I have an old Magellan 315, that I bought primarily to have a toy to play with when GPS prices started to drop. It has a major problem finding satellites under tree cover. I might actually get a newer one, if I could be convinced they’ve gotten appreciably better at locking on to satellites and being useful for hiking in places like the Santa Cruz mountains - redwood forests and canyons. Actually, I can accept that you are going to have problems at the bottom of a steep canyon, but tree cover where there’s an appreciable area of sky above the trees shouldn’t kill the thing.
Have they gotten better? Any particular small handhelds that are notably good in this regard? The published reviews I can find seem rather inconclusive.
I’m still pretty much a newbie at geotracking, but I got a Garmin Etrex Legend for Christmas. While it is not a top-of-the-line model, I understand that it is far from the bottom. I have problems in heavily wooded areas with it.
I have a Garmin III+ and it works in the woods around home. Most of the time anyway. I do find that if I drive some distance and enter the woods before turning the unit on, it takes some time to acquire the satilites. If the unit is on and tracking before entering a wooded area, it seems to work better.
This unit is several years old and newer models may work better.
Buy it from somelace with a good return policy, making sure to tell the sales person of your concerns. If they say it’s going to work fine and it doesn’t, take it back.
You may want to wait a while. There has been a great deal of money spent on R&D for improved GPS receivers, much of it due to FCC requirements for E911 location determination for cell phones. A number of chips have been announced that offer big improvements in receiver sensitivity, the goal being reliable GPS operation indoors. It is probably going to take a while for the new chips to get into production and start showing up in handheld GPS receivers.
The Etrex is more rugged for hiking use, water resistent etc.
THe eMap is actually much better at finding satellites under a forest canopy. The emap also has a plug in for an external antenna, although I don’t have one.
I actually prefer using the eMap most of the time, even though I paid almost twice as much for the Etrex.
You can search the geocaching.com message boards, this topic comes up often.
The III+ (now long discontinued) was known as one of the best recievers for the ability to get and hold a lock, I think it is replaced by the V. Both are ‘hybrid’ models, meaning it’s a compromise between handheld and vechical navigation.
There are 2 types of antennas, the patch antenna (not as good) and the , well I forget the term exactly but something like quad-rectifier, which use to be much much better. I think recently the patch antenna’s have improved, so maybe the Quad-R is just a bit better.
It helps if you can get it locked before you enter the woods, keep it high (good view of the sky) while you travel. Water absorbs the signal, so rail, fog and dew on trees will make it harder to get a lock.
Any quick buzzwords besides “e911” I should do a search on to get a handle on the progress of these new chips?
I think that’s “quad helix”, present on the Magellan SporTraks and Meridians and Garmin 60 / 76 series, as opposed to “patch” on the Garmin eTrex and Magellan Explorist units.
Hmm. I’m interested in and skeptical of this claim at the same time. I just had a demonstration this very afternoon from a sales rep for survey grade GPS (Trimble). We also had problems tracking satelites under tree cover.
He claimed that there were new satelites with a more robust signal coming on line soon that could only be picked up by new receivers, and that those would likely be better under trees. But nothing about new more sensitive chips. He was an old hand at GPS surveying but new at the sales gig so it is posssible that he just wasn’t up on all the upcoming tech. But strong enough to receive indoors? Hmmm.
Many current receivers have an acquisition sensitivity of about -135…-140 dBm. Most of the new and improved chips are in the -155…-160 dBm range. That is a huge improvement.
I have a Garmin 38 that is maybe 10 years old or so, and I bought a Garmin 76Map this year (it has a quadrafilar helix antenna and an external antenna connector which I sometimes use.
The newer unit does quite a bit better in forest, though it does better still in the open. I can often use 5, 6, 7 or 8 satellites in the forest, maybe 10 in rare moments. In the open I’ve seen it use 11 satellites a few times and 12 one time for a few seconds.
I think if you had an old 8 channel sequential GPS receiver and bought a new 12 channel parallel unit with a quad helix antenna you’d notice a nice improvement.
No advice, though, on whether it’s about to get a lot better, due to receiver chips or satellites or both.
My Garmin 60 CS will acquire a multi-satellite lock indoors. It will lose signal if I go into the basement, however. The only times I have lost signal outdoors was when walking in a deep, narrow canyon or when the unit was on the floor of my car (sitting on the car seat works OK). It seems to laugh at tree cover, even in the Pacific NW where the cover was very dense.
Users of handheld GPS receivers should not confuse getting a position with getting a good quality position. It’s not a black and white scenario… a receiver achieving lock and generating a position does not always indicate that the position is of a high order of precision.
When operating in foliage or in urban ares with many high sided buildings, the resultant cycle slips and signal multipath can cause the precision of the position to degrade significantly. There are many factors affecting GPS position accuracy. As a rule of thumb, you get what you pay for in GPS equipment. Cheaper handheld receivers do not have as high quality antennae or as good on-board software.
Users should also be wary of GPS positions generated indoors. Depending on the accuracy you want to achieve of course. GPS signals which have bounced around inside the building before being picked up by the antenna are going to generate position errors.
I had a III+ was was unhappy with it’s basemap (used it more for driving directions than geocaching), tried to go cheap with a Holux gr-230 Bluetooth GPS unit and a copy of Microsoft Street and trips. The good news is, the street map detail is exceptional, the bad news is: I miss my little battery powered instant on always there handheld unit (long since departed via ebay)
The holux does a pretty good job of pulling in satellites, but it depends on how old the Bus I’m riding in is. an 80’s-90’s vintage bus has coated windows that make a lock impossible, a newer bus doesn’t have coated windows an the unit can get a pretty good lock (patch antenna).
But if I want to get a position, i’ve gotta get out the unit, turn it on, wait for the laptop to boot, get into street n trips, wonder why the bluetooth won’t sync, place the laptop where I can see the screen, then hit the road. I miss the turn it on, place on dash, go! But I also have a hard time justifying 600-1000 for an improved unit.
Thanks for the info. Looks like something still coming out of the labs and not into any products yet? My sales guy was new, so he likely would not have been up on such things. Good to know that’s coming.