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Sat lock - indoors vs under tree cover


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I am a brand spanking newbie - I've logged one cache and failed on a couple others. One of my failures was under tree cover and it seemed I couldn't get better than 40 feet of accuracy (I own the little yellow etrex), and even at that it would lose its sat lock every few seconds. The other day I was playing around with the gps at home and I got 20 feet of accuracy sitting on my couch! Why would I get better accuracy indoors than under tree cover?

 

Thanks,

Zig

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got a sunroof? my experience is that it's simply about line of sight to the satellite. If you look at the satellite page, you can kind of tell where each of the 3-4 satellites are in the sky. Might be that your windows are positioned well enough.

 

Others probably know better than me though. Must say though, that given your nickname, this is an ironic issue, and good first post!

 

<timpaula>

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Mostly depends on where and which satellites (some may be sending stronger signals) are positioned relative to your GPS at the time (some may have a better 'straight-shot' to your GPS), cloud cover, how you are holding the GPS (you're body can block the signal a little) and probably that trees have much more water in them than your house (I would hope so anyway). The water in the leaves will conduct the signal to ground reducing your signal received by the GPS. Could just be the phase of the moon too. icon_smile.gif

 

"The best way to accelerate a Macintosh is at 9.8m/sec/sec."

-Marcus Dolengo

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Opinions vary, but it is fairly common to hear that people's experiences are less than favourable when considering the Garmin etrex series and moderate tree cover.

 

You may want to have a compass with you; this will allow you to take readings in the clear, and then pace off the last bit. If the compass doesn't have declination adjustment, just set your north ref on the GPS to Magnetic. A $10 or $20 compass is sufficient. I notice that many Garmin users use compasses; I am primarily a magellan user, and using a compass is something I only do on occasion.

 

Good luck

 

canadazuuk

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I have an eTrex and rarely have reception problems under tree cover. One key is to make sure you are holding it horizontally, in front of you. If you turn the unit over, or hold it upside down, it will lose its lock.

 

Anyway, 40 ft. accuracy should be sufficient to find a cache.

 

"Au pays des aveugles, les borgnes sont rois"

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40 feet is not bad for under the trees, especially considering that the hider was having the same problems in getting a satellite loc when they placed the cache. That might add to more error. Reception on your porch would be OK if the satellites were on that side of the building but indoors won't get any reception (except near the windows).

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Water blocks the satalite signals. Tree cover and your body both have water (you will notice over time that while doing your cache biz your body blocks the signal).

 

Your roof also blocks signal but not as well as water. Thus depending on materials etc. you will get a lock in your house, but not as good as you would of got outside. You probably won't get a lock in your basement.

 

=====================

Wherever you go there you are.

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RK is right. Any where that there is a grounded conductor betwen you and the sats, the signal will be "sheilded" from your GPSr. House framing doesn't make a particularly good shield, unless there is a considerable amount of electrical wiring in the attic - or metal roofing. trees, OTOH, are full of water (just cut a branch off a live cottonwood tre sometime and you'll see what I mean), and of course they are well grounded. Water increases conductivity of wood, so they will divert more of the signal than you might think.

 

As an aside - a long, long time ago, I acually plugged the antenna lead of my short-wave receiver into a giant maple tree in my back yard. It made a pretty acceptable antenna for receiving international broadcasts.

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You should also consider that sitting on the couch means the receiver is stable. Under the trees, you are usually moving around which causes the satellites to be alternately visible and hidden. It usually seems to take a few seconds for the receiver to “see” and then attempt a lock on a signal. Signals that are there one second and gone the next are not reliable enough to get lock.

 

http://fp1.centurytel.net/Criminal_Page/

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quote:
Originally posted by Criminal:

You should also consider that sitting on the couch means the receiver is stable. Under the trees, you are usually moving around which causes the satellites to be alternately visible and hidden. It usually seems to take a few seconds for the receiver to “see” and then attempt a lock on a signal. Signals that are there one second and gone the next are not reliable enough to get lock.

 

http://fp1.centurytel.net/Criminal_Page/

 

And even if you're not moving, often the tree is - so even if you get reception, your GPSr *thinks* you're moving...

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I have a Magellan that works well in tree cover and my living room. I can usually lock 7 sats in my living room and have at least 6 sats in tree cover. Etrex units have whats called a patch antenna and Maggies have quadrifier helix antenna, the latter better in terms of antennas. moving around doesn't help the sat lock much either. But no matter about antennas, the more sats the better, thats just me.

 

Don't Drink And Park: Accidents Cause People.

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quote:
Originally posted by -ZigZag-:

I am a brand spanking newbie - I've logged one cache and failed on a couple others. One of my failures was under tree cover and it seemed I couldn't get better than 40 feet of accuracy (I own the little yellow etrex), and even at that it would lose its sat lock every few seconds. The other day I was playing around with the gps at home and I got 20 feet of accuracy sitting on my couch! Why would I get better accuracy indoors than under tree cover?

 

Thanks,

Zig


 

I always wait a few times before I try spanking icon_smile.gif

I started geocaching early this spring, tree cover was much thinner then, and my yellow eTrex worked fantastic. Now that the trees have filled out, it's much spottier, and has been over 100' off under heavy tree cover, while reporting 25' accuracy. I can usually get a lock sitting in my den, and my living room, but around 40' accuracy.

