whish (but know what you are doing ;-). The third (/etc/cron.hourly) contains shell scripts that are run once per hour. They are most likely necessary, but might not be. If you don't want/need them, it's best to uninstall the package that they came with. The last one is one (/var/spool/cron/crontabs/) is one you shouldn't touch by hand. These are the files stored by the crontab command, for the respective user. If you need to disable/edit those, use the crontab command. BTW: i reccomend you getting a book on linux. Dealing with embedded devices you will need a good understanding of the inner workings of linux to effectively deal with them. I have heard good things about "linux for dummies" but i have never read it myself. > I had looked at [1] but I'm not using his special timer setup, just GPIO > pins. Unfortunately he doesn't quote any of the usual NTP parameters with > which to compare. Yes. But it gives an idea how stable the oscillator is. You have large deviations of over 10us, which contradict the number Dan Drown is getting. HTH Attila Kinali -- < _av500_> phd is easy < _av500_> getting dsl is hard ___ 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.
Re: [time-nuts] Comparing the BeagleBone Black & Raspberry Pi as NTP servers
On Sun, 22 Mar 2015 16:41:56 -0400
Paul wrote:
> 1) Did you start out using the attached patch antenna? D Drown implies
> successfully using the patch on the Adafruit until it was soldered in
> place. He fixed that by switching to an external antenna. I've never had
> any success with attached patch antennas but my receivers are inside.
The BBB is known to have a bad EMI behaviour. You should not put
any sensitive RF components near it, without proper shielding.
Attila kinali
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Re: [time-nuts] Z3810AS PPS to a Raspberry Pi
On Mon, 23 Mar 2015 19:25:33 -0700 Chris Albertson wrote: > I'm surprised to can't > get the Pi to interrupt on the raising edge of the PPS and that you had to > make the pulse longer. That's because the rpi does not have GPIO's like other SoC or uC. When i wrote that it's a graphics card with attached usb controller, i wasn't joking. The processor on the rpi was originally designed as a test system to verify the graphics core on real workload. To interface it to the outside world, they decided to use USB. For unknown reasons they decided to use an arm9 core with a bit of glue logic as USB controller (the best guess i've heard sofar is, that they would have had to pay for a real USB controller, while an old arm core like that costs (almost) nothing if you buy a big/new one anyways). This is the reason why there are no I2C or SPI interfaces, and everything needs to be bitbanged (aka, you write single bits to outputs in software and poll whether anything changes on the inputs). Or that the "USB controller" generates an interrupt every 125us that _must_ be handled imediatly (the arm core has to set up the next USB microframe otherwise USB stops working). That is also the reason why Eben Upton got it so cheaply. Apparently, broadcom had produced quite a few of those (couple thousand, don't ask me why). And there was no risk that anyone would buy those (for above reasons, they were never intended to be sold). Also, the mask set (the most expensive part of chip production) was already there and amortized by other means, so producing more wouldn't cost much either. Attila Kinali -- < _av500_> phd is easy < _av500_> getting dsl is hard ___ 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.
Re: [time-nuts] M12+ Site Survey
On Tue, 24 Mar 2015 19:52:30 - "Martyn Smith" wrote: > If I then move the unit, for example 30 miles and leave it in position hold > (without doing another site survey) > > How will the accuracy of the 1 pps pulse be affected? > > In this instance, I don’t actually care about alignment to UTC. > > I’m just worried about the accuracy of the 1 pps pulse and ultimately the > accuracy of my rubidium’s frequency. I think you mean "precision" and not "accuracy"[1] :-) If you leave the module in position hold and the module does not realize itself it has been moved, then the PPS will be very jittery. How much, I cannot tell (I have not seen any data of extreme off positions like that). I would guess several ms. But it would be still a pulse roughly every second. Poul-Henning had some experience with "a bit off" position with his M12 due to high solar activity (I've seen it on his webpage, but cannot find it at the moment). He used (uses?) an algorithm with which the receiver can "creep" up to its actual position over time[2]. If you move around often, i would simply disable position-hold and live with "normal" GPS precision, which is better than 100ns for most receivers and good sky view. HTH Attila Kinali [1] http://en.wikipedia.org/wiki/Accuracy_and_precision [2] http://phk.freebsd.dk/raga/sneak/ -- < _av500_> phd is easy < _av500_> getting dsl is hard ___ 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.
