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Old 09-26-07, 06:36 AM   #1
tandemonium
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GPS that works under tree cover

I need advice on a basic GPS to offload mapped trails . I don't care about heart rate monitoring or cadence. I just want it to work consistently. - had to return a 'sports model' as it was dropping out every time I was in a valley or under trees. What really works?
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Old 09-26-07, 07:31 AM   #2
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Whenever there is something near or above your antenna that the signal can be bounced off (leaves, buildings, water, etc.) the accuracy of your solution will suffer. A WAAS or GLONASS enabled receiver can help, but that's about the best you'll be able to do with consumer grade equipment.
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Old 09-26-07, 08:16 AM   #3
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Units with an external antenna work better. I have a Garmin III+ (older model) with an external antenna that does fine in the woods. Also have an eTrex (internal antenna) that seems to stop working if I so much as look at a tree half a mile away.

If you're in mountainous terrain with heavy tree cover and a poor satellite spread, you're probably going to have problems with reception no matter what.
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Old 09-26-07, 08:31 AM   #4
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It depends on the thickness of the cover. The suggested external antenna is a good idea. One of the planned upgrades to GPS is a stronger signal level and advanced receiver processing to eliminate the problem. These are a few years away I believe.

In the first Gulf war, the thick smoke from the burning oil fields could also interfere with reception.

Al
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Old 09-26-07, 08:42 AM   #5
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I have the Garmin 60CSX and has been a serious trooper. It picks up satellites usually under 1 minute, and works in the cup holder between the front seats of my truck just as well as it does outside.

I have been under heavy tree cover, and heavy cloud cover and had some good results. BUT, there will be times when it just ain't gonna work, but it is not often with this unit. Last week, I was at 4500 feet going around the mountain with some heavy clouds, and it didn't work well at all for about 30 minutes, but after that it came back. It was weird. But all in all, this newer antenae is great! It retails for $450, but CHECK THIS OUT! and it has a $50 rebate.

If your going to but one, this is the one. It is also remote antennae capable if you need it. Oh, sorry, you wanted basic. This is far from basic, but will do everything you ever want.
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Old 09-26-07, 08:50 AM   #6
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External antennae. Failing that, bigger modern units like the Garmin 76 series (i.e. bigger internal antennae).


If the goal is to map trails with tracklogs, Trimble used to make a free program to predict when the best satellite view will be, based on your input location and skyview, so you can schedule your trail mapping based on best signal times. You can probably download it somewhere. But the best accuracy, alas, tends to be at night in the winter, with the minimal atmospheric and leaf interference.
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Old 09-28-07, 06:39 AM   #7
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So far, the 60csx or 76 series look like good solutions. With the coupon discount the 60csx deal is similar to the Etrex that I had issues with. Mapping is important . -looks like I have a few manuals to read to discern the differences.
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Old 09-28-07, 12:05 PM   #8
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i just got the 60csx. i can get up to 18 foot accuracy in my house! it's rediculous and has wonderful reception. Took it into the bell river valley for a three day trip and never had trouple finding a signal. REI had them for about 300 dollars (including the $50 dollar mail in rebate) durring there memorial day sale. i'd say go for it. it's a beautiful unit.
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Old 09-28-07, 12:29 PM   #9
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i can get up to 18 foot accuracy in my house!
Just curious - how did you determine that?
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Old 09-28-07, 12:48 PM   #10
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It seems pretty obvious. Stand at one end of your house and see where the GPS is telling you were you are. Then just calculate the distance with a tape measure.
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Old 09-28-07, 12:56 PM   #11
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And how many people know the exact UTM coordinates of the corner of their house?

The GPS provides an estimate of it's own accuracy based on a number of factors that you can wiki. Keyword is "estimate".

I have found that due to signal reflection, the accuracy of a unit in a building (if such a location solution can be obtained) tends to be a function of the size of said building.
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Old 09-28-07, 02:04 PM   #12
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and remember, you need atleast 3 satelites to get an accurate reading
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Old 09-28-07, 02:15 PM   #13
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i get five satellites indoors. the 18' estimate is a function of the unit itself.
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Old 09-28-07, 03:22 PM   #14
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The estimate of the unit is one of precision, not accuracy. Accuracy levels of recreational grade receivers are plus or minus 10 meters horizontally in optimal conditions, and significantly worse in high multipath environments (e.g. inside buildings).

And norco_rider77, it takes at least 4 SV's to resolve a position.
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Old 09-28-07, 04:35 PM   #15
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well there you have it then. either or, i usually don't mark a waypoint for where i left my wallet last so i think it's okay. i guess the point that i was trying to get across is that the gpsmap60 gets great reception. point and case is myself being able to get 5 sv's indoors. pretty good for a recreational grade receiver huh?
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Old 09-28-07, 06:55 PM   #16
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well there you have it then. either or, i usually don't mark a waypoint for where i left my wallet last so i think it's okay. i guess the point that i was trying to get across is that the gpsmap60 gets great reception. point and case is myself being able to get 5 sv's indoors. pretty good for a recreational grade receiver huh?
I can see that being a big plus if you frequently become lost while indoors.


Seriously, that surprises me. I wonder what type of results you'd see if you set a waypoint indoors, restarted the receiver, and then attempted to navigate back to it?
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Old 09-28-07, 07:21 PM   #17
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ha ha http://www.youtube.com/watch?v=ZZqrN4fyI0s
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Old 09-28-07, 07:29 PM   #18
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It's a good thing that the lead rider had that big floppy backpack for the one mile ride inside a building. You can never be too prepared. Thankfully he didn't need to bust out his survival gear due to getting lost inside the buildings.
lol, thats the guy that set the race up but I don't know why he has that pack on
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