Gps?

[WhiteMTHike]

I'm sure this question has been asked before on this board but I haven't been posting here for that long so please forgive me if I'm being repetetive.

How many of you use a GPS when you are hiking the Whites? how well is the satellite signal? I've just gotten a GPS recently and I am in the process of learning how to use it. While I've hiked the WMNF many times without one, I'd like to exercise it on a few trails off the Kanc. Would the signal be good enough where it'd be worth the time to bring it? thanks for any advice.

 

[DougPaul]

A GPS will work in most places in the Whites. Signals are attenuated/blocked/reflected by rock and wet objects (including flesh), but not snow, rain, or fog.

Take it along on some hikes where you don't need it to learn how to use it.

There is a bunch of advice in a recent thread: General Backcountry > Help with GPS, last entry 05-16-2005. Current url is http://www.vftt.org/forums/showthread.php?t=6583.

Search on "Garmin GPS", if the link doesn't work. (The search won't work on "GPS" alone. Grrrrrrrrrrr.) This also brings up several more threads that might be worth reading.

Also lots of info at http://www.gpsinformation.net.

Doug

 

[Remix]

The main issue with useability is having the signal blocked by the mountains when you are in a valley, ravine, or notch.

Sometimes its not an issue, because there are at least 3 satellites very high on the horizon, always in your view. But, since they are always moving, some or all may be lower on the horizon; in this case your gps unit wont be able to see a minimum of 3 satellites--you will not get a fix.

 

[cp2000]

The few times I have used my GPS in the whites I had only a couple of times when there was no signal. Always keep in mind that it should be a supplement to your navigation and not a replacement for good map and compass skills..

Bring extra batteries!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

 

[spider solo]

I bring one with me these days when I go hiking. Though still a beginner in using it, I've learned a lot from the good folks here on the forums.
good luck...spdr

 

[arghman]

When I bring mine, I almost never rely on it, I usually bring it to
(a) mark places for future reference
(b) use as a gratuitous piece of technology

Two exceptions:
(c) that one time my friend & I used GPS to find the top of Mt Kelsey through thick spruce, but I won't repeat that again.
(d) once at one of the Public Reserved Lands in Maine, it was extremely foggy and there were several confusing trails all near each other ("you are in a maze of twisty little trails"), I was able to see where I was, in relation to where I had been.

It's worth having, just don't plan on depending on it.

 

[DougPaul]

Sometimes its not an issue, because there are at least 3 satellites very high on the horizon, always in your view.

You need 4 satellites for a proper fix. Anything less is based upon guesses by the GPS (eg assuming the altitude hasn't changed since the last fix).

The 4th satellite is required because the GPS also has to solve for time as well as 3D location.

See, for instance, http://www.edu-observatory.org/gps/tutorials.html.

Doug

 

[solo_hiker]

yeah they work if you're in the clear, but I find they're not dependable under the forest canopy without an external antenna:

http://www.gilsson.com/gps_antennas.htm

the extra batteries issues is no joke as they have a nasty habit of going dead right when you need them most. usgs topos have little blue UTM tickmarks on the edges so you can grid them out yourself with a yardstick. way easier than lat/long.

Solo

 

[adkleaddog]

yeah they work if you're in the clear, but I find they're not dependable under the forest canopy without an external antenna:

I've seen a lot of replies about losing signal under canopy, I've guess I'm pretty lucky, I use my GPS quite often bushwhacking and hardley ever lose signal...maybe it's the unit? I've been using Magellan products since they were availible,The 4000XL, Map 330 and most recently the Meridian series. It seems that most are using Garmin units, but I really wouldn't expect much of a difference in the two makes. Maybe there is a better quadrifilar antenna on the Magellan? If I'm in a valley or blocked by a steep ridge, I'll lose some satts, placing the unit in 2D mode until I'm clear. But that happens not very often. I've been in very heavy snow squalls as well and had no problems...yet!

 

[imarchant]

I use A garmin E-trex. To get the best signal stregnth I use the case with a belt hook.

I wear it on the top of my shoulder strap of my daypack. I also attach the lanyard to my pack so I don't accidentally lose it. I have had good results.

 

[Remix]

Honestly, I do not think I ever got a loss of fix with my Magellan Meridian due to tree cover. When I use it to record a hike, I have the beeper set to chime on loss of fix.
Its always terrain related.

Doug- The unit I have will get a fix with 3 satellites, but there is a warning that it is a 2D fix. But it still gets a fix.

