How to find your Grid for VHF work

Discussion in 'Ham Radio Discussions' started by KJ4RT, May 24, 2020.

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  1. AF7TS

    AF7TS Ham Member QRZ Page


    It is possible that the survey markers are in exactly the correct place if you use the correct geodetic datum. It is also possible that these markers were in the correct place but moved because of plate tectonics, in which case they might still legally define the border and thus be in exactly the right place by definition.

    My favorite story along these lines is the location of the prime meridian at the Greenwich Observatory. If you go to visit, you will see a line marked in concrete and metal on the ground, identifying the prime meridian. If you pull out your GPS unit, you will find that the prime meridian is off by about 100 meters. It turns out that if you start at the actual observatory definition of the prime meridian, and go straight up as defined by local gravity, then the angle that you would be traveling is the angle of the prime meridian, within modern experimental accuracy. However local vertical (again, as defined by local gravity) misses the center of the Earth by about 100 meters. With GPS, the defined reference frame shifted to the actual center of the Earth, thus the apparent error.

  2. WN1MB

    WN1MB XML Subscriber QRZ Page

    Removed by poster.
    Last edited: May 24, 2020
  3. W6RZ

    W6RZ Premium Subscriber QRZ Page

  4. KG5THG

    KG5THG Platinum Subscriber Platinum Subscriber QRZ Page

  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Anything's possible I guess, but in the case of the California markers, a couple were miles off, not hundreds of feet but actually miles.

    In fact, they showed a little restaurant in "Oregon" (near the CA border) that had been in operation for several decades and based on GPS location, was actually in California.:p Bad to find this, because if it was really in CA, they should have been collecting CA sales tax and paying CA business tax for a long time and weren't. They may be "grandfathered" in without paying back taxes because per the geodetic survey markers, they appeared to be in Oregon.;)

    We do have substantial seismic activity so maybe stuff really did shift that much over time, but that seemed like a lot of shifting.
  6. KP4SX

    KP4SX Premium Subscriber QRZ Page

    Surveyors make mistakes too! Hopefully fewer than in the past.
  7. KT1F

    KT1F Ham Member QRZ Page

    The perils of floating point numbers. This caught my eye today while making an order from Whole Foods.
    Screen Shot 2020-05-24 at 12.30.28 PM.png
    Last edited: May 24, 2020
  8. AF7TS

    AF7TS Ham Member QRZ Page

    That is a pretty huge error by survey standards. And there has been quite a history of such errors. I guess once you put a number down on a treaty, then things can get screwy when your surveys get better and the border has to move with the numbers.

    And according to an article in the Guardian " Louis XIV is said to have quipped that his astronomers had lost him more territory than his generals had won."

    Several news articles say that it is a real error. Pretty impressive, although given the technology of the day pretty impressive how close they got it right. When measuring longitude, an error of 1 second in time gives an error of about a quarter mile at the middle latitudes.

  9. AF7TS

    AF7TS Ham Member QRZ Page

    What did the do with the other 0.00000000000000003 oz????
  10. KP4SX

    KP4SX Premium Subscriber QRZ Page

    Talk about losing area...St Kitts-Nevis topped the list and the foolish local newspaper bit the bait and published it.
    None of the brainiacs took into account that Anguilla is no longer in the Federation as it was in 1961.
    They say that approx 34.7 sq miles were lost. That conveniently matches the size of Anguilla, duh.
    #2 Ecuador lost some land to Peru in various border disputes. Not sea level rise or erosion.
    Like Abraham Lincoln said, "don't believe everything you read on the interwebs".

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