GPS Antenna Question

Discussion in 'The Projects Forum' started by JH314, Jan 31, 2014.

  1. JH314

    Thread Starter New Member

    Jan 31, 2014
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    Using GPS in my phone to record a trip, the battery gets drained pretty quickly. A fully charged battery gets down to about 30% in 3 hours. I would like to try building myself a GPS logger, prefer the design to be as small as possible to put in a backpack.

    There seems to be many different choices of selection. Adafruit’s 26mm x 35mm Ultimate GPS Breakout seems ideal, with 15mm x 15mm antenna and 64K internal data logging for about 4K data points. A recent 18mm x 38mm NavSpark with detachable 1”x1” antenna that offers GPS with 50MIPS + 500KB memory for user programming seems another interesting choice.

    My question is how much does antenna size affects GPS performance? Would the Ultimate GPS be a good choice for my application? Or should I choose one with larger 1”x1” antenna?
     
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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  3. poopscoop

    Member

    Dec 12, 2012
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    http://www.i-gotu.com/

    Personal favorite. Software isn't perfect and it loses signal sometimes, but if you're in the market to use GPS logging in a small, power-efficient package, you're going to be underwhelmed. I've dealt with some of the best equipment in the world and I can honestly say it all sucks.
     
  4. poopscoop

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    Dec 12, 2012
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    Also, GPS is processor intensive. That tiny device is searching for a lot of signals and doing a lot of math in real time. One reason your phone loses battery power so quickly is because it is attempting to keep a continuous fix, whereas many of the dedicated loggers sit in standby, get a fix, then return to standby. Its less accurate but more efficient.
     
  5. JH314

    Thread Starter New Member

    Jan 31, 2014
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    Yes I did think of turning GPS on and off periodically to save power. The i-gotu logger using motion sensor is clever, if not moving then no need to turn on GPS trying to log new point. When you say even the best logger equipment still sucks, what do you mean?
     
  6. wayneh

    Expert

    Sep 9, 2010
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    It would be easier to solve the power issue. Just use one of those booster packs that use rechargeable AAs to recharge the phone. It will have uses elsewhere as well, such as recharging an iPhone on the go. I just got an ad in my e-mail for this thing, for instance. Just $14 on sale.

    I use a GlobalSat BT-359 bluetooth GPS puck. My first one got wet so I found one online (new, old stock) for just $15. Tough to beat.
     
    Last edited: Feb 1, 2014
  7. poopscoop

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    Dec 12, 2012
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    Most of the dedicated GPS loggers below a certain size lose signal as soon as it gets too urban or too wooded. Tell me what you're trying to do and what kind of terrain and I'll furnish a better recommendation.
     
  8. davebee

    Well-Known Member

    Oct 22, 2008
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    I've built a couple of gps loggers, and the gps sensor was the primary power drain in all of them. If you do buy a sensor and build your own logger, you'll at least be able to know from the sensor data sheet how much power the sensor is going to need, and with that, you're free to build in battery capacity for as much battery life as you want.

    My really old Garmin sensor drew about 150 mA, quite a lot by today's standards. My newer Polestar PMB-688 with the SIRFstar III chipset only draws about 65 mA.

    I bought the optional external antenna for the Polestar, and it's great - it really increases sensitivity. The Garmin has to be outside, with no trees in the way, to get a lock on satellites, but with the external antenna, the Polestar can get a lock inside my house, not even near a window.

    If you decide to buy one instead of building, I'll second the recommendation of the iGotU. I've got an GT 820-pro with the optional heartrate logger. It was relatively inexpensive and it works great. The online software for displaying trip logs is only ok; I wish it would allow more data manipulation, such as being able to superimpose speed and heartrates for different days of working out over the same route, but it does pretty well for showing logged info on individual trips.
     
  9. wayneh

    Expert

    Sep 9, 2010
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    I'll reiterate my pitch to solve this with existing, off-the-shelf solutions. I use RunKeeper on my iPod to log all my tracks these days, getting the GPS data from an external puck. (There are other good apps too.) If I refrain from looking at the screen, I think I'd get maybe 6 hours before the iPod croaks. A 3-hour bike ride is no issue. The GPS puck I linked earlier will give 10-15 hours, I think, before it needs a recharge.

    If I'm doing geocaching, which requires near constant screen use, the iPod goes dark in a couple hours or so. If I wanted more time, I'd just get that external battery pack.

    The trouble with a DIY solution is software. The many commercial options are quite slick, with web access to saved tracks and so on, and it would be a huge waste of time to write your own programming.

    I've even used an app that gives friends a live update of my track at a custom website. That was great for rafting, so the land team could bring us our lunch!
     
  10. JH314

    Thread Starter New Member

    Jan 31, 2014
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    Thanks for all the answers. Instead of buying off the shelf GPS loggers, I would like to try building one, in the process honing my program skills. For hiking to the hills, visiting some tourist attractions on the weekends …etc., I would expect to turn on the logger, put in backpack and forget about it. Later getting home can retrieve logged data to show on Google Earth the trip taken. The Adafruit’s Ultimate GPS has 15mm x 15mm antenna onboard, and has provision for external active antenna connection. NavSpark already comes with removable 1”x1” internal active antenna, which could also use external active antenna. I’m not sure how size impact reception performance in GPS logger application. If size doesn’t matter much and 15mm x 15mm good enough, I would choosing the Ultimate GPS. If antenna size does matter much, then I’ll choose the latter for its bigger 1”x1” antenna. I don’t expect GPS to be working inside buildings, just normal outdoor use.
     
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