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Re: [dxatlas] Re: Timing Question

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  • Philip Gladstone
    This conversation is a bit puzzling to me. I m not a Faros user, but I am a timing person from way back (I did the original version of the Linux timing code to
    Message 1 of 29 , Nov 19, 2009
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      This conversation is a bit puzzling to me. I'm not a Faros user, but I
      am a timing person from way back (I did the original version of the
      Linux timing code to support NTP).

      In order for Faros to work, it seems that the time on the PC should be
      correct to within a few hundred milliseconds. The normal errors in NTP
      are over the order of a few milliseconds PLUS any latency differences
      between upstream and downstream on the access link. 3G networks do have
      "interesting" latency characteristics -- though I don't know whether the
      upstream latency is significantly different to downstream latency. This
      seems like an interesting experiment to try.

      It would be interesting to see the ntpq output for systems where you
      don't think that the timing accuracy is good enough. In the interests of
      full disclosure, here is mine:

      *tock.usno.navy. .USNO. 1 u 1005 1024 377 30.675 1.084
      0.882
      +cs.columbia.edu clepsydra.dec.c 2 u 4 1024 377 14.186 1.416
      0.705
      CDMA-2.MIT.EDU 0.0.0.0 16 u - 1024 0 0.000 0.000
      4000.00
      +broadbandjam.co ntp.pbx.org 3 u 85 1024 377 104.393 2.772
      1.097
      -14.1e.5546.stat ntp.tmc.edu 3 u 17 1024 377 71.560 -5.013
      2.797
      -198.186.191.229 nist1-la.witime 2 u 524 1024 377 98.060 -4.563
      0.602

      It seems likely that my clock is right to within a few milliseconds.
      Because I am a timing geek, I'm intending to add some local clock
      sources (including GPS PPS).

      Getting time right to less than a millisecond is pretty difficult......

      Philip

      Peter wrote:
      >
      >
      > G'Day all,
      >
      > It seems I am a bit wrong on the info on radio time signals below.
      > There are six standard drivers in the NTP software to take a time feed
      > via radio transmissions - mostly various implementations of WWV and
      > different radios. You can read what you need to do to use them here
      > <http://www.eecis.udel.edu/%7Emills/ntp/html/refclock.html#list
      > <http://www.eecis.udel.edu/%7Emills/ntp/html/refclock.html#list>>. They
      > would not be much use to me here in the Southern Hemisphere, because the
      > signal is subject to fade and too much propagation delay. But, if you
      > are relatively close to a transmitter, they could be worth a go.
      >
      > Most likely, a GPS with PPS output would be much cheaper to implement,
      > and more reliable, than the appropriate radios and antennas in addition
      > to those for Faros.
      >
      > Peter VK4IU
      >
    • Dave
      Okay, Peter, great start, let s focus on GPS with PPS signals. What do we need to do to make that work? Will my Earthmate USB do the trick? Earthmate GPS
      Message 2 of 29 , Nov 19, 2009
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        Okay, Peter, great start, let's focus on GPS with PPS signals.

        What do we need to do to make that work? Will my Earthmate USB do the
        trick?

        Earthmate GPS LT-40 Specs:
        » NMEA-compliant 16-channel receiver
        » WAAS-enabled
        » STMicroelectronics new high-sensitivity Teseo chipset featuring DeLorme
        ConstantLocktm technologies for outstanding time-to-first-fix and signal
        retention
        » Cold start: < 39 seconds
        » Warm start: < 34 seconds
        » Hot start: < 3 seconds
        » Supply requirements: 90mA (through USB connector)
        » Maximum Velocity: 1000 knots
        » Advanced high-sensitivity algorithms for superior tracking in urban
        environments
        » Initial acquisition sensitivity down to -149dBm
        » Weak signal tracking down to -159dBm
        » Proprietary Kalman filter for enhanced position accuracy
        » Superior noise rejection for high EMI environments
        » Environmental Characterisitics:
        › Operating temperature range -40 ºC to +85 ºC
        › Storage temperature range -55 ºC to +100 ºC


        I see nothing here for timing pulse outputs except the NMEA-compliant
        reference.

