Hello Mark
By "hosing" do you mean that you lose messages for the next second? That
was a problem with the Resolution T too. I wanted to get ephemerides from
the receiver so I ended up minimising lost messages by tracking satellites
as they popped into view, and then requesting an ephemeris after
The US-based services work fine with non-local data. I've used them with
Australian locations. The IGS network is global so nearby stations in the
IGS network are used for the solution. There are non-US services too, like
AusPos.
The topic of better antenna coordinates seems to come up now and ag
Hello Jim,
There's a Perl script here
https://github.com/openttp/openttp/blob/develop/software/gpscv/ublox/ubloxlog.pl
that's for configuring and logging a ublox NEO-8MT. The caveat is that
it uses a custom file format. However, the associated processing
software, mktimetx,
will read this and prod
India has IRNSS, their own GNSS augmentation system.
FWIW, S Korea is about to start testing its own radio time signal but the
range is only 500 km or so as I remember.
Cheers
Michael
On Thu, 5 Apr 2018 at 12:23 am, Bob kb8tq wrote:
> Hi
>
> It’s also *way* cheaper than putting up your own sate
Hello Arnold,
A frequency offset of a part in 10E-11 still sounds healthy to me. I wonder
whether there is some kind of electronic problem?
I have run 40 or so PRs10s and the lamp is the usual bit that dies.
If you hook up a computer to the RS232 port, there are lots of diagnostics
available.
Che
Sorry, missed the last character in the URL:
https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.118.073601
On Thu, 15 Feb 2018 at 4:42 pm, Michael Wouters
wrote:
> There's a photo here:
>
> https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.118.07360
>
> Che
There's a photo here:
https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.118.07360
Cheers
Michael
On Thu, 15 Feb 2018 at 1:47 pm, Chris Caudle wrote:
> On Wed, February 14, 2018 7:06 pm, jimlux wrote:
> > At substantially more expense, and with an experimental lattice clock,
>
> Does th
our worst
> case path has a foot or so of PVC in it compared to a best case path with
> well under
> a tenth of an inch. That’s going to give you a bit of variation ….. Add
> some dirt or water
> or ice to the equation and who knows what the result might be.
>
> Bob
>
> &
I can see why the geodetic community would worry about antenna phase centre
variation when a radome is installed but is it really an issue in timing
applications? The few papers I've read suggest PCVs of less than 10 mm, or
equivalently, 30 ps. This is at the level of precision available from
post-
If UTC accuracy is your goal then the practical limits are well-established.
National labs operating clock ensembles (multiple Cs , H-masers) with
calibrated time links ( GPS, two way satellite time- transfer) and steering
them to UTC with predictive algorithms typically achieve 5 to 10 ns
accurac
Hello Jim
We are using BeagleBone Black + GPS 1 pps etc in our time-transfer system
You can see the overlays in
https://github.com/openttp/openttp/tree/develop/software/system/device-tree-overlays
Best regards
Michael
On Wed, Oct 25, 2017 at 11:43 AM, jimlux wrote:
> On 10/24/17 5:04 PM, Nick
I've been caught by that one.
Someone used 240V IEC inlets as convenient 10A DC inputs to an oven in an
ion trap. Fiddling around in the back of the racks, I made the inevitable
mistake and Poof! there went $1000 worth of isotopically separated Yb 171.
A few years later, someone else did the same
Try again ...,
Since 1cm of motion is equivalent to 30 ps, there's probably not much point
in putting your GNSS antenna on a geodetic monument if all you care about
is timing. But it does matter if you're trying to track continental drift.
Michael
On Tue, 20 Jun 2017 at 10:44 p
Since 1cm of motion is equivalent to 30ps, there's probably not
On Tue, 20 Jun 2017 at 10:11 pm, Didier Juges wrote:
> If that is not time-nutty, I do not know what will :)
>
> On Jun 20, 2017 7:04 AM, "jimlux" wrote:
>
> >
> > for geodetic measurements, they drill a hole down to bedrock, and r
Apologies, I didn't read the paper carefully enough. The original claim
does appear to be for a comparison of like clocks eg Cs vs Cs, with a claim
of greater effects for a comparison of clocks in and out of the eclipse
path.
