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GPSr vs. THE COLD


roasteroo
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Does anyone here have problems with their GPSr while caching in the winter? My Magellan Meridian seemed to slow up and get dim. Putting it my jacket inside pocket helped a little but it seemed slow. All gps corr. from that trip seem just a little off. I dont think I really exceeded its temp range specs. Here they are:

Operating 14°F to 140°F to (-10°C to 60°C)

Storage -4°F to 158°F (-20°C to 70°C)

 

Any Ideas?

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Yes indeed. Use lithium batteries when it gets cold. They are a bit more expensive but are not so affected by the cold (they are made for such conditions) and are much lighter (last a bit longer too). I have seen my alkilines slow the operation of my GPS down significantly in a blizzard. This is the cure.

 

4497_300.jpg

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I was out this morning with a Meridian GPSr. Temp was 15 on digital thermometer I had with. I was noticing the display getting a bit 'whacked' on some screens more than others. Figured it was the cold. Was out several hours yesterday, temp about 25, and didn't notice problem. Had freshly charged batteries this morning too. I see I was right at the lower threshold of operation. The map screen seemed the worst. Probably because of all the detail. Accuracy didn't seem to be too effected as I found both caches I set out for. Probably wasn't out more than .5 hours either one .

Stay Warm!

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I bought a pair of woolen mittens (army surplus) and cut a small square hole in the palm of one glove. I craddle my GPSV in one hand, slip the mitten over my entire hand AND the GPSr -- the hole lets me see the screen. another smaller hole lets the antennae stick out. I've found this keeps my hand warm and my body heat keeps the GPSr very toasty.

 

When it gets REALLY cold (like yesterday when it was 5 degrees) I put one of those chemical-pack hand warmers in the glove.

 

Jolly R. Blackburn

http://kenzerco.com

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I haven't managed to take my sportrak into any temp extremes yet as I haven't had it long enough, and our winter here hasn't gotten very cold. My old etrex's though have been through a lot. Here's what I've come to expect:

 

Alkaline batteries tend to loose powere quick when the temp drops, generally worthless by freezing. NiMh will work down to about zero sometimes. Lithiums cost a bunch but I always take a set on my winter adventure. They seem to be good for lower temps than the eTrex will handle which is somewhere in the -10F range. The display gets really slow and strange prior to actually going blank. I have noticed the receiver keeps recording my track however, you just can't use it to navigate by, which is generally the whole point. To get around the problem I keep the unit inside my clothing most of the time.

 

On hot sunny days down in the desserts, if I carry the unit on my shoulder strap facing up, it gets hot enough that the display will turn completely black and unreadable sometimes. I also have experienced the problem on my boat dash down at Lake Powell or Mead. Just don't leave them face up in the sun and it doesn't seem to be a problem.

 

For what it's worth

 

Jeff

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Although I always get blasted by Magellan diehards, I've mentioned this before. I've yet to see a Magellan handheld not get funky somewhere around freezing, say 25 F.

 

The Garmin eTrex units all seem to stay sane until about 0 F. My compass has worked flawlessly down to about -25 F, which is why I'll always take it! icon_wink.gif

 

You can coax the handheld receivers to give you readings when it is chilly by warming them with body heat. But reading accuracy will suffer. Most units use an internal temperature sensor to help correct for atmospheric conditions.

 

-jjf

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I hadn't thought of that. I wonder how much of an error that it creates?

 

quote:

 

You can coax the handheld receivers to give you readings when it is chilly by warming them with body heat. But reading accuracy will suffer. Most units use an internal temperature sensor to help correct for atmospheric conditions.

 

-jjf


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It was 5 degrees overnight (that's Farenheit, and in my car, in my garage), and I started up my MeriGold this morning. The display was almost impossible to read, but I was able to bump up the contrast. Despite a nice geometry, the MeriGold was unable to get a lock on a single satellite for about 5 minutes, until the heat from the defrosters was able to warm up the unit a bit. It took about 8 minutes in a warming-up car to get a position fix, which was right on, according to my previous tracks on the same route. About 10 minutes from start-up, I had to put the contrast back to normal because the display was blacking out.