        I also found this:
        http://wildcard.pctel.com/images_product_overview/pdf_docs/5012D_CE.pdf

        And

        http://wildcard.pctel.com/images_announcements/files/PCTEL_Pricelist_100509.
        xls

        I'm sure there's plenty of others, so what direction do we now go?


        Dave
        /++++++++++++++++++++++++++++++++/





        -----Original Message-----
        From: dxatlas_group@yahoogroups.com [mailto:dxatlas_group@yahoogroups.com]
        On Behalf Of Peter
        Sent: Thursday, November 19, 2009 05:09
        To: dxatlas_group@yahoogroups.com
        Subject: Re: [dxatlas] Re: Timing Question

        G'Day all,

        It seems I am a bit wrong on the info on radio time signals below.
        There are six standard drivers in the NTP software to take a time feed via
        radio transmissions - mostly various implementations of WWV and different
        radios. You can read what you need to do to use them here
        <http://www.eecis.udel.edu/%7Emills/ntp/html/refclock.html#list>. They
        would not be much use to me here in the Southern Hemisphere, because the
        signal is subject to fade and too much propagation delay. But, if you are
        relatively close to a transmitter, they could be worth a go.

        Most likely, a GPS with PPS output would be much cheaper to implement, and
        more reliable, than the appropriate radios and antennas in addition to those
        for Faros.

