Etrex Legend

[+RVA_Scooter_Girl & Matty Syxx]

I just bought a Legend, and although I haven't had much time with it, I've noticed it's had problems locking on on cloudy days. Is this typical of this particular unit or of most lower level GPSs in general?

 

(Please don't tell me I should have bought different unit...I just want to know others experiences..)

 

Thanks a bunch!

[+Renegade Knight]

You will get different comment's on this.

 

I have a GPS V which is a few steps up from the Legend and which has a better antanea for some situations though I'm also willing to admit the Legend has a better antanea for other situations both of which I run into in Idaho.

 

Anyway On a cloudy/foggy day I've noticed my GPS tends to not be as accurate. Where I'm normally 20' from a cache I'm now 50' when I find it. It could be just a bad day of coordinates but since the fog was handy I blamed it.

 

Water does affect the satallite signal that your GPS is looking for. Generally though light cloud cover has never been an issue that I've seen. Being in Idaho Heavy cloud cover is something I don't expereince very often. Fog though...

 

So there is your wishy washy not much of an answer. You will find that if you drive a distance from where you last used your GPS it will take longer to get a lock. If you are driving while trying to get a lock it will take longer etc.

[peter]

My eMap has the same antenna as the Legend and I've never been able to detect any direct effect of clouds, rain, thunderstorms, or other weather on the reception. The GPS frequencies were chosen in a band that is only minimally affected by weather conditions since the military is depending on this for all-weather navigation.

 

The water droplets in fog or rain are very small compared to the wavelength of the GPS signals and therefore don't cause any significant absorption.

OTOH, the signals are attenuated by any larger sheet of water, so there can be an effect if overhead foliage is covered with a film of water from dew, fog, or rain.

 

Note that when first getting a lock the unit needs to receive the satellite ephemeris data in an uninterrupted stream. If you're moving and the signal is being obstructed momentarily by trees, buildings, poles, etc. this will prevent acquisition of the needed data. It's best to remain stationary until the unit has a good lock.

[DiverMan]

I have had my legend for about a year now. I love it. It is a great all around unit. You will find lower accuracy under tree cover, cloud cover, and around tall buildings but for the price, you can't beat it.

 

Have you upgraded the firmware of the unit yet?

 

Good luck and have a blessed weekend

Edited June 26, 2004 by DiverMan

[+SunnyCyndi]

Did you by chance buy a refurbished unit? I recently returned my second Legend to Sportsman's Warehouse. I was told that they had had many returned because of problems with satellite lock. I still was using my little cheap Gecko 101 ( still working great!) along side so I knew it wasn't just the atmospheric conditions.

[+Team GPSaxophone]

I just bought a Legend, and although I haven't had much time with it, I've noticed it's had problems locking on on cloudy days. Is this typical of this particular unit or of most lower level GPSs in general?

 

(Please don't tell me I should have bought different unit...I just want to know others experiences..)

 

Thanks a bunch!

I have a Legend. I hadn't noticed the cloud-cover problem until I visited Las Cruces earlier this week. It actually rains during monsoon season down there! Either that, or since Albuquerque's monsoons haven't started, I've forgotten how much it rains here.

Anyway, I had lousy reception all day. Just hold your GPS flat to optimize the signal.

[+ohgr]

I live in SoCal, and the highest accuracy I've even seen on my legend was on a very cloudy overcast day, Accurate to 5feet. At least that's what it said. Never saw it that accurate again.

 

I will say that my girlfriends Gecko 101 sometimes seems more accurate than my Legend. But I still think it's a great little GPSr, and it has never failed to get me close enough to a cache to be able to find it.

 

Ohgr

[+Tahoe Skier5000]

The weather should affect GPS signals very little. Frequency waves travel through clouds and moisture easily.

[+Cacheoholic]

I have a Legend and a Magellan Meridian. I put them in the same class price wise, but the Meridian out performs the Legend every time. The Legend constantly looses its fix under trees. I suppose the Meridian does to, but it seems to give an accurate average of where to go. The Legend just goes out.

[+EraSeek]

And I Quote:

 

Rain, Snow, Clouds and GPS Reception

1) Does RAIN or SNOW or CLOUDS affect the reception of my GPS receiver?

Answer: No. Not so as the user can tell without instrumentation.

 

2) I notice that when it rains and I turn on my windshield wipers my GPS has trouble locking. Doesn't this mean that rain affects my GPS reception