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  1. #1
    Nat
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    Why does my GPS watch take longer than my iPhone to grab a satellite?

    My GPS watch needs to be outdoors and takes around 5 minutes to grab a signal, whereas Strava or MapMyRide on my phone pretty much locks on immediately, even indoors.

    Do they use different GPS technology, is it a subscriber issue (Strava v. Garmin), or something else?

  2. #2
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    Quote Originally Posted by Nat View Post
    My GPS watch needs to be outdoors and takes around 5 minutes to grab a signal, whereas Strava or MapMyRide on my phone pretty much locks on immediately, even indoors.

    Do they use different GPS technology, is it a subscriber issue (Strava v. Garmin), or something else?

    probably a different gps chip. cellphones with gps also do a-gps, assisted gps, where they will triangulate via cellular to assist the gps system in locating where you are.

  3. #3
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    I have both a Garmin 405 watch and an Edge 800 bike computer. The watch is definitely slower at locking onto satellites than the bike computer. I imagine it is probably a slower internal processor or less sensitive receiver. Sometimes the watch will take 1/4 - 1/2 mile of walking before it'll sync up. The Edge 800 usually locks up while I am putting on my shoes, gloves and helmet. And both cases, the GPS is started up at the same location as it was last shut off. But ever once in a while the watch will lock up before I get out off the front porch, so it can do so quickly at times.

  4. #4
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    Why does my GPS watch take longer than my iPhone to grab a satellite?

    Quote Originally Posted by drwx View Post
    probably a different gps chip. cellphones with gps also do a-gps, assisted gps, where they will triangulate via cellular to assist the gps system in locating where you are.
    I would bet the phone connects to fewer satellites than the GPS units before they "lock."
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  5. #5
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    Quote Originally Posted by shiggy View Post
    I would bet the phone connects to fewer satellites than the GPS units before they "lock."
    there's a good chance of that, especially if it's getting assistance from cell towers. Also, the watch is TINY in comparison. it's got a better processor chip in it (GPS processor chip, not the same thing as the phone's CPU), but the antenna will be TINY. It also matters how long it was since it last had a GPS signal and how far away it was when that happened. The GPS needs to know which satellites to look for, and that information changes over time. This is called "ephemeris".

    Your phone can download ephemeris data from the cellular network. Your GPS cannot. It gets that data from the satellites (there are a couple satellites that specifically send ephemeris data). Their data transfer speed is much slower.

    GPS receivers that connect to the Russian GLONASS system (similar to GPS) frequently connect more quickly. That is one of the features of GLONASS. It's not quite as accurate as GPS, but it offers faster signal acquisition. Connecting to a few GPS birds and one or two GLONASS birds at the same time will also boost accuracy a little bit. Some phones can connect to GLONASS satellites, but still do not have an equivalent GPS processor chip that your watch has. It helps them somewhat to overcome that limitation to have access to more satellites. A dedicated GPS with access to GLONASS birds (like the eTrexes, Edge 510, Oregon 600 series) see benefits, too. I suspect the next generation of watches will begin to add GLONASS support, too.

  6. #6
    Nat
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    Thanks for the input, guys. If there's anything anyone would like to add I'll still be checking this thread.

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