        Peter VK4IU

        vk4iu wrote:
        >
        >
        > Morning Dave,
        >
        > ... it is 5am here. I'm enjoying the sun rise after 48 hours of storms
        > and hot weather.
        >
        > It looks like our journeys with Faros have a very similar feel to
        > them. But, I am a bit puzzled. While our Internet connections have
        > similar figures for "latency", you are not getting a good result,
        > whereas, here, I have got Faros giving acceptable results.
        >
        > All this discussion that Alex should put more "stuff" into Faros to
        > solve our problems, is missing the point about getting accurate time.
        > The task of Faros is to listen to the sound stream, analyse it, and
        > make a report. Alex has implemented a good solution for time, we just
        > have to deliver to his algorithm time data that is good enough, and
        > his Kalman filter will sort out the variations.
        >
        > Time on the Internet has always been a difficult thing - witness the
        > size of the information on ntp at the SatSignal site. Variability is
        > the order of the day, and the ntpd implementation does a fantastic job
        > of delivery of time under difficult circumstances. The "radio based
        > time services" only exist in the USA and Europe. There are none here -
        > only GPS, which is universal. The world wide radio based time services
        > are just not suitable for what we want to do. The Internet, or GPS,
        > are the only real alternatives for amateur radio. There will never be
        > an RF feed of any sort into an NTP server - its fundamentally not a
        > useful technique - they used an atomic clock to time the broadcast -
        > at the other end it has to be too grossly degraded for use by ntpd -
        > and, with the Internet so wide spread few will be bothered to attempt it.
        >
        > Ones own "time reference" is clearly the solution - if the Internet
        > fails to deliver with sufficient accuracy. The most appropriate is
        > GPS. For around $600 US http://www.beaglesoft.com/stsyhome.htm
        > <http://www.beaglesoft.com/stsyhome.htm> will provide a complete
        > solution - just as Dave has attempted, and I want to implement, right
        > out of the box. Its down side, apart from the price, is the use of a
        > Windows PC. But, I would not be surprised to find one could get a good
        > enough result with it and Faros on the ONE PC.
        >
        > I find the $600 US too expensive, when I can buy the same GPS 18x LVS
        > for about $90 US, and implement my own system using ntpd. I am lucky
        > that I have 30 years experience in IT Technical Support from old
        > mainframes to multiple PC servers and large PC networks. But, Dave's
        > experience with the Garmin 16 LVS has given me plenty of reason to
        > tread carefully. My first look at the sites referenced in my previous
        > messages got me very excited. The devil may be in the serial port of
        > the PC.
        >
        > Dave is correct, in that most of us simply want to know that we can
        > hear the beacons. I want to do a lot more than that. Let me state the
        > problem we are trying to solve as I see it.
        >
        > We want Faros to record observations of beacons, with sufficient
        > accuracy that we: 1) don't miss any observations, and 2) can easily
        > tell short path from long path. Faros time needs continuous time data
        > randomly distributed within about 60ms of the correct time.
        >
        > Using the data we can then: Analyse band openings over time to improve
        > our DX - find/create matching holes in our busy schedules to work DX;
        > Use different antennas and work out the actual radiation patterns -
        > help us tune the antenna; Compare antennas; Study RF propagation; Plan
        > contest operation to maximise our score; Listen in real time during a
        > contest for band openings; Compare QTHs; and lots more I have not
        > thought of yet.
        >
        > Note that I said "we" can tell short path from long path. Let me
        > describe what I do with Faros to help sort out signals, and compensate
        > for minor time variation.
        >
        > I have an ICOM IC-706IIG, and a muli-band vertical antenna, disconnect
        > the antenna when storms are about, but otherwise the system runs
        > continuously. Faros creates a GIF image to a schedule. I personally
        > make little use of them. The Details Panel, and the History panel, are
        > created from, and can be re-created from the beacon logs. So I simply
        > let Faros do its thing day after day. I use a "scheduled task" at
        > 00:01 UTC in Windows, and a free Windows SDK tool, called ROBOCOPY to
        > copy the logs from the Faros directory to a "holding directory" which
        > is "shared" to my network - I carefully avoid the "current" beacon log
        > created at 00:00. When time permits, on anther PC, I start TWO copies
        > of Faros, click on pause, arrange the windows side by side, and on
        > each Details panel, load a beacon log from the month/day I want to
        > analyse/compare from the "holding directory". The "delay correction"
        > on the second PC could be anything - I adjust it to put the signals
        > where I want them - the SP line probably, then make the analysis. If I
        > need to, I save a GIF image of the period for reference in my notes -
        > mainly I use GreenShot or Snagit or MS OneNote to take snapshots of
        > the screen.
        >
        > Clearly if time is all over the place, this technique becomes less
        > useful. But, even with a high, and variable, latency Internet
        > connection I have found acceptable results - that is signals that
        > follow the SP line 90% of the time intra-day, with only small
        > variation over days, small enough that I can compensate with the
        > technique described. The results are good enough one can see the
        > Ionosphere's "path time" changing for some beacons. I would provide
        > images, but the "black hats" on the Internet have caused that to be
        > off limits.
        >
        > As you seem to have discovered with the Garmin 16lvs, the devil is in
        > the detail, in getting any system of anything to work correctly. I am
        > headed in the same direction, I am sure I will need a lot of luck.
        >
        > How can I help you find a "configuration of time servers" that will
        > give you better results. Over time I may be able to help with the
        > Garmin 16 LVS and the Linux software. My Garmin 18x LVS is on back
        > order - I expect delivery in a few weeks, and will implement it over
        > the coming months. These days, I am a "house husband" and I have a new
        > found appreciation for the effort of house wives and mothers and
        > carers. Time to make the troops breakfast!
        >
        > Peter VK4IU
        >
        > Dave Baxter wrote:
        > >
        > >
        > > Hi Peter (David)
        > >
        > > Just got back from a frustrating on site service visit.
        > >
