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    Re: Sextant and iPhone on the QM2
    From: Don Seltzer
    Date: 2013 Dec 5, 08:15 -0800

    There is an interesting thread on this problem at
    https://discussions.apple.com/thread/2434877

    The original poster is a ship's communication officer, so he was quite familiar with different iPhone modes, the general aspects of GPS, and good radio reception. It was his experience with an iPhone that even 35 minutes in a good topside location was not sufficient to acquire a satellite fix.

    As Frank previously posted, it is likely that the problem is lack of current orbital data to work with. This is one of the things that A-GPS provides. An iPhone operating completely autonomously must slowly download this data over many minutes before it can filter out and acquire individual satellite data. Any interruption in reception (perhaps going into sleep mode?) and the download must begin over from scratch.

    In the case of the ship's officer, he found that connecting to the ship's local WiFi data connection, he could immediately get a good fix on his iPhone. This could be simply because the proper almanac info was quickly available to the iPhone. However, it is also be that the ship's WiFi also provided its own GPS-based location data.

    Don Seltzer
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