Cheers
Michael
On Mon, 29 May 2017 at 8:20 am, iovane--- via time-nuts
The effect you're looking for depends on a comparison of two different
kinds of atomic clocks eg Cs vs H-maser so the maser comparison presumably
will be a null measurement.
But I see the path of totality passes a bit north of NIST Boulder and I'm
pretty sure they will notice if there is an effect
There are 'better' ways of handling gaps when calculating ADEV and
siblings. Patrizia Tavela has a nice method: you pad out the time series,
tagging missing points with NaNs say, and then if a difference contains a
missing data point, you drop it. It works very well. I expect this is in
Stable32. I
Hmm, it appears that Symmetricom has an interpretation from IATA which
classifies their rubidium-containing products as non-hazardous.
I went through all of this some time ago because we were shipping
rubidiums about domestically (Australia) and there was no permissible
maximum qty of rubidium all
Dear Chris,
I believe IATA prohibits the carriage of any quantity of rubidium on
passenger aircraft.
You have to complete a "Dangerous Goods Declaration" and it then has
to go by cargo aircraft.
Cheers
Michael
On Wed, Mar 22, 2017 at 1:12 PM, Chris Albertson
wrote:
> "flight" there is the word
Yes, that's what I was quoted by the Microsemi agent and the price on
Mouser is similar.
The $1568 version was EOL'ed in December 2016; the more expensive unit is
the '2nd generation'.
Cheers
Michael
On Wed, 22 Mar 2017 at 9:06 am, jimlux wrote:
> On 3/21/17 1:40 PM
These are less stable than a rubidium eg tau=10e-11@1000s and monthly
ageing of 9e-10.
The price of these has gone up too- they're now about US5000.
Cheers
Michael
On Wed, 22 Mar 2017 at 7:03 am, Scott McGrath wrote:
> Or perhaps use the Symmetricom CSAC ...
>
> Relatively expensive but might
The Allan deviation is not frequency stability - it's the ADEV of the noise
on the receiver signal.
Cheers
Michael
On Thu, 9 Mar 2017 at 3:00 am, jimlux wrote:
> On 3/7/17 9:29 PM, jimlux wrote:
>
> >> Sent from my smartphone.
> >> Original message From: jimlux
> >> Date: 07/0
y good.
So that means it's not very useful for time comparisons.
Cheers
Michael
On Sat, 25 Feb 2017 at 1:00 am, Bob Camp wrote:
> Hi
>
> > On Feb 24, 2017, at 5:02 AM, Michael Wouters
> wrote:
> >
> > On Fri, Feb 24, 2017 at 10:27 AM, Bob Camp wrote:
> >>
On Fri, 24 Feb 2017 at 9:00 am, Poul-Henning Kamp
wrote:
> Have we talked about this yet ?
>
> https://arxiv.org/abs/1609.06183
>
> https://arxiv.org/abs/1607.03731
>
>
>
> --
> Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
> p...@freebsd.org | TCP/IP since RFC 956
> FreeBSD commit
On Fri, Feb 24, 2017 at 10:27 AM, Bob Camp wrote:
> Hi
>
> I agree with their premise that to be useful you need transportable clocks.
> I’m not quite sure
> that something the size (and weight) of a pickup truck is really
> transportable. Yes one can
> move it around (unlike a small mountain)
One application is advanced network diagnostics eg cards like this:
https://www.endace.com/endace-dag-high-speed-packet-capture-cards.html
So for a 40 GbE card, time-stamping 1 kilobyte packets demands
sub-microsecond accuracy, if you want to compare at different points
in your network.
