I have only worked with the GPS part of the KS system but some time nuts may be
able to explore the use of the second half and they are available at
areasonabble price Bert KehrenSent from my Galaxy Tab® A
-------- Original message --------From: Bob kb8tq <[email protected]> Date:
10/30/18 5:43 PM (GMT-05:00) To: Discussion of precise time and frequency
measurement <[email protected]> Subject: Re: [time-nuts] Question about
the PLL of Trimble Thunderbold HiThe Trimble Thunderbolt does not have a 1 pps
between the GPS chips and the OCXO. It makes the link between the two portions
of the system in a different way than the typical GPSDO. It uses the OCXO as
the clock reference for the GPS chip set. It then uses phase data on the
received signal to “lock” the OCXO. The whole process is very much unique to
the Trimble product line. To do a mod and extract a PPS, you would need to find
a GPSDO based on something like a uBlox chip set or module. You potentially
*could* cut a trace and inject a new PPS. For most devices, you would also have
to generate the proper “status” messages that go from the uBox (or other
module) to the control loop processor. Some of these messages are in response
to specific queries. Others are generated automatically. Bob> On Oct 30, 2018,
at 4:22 PM, Ferran Valdés <[email protected]> wrote:> > Thank you all for your
answers,> > > > I do have an additional question. Did anybody install an
external 1PPS/10MHz input to the Trimble Thunderbolt board ??> > With the idea
that, when the adjustment loop is deactivated, an external signal can be
supplied to the Thunderbolt, and the Time Interval circuit could show the
difference in between this signal and the feedback of the VCO.> > > > > > @ Bob
kb8tq> > > > The aim of this project has no commercial purposes and the project
itself is to develop the algorithm which will be in charge of adjusting the
clocks. Also is yet to be determined the information that will be exchanged in
between nodes in order to achieve as accurate synchronization as possible.> > >
>> Hi> >> Unfortunately there are no ?stock? boards to do this sort of thing.
If this is a commercial> >> requirement, there are companies who do this kind
of thing on a custom basis. Figure on> >> a few thousand dollars NRE and a
minimum order of a few hundred to get somebody> >> interested. At the ?couple
ps? level, the NRE may be a bit above the few thousand> >> level. Also expect
to supply a full spec requirement when you go shopping ?.> >> Bob> > > >
@Attila Kinali> > > > > > Could you please share a link/name of the paper ? All
information is welcome !> > > > The method that you've developed, synchronizes
4 local clocks in reference to one, or they keep a certain difference all
together in between themselves ?? Which FPGA are you using ?> > > >> I have
something ready, that can synchronize 4 independent clocks> >> to eachother at
the 180ps level, limited by the FPGA based TDC.> >> The current incarnation
does not allow for an external clock source> >> to syncrhonize to, but that
should be easy to add. That is, if you> >> don't mind using some half-finished
we-have-published-a-paper research> >> tool.> > > > Lets say that the objective
is to reach 50ps. Of course is not an easy to achieve goal, but that's the
purpose of the project, to try to achieve as best synchronization as possible
within an strict time frame.> > Part of the project will consist in taking into
account the propagation delay in between the medium used, be it a cable, fiber
or radio link. Still to be determined, but most likely it will be a cable.> > >
> Nice tips on the cables, I will do a documentation research to learn
further.> > > >> But going to ps level of synchronization, especially if you
mean <10ps,> >> is not going to be easy. There are not many ways to measure
pulses> >> with this accuracy. If you know what you are doing, about 1-3ps RMS
is the> >> practical limit you can achieve, more likely it'll be in the order
of 10-30ps,> >> for a one-off design. Also keep in mind that ~2mm of cable is
already 10ps of> >> phase shift. Ie you will need to calibrate your cables as
well. Cables,> >> which are of course low dispersion and low temperature
coefficient cables.> >> The dispersion is important so that your pulse remains
a sharp pulse.> >> through the cable and doesn't come out grabled as a weird
wave packet,> >> Quite counter-intuitively, limiting the slew rate might help
with this.> >> The low TC is important if there is any distance between the
two> >> oscillators. Otherwise you can get up to several ps per ?C temperature>
>> change and meter cable length for run of the mill cables. If you have> >>
PTFE cables, you also want to keep them well above 25?C or well below 15?C,> >>
for the same reason.> >> Attila Kinali> > > > > > > > @Tom Van Baak> > > >> I'm
glad you mentioned your requirements. Note that time synchronization at a >"ps
level" is 3 to 4 orders of magnitude beyond what the typical commercial or
>eBay or DIY GPSDO will do.> > Well, I did a research in order to find suitable
boards, and the ones on eBay got my attention, because they were quite
affordable and were using used GPSDO's from Trimble or Symmetricon. And I saw
some people getting good results with them, so I had to ask.> >> But as you
imply, you're only using GPS to get close (ns levels) and then using your own
two-way communication to narrow it down to ps levels, right?> > Yes, the GPS is
intended to provide a “coarse” adjustment, but even in the case that there's no
GPS signal at all, the nodes will need to synchronize in between themselves
without an external reference but in respect to a single node. As the method
that all the nodes exchange information and correct with each other, would
increase the complexity of the project notably.> > > >> Yes. Section "A.10.31
Report Packet 0x8F-AC Secondary Timing Packet" says:> > > >> "PPS Offset: This
field carries the offset of the PPS output relative to UTC >or GPS as reported
by the GPS receiver in nanoseconds. Positive values indicate >that the
ThunderBolt’s PPS is coming out late relative to GPS or UTC."> > > >> The range
and precision of that time interval value would look something like >this:> > >
>> http://leapsecond.com/pages/tbolt-8d/> > > >> I can send you the raw data if
you want to play with it. Attached is a histogram. Note the standard deviation
is about 2 ns.> > Thanks for the plots !! For the moment is enough just to see
how good the thunderbolt performs.> > > >> Remember that all the ingredients in
your system will then need to be stable to >ps levels: the oscillator, the DAC,
the 1PPS pulse, the cables, the input >signal conditioning, and time or phase
comparator, etc. That's a pretty tall >order but not impossible.> > Yes, is
ambitious, we will see where do I get.> > > >> You may want to synchronize
using 10 MHz instead of 1PPS to reduce your noise >and improve the tight lock.
How far apart are your two oscillators?> > > > The idea of using 1PPS is for
compatibility reasons, but the 10MHz signal sounds like a good idea.> > > > At
the beginning, the oscillators will be maximum 5 meters apart, but at a later
stage, the distance would be increased, depends on how the development
advances.> > > > > > _______________________________________________> time-nuts
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