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Houston-We have a problem....78 track drift

First trip out for my 78S on my "Test Hike loop".

Loop is an approx 5 mile Narrow single track only maybe 18" wide which assures user does not vary path trip to trip.

Carried 3 GPSs. A 76CSx, an Oregon 550(SW 3.52 / 4.46) and a new 78S (orig SW2.10) all set with "Auto" and "Most Often" for track logging.

Hike is in canyon country terrain with 4 general areas around loop that give GPSs "fits" with multipath conditions. Traveled CCW around loop.

Carried all three units with cases touching each other high on my right shoulder (that is the shoulder AWAY from canyon wall). This position has previously given the best tracklog from multiple units and multiple trips. Anything that shielded or blocked signals to one should have affected all three equally.
78S was farthest right,outside, 550 was middle, and 76CSx was L of 550 ( but still on right shoulder. It's amazing how much of the composite tracklog displays that positioning.

Short synopsis of results:
The multipath errors today in several spots ate the 76CSx's lunch and spit it out! Seemed OK in areas other than multipath prone areas where it was lousy with a capitol L. Even lost signal in one MP spot.

Oregon 550- Best of the bunch today ! I am proud of the little "pregnant potato"

78S-First results generally good except for three totally random areas where track showed to "go tooling off the trail" (again, physically impossible) then suddenly snap back to reality. I haven't measured amount, but it's noticeable since I was looking for any problems at high magnification.

I can't attach a file but I'll send it to anyone that is interested in looking at it.
78S_1, 78S_2, 78S_3 are the three "drift" areas.

Boyd, I would send it to you ...how?...and you can post it if you like.

Comments

  • Tim 1480 Points
    Carried all three units with cases touching each other
    According to a couple of engineers I've talked to at GPS companies, when comparing multiple GPS devices you want to keep them close together for comparison purposes, but you should keep them six inches apart due to electromagnetic interference. I can't say I've experienced the issue myself-- but I have heard it from multiple industry sources.
  • Good thought!

    I know that definitely applies to the compass(s).

    It's my standard "test" loop, so next trip I'll carry one on my shoulder front high and the other in back high. ....and then swap them for the trip after that.

    And let my 76CSx rest up at home from it's chewing wounds.
  • sviking 141 Points

    According to a couple of engineers I've talked to at GPS companies, when comparing multiple GPS devices you want to keep them close together for comparison purposes, but you should keep them six inches apart due to electromagnetic interference.
    I wonder what their reasoning is for this. The units all receive the exact same signals (multi-path or not) and the mathematical position processing/plotting is done internally. There should be no interference issues as there would be with pulling the electronic compass off or something, as previously mentioned.
  • Marc 301 Points
    I know in the Colorado and Etrex H line there was an effect where the GPS position would slowly but steadily drift off from the actual position to the point where it could be off by hundreds of yards. Power cycling the unit would immediately correct the problem, so it obviously was not due to multipath. My guess is that there are plenty of bugs in the firmware, and this is one of them.
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