Cheers
Mi
Dear Attila
You don't need a cryo-cooler, you can just use a cryostat if a break in
operation (when you top up the helium) is not a problem. We operated one of
the UWA CSOs like this as the flywheel for our Yb trapped ion frequency
standard.
A few other national standards labs use the CSOs - one
other lab. The price
was US 2 million and I'm guessing that was "mates' rates".
Cheers
Michael
On Thu, Nov 3, 2016 at 8:13 AM, Attila Kinali wrote:
> On Thu, 3 Nov 2016 07:42:13 +1100
> Michael Wouters wrote:
>
>> One other vital component is the flywhee
the time to do it.
>
> Bob - AE6RV --
> ---
> AE6RV.com
>
> GFS GPSDO list:
> groups.yahoo.com/neo/groups/GFS-GPSDOs/info
>
> From: Michael Wouters >
> To: Discussion of precise time and frequency measurement &l
I worked on a trapped ion frequency standard 20 years ago, a 12.6Ghz Yb
clock. It's still in the lab across from me and looking at it, and the
electronics, I think it is the sort of thing that a physicist might
contemplate building in his/her garage but ...
Building it took about 10 man years of c
Dear Stewart
FWIW, if you do the experiment I suggested (TI measurement on
identical 10 MHZ etc) on a HP53132A counter, you get ADEV = 2.0x10^-10
at 1 second.
The manual says the LSD is 150 ps; when you include trigger errors, it
specifies a resolution of 300 ps. The 200 ps implied by the
measure
Dear Stuart
In a perfect world, your TI measurements would have a uniform
probability distribution function with amplitude 0.5 ns and mean value
0 ns. At least, this is the kind of PDF you would assume for
"resolution error". For this distribution, ADEV is 0.5 ns.
I don't know the HP5334B, perhap
The Red Pitaya is a lower cost (but lower performance) alternative to
the USRP boxes.
I've implemented a RF phase meter using the RP and get about 1 ps time
resolution at an averaging time of 1 s.
The RP analog input side seems to be a bit noisy so loses a few bits.
There was some discussion about
(Restarting the thread with a more apposite topic name)
On Sun, Aug 14, 2016 at 12:47 PM, Mark Sims wrote:
> The NVS NV08C GPS receiver module is a rather nice little 32 channel
> GPS/GLONASS/SBAS receiver that has an output message that gives you the raw
> satellite bit streams. They can be
This board just seems to be the RF front end for a GNSS receiver. You then
have to do the whole business of acquiring and tracking the code, and then
do the PVT solution, at which point you can make your own 1 PPS.
Cheers
Michael
On Sunday, 14 August 2016, Gregory Maxwell wrote:
> On Thu, Aug
The Red Pitaya uses a Zynq, and there's an (unofficial) SDR application
available to experiment with.
Cheers
Michael
On Thursday, 11 August 2016, Chris Albertson
wrote:
> Thanks for pointing out the Zynq. Wow you get a dual core ARM and an
> FPGA all in one package. It seems overkill for a GP
On Sat, Aug 6, 2016 at 9:34 AM, KA2WEU--- via time-nuts
wrote:
> Leeson produced a somewhat random selection of papers , omitting important
> things like the sapphire based best in the word . This was not even
> referenced .
The reference [145] at the end of the sentence that mentions sapphire
On Sat, Aug 6, 2016 at 6:41 AM, Attila Kinali wrote:
> So, best you can hope for is an jitter of ~50us rms within the same
> city with _good_ network connections. Once the distance increases
> and especially if you get routers with conquestion inbetween, then
> the delay and its jitter rise quick
On Wed, Jul 27, 2016 at 8:08 AM, Attila Kinali wrote:
"I am not sure you can apply this definition of Q onto earth."
It doesn't make sense to me either.