Re: [time-nuts] Comparing the BeagleBone Black & Raspberry Pi asNTP servers
On Wed, 25 Mar 2015 09:46:05 -0700
Chris Albertson wrote:
> So if NTP always compensates for network delay why do you get improved
> performance with less delay? That is because what messes up NTP is
> uncertainly in the delay and likely it's the case that reducing the delay
> also reduces the standard deviation of the delay. The other thing the
> messes up NTP is its assumption that the delay is symmetric (that the
> one-way delay = one half the round trip delay) I think reducing the round
> trip time also reduces error in this assumption.
There is another assumption, that most people (especially engineers)
do (and NTP is forced to do), which does not always hold true: that
measurement noise is mean-free and uncorrelated. Especially in this
case, USB delay is definitly not mean-free if you queue up packages
(i would go so far as to say, that USB induced delay is never mean-free)
and has a non-zero auto- and cross-correlation, mediated trough
the USB clock, which is synced to the system clock's source (they
are derived from the same crystal).
AFAIK, and without checking, I think that NTP also makes the assumption,
that the noise is ergodic and time-invariant during measurement.
Again, in the case of USB (and to some extend all network based
communication systems), this does not hold true.
Attila Kinali
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Re: [time-nuts] Need advice for multilateration setup
On Wed, 25 Mar 2015 21:27:35 -0500 Robert Watzlavick wrote: > I'm working on a project that I could use some advice on and also might > be of interest to the list. If it's not appropriate for the list, my > apologies. The gods have apporved of your request. You may speak now. ;-) > I want to develop a tracking system for an amateur rocket that can allow > me to track the rocket even if onboard GPS is lost (as is typical during > ascent and sometimes during descent) or if telemetry is lost. Given you can synchronize the clocks of the ground stations well enough, then the rest is "easy". Then you can get away with having a simple signal generator that only needs an XO. Or you can go for a TCXO to make your signal processing life easier. What you need to do, is actually the same as GPS does: Create a direct spread spectrum signal and track it on all ground stations. The DSSS has the advantage over the single pulse, that it's more resilient against noise and interference. The disadvantage is, that you have to have more complicated hardware. One viable way would be, that you have precisly synchronized sampling systems (e.g. SDR's like the bladeRF which can take an external clock) and then feed the data to a PC where you do the heavy lifting. Then you don't need to build custom hardware at least. Also, if the precision by the DSSS signal is not good enough, you can apply various tricks from the GPS world, like carrier phase tracking, etc. HTH 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 ___ 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.
Re: [time-nuts] Some observations of the BG7T BL GPSDO (John Miles)
On Thu, 26 Mar 2015 18:57:25 -0700
"Willis" wrote:
[u-blox LEA6-T]
> Is it possible that this also has a systematic offset or is this just
> contributing to the observed noise level around the mean?
No, the PPS is calculated from the time send by the satellites.
In worst case, the PPS is off from the real GPS second by transmission
delay (modulo calculation errors). As the error is bounded, the phase
offsest is bounded, which means the (average) frequency offset is zero.
> Being new to the
> concept of GPSDOs I have no idea how much these intrinsic errors in the GPS
> receiver itself bleed through to the performance of the output frequency
> from the OCXO - or is it all masked by the long time constants and filtering
> in the Software PLL loop?
Yes. Most GPSDO's use a PLL, measure the phase of the oscillator
relative to the PPS. There is at least one design that i know of,
which meassures the frequency, thus implementing an FLL. Of course,
this results than in a slight frequency error.
Attila kinali
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Re: [time-nuts] Need advice for multilateration setup
On Thu, 26 Mar 2015 12:32:33 -0500
Robert Watzlavick wrote:
> Thanks for the suggestion. Does the DSSS make it easier to correlate
> between ground stations? I'm not sure how to handle the phase offset
> on the 10 MHz ref clocks.
The DSSS allows you to make the integer ambiguity, you have with all
periodic signals low enough that you dont care anymore. Ie. if you
have a PRN that repeates every millisecond, then your you will have
an ambiguity of n*300km, which you can easily resolve. The other advantage
is that you have multiple edges (not just one, when you have a single pulse)
over which you can average, thus getting a better precision.
The downside of this is, that you have not only to solve for position and time,
but for position, velocity and time (or rather frequency of the oscillator).
The idea with the reference station on ground, to sync up all
other stations is quite good. Then you can use simple DVB-T dongles
(google RTL-SDR) as receivers, which you get almost for free on ebay.
