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RE: [tracker2] How to deal with GPS drift with OT2?

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  • Fred Hillhouse
    I got a brand new GlobalSat BR-355 SiRF GPS which I use on the secondary port of the OT2. Unfortunately, I discovered that the position is drifting severely
    Message 1 of 16 , Nov 2, 2009
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      I got a brand new GlobalSat BR-355 SiRF GPS which I use on
      the secondary port of the OT2. Unfortunately, I discovered
      that the position is drifting severely when the car is parked
      for several hours at the same place (covered or uncovered),
      sometimes up to 300ft. This may be due to reflections.
       
      This is a common. The satellites are always moving in the constellation. I wonder if your receiver is more sensitive than mine. Or does mine have more filtering to keep from ping-ponging me around. Covered is usually not a good place place to park for a GPS, especially if it is a metal cover. Any signal it receives will be either from low on the horizon or reflecting from some other surface. Judging by the overhead view, your view to the horizon is blocked.
       
      I tried with WAAS enabled and disabled, 
       
      This will only matter if you can actually see the WAAS satellites. They are geo-stationary which means they are lower in the sky (New England anyway). Building, trees will attenuate then quite a bit. BTW, with software packages like Orbitron you can see where in the sky the WAAS satellites are as well as the regular constellation.
       
      I found this to be an interesting and educational read.
       
       
      and with Static Navigation enabled and disabled and get the
      same problem. Static Navigation is supposed to fix this by
      correcting the coordinates if the calculated position moves
      slower than 1.6 m/s. It does not work: calculated moves
      are grater than that. 
       
      If the GPS is turned off then the last valid location will be remembered as used. However, turning the GPS off means that there is a delay until the unit reacquires. A relay breaking the GPS TX line to the T2 might serve well. I have not tried that but it may work for you.

      I contacted the manufacturer and they said
      the best option is to have the software deal with it. 
       
      That is true in regards to their GPS. Some units do some filtering, some do none. Yours apparently does none and may be more sensitive as well.

      Does anybody sees how to eliminate drift in the OT2?
       
      I saw other answers like increasing your slow speed. That is a good direction to try.
       
       
      Best regards,
      Fred
    • Bob Poortinga
      ... He is probably referring to the Static Navigation option that can be configured for SiRF III GPSs by using the SiRFdemo software. I wonder if Bernard has
      Message 2 of 16 , Nov 2, 2009
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        "Keith VE7GDH" <ve7gdh@...> writes:

        > What do you mean by "Static Navigation"?

        He is probably referring to the "Static Navigation" option that can be
        configured for SiRF III GPSs by using the SiRFdemo software.

        I wonder if Bernard has tried "Track Smoothing" or increasing the acceptable
        minimum signal satellite strength and turning off degraded mode and dead
        reckoning?

        --
        Bob Poortinga K9SQL <http://www.linkedin.com/in/bobpoortinga>
        Bloomington, Indiana US
      • Scott Miller
        ... If you have AUTOSAVE on in profile 2, you can set profile 2 to BMODE FLOW, or anything but AUTO, and it ll lose GPS lock and save the last position.
        Message 3 of 16 , Nov 2, 2009
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          > I was wondering if using the AUTOSAVE followed by POSITION X,Y commands
          > when entering Profile 2 would let the OT2 save the last known fix rather
          > than X,Y if X,Y are given special values like 0,0 or illegal values.

          If you have AUTOSAVE on in profile 2, you can set profile 2 to BMODE
          FLOW, or anything but AUTO, and it'll 'lose' GPS lock and save the last
          position.

          Scott
        • James Ewen
          ... Take a look at your surroundings... If you park the car nose in, you ve got a wall and car port with a roof that looks to be at least 9 feet high right in
          Message 4 of 16 , Nov 2, 2009
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            On Mon, Nov 2, 2009 at 1:43 AM, ki6tsf <ki6tsf@...> wrote:

            > I posted a pict showing GPS drift at http://groups.yahoo.com/group
            > /tracker2/photos/album/411553253/pic/812065518/view?picmode=
            >&mode=tn&order=ordinal&start=1&count=20&dir=asc
            >
            > That's not very nice for a portable or mobile digipeater.

            Take a look at your surroundings... If you park the car nose in,
            you've got a wall and car port with a roof that looks to be at least 9
            feet high right in front of the car. Behind you is a 3 storey
            building, maybe 30 feet away. At least you didn't park under the tree.
            (Gotta love Google Streetview!)

            You'll have blocked views of the horizon for most of the azimuth
            around you. The 3 storey wall behind you will probably bounce signals
            like crazy, leading to position accuracy problems with the GPS.