 

[DougPaul]

yeah they work if you're in the clear, but I find they're not dependable under the forest canopy without an external antenna:

I've seen a lot of replies about losing signal under canopy, I've guess I'm pretty lucky

Its more than luck--there are a number of things on can do to improve reception in the trees and mountains (and a number of things to avoid doing.) I listed a number of them in the earlier thread mentioned in post #2 of this thread.

I can pretty much always get a fix when I need one using the internal patch antenna in my GPS. An external antenna can help, but if you place the GPS in the same location (eg on top of your head or on a pole) and orient it properly it should work as well. There is no magic in the external antenna (its primary advantage is that it allows you to separate the antenna from the display and buttons).

Doug

 

[DougPaul]

The unit I have will get a fix with 3 satellites, but there is a warning that it is a 2D fix. But it still gets a fix.

Many GPSes will do that.

And as I explained, it is not a full fix--it requires assumptions which may be inaccurate giving you a location which can be wildly inaccurate. And the farther you have moved since the last full fix, the less accurate the assumptions.

The 2D fix is an attempt at graceful degradation when the GPS cannot get 4 satellites. Usually it works reasonably, but it is _not_ equivalent to a full 4 (or more) satellite fix.

To get a full fix from 3 satellites you need an atomic clock in your GPS. Not something many of us can afford.

Doug

 

[spider solo]

Ok beginner that I am I personally will not wear a GPS or an antenna on the top of my head. I have noticed a number of people who mention that or coil an atenna into their hats
Call it superstitous or whatever, but I wouldn't carry one there any more than I would be wearing one in my crotch or in a pocket over my heart.
I'm sure there's probably plenty of studies saying it's harmless..but I'll let other people put it to the test....
I have visions of years from now when studies come out that say "remember when we used to think it was harmless...well we were wrong..."

 

[DougPaul]

Ok beginner that I am I personally will not wear a GPS or an antenna on the top of my head.
Call it superstitous or whatever, but I wouldn't carry one there any more than I would be wearing one in my crotch or in a pocket over my heart.
I'm sure there's probably plenty of studies saying it's harmless..but I'll let other people put it to the test....

I wouldn't worry--the GPS is a receiver, not a transmitter. The largest risk is embarassment.

On the other hand, a cell phone is a transmitter held close to one's head...

Doug

 

[John Graham]

I carry my GPSr in a pouch on the top of my pack strap. I have a Garmin GPS76S, which has a better antenna than my old Garmin E-trex, which did not work as well in this configuration. The patch antenna in the e-trex must be horizontal to the sky for optimal performance, whilst the quadrilinial antenna in the GPS76 performs best at a 45 degree angle, which is how it is at the top of my pack strap.
It seems that the Garmin GPS 60 has an even better antenna, which works just as well in the vertical position. I have broken three external antennae by having the wires snag in the brush, and gave up on them.

 

[DougPaul]

I carry my GPSr in a pouch on the top of my pack strap. I have a Garmin GPS76S, which has a better antenna than my old Garmin E-trex, which did not work as well in this configuration. The patch antenna in the e-trex must be horizontal to the sky for optimal performance, whilst the quadrilinial antenna in the GPS76 performs best at a 45 degree angle, which is how it is at the top of my pack strap.
It seems that the Garmin GPS 60 has an even better antenna, which works just as well in the vertical position. I have broken three external antennae by having the wires snag in the brush, and gave up on them.

My eTrex Vista works well in a pouch on top of a pack shoulder strap. Don't know what the difference might be. I have occasionally carried my Vista clipped to the strap at the back of a baseball cap--relatively clear of shadowing by my body, but a suboptimal orientation. Works well there too--perhaps even better. Haven't tried on top of my head, but that would probably be best.

The best orientation for a quadrifilar helix with a clear skyview is generally with its axis vertical. The orientation of either type of antenna needn't be perfect--the main lobe is rather broad.

The GPSMap60 series has the same antenna as the GPSMap76 series. Its simply buried in the plastic case. (The case is transparent to the signals.) The 60 series and the 76 series appear to be electrically identical except for minor differences--eg amount of memory, the basemap, tide charts. They run the same software.

An external antenna cable is a problem while hiking. When I experimented with an external antenna, I stuck the antenna in the top pocket of my pack (attached to a flat object to keep it oriented properly). Between the forward lean caused by the pack weight and the forward tilt of my head, the antenna had a fairly good skyview. I routed the cable along the shoulder strap to the GPS in its usual pouch on the front of my shoulder. Good enough for a trail, probably not good enough for bushwacking.