        > > Yes, I know the Satsignal site, and have had a good exchange with
        > > the David Taylor there and have successfully got a FreeBSD machine
        > > suposedly configured to work as needed, from the same distro and
        > > version as he used, but I've yet to get it to successfully see and
        > > work with a Garmin GPS16LVC, that has a PPS output (yes, I buffered
        > > it to RS232 levels.) The problem I have with all that, is I know
        > > next to nothing about that level of tweakage at the kernel level of
        > > any 'nix, that and the 'nix community seems intent on flaming anyone
        > > who asks questions that they do not see as relavant to their latest
        > > and greatest distro. (or more relevantly, they do not themselves
        > > understand.)
        > >
        > > You also it seems found out the hard way what I was told, that the
        > > timing accuracy of the NMEA sentence delivery from any GPS receiver
        > > currently available, is not good enough for time keeping to the
        > > level we need. The eTrex (I have one of the "Yellow" ones too) is
        > > otherwise a good bit of kit, but useless for any accurate timekeeping.
        > >
        > > Also, like you, I've found that protocols like NTP don't play well
        > > with mobile internet services. 3G or otherwise.
        > >
        > > VLF Radio time keeping broadcasts could be another way to go, but
        > > again, the hardware to do the job is prohibitivey expensive, and
        > > none of the PC software I've found so far that can decode signals
        > > like MSF, DCF, WWV etc, provide a true full NTP server function.
        > > (Some do SNTP, that's about the best it gets, and Faros doesnt do
        > > SNTP, only NTP it seems.)
        > >
        > > My ISP issues. Well, (long story short) during the business day,
        > > there seems to be a drastic increase in the network latency getting
        > > to anything, evne in their own domain/network! If that is not bad
        > > enough, it's variable one ping to the next, by a wide margin (10's
        > > to 100's of mS variation, but no packet loss, that is their goal it
        > > seems.) Evenings, early mornings and weekends, Latency is down to
        typicaly 25mS.
        > > During the day, it can go to as much as 500mS, but routinely
        > > stretches out to 150 to 300mS, depending on the exact time of day,
        > > day of week etc. Some days are better, some worse. Watching the time
        > > accuracy plot in Faros, at certain times of day, you can see what
        > > looks like the effect of someone throwing a switch somewhere. I did
        > > some checks, and it's not just me, other users of the same ISP are
        > > experiencing similar effects, though they don't use NTP as we do. It
        > > is however messing with lots of other systems it seems too.
        > >
        > > As a result, it totaly screws up NTP for any sort of accurate time
        > > synching, like Faros needs. Hence why I was messing with FreeBSD
        > > trying to setup a local Stratum 1 server etc. It's getting to the
        > > state at home now, where I am going to take another serious stab at
        > > it, and see if I can get it going on an old early pentium laptop, as
        > > that is much smaller, quieter, and uses less power, than the current
        > > desktop I have sort of working.
        > >
        > > I'd idealy like to have a "Time Appliance", but commercial units are
        > > way outside my pocket money range, and like hen's teeth to find too.
        > > The people who port 'nix etc onto old router hardware are also
        > > uninterested in helping, from the few exchanges I've had on other
        > > forums, and I don't know enough to do it myself.
        > >
        > > I did find this... http://scss.com.au/family/andrew/gps/ntp/
        > <http://scss.com.au/family/andrew/gps/ntp/> But...
        > >
        > > When I asked if he would release a copy of the BINARY (not the
        > > propriatry TCP stack 'C' code from the compiler) he's gone all
        > > silent (like no reply, ever!) Pity, as that seems to be what we
        > > need. Maybe someone else could persuade him to if not release the
        > > BINARY, then perhaps sell pre-programed (and copy protected) PIC's for
        such use?
        > >
        > > For now, Faros bumbles along otherwise OK, but when you look at the
        > > plots, the path charts in the UK afternoon, are often showing a snow
        > > storm of white "unknown" spots. http://g8kbv.homeip.net:8008/
        > <http://g8kbv.homeip.net:8008/>
        > >
        > > As a reception report, most people are interested in the fact that a
        > > beacon has been realiably heard, not what path it was heard by, I think.
        > >
        > > What I'd like to see long term, is GPS PPS support built into Faros
        > > itself, that's where it's needed, NTP could still be used if GPS
        > > reception is not posible, or as a fall back. That alone would make
        > > Faros most valuable when out portable, or for DXpeditions etc. But
        > > of course, only Alex can implement that.
        > >
        > > Another option, but would also no doubt be a major undertaking on
        > > Alex's part, would be to use one channel of the soundcard for the
        > > beacons, and one channel for a radio code input (WWV, MSF etc) No
        > > GPS needed, just two RX's, and one of them could be a realy simple SDR
        like thing.
        > > (Keeping the audio tones very different, so any crosstalk would be
        > > ignored.
        > >
        > > Or, take a pulse train from any of the commonly available miniature
        > > VLF clock receiver modules, into a com port line somewhere, and use
        > > that to set Faros's time.
        > >
        > > That's enough from me I suspect. Oh, one more thing. The Javascript
        > > I use, is more or less that, that is cited as an example to use, if
        > > you look on the main NCDXF IBP site links. http://faros.ve3sun.com/
        > <http://faros.ve3sun.com/> is
        > > where you need to go to start that learning exersize! I make no
        > > claims for originality on that subject.
        > >
        > > Cheers All.
        > >
        > > Dave Baxter
        > > G0WBX.
        > >
        > > --- Original Message ---
        > >
        > > My current plan.
        > >
        > > I initially dismissed creating a stratum 0 reference time server -
        > > the Meinberg PCI card is priced at $3500 in Australia. But ...
        > >
        > > Alex VE3NEA alerted me to the following web site
        > http://time.qnan.org <http://time.qnan.org> I
        > > have ordered a Garmin 18x LVS, $100 n Australia, and I will proceed
        > > to integrate it into my Linux server. On that site there is a
        > > reference to http://www.satsignal.eu/ntp/index.html
        > <http://www.satsignal.eu/ntp/index.html> which is a fantastic source
        > of
        > > information relevant to getting Faros a good time signal. I have
        > > high hopes of having a fantastic Faros installation for propagation
        > > study, site and antenna comparisons.
        > >
        > > Peter VK4IU
        > >
        >
        >


