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Systematic differences in GPS antennas  


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(@totalsurv)
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I am testing elevation results on 2 different GPS antennas one being a Topcon PGA and the other a Topcon Hiper. There seems to be a consistent difference of 15mm between the 2 antennas on the same points. This is is with days of static data on each, different locations, correct antenna models in Magnet tools, correct height measurements etc.

Is it normal for there to be a systematic difference in antennas like this? The PGA is meant to be better for static so I will probably rely on that more.

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Paul in PA
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I recall that being a persistent problem with certain Topcon antennae from several years ago. Do a search to see if there ever was a correction established.

Paul in PA

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@paul-in-pa

I am not finding anything other than a previous post of mine. Is it here you have seen it?

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Rover83
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@totalsurv

I believe this thread is the one referenced.

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Paul in PA
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The thread I am thinking about may have been on another board in another place. Do not know if it is still accessible in some way.

As I recall a suggestion was to first test the receivers/antennas  in the manner of a peg test. Observe, swap positions and reobserve to check the differences.

Paul in PA

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Loyal
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Posted by: @paul-in-pa

The thread I am thinking about may have been on another board in another place. Do not know if it is still accessible in some way.

As I recall a suggestion was to first test the receivers/antennas  in the manner of a peg test. Observe, swap positions and reobserve to check the differences.

Paul in PA

You might be right Paul, I remember the thread/discussion as well, but I don't remember when or where it was.

CHECKING (empirically) all of the antennas used in a given survey used to be SOP for me. I have a half-dozen or so Novatel 502 antennas, of which all but TWO are AeroAntenna AT2775-19(s), but the other two are AreoAntenna AT2775-42(s). They look identical and even have the same "Phase Center Offset" stickers, but the NGS calibration data IS different between the two "models." I don't recall how much different (not much), but it was enough to be concerned about.

I verified the NGS ARP-L1 data by spending a few days in the backyard, and added my 503 Choke Ring antennas into the test for good measure.

Loyal

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thebionicman
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Run the elevation checks through alternative software if possible. I've caught two major releases that applied the vertical offset twice. One was an early version of topcon office software.

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