If you mark a point on the surface of a sphere then you can observe
that point as the sphere
rotates and count rotations to make a clock. If
I'd be interested to know how 10ns less latency is useful. AFAIK, a high
speed trading system consists of multiple processing nodes, which certainly
could have a 10ns accurate time reference eg via PTP, but latency and
jitter would limit time stamping of transactions to the microsecond level.
Unles
Apropos Bob's comments, the problem of ambiguous timestamps during a
leap second, at least with current operating systems, is only made
worse by more frequent leap seconds.
Making critical systems run on a leap second free time scale like TAI,
for example, just shifts the problem to the interface
Hello Michael
> Thinking out loud, I wonder how bad L1-only, post-processed, would be for
> time-nuts use? Especially with a timing-grade antenna (e.g. the common
> Trimble Bullet). Dual frequency is great when your receiver has the potential
> to move, you have to resolve carrier phase ambiguit
"Full tested by Agilent 53132A with US-012 option and Ex-ref from
trimble thunderbolt
GPSDO."
I think what the seller saying is that the counter was externally
referenced to the Thunderbolt for the frequency measurements that they
state.
Cheers
Michael
On Sun, Jul 10, 2016 at 10:58 AM, Charles S
As a practical matter, in the lab we seldom need a cable delay
measured to better than +/- 0.5 ns, which we usually do as a time
interval measurement, with a 1 pps into a tee on channel A of a TIC
and then the cable from the tee to channel B.
For cables up to 40 m or so, just measuring the physica
The discussion about antenna cable delays made me think of the issue of the
antenna delay. An antenna typically has a bandpass filter and amplifier so
there clearly is some non-negligible delay associated with this.
The issue is usually sidestepped by calibrating the delay of
receiver+antenna (aga
Tom Van Baak said:
"This note is just a plea not to apply the speed-of-light number or
the "nanosecond a foot" rule-of-thumb out of context."
It works reasonably well as a rule of thumb. It's an upper limit but
if you wanted to refine it a bit, divide by two. The average value of
sin(x) on [0,pi
Poor coordinates for the antenna couple into the apparent distance to
a satellite in such a way that the error in the distance tracks a
parabola-shape as the satellite rises and descends, with a
corresponding error in the apparent satellite time. At any instant,
the combination of N satellites then
hard/spend big to get a relatively
modest improvement.
Hope this helps.
Cheers
Michael
On Wed, Jun 15, 2016 at 4:21 PM, Michael Wouters
wrote:
> I should have added, if you do all of the above, the improvement in
> stability over just using a sawtooth-corrected PPS is not all that
>
I should have added, if you do all of the above, the improvement in
stability over just using a sawtooth-corrected PPS is not all that
spectacular, a factor of two or three. I'll post a plot of some data
tomorrow.
Cheers
Michael.
On Wednesday, 15 June 2016, Michael Wouters
wrote:
>
If you followed the link to www.openttp.org and are wondering where the
software is, follow the link on the home page to GitHub and then look in
the Develop branch. The ublox branch is for the new '8' series receivers.
Cheers
Michael
On Tuesday, 14 June 2016, Michael Wouters wrote
Hello Angus
If you have 3 rubidiums of similar stability + 3 counters, you could
do a 3-cornered hat.
Otherwise, GPS common view to a better clock may be an option. If you
are reasonably close to a national standards lab, you might be able to
use their time-transfer files to compare your rubidium
The local clock bias value reported by the Res T is the difference between
the receiver's clock and the reference time scale ( GPS or UTC). You need
it to correct the raw pseudo ranges reported by the receiver, which are
with respect to the receiver's clock.
Cheers
Michael
On Wednesday, 1 June 20
ndesirable.
So for other applications eg a 10 MHz phase comparison where frequency
differences are quite small, the data width could be dropped
significantly.