            If you put a relay in the data line between the GPS and the OT2,
            triggered by the accessory line in the vehicle, you will basically
            disconnect the GPS from the OT2. Configure the OT2 to use the last
            known position. Leave the GPS power on constant 12 volts, and the GPS
            will always be active, leading to faster position acquisition when you
            start the vehicle. (By faster, I mean instantaneous, unless you have
            parked in an underground or covered parking area)

            James
            VE6SRV
          • ki6tsf
            Hello, Thank you to all who replied and for all the suggestions! Yes, Static Navigation is a feature built-in in SiRF III-based GPSs and I used SiRFDemo to set
            Message 5 of 16 , Nov 2, 2009
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              Hello,

              Thank you to all who replied and for all the suggestions!

              Yes, Static Navigation is a feature built-in in SiRF III-based
              GPSs and I used SiRFDemo to set it. It is supposed to eliminate
              drift. I'll check with SiRF directly if they can advise how
              to tune it.

              Actually yes, I enabled Track Smoothing too and that didn't help.
              I have not raised the satellite signal strenght threshold, this is
              next on my checklist.

              I set degraded mode and dead reckoning on (I found it really cool
              to have a GPS receiver that supports those modes!!!). I'll have
              to try with these features turned off.

              Anyways I hope a combination of all or some of the suggestions
              received on this newsgroup will solve that drift problem!

              Thanks to all,

              Bernard KI6TSF

              --- In tracker2@yahoogroups.com, Bob Poortinga <bobp+yahoo@...> wrote:
              >
              > "Keith VE7GDH" <ve7gdh@...> writes:
              >
              > > What do you mean by "Static Navigation"?
              >
              > He is probably referring to the "Static Navigation" option that can be
              > configured for SiRF III GPSs by using the SiRFdemo software.
              >
              > I wonder if Bernard has tried "Track Smoothing" or increasing the acceptable
              > minimum signal satellite strength and turning off degraded mode and dead
              > reckoning?
              >
              > --
              > Bob Poortinga K9SQL <http://www.linkedin.com/in/bobpoortinga>
              > Bloomington, Indiana US
              >
            • k7ybz
              When I originally read your post I was thinking unit sensitivity of the BR-355 compared to Garmin pucks. I had remembered reading the sensitivity of the BR-355
              Message 6 of 16 , Nov 2, 2009
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                When I originally read your post I was thinking unit sensitivity of the BR-355 compared to Garmin pucks. I had remembered reading the sensitivity of the BR-355 as being around -160 and Garmin around -185.
                Then I went back and looked at the specs again and noticed Garmin specifies their sensitivity as dBW and everyone else specifies it in dBm. There in lies the difference (and another Garmin marketing ploy): 0dBW = +30dBm.

                Ahhh, the numbers game!

                I may have missed where the puck was placed, but the puck is much better off on the roof of the vehicle than on the dash. On some units, the magnet can be removed and mounted directly to a surface. I did not investigate this for your particular unit though.

                Larry
                K7YBZ

                --- In tracker2@yahoogroups.com, "ki6tsf" <ki6tsf@...> wrote:
                >
                > Hello,
                >
                > Thank you to all who replied and for all the suggestions!
                >
                > Yes, Static Navigation is a feature built-in in SiRF III-based
                > GPSs and I used SiRFDemo to set it. It is supposed to eliminate
                > drift. I'll check with SiRF directly if they can advise how
                > to tune it.
                >
                > Actually yes, I enabled Track Smoothing too and that didn't help.
                > I have not raised the satellite signal strenght threshold, this is
                > next on my checklist.
                >
                > I set degraded mode and dead reckoning on (I found it really cool
                > to have a GPS receiver that supports those modes!!!). I'll have
                > to try with these features turned off.
                >
                > Anyways I hope a combination of all or some of the suggestions
                > received on this newsgroup will solve that drift problem!
                >
                > Thanks to all,
                >
                > Bernard KI6TSF
                >
                > --- In tracker2@yahoogroups.com, Bob Poortinga <bobp+yahoo@> wrote:
                > >
                > > "Keith VE7GDH" <ve7gdh@> writes:
                > >
                > > > What do you mean by "Static Navigation"?
                > >
                > > He is probably referring to the "Static Navigation" option that can be
                > > configured for SiRF III GPSs by using the SiRFdemo software.
                > >
                > > I wonder if Bernard has tried "Track Smoothing" or increasing the acceptable
                > > minimum signal satellite strength and turning off degraded mode and dead
                > > reckoning?
                > >
                > > --
                > > Bob Poortinga K9SQL <http://www.linkedin.com/in/bobpoortinga>
                > > Bloomington, Indiana US
                > >
                >
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