But you pay for that in higher calculation complexity. On the other
hand, adding another measurment station is just another PC + USB dongle.
I think that most of the receiver work can be done with gnu radio
as basis. But i have never done any DSSS system in GR, so i cannot
say for sure.
HTH
Attila Kinali
--
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use without that foundation.
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[time-nuts] audio-visual perception of time (was: Striking change in iPhone time accuracy with 8.2)
On Wed, 1 Apr 2015 16:11:54 -0700 Chris Albertson wrote: > The key jingle experiment is detecting a phase difference between > ears. I was writing about our ability to know if a sound is "in > time" with some other sound. For example if a bass player is keeping > time with a drummer. I figure we can do that to about 20 ms or maybe > a little better. Actually, quite a lot better. I cannot give you any "hard" numbers as I dont have my perception psychology books with me and my google skills fail to locate any good website, but quoting from memory: You can assume that an average human can perceive audio-visual time differences down to 3-10ms (flash to click), with a bit training probably better. Just auditory time differences are quite a bit better, in the couple 100us range (if you can avoid temporal masking effects). But, a word of caution here: lot of the performance of the sensory system depends on the training. Most people do not train neither hearing nor seeing. They are contempt with flickering TV sets or movies where audio is delayed by 30-40ms. They do not even perceive it conciously and ignore it unconciously. But on the other side, if you have someone who trains them, you can have "interesting" results. For example ask one of your nices, who play first person shooters a lot, about the "jerking" special effects in movies. Anyways.. so much from my side on this OT. 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 ___ 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.
Re: [time-nuts] Striking change in iPhone time accuracy with 8.2
On Wed, 1 Apr 2015 23:20:19 -0400
David McGaw wrote:
> There is evidence that the ear can discern differences in timing down to
> the uS range. See a discussion by David Blackmer of DBX and Earthworks:
>
> http://www.earthworksaudio.com/wp-content/uploads/2012/07/The-world-beyond-20kHz.pdf
I am not an expert on hearing, by far not. But this text reads a lot
like half informed, pseudo scientific gibberish, made up from real
facts but distorted heavily to support the point of an audiophool
manufacturer. So i would be very carefull what you take out of that text.
Attila Kinali
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Re: [time-nuts] Need advice for multilateration setup
Moin, On Fri, 03 Apr 2015 22:51:34 -0500 Robert Watzlavick wrote: > On 04/03/2015 10:12 PM, Robert Watzlavick wrote: > > I have an amateur radio license (mostly CW/HF and some VHF/UHF > > experience) and I've written some driver software for an IQ > > demodulation board but I have to admit, I would have no idea how to > > begin setting up that system as initially described by Attila and > > expanded by you and others. I have a rudimentary understanding of the > > modulation schemes involved but I don't fully understand how the > > various codes mentioned fit in. I've poked around a bit at some > > articles on PN codes and I can see how data would be transmitted but I > > think I'm missing something key that allows you to extract positions, > > velocities, etc. out of the various links. I think I have some more > > reading to do :) The basic system is that of an DSSS modulator/demodulator. The best text on spread spectrum systems I have found sofar is [1]. I explains modulation and demodulation in a hands on fashion. But, due to the age of the book, it does not contain any of the advanced stuff done today. But I think you don't need anything more fancy than an early-prompt-late correlator architecture for tracking. For the way how GPS works and how correlation and everything is done, I would suggest [2,3,4]. [2] is a good overview of how GPS is done and contains 99% of everything you need to know (special thanks to Magnus for mentioning it). It lacks some details on how to actually implement the system though. There [3] helps a lot, as it's a book specifically on building a GPS/Galileo receiver. I only skimmed trough a digital copy of [4] yet, so I cannot say too much about it, but that it's probably the most complete book on radio and inertial navigation I have seen sofar. The level of detail seems to vary from topic to topic quite a bit, but it is a treasure trove of references for everything the book covers (which is a damn lot!) If you are tight on time I would probably recommend to start with [3] and have a look at [1] and [2] when things don't make sense. > To head off a bunch of replies - I think I stumbled upon what is being > suggested. To extract the pseudorange, you have to figure out the > offset of the locally generated PN code against the one that is > received. In this reverse GPS case, I assume each ground station would > have to start their local PN codes at the same time? Then you would be > able to get the pseudoranges at each ground station and use those values > for the multilateration equations. You still would have an uncertainty > of one clock cycle since the phases of the local clocks at the stations > wouldn't be aligned but several folks have suggested ways around that. There are multiple things here: * PRN generation: The locally generated