 

I just borrowed a friends GPS III+ for a few weeks, and it does MUCH better under tree cover, but can't lock in my house.

 

_________________________________________________________

If trees could scream, would we still cut them down?

Well, maybe if they screamed all the time, for no reason.

Click here for my Geocaching pictures and Here (newest)

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Having started last fall w/my Yellow eTrex, and now seen the difference the foliage makes, here are my observations.

 

My Yellow eTrex seems to work better than average. At the recent Geo Jamboree event, I went caching w/1/2 dozen folks, and never had problems gettings sats while they went huge lengths without locking on (I didn't pay attention to which models they had).

 

Only one other person had a yellow, and that unit performed similarly to mine.

 

I've never had a cache yet (out of 50ish) that I couldn't find due to foliage, while there had been prior logs on the page of such.

 

I used to use a compass when I started, but haven't looked at it in months, you start to "get the feel" after a while. I do reference a cheap keychain compass when standing still to orient the GPS.

 

I can get lock in the house depending on which windows I'm near. I can get lock in an airplane only from the window-side of the window-seat.

 

I once placed my eTrex down on a rock while watching the sat. screen (the advanced one, not the stupid animation) bar graph levels. They dropped when on the rock, came back up when I lifted it a couple inches.

 

My procedure under foliage is thus: First, find a spot where it sees some satellites then STAND STILL and wait for it to lock on to as many as you have patience for. The software "remembers" those signals, and will reaquire them more quickly. If you have a nearby clear area, let it catch as many as it can, then move into the trees. As you move, it won't matter if they cut out, because they'll come right back in.

 

Of greater challenge for me was placing caches under bad foliage! (In the rain for that matter.) I spent some good long time making sure those coordinates were good! Sometimes it's as simple as turning around and standing still. Either say, hold the eTrex out in front of you away from your body, horizontally with the screen facing the sky. If you're looking at the advanced sat screen, it shows where the sats are and you can tilt it a little to favor a side or get your body out of the way if three are in the East and the horizon is low over there.

 

Oh yeah, that screen also shows if sats are closer to the horizon or right overhead. In foliage those overhead tend to come through better but offer less accuracy (the triangulation isn't as extreme). You want those at the horizon for that 19' accuracy, which tend to be more obscured, particularly in hilly terrain like around here.

 

Hope this helps,

 

Randy

 

PS: The question that occurred to me last night, which makes it amusing that this thread came up, if you are under bad foliage long enough for an eTrex to prompt, "Are you indoors now?" Should you say yes? (Which presumably changes the software's parameters... I know it immediately helps when you ARE indoors.)

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I have been caching since January and am on my second E-trex, the first being replaced due to a cracked screen. In my experience, If you are in tree cover and can see little sky, the E-trex is worthless, won't even orient itself, much less get within 40 or 100 feet of a cache. This is in spite of what the Garmin site claims "works well even under tree cover." I'm more than a little ticked, having bought the unit based on the representations, then been on several caches and drove a long distance only to have the unit be completely non-functional when you get into the woods. I nearly pitched the thing into the river yesterday because of it.

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quote:
Water blocks the satalite signals. Tree cover and your body both have water (you will notice over time that while doing your cache biz your body blocks the signal).


 

I read this today, and then drove home in the rain while my Garmin eTrex Vista was able to keep track of my path on the map just fine, usually within 20-30 feet. Maybe there's more to it than just 'water' in the tree cover and your body that blocks the signal? I'll see if I can ask an RF engineer friend of mine and see if she knows something I can pass along.

 

There are three kinds of people in the world. Those that can count, and those that cannot.

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TopSecret-

I've used the Etrex models quite a bit in the area where Kansas, Nebraska, Missouri, and Iowa get together. (I'm there now, in fact)

 

The E-trex works just fine in the area. I was under dense tree cover near the Missouri River yesterday, and the reception was suprisingly solid, even though I saw little sky.

 

You might want to check how you're holding the unit...it should be held horizontally and away from your body for the best performance.

 

George

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Figuring out what will, and will not interfere with GPS reception on any given day is tough. I tried carrying two receivers for a hundred caches, primarily in order to compare behavior. One of the main things I learned was that if you have two units, it's actually a little harder to find the cache, if and when they do disagree a bit. First you have to try and figure out which one is right. Seems no matter how well you think you've figured them out, normal doesn't apply in the situation you're currently in. In the end, both of them are generally pretty close to where had you just got around to searching rather than wasting time trying to figure out where to start from, you'll fidn the cache quicker.

 

When you get in the crud, it doesn't seem to matter much what you use in my experience. You'll often have glitches. In the type of terrain I generally play in (Steep mountains, often with forests, or sandstone desert), I've found that my sportraks tendancy to wander, and suffer position lag is generally just as problematic as any reception issues with the eTex. I personally find it pretty much a draw as to which one works better. Seems more of a case of which quirk I prefer dealing with to me.

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Thanks for the suggestion, George, I hold it out at arms length, and have even held my son up on my shoulders and had him hold it horizontal at arm's length for elevation and it doesn't seem to matter. I know I'm in trouble when the readings on GOTO start changing slowly, then I'll back track and the readings still climb and the direction arrow doesn't change. Usually its in thick woods with stickers shredding my legs, mosquitos and ticks feasting on me, spider webs in my face and a long walk back to the truck, so its really aggravating. Maybe I should try foil on the antenna, it worked for the old B&W tv we had...

Dave

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