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1581Re: Timing Question

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  • Dave Baxter
    Nov 18, 2009
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      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/ 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/

      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/ 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 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 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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