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      • Peter
        Hi Philip, Great to hear from you. I much appreciate the views of someone with your experience. You are correct, I think the interesting characteristics of
        Message 3 of 29 , Nov 19, 2009
        • 0 Attachment
          Hi Philip,

          Great to hear from you. I much appreciate the views of someone with your
          experience.

          You are correct, I think the "interesting characteristics" of my
          wireless broadband link is fundamentally where the problem lies. There
          are significant differences in the two directions in terms of delay,
          particularly as my link goes through a repeater before hitting the phone
          cell and onto the wired network. Also, my link is used by others on this
          local area network - I have at least 6 PCs using the link creating
          congestion. All but two are mine - so I have some control over the
          congestion.

          A college has a wired ADLS2+ Internet connection and has very good time
          for Faros - no problems at all. Interestingly, his "delay correction" in
          Faros is 10ms, mine is 60ms.

          No use is made of the time on the local PC by the Faros software. The
          beacons we are listening to, use a PPS, GPS based time reference. We
          need to be close to the beacon time, so we can know from which direction
          the signal came - the short way around the earth, or the long way around
          - and not too far off, or we miss the beacon completely. Exactly how
          accurate we need to be is difficult to work out as its a factor of many
          things including delays in the PC, the radio, the RF propagation, the
          beacons themselves. Faros has a "delay correction" to compensate for the
          actual delay we experience in the PC and other components. Most
          importantly we need stable time, and then use the "delay correction" in
          Faros to compensate for any offset. That way all the differences in the
          observation of the signal are due to the RF paths, and we can do RF
          propagation studies with the data.

          I'm not sure what "command" you used. Here is my output for one my NTP
          servers - on the same PC as Faros - for the command "peers", a few
          minutes ago.

          remote refid st t when poll reach delay offset jitter
          ==============================================================================
          -mirror.dedicate 128.250.36.2 2 u 79 256 377 58.258 -10.218 4.514
          duffman.springf 210.23.158.201 3 u 98 256 377 98.802 -9.846 33.042
          *cachens1.onqnet 128.250.36.3 2 u 116 256 377 59.203 -12.518 3.518
          +ntp.bigcheese.o 128.250.36.2 2 u 127 256 377 109.652 -22.972 26.313
          hit-nxdomain.op .STEP. 16 u - 1024 0 0.000 0.000 0.000
          +toc.ntp.telstra 203.35.83.242 2 u 238 256 377 72.537 -21.892 6.308

          The above is the result of several weeks of experimentation with several
          lists of servers. I no longer use this local server, or several others,
          with Faros. Faros goes to the server list directly - I get a much better
          result from Faros going directly to the Internet servers rather than
          having the local servers included.