Cheers
Michael
On Sat, May 28, 2016 at 3:11 PM, Attila Kinali wrote:
> On Sat, 28 May 2016 12:08:18 +1000
> Michael Wouters wrote:
>
&
The following may be of interest to those playing with low-cost SDR hardware:
I also have been looking at low-cost SDR hardware for T&F measurements
and have made an RF phase meter based on the Red Pitaya. The
performance of this was not as good as I was hoping for: the
fractional frequency resolu
Earlier this year, a venerable VP Oncore in one of our systems started
outputting a time of day which was 1024 weeks in the past. This was
presumably because it had some reference time in its firmware which it
was using to resolve the n*1024 weeks ambiguity in broadcast GPS time,
and it was now mor
> Multipath on GPS normally requires a couple of things:
>
> 3) The signal path length has to be close enough that the normal firmware
> does not reject
> the solution.
>
Expanding on this a bit, because it's relevant to the "aircraft
causing multipath" question, the pseudo random noise rang
.
Cheers
Michael
On Sat, May 7, 2016 at 6:05 PM, Michael Wouters
wrote:
> Dear Ilia
>
> Emission of light is a quantum mechanical process. It is fundamentally
> statistical in nature and as someone commented earlier, makes a good
> random number generator. Here's one, f
Dear Ilia
Emission of light is a quantum mechanical process. It is fundamentally
statistical in nature and as someone commented earlier, makes a good
random number generator. Here's one, for example:
http://www.nature.com/articles/srep10214
If you attenuate any light source, lasers included, to
On Thu, May 5, 2016 at 4:53 AM, jimlux wrote:
> On 5/4/16 11:52 AM, Ilia Platone wrote:
>>
>> You got it, however: It only matters relative time. Start and Stop times
>> will be known, and that is solved.
>> Someone has proposed using TV or other broadcasting carrier as reference
>> clock: this ca
Not stable enough unfortunately. An ageing rate of a few parts in 10^12 per
day is typical, which translates to 100 ns. You could be brave and model
that as linear frequency drift to predict the time offset to the required
0.5 ns or so but I suspect that it could be a very frustrating exercise. We
Dear Attila
On Tue, May 3, 2016 at 10:05 PM, Attila Kinali wrote:
>I have some numbers of an project of the ETH that did use standard
>LEA-6T recording the phase data and got in the post processing
>to an uncertainty of <4mm averaging over several hours. Translating
>that to timing resolution wo
One other possibility occurs to me that might be doable with surplus
gear and sticks to the budget. Instead of using WR, give up on
getting time of day and just send a 1 kHz pulse stream in each
direction. Each station then measures against its own GPSDO clock
using a standard/homebrew TIC and rec
les local oscillator to the satellites
> and from there to the other locations.
>
> This should bring you at least down to a 1ns uncertainty level
> (after calibration). Judging from Michael Wouters said, probably
> close to 200-300ps.
>
The number I quoted is for high qualit
Dear Ilia
On Sun, May 1, 2016 at 6:40 PM, Ilia Platone wrote:
> The problem would be modulating a 10GBASE-T signals into a single laser
> beam, and demodulating it using (I think) an APD.
>
The White Rabbit cards use SFP (small form-factor pluggable) lasers
that plug into the card. These incorpo
On Sat, Apr 30, 2016 at 6:14 AM, Magnus Danielson
wrote:
> Well, giving the conditions mentioned, doing ranging codes such as those
> used by GPS is very easy and cheap. Doing this in bidirectional isn't too
> hard. Doing a suitably high chip-rate should cost very little.
I've done two-way time-t
So why not do White Rabbit free space ?
Cheers
Michael
On Sat, Apr 30, 2016 at 4:04 AM, Paul Boven wrote:
> Hi everyone,
>
> On 04/29/2016 03:28 PM, Magnus Danielson wrote:
>>
>> Phase/time transfer over fiber is shaping up, but White Rabbit is
>> starting to grow up and more reports for long di
On Fri, Apr 29, 2016 at 1:18 PM, Bruce Griffiths
wrote:
> Quoting Michael Wouters: "According to this,
>
> http://www.nist.gov/manuscript-publication-search.cfm?pub_id=912449
>
> there are many practical challenges with a one way free-space optical link."