PRN has to be time synchronous with the one received from the rocket transmitter. If you are more than one clock period off, you will only get noise out of the demodulator. What you measure is the time difference of the locally generated PRN to your ground station system time. * Uncertainty: The autocorrelation function of a PRN sequence has a quite steep peak at \tau=0 with width of the clock period. Yes, this does mean that you get a one clock period uncertainty, if you do a hit/miss correlation. But as the correlation function is actually triangle shaped, you can get quite a bit better than that. The limit is afaik around your sampling clock period for naive approaches, which you can further improve with some statistics (you have multiple edges to work with, ie can average over those). * Synchronisation of ground stations: There are easy and diffuclt ways to do that. Probably the easiest is to use to use an additional transmitter at the launch point on the same frequency, but with a different PRN than the rocket. This way you can do a difference of the two PRN codes in your receiver, which gets away with a lot of nasty effects that you would need to account for otherwise. Another approach would be to use a GPSDO on each ground station and run all the receivers already synchronized. This also enables you to get the position of all stations very accurately, especially if you let the GPSDO average its position for some time. But for ultimate accuracy, you'd need to calibrate the GPSDO's (including antennas) against each other, to know what the systematic offsets are (ie set them up all together at the same location and measure the time difference of the PPS). Of course, it's possible to use a combination of multiple approaches. Eg a nice one would be to GPSDO's to provide position and a precise frequency reference, but then use a central transmitter for the synchronization. HTH
Re: [time-nuts] Need advice for multilateration setup
On Sat, 04 Apr 2015 08:49:01 +0200
Magnus Danielson wrote:
> This is on either side of the amateur 23 cm band. That's also the first
> band where you have bandwidth enough to fool around with stuff like this
> without breaking the bandplan.
This shouldn't be much of a problem. Using a chiping rate of a couple
of kHz should be enough for this application. The signal strength
can be rather large, directive antennas can be used and the expected
noise level is rather low. So there no need to use a high chipping
rate to compensate for noise effects. Of course, using a higher
chipping rate makes it also easier to get an higher accuracy, but
I would start with something easy to do first, like a 100mW transmitter
in the 70cm band with 10kHz chipping rate (or go to a sub-band,
where 200kHz signals are allowed). With that kind of setup it should
be possible to use something like RTL-SDR for the first experiments
and then gradually upgrade to better hardware to improve accuracy.
Attila Kinali
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Re: [time-nuts] Modern HW replacement for ATOM based NTP server?
On Mon, 6 Apr 2015 22:29:23 + (UTC)
Frank Hughes via time-nuts wrote:
> Looking for a platform not needing a fan. While the ATOM and SSD seem to be
> OK w/o direct airflow, the Mini ITX Power Supply fan is needed.
That depends highly on how much knowledge in linux and especially
embedded linux you have.
If you know how to build your own kernel, what initrd means and today
it's actually initramfs and not initrd and you do not fear to build
whole software systems by hand, then you can go for one of the many
embedded boards. The beaglebone black, the minnow max and SAMA5D come
to mind. The Minnow Max has the advantage of being an x86 based system
and thus behaves very much like it (not completely though). The BBB
has a huge supporting community and you can find a lot of information
online. The SAMA5D based systems are nice because Atmel seems to care
very much about proper support in the kernel.
If you don't feel confortable with the challenges of an embedded
system, i would recommend to stick with an ITX (or smaller) PC.
Eg The APU[1] from pc-engines, which is the successor of his successful
ALIX boards. Pascal Dornier is very helpfull if you have any issues
with his boards, and full documentation (including schematics) is online.
Attila Kinali
[1] http://www.pcengines.ch/apu.htm
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Re: [time-nuts] Need advice for multilateration setup
On Mon, 06 Apr 2015 23:02:01 +0200 Magnus Danielson wrote: > You want to keep your chip-rate up to make the integer ambiguity of the > carrier phase simple. The carrier frequency divided by chipping rate > ratio indicate how difficult problem it is to solve (GPS L1 C/A code has > 1540). The 70 cm band has rather narrow allocations. The 23 cm band > allow for much wide allocations. The benefit of the 70 cm band is > naturally the easy of getting hardware. Yes. But I would do carrier phase tracking only after code phase tracking proved to be not accurate enough. Improving later and switching to another band is relatively easy, once you've proven that the system in principle works. > Another benefit of a higher chipping rate is that it can allow for a > higher bandwidth, allowing for tighter tracking of the rocket dynamics. > The chipping rate at some code legnth creates the maximum tracking rate, > and some fraction of that is the highest bandwidth tolerable. That's a very good argument for higher chiping rates. 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 ___ 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.
