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    Three GPS data comparison: All different. Huh?
    From: Mark Coady
    Date: 2021 May 24, 10:55 -0700

    The attached .pdf compares 3 GPS simultaneous satellite data outputs  (ok;  cell is 4 sec later to allow time to screen cap after taking pic of bridge outputs).  All were tracking similar Sat groups (pics). 

    1 is a Raytheon GPS on the bridge of M/V Syrena

    2 is the Raytheon Radar system GPS from the bridge of M/V Syrena.

    These two ship GPS have redundant antennas within a very few feet of each other.

    The last GPS output is from a Samsung Android smartphone also operated from the bridge a few feet away at the exact same time to add more data.

    The antenna/reciever location of the three are within a few feet, both altitude and surface locations,  but the sat tracker Azimuth/Elevation output differences surprised me.

    I expected that they would match closely and discrepancies would be small and very consistent.

     Clearly they are rounded to whole numbers, but that does not account for the uneven degree-plus gaps.

     I was expecting the larger azimuth discrepancy is explainable by mag vs true in the output settings of the two devices, based on an expected west variation at location, but it does not explain the other kinks and the varying range of values. (P/S changing from true to magnetic on the phone did nothing to the azimuth when the image regenerated?).

     I get satellites are not geostationary, but the updates are visible & constant so it doesn’t seem like update lag explains anything.

     What am I missing? In celestial we quibble on minutes and tenths...here I am swinging as much 2 degrees in some cases.

    I feel like I have my head in the oven and my feet in a bucket of ice water, but on the average I feel fine.

    Captain Confused

    M/V Syrena



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