A better location for the antenna would be in/on a hat with the cable routed down the back of one's neck. (One has to remember to take one's hat off before taking one's pack off...) The Tilley hat has a pocket in the crown. Other solutions involve sewing a pocket or attaching some metal for the magnetic-mount. I have an antenna that is 1.5x1.6x.5 in--small enough that it is hard to notice. Haven't tried this one yet.

There is a group that believes the quadrifilar helix antenna to be better than the patch antenna. I haven't seen any real data to support this view. Many of these same people also believe an external antenna to work better than internal antennas (of either type). The consumer external antennas are patch antennas...

See http://www.gpsinformation.org/joe/gpsantennaspecs.htm.

Both antennas have a reception pattern with a single very broad vertical lobe. Both are circularly polarized. Foliage and terrain tends to block low elevation angle satellites--the same satellites that give the best position information. There have been some attempts at objective studies in forrested/hilly condiitons--IIRC, they don't show any strong preference either way.

Refs:
General:
http://www.gpsinformation.org/joe/gpsantennaspecs.htm
Quadrifilar Helix:
http://scholar.lib.vt.edu/theses/available/etd-11242003-123529/unrestricted/Barts_etd_CH2.pdf
http://ic.arc.nasa.gov/projects/esg/research/antenna.htm
Patch:
http://scholar.lib.vt.edu/theses/available/etd-7697-21043/unrestricted/CH6.PDF


I generally just carry my GPS in a pocket attached to my pack strap. No external antenna. KISS (Keep It Simple Stupid). It occasionally loses track in trees and terrain, but not a problem. If I need a fix, I stop (perhaps in a better location) and hold it above my head. Pretty much always works. But there are also places--such as the bottom of a slot canyon--where GPS is unlikely to ever work.

Doug

 

[Tramper Al]

Would the signal be good enough where it'd be worth the time to bring it?

I carry my GPSR fairly often, for different purposes. You must think of it as just one of many tools, of course. Have your map and compass and so on and so on.

Aside: I'm not one of those who believes, for example, that carrying a cell phone causally reduces your backcountry acumen.

I have only had the GPSR fail me twice when I really wanted to use it. Once, I ran out of battery power on a peak bushwhack while my spares were back at basecamp. You might consider that one human error! Another time on a windy whiteout February day on Mt. Jefferson, the display screen image started to get sluggish and eventually disintegrated. I believe this was a temperature issue, as it recovered just fine.

It just another tool, sometimes quite useful.

 

[DougPaul]

Honestly, I do not think I ever got a loss of fix with my Magellan Meridian due to tree cover. When I use it to record a hike, I have the beeper set to chime on loss of fix. Its always terrain related.

All GPSes intended to be used on a moving platform (eg a car or hiker) have to deal with temporary loss of signal from some or all of the sattelites. Users, on the other hand, generally do not want to be notified at every little interruption--but if the interruption is long enough or bad enough, then the GPS should indicate a loss of lock. GPSes use various forms of dead-reckoning to carry the position and speed fix over short dead spots and present these data to the user as if the signals were always present. But, the longer that one dead-reckons, the poorer the position estimates. And different manufacturers use different strategies and thresholds on when to give up and indicate a loss of lock.

Magellans have been observed to have a longer time-before-giving-up than Garmins. Some comparisons between the two have shown situations where a Garmin GPS indicates more loss-of-lock but gives a higher quality recorded track than does a seemingly similar Magellan unit.

One situation where this process is very clear is driving into a tunnel (complete signal block). The GPS will generally indicate a (dead-reckoned) position, speed, and direction until it gives up and indicates a loss of lock. When you exit the tunnel and reacquire the signals, the GPS will again show a fix and may "reach back in time" and re-dead-reckon the track during the blackout period.

If one is stationary with a 3D lock (4 or more satellites) for a minute or longer, indicated positions should generally be free from dead-reckoning error.

Doug

 

[DougPaul]

Another time on a windy whiteout February day on Mt. Jefferson, the display screen image started to get sluggish and eventually disintegrated. I believe this was a temperature issue, as it recovered just fine.

It just another tool, sometimes quite useful.

3 possible causes of the problem: cold batteries, cold electronics (less likely), or cold display. The sluggish update is typical of a cold display. Also the brightness of the display is affected by temp (I think it will get lighter as it gets cold)--adjusting the brightness of the display might help. And you can always warm it up in your jacket.

Agreed--it is just a tool. As are map, compass, and altimeter. Add a bit of situaitonal awareness and smarts and one should be able to navigate if any of the tools fails.

Doug