> That p
According to this,
http://www.nist.gov/manuscript-publication-search.cfm?pub_id=912449
there are many practical challenges with a one way free-space optical link.
They were, however, aiming for much higher stability than is needed here.
There are a lot of ideas being tossed around here. It wou
On Wed, Apr 27, 2016 at 7:21 PM, Bruce Griffiths
wrote:
> Stabilising the GPS receiver antenna temperature is probably a good idea
> particularly if it has bandpass filter(s).
It's not so clear that temperature stabilization of the antenna is
necessary. There have been reports of tempcos of 0.2
On Wed, Apr 27, 2016 at 7:51 AM, Attila Kinali wrote:
>
>
>
> Another way would be to use L1/L2 receivers with calibrated antennas.
> I know that BIPM has a GPS station that can deliver time transfer
> accuracy <2ns over a distance of several 100km. It could be possible
> to use such receivers wit
The technique used for dealing with gaps is really about handling random
gaps in an otherwise uniformly sampled sequence. The idea is that you take
your sequence, pad it out with the missing data (tagging those points with
a NaN or whatever) and then when you're computing ADEV, if a data triplet
is
One simple trick I have used many times is to split the TX pin from the GPS
receiver - ntpd really only needs to receive. Some ntpd refclock drivers
will attempt to configure the receiver but if you can ensure that ntpd is
getting the messages it needs, then all should be fine. Otherwise, hack the
ituation with a very
> low
> >> satellite count.
> >> As a single observed satellite goes in and out of multi path, the
> solution
> >> goes all over the place.
> >> Again, you need a challenged antenna for this to happen. Pretty much all
> >> of this
> >>
en. Pretty much all
> of this
> would be apparent from the normal messages out of the part.
>
> Bob
>
>
>
> > On Apr 18, 2016, at 10:13 PM, Michael Wouters > wrote:
> >
> > Does anyone have experience with the Trimble SMT 360 ?
> >
> > I bought
Does anyone have experience with the Trimble SMT 360 ?
I bought some of these four or five months after they were released. During
testing, the 1 pps output evidenced a problem, as shown in the attached
plot (the 1 pps is being measured against a Cs beam standard), which is
not sawtooth-correcte
Dear Sean,
The USNO is the main source of precise time in the US via the GPS system.
It has an ensemble of caesium clocks and hydrogen masers in Washington that
it uses as the reference to provide corrections for the clocks that are
onboard each of the GPS satellites. These corrections are broadca
Dear Bruce
Posted too hastily ...
Since you don't care about absolute time, maybe using identical receivers
you might be able to get a few hundred ps synchronization using a PPP
solution, for example.
Attached is 6 months of data for two Javad receivers, with daily PPP
solutions. The antennas f
Dear Bruce
I think it will be very difficult to achieve synchronization at the level
you want using GNSS signals. The BIPM would only claim 2 ns accuracy for
calibration of the delays in a GNSS receiver plus antenna. When you process
carrier phase data, you typically see jumps at the day boundary
Dear Mike,
I have a Perl script and a C++ application that may be of use. The Perl
script logs continuously, but is mainly for logging TT? responses. The C++
application is used interactively. Either could be modified to do what you
want.
Take a look at:
https://github.com/openttp/openttp/blob/d
Dear Paul,
You are probably thinking of one of these:
Chadsey et al “Maintenance of HP5071A frequency standards at
USNO” in Proc. 29th PTTI, p49-60 (1997)
Chadsey “An automated alarm program for HP5071A frequency
standards” in Proc. 31st PTTI, p649-655 (1999)
Brock et al “End-of-life indicators
Dear Luciano
I run a T&F calibration laboratory.
It sounds like what you're after is a Test Method (TM), which we use as
part of our quality system. Any accredited calibration laboratory will have
documents like this. They vary greatly in their detail according to the
needs of each laboratory, an
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