Re: [time-nuts] Modern HW replacement for ATOM based NTP server?
On Tue, 7 Apr 2015 17:39:01 +0100
"David J Taylor" wrote:
> "Problematic" if you are after microsecond-level accuracy, perhaps, but so
> would the BeagleBone be. If your needs are more in the 100 microsecond
> range, either would be fine with a reasonably wide PPS pulse.
Not really. If you know how to write C, you can use the
timer on the BBB and get to sub-us accuracy levels (IIRC ~10ns).
The biggest problem would be to get the data into ntp
in the right way, as I am not sure whether ntp supports
that kind of input. But I know at least someone working
on this.
The rpi has, AFAIK, no timer units
Attila Kinali
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Re: [time-nuts] Modern HW replacement for ATOM based NTP server?
On Tue, 7 Apr 2015 17:09:28 + (UTC)
cfo wrote:
> What about the Odroid C1 ?
> http://tinyurl.com/qd7m4cz
I recommend against using an Odroid. What I have heard from friends
is that you do not get any support from the manufacturer in any
way. Which means you have to build your own software stack for
everything, as there is also no community around these boards.
This might work if you have time to tinker, but i guess most
of the people here are less into getting an embedded linux
system working and more into using such a system as an
"black box" tool.
The Cubie borads and the stuff done by Olimex would be also
quite good. Especially Olimex is known for their very good
user support, as they specifically sell to tinkerers and
engineering companies. This also includes that their boards
have almost all I/O pins available on connectors.
Attila Kinali
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Re: [time-nuts] Ultra High Stability Time Base Options for 53132A
On Sun, 12 Apr 2015 16:48:37 -0700 "Richard (Rick) Karlquist" wrote: > Of course you're right, any comparator will add jitter to a 10811. > The faster they are, the more jitter they add. It might be that I'm already too sleepy, but I don't see why a faster comparator would add more jitter. Actually, my intuition (which is clearly wrong) would say the contrary. So, which effect does increase the jitter with comparator speed? > I noticed that the standard 10 MHz oscillator is built with > an ECL line receiver. Another example of Menken's saying. > This is a TERRIBLE oscillator design, but one that would appeal > to the non-initiated. Well, for that you'd need to understand what an oscillator actually is and how it works. The knowledge of that is hardly taught anymore. And those people who know how to properly design an oscillator are either nearing retirement or are already retired. BTW: If anyone here has any good text to read on oscillator design, please let me know. I'm collecting those :-) Attila Kinali -- < _av500_> phd is easy < _av500_> getting dsl is hard ___ 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.
Re: [time-nuts] GPSDO disciplining algorithms
On Mon, 13 Apr 2015 13:03:36 + Alan Ambrose wrote: > I'm interested in GPSDO disciplining algorithms - presumably the good ones > are really well thought out stochastic control algorithms. > > Is it possible to point me to the seminal references / papers / datasheets > that describe typical algorithms and the advantages and disadvantages of the > various approaches? > > I can see, for example: > > http://tycho.usno.navy.mil/papers/ts-2000/gpstime.steering.kmm.ion.sep00.pdf The paper you refer to is a about how to generate UTC(GPS), ie how to stear the clocks of the satellites in order to get a correct time on the ground. It has nothing to do with stearing a GPSDO. You are right that GPSDOs are nothing but control loops with added noise. You can approach the whole thing by standard control theory and ignore noise in a first approximation. The book by Franklin et al.[1] is a good start, IMHO. The next step is to model the system with all non-idealities that affect the oscillator frequency (temperature, aging, retrace,..). The field you want to have a look for this is called "System Identification". For that you will also need to know how a quartz crystall oscillator behaves under different conditions. A good place to start for this is Vig's Crystall Oscillator Tutorial[2], as it contains many references. If you have done that, you can apply addaptive control, ie measure the systems inputs and outputs and guess from that the internal parameters for better control. The generic technique here is called Kalman Filters. But fellow time-nut Marek Peca would tell you that a Wiener filter is better suited[3]. Of course, the field of adaptive control is vast and there are many more methods to have a look at. "Model Predictive Control" might be one of the key words you'd like to search for. If you are asking yourself why I am not refering you to specifc literature on GPSDOs, then I have to tell you that there is hardly any. The best fit for you that I am aware of is [4], but this is nothing other than what i have written above. And you will need to understand these things to understand the paper. Attila Kinali [1] "Feedback Control of Dynamic Systems", by Franklin, DaPowell, Emami-Naeini [2] "Quartz Crystal Resonators and Oscillators", by Vig, multiple versions http://ko4bb.com/manuals/index.php?dir=02_GPS_Timing/John_Vig_Tutorials_on_Crystal_Oscillators [3] "Clock composition by wiener filtering illustrated on two atomic clocks", by Peca, Michalek, Vacek, 2013 http://dx.doi.org/10.1109/EFTF-IFC.2013.6702293 https://rtime.felk.cvut.cz/~pecam1/eftf/ [4] "Adaptive OCXO Drift Correction Algorithm", by Nicholls, Carleton, 2004 http://dx.doi.org/10.1109/FREQ.2004.1418510 -- < _av500_> phd is easy < _av500_> getting dsl is hard ___ 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.
