Why Do Gps Units Get Crummy Reception?

[BloodhoundBrown]

Why do GPS unit's not work well in wooded areas? It seems that hand held GPS units most of us use don't work well unless in an open area and I'm curious as to why.

 

Many Geocaches are in wooded areas up in the Northwest and once you get on a trail you get very inaccurate/tempermental reception or none at all. I use Garmin Venture and my friends use Vistas.

 

Don't respond if you don't know with some stupid answer like "Check you batteries"..what I want to know is why for example my Cell phone can work so well in the woods but my GPS won't work....is this a Wave/Freq. thing...

 

I mean heck, if we can control robot landers on Mars, Get Sat. TV stations...why is a GPS so weak? Does Garmin have any Super Antennas? or what's the scoop here?

 

Curious...thanks,

[+Jamie Z]

Yes, it is a wavelength/frequency thing.

 

The frequency used in GPS is not good at passing through solid objects like buildings or trees. Basically, it's line-of-sight.

 

Your cellular phone does not suffer from this, however a cellular phone's range is many times smaller than a GPS reciever.

 

Jamie

[+StarBrand]

Actually part of the problem is deliberate, a strong signal would tend to bounce off solid objects and add to the error. Unintended propogation lengthens the path of the signal and gives bad readings. Multipath error is what it is called. Weak signals are less likely to bounce.

Edited February 19, 2005 by StarBrand

[+GPS_David]

I have a Garmin Etrex and it has worked fine for me in wooded areas with exception to the times that I slow my pace down, stop or walk in circles, The GPS does not know the direction I am heading in. Usually I back track about 25-50 feet and then start my search again.

 

I agree with one of the other posters, it is basically line of sight. If you had a Sat Dish and there was a tree in the way, your often not going to get a good signal.

 

When I hid my first cache, I had create 10 different wavepoints just to make sure the coordinates were right on target. Even then, the next time I went to visit it, it showed I was about 15 feet off when I was right on top of it.

 

It's a great device but not a perfect science.

 

Dave

[+BlueDeuce]

Actually part of the problem is deliberate, a strong signal would tend to bounce off solid objects and add to the error. Unintended propogation lengthens the path of the signal and gives bad readings. Multipath error is what it is called. Weak signals are less likely to bounce.

Interesting, I never considered that.

 

Yes, I've been in heavy tree cover, walking around trying to find a clear area hoping I can get enough signal to at least get a line of sight on the cache location.

[+OccidentalErrant]

GPS signals are line of sight to the satellite(s). Therefore, when you are under a canopy of trees that interferes with the signal... weakens it... and you will notice that your accuracy goes off. Mine has been off by 15 to 18 feet and that is under just a few trees in a city park.

 

I used to use this GPS V in a courier business in Eastern Oregon as I needed to know where addresses were when the dispatcher would call me (on the road) to tell me to go pick something up in small towns out there.

 

Well, I didn't have a problem with doing that as there are no trees out there for the most part. I am finding the same problem that you are when it comes to looking for caches in wooded areas.

 

Garmin makes an extended attenna. As to the accuracy of it when you are in wooded areas I cannot attest to as I don't use it. Moot Point: You would have to attach the extended attenna to your body somewhere or hold it out at arms length... what good would that do unless you are in an open field or at the very top of a douglas fir.. so I don't use extentions in my geocaching activities. Unless somebody else has a better idea, I think we are all waiting for improvements in the technology here.

[+NightPilot]

The GPS signals are very weak - after all, they're coming from 11,000 miles away. And the frequency is such that they are easily absorbed and reflected. New satellites are being built that will make the reception much more reliable, but the actual implementation, getting the satellites in orbit, is still a few years away. In the meantime, you'll have to live with what you get from the guv'mint.

[stude]

I went from the yellow etrex to the map60 .I had lots of trouble with reception in wooded areas and having my thumb over the top part.The newer gps60 is lots better.

[+BigHank]

I like old Studebakers.

 

Even heavy cloud cover can affect your GPS reception as clouds are made up of water (basically) and can alter or block the signal path. The type and orientation of the antenna in the GPS can also make a difference in reception quality.

[+Poindexter]

Weather has so little effect on signal strength that the end user would not see any difference. This is another common myth plastered all over the web.

 

Rain, snow, clouds and GPS reception.

[+DaveA]

I went from the yellow etrex to the map60 .I had lots of trouble with reception in wooded areas and having my thumb over the top part.The newer gps60 is lots better.

I was going to just say 'buy a Magellan'.

 

The reason your Garmin does poorly under tree cover is because the patch antenna they used on their units until recently was simply quite poor under any kind of overhead cover.

 

Magellans do not have this problem because they use a different type of antenna.

 

The GPS 60 also uses the same antenna as the Magellans.

 

Here it is from Garmins web site discussing the 60.

 

built-in quad-helix antenna for better satellite reception

 

Better than what? Better than the patch antenna they use on the older units.

 

For years I have been reading Garmin users make excuses for why the sat signal is so weak, so easily lost and all that. All the time I have used Magellan units and not experienced the problem.

 

I am not slamming Garmin, I could certain point out flaws with Magellan like all their older software uses Tiger data which is horridly innaccurate in some locales.

 

The point is that the spotty reception the older Garmins get under cover is due to their inferior antenna.

[+Skyman]

Why do GPS unit's not work well in wooded areas?  It seems that hand held GPS units most of us use don't work well unless in an open area and I'm curious as to why.

 

There micro waves

 

Here is some info

[+geobc]

The point is that the spotty reception the older Garmins get under cover is due to their inferior antenna.

Only _some_ Garmins used patch antennas. Even the ancient Garmin 45 I had came with a quad helix antenna. For as long as I've owned Garmins, they've always had quite a few consumer handheld models that sport quad helix antennas. The ones I have owned are: G45, GII, GIII+, and now my 76C.

 

But even so, from what I've read, there isn't a _huge_ difference btwn patch and quad helix. There are pros and cons for both. Some GPS units just don't perform as well as others, even if they use the same type of antenna. For instance, the satellite acquisition and signal lock maintenance seems to be better with my 76C than my GIII+.

 

GeoBC