          When I included the local servers in the list of servers for Faros, I
          finished up with Faros giving too high a preference to the local servers
          - small symmetric delay and low dispersion - and "faros time" became a
          straight line following the offset of the local server(s) - a straight
          line with accumulative error as high as 50ms every 15 minutes, which
          then "corrected", sending Faros off in another direction. This sent the
          beacon observations on a roller coaster ride up and down for which the
          "delay correction" in "Faros" was unable to compensate.

          My conclusion was that I needed more "randomness" in the time
          observations made by Faros - to avoid skew in the input to its Kalman
          filter - that is more randomness in the "delay", and offset, so Faros
          would not weight one server over another, allow the Faros Kalman filter
          to do its job, better.

          This has proved correct, as I now have stable time and acceptable
          observations from Faros. Given I seem to be able to implement a GPS
          based solution, the same as the beacons, for around $100 US, and given
          this is my hobby, I choose to attempt the best result I can get - a PPS
          GPS time reference.

          But, fundamentally, I am happy with the NTP time service from the
          Internet - so far, touch wood!

          Peter VK4IU

          Philip Gladstone wrote:
          >
          > This conversation is a bit puzzling to me. I'm not a Faros user, but I
          > am a timing person from way back (I did the original version of the
          > Linux timing code to support NTP).
          >
          > In order for Faros to work, it seems that the time on the PC should be
          > correct to within a few hundred milliseconds. The normal errors in NTP
          > are over the order of a few milliseconds PLUS any latency differences
          > between upstream and downstream on the access link. 3G networks do have
          > "interesting" latency characteristics -- though I don't know whether the
          > upstream latency is significantly different to downstream latency. This
          > seems like an interesting experiment to try.
          >
          > It would be interesting to see the ntpq output for systems where you
          > don't think that the timing accuracy is good enough. In the interests of
          > full disclosure, here is mine:
          >
          > *tock.usno.navy. .USNO. 1 u 1005 1024 377 30.675 1.084
          > 0.882
          > +cs.columbia.edu clepsydra.dec.c 2 u 4 1024 377 14.186 1.416
          > 0.705
          > CDMA-2.MIT.EDU 0.0.0.0 16 u - 1024 0 0.000 0.000
          > 4000.00
          > +broadbandjam.co ntp.pbx.org 3 u 85 1024 377 104.393 2.772
          > 1.097
          > -14.1e.5546.stat ntp.tmc.edu 3 u 17 1024 377 71.560 -5.013
          > 2.797
          > -198.186.191.229 nist1-la.witime 2 u 524 1024 377 98.060 -4.563
          > 0.602
          >
          > It seems likely that my clock is right to within a few milliseconds.
          > Because I am a timing geek, I'm intending to add some local clock
          > sources (including GPS PPS).
          >
          > Getting time right to less than a millisecond is pretty difficult......
          >
          > Philip
          >
          > Peter wrote:
          > >
          > >
          > > G'Day all,
          > >
          > > It seems I am a bit wrong on the info on radio time signals below.
          > > There are six standard drivers in the NTP software to take a time feed
          > > via radio transmissions - mostly various implementations of WWV and
          > > different radios. You can read what you need to do to use them here
          > > <http://www.eecis.udel.edu/%7Emills/ntp/html/refclock.html#list
          > <http://www.eecis.udel.edu/%7Emills/ntp/html/refclock.html#list>
          > > <http://www.eecis.udel.edu/%7Emills/ntp/html/refclock.html#list
          > <http://www.eecis.udel.edu/%7Emills/ntp/html/refclock.html#list>>>. They
          > > would not be much use to me here in the Southern Hemisphere, because the
          > > signal is subject to fade and too much propagation delay. But, if you
          > > are relatively close to a transmitter, they could be worth a go.
          > >
          > > Most likely, a GPS with PPS output would be much cheaper to implement,
          > > and more reliable, than the appropriate radios and antennas in addition
          > > to those for Faros.
          > >
          > > Peter VK4IU
          > >
          >
          >
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