 

It was 15 below outside overnight. Wind chills were about 40 below, which, incidentally, is the same Celsius or Farenheit.

 

Too cold to cache today, at least in Minnesota.

 

-Craig/TeamCNJC

 

... Two roads diverged in a wood, and I--

I took off through the thorns, chest high, ...

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When I left my house this morning it was -3F an hour and a half later and 30 miles south it may have gotten up to 10F. My Garmin map 76s w/ alkalines led me right to the cache no prob. I really didn't even notice much of a delayed updating....1.5/1 cache though that had me outside about half an hour...much longer than that and I probably would have quit before the garmin did.

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quote:
But reading accuracy will suffer. Most units use an internal temperature sensor to help correct for atmospheric conditions.

 

-jjf


Do they? I thought that temperature sensor was for correction of internal temperature dependent oscillator drift, not signals in the atmosphere. Since the temperature inside the GPS is rather likely to be different than in the near vicinity, and most certainly different compared to the atmosphere a bit higher up in the air, it sounds very unlikely to me that they can get any useful information regarding the signals through space by checking the internal temperature of the receiver.

 

Anders

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I was out on Tuesday with temps probably below 20F. I had some sluggish LCD action (about as sluggish as my numb fingers icon_razz.gif), but what got me was when it came time to change batteries (NiMH), I couldn't get my eTrex turned on until I warmed the batteries up in my hands.

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quote:
Originally posted by Anders:

quote:
But reading accuracy will suffer. Most units use an internal temperature sensor to help correct for atmospheric conditions.

 

-jjf


Do they? I thought that temperature sensor was for correction of internal temperature dependent oscillator drift, not signals in the atmosphere.

Anders


 

Anders, you are quite correct. Atmospheric error sources contribute to most of the total error along with multipath errors. Almost all of the atmospheric error occurs in the ionosphere. The troposhere (that's where we are) only causes errors of a few centimeters. Values of temperature, pressure and relative humidity are required to compensate for these error's. This is not taken into account with our consumer grade recreational receivers.

 

Poindexter

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Poindexter, Anders,

 

My understanding is that the firmware in most units applys a lookup table correction based on deviation from 'standard' temperature. But, my source on this was someone in GPS Avionics, not low end handhelds, so I could be totally wrong.

 

Regarding source of error, my physics recollection would agree with Poindexter, EMR travels different speeds in different atmospheric conditions.

 

-jjf

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quote:
Originally posted by jfitzpat:

Poindexter, Anders,

 

My understanding is that the firmware in most units applys a lookup table correction based on deviation from 'standard' temperature. But, my source on this was someone in GPS Avionics, not low end handhelds, so I could be totally wrong.

-jjf


 

There is a lookup table based on temperature, but it's for timer oscillator compensation. Here's a portion of an e-mail from Garmin engineering on the subject.

 

Poindexter

 

The answer from Garmin Engineering Follows:

 

Obviously, timimg is everything. We must have a precise timing source for this to work. We could install a rubidium or cesium beam oscillator in our GPS receivers, but this would be a little pricey, use a lot more battery power, and the unit would be a little bulky. Instead, we use a relatively cheap oscillator, and a lot of software finesse. Oscillator compensation data is stored in the unit as a table based upon temperature. When the unit locks on, it calculates the unit's oscillator error and enters a correction factor into this table based upon current internal temperature. In this fashion the unit is CONSTANTLY "learning" and fine tuning itself. We burn these units in when new to calculate and store calibration constants across the

entire rated temperature range of the product.

 

GARMIN International

1200 E. 151st Street

Olathe, KS 66062 USA

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My Meridian Platinum does seem to slow down in the cold. I walked 100 feet past the cache before it started to point in the direction of the cache. It has been in the single digits and bellow here and I've learned to stop for a minute or two when I get within 150 feet of the cache. And when ever possible keep it in the case.

quote:

Through rain, sleet, snow, or dead of night... The cacher must go through...
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