Re: [time-nuts] Ultra High Stability Time Base Options for 53132A
On Mon, 13 Apr 2015 01:16:08 -0400 Charles Steinmetz wrote: > >The faster the comparator, the greater its analog bandwidth. > >Thus there is more total noise to cause jitter. The DC to > >daylight comparator is the opposite of the John Dick (JPL) > >paper on zero crossing detectors in PTTI around 1990. John > >teaches that you use the MINIMUM bandwidth amplifier to > >square up a sine wave. > > For Dick's paper, see: Charles, Rick, thanks for the list. I will work trough it :-) Attila Kinali -- < _av500_> phd is easy < _av500_> getting dsl is hard ___ 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.
Re: [time-nuts] UBlox GPSDO
On Thu, 16 Apr 2015 09:24:02 -0700 Wayne Holder wrote: > According to page 51 of the protocol manual for the UBlox NEO-M* series GPS > modules, the timepulse can be programmed to output a 10 MHz signal rather > than a 1 PPS signal: > > > http://www.u-blox.com/images/downloads/Product_Docs/u-bloxM8_ReceiverDescriptionProtocolSpec_(UBX-13003221)_Public.pdf > > I'm curious if anyone has tried this. Seems like a possible way to get an > inexpensive GPSDO, as these modules are very inexpensive. Yes, this feature has been introduced with the LEA-6T and AFAIK a couple of people were using this output for building an GPSDO. For the main user of this, they introduced a special variant that could directly produce the needed "odd" frequency: the LEA-M8F (you have one guess who the main user of this is ;-) Hint: Set the clock ouput to 8MHz instead, as the internal clock is a 48MHz clock and the timepulse is generated from it by division (or rather a counter). Having an interger divisior avoids quite a bit of phase noise. Additionally, there are two modi at which the time pulse can run: constant frequency or constant phase. The latter will have phase jumps (and thus phase noise) with new fixes (or was it once a second?) to adjust for internal oscillator frequency/phase offset. While the former mode will try to keep the phase continous by keeping the frequency approximately constant (and thus introduce a phase error) (Dont ask me where this is documented, i've found it somewhere in one of the many u-blox documents, many many moons ago) Attila Kinali -- < _av500_> phd is easy < _av500_> getting dsl is hard ___ 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.
Re: [time-nuts] Need advice for multilateration setup
Moin,
On Mon, 06 Apr 2015 07:37:53 -0500
Robert Watzlavick wrote:
> Thank you very much for the references. I had come across [4] when
> searching on Kalman filters for GPS aiding of INS measurements. I
> didn't pay much attention to the GPS chapter at the time but I'll look
> at it again. I just downloaded [3] and it appears to have a good mix of
> practical vs. theoretical aspects. I appreciate the help!
While looking for something completely different[tm] I stumbled over
the paper below. It is definitly not the best paper I have seen, but
it might give you some ideas.
"A reverse GPS architecture for tracking and location of small objects",
by Andrade, Alves, Cuipdo, Santos, 2011
http://dx.doi.org/10.1109/ICL-GNSS.2011.5955273
Attila Kinali
--
< _av500_> phd is easy
< _av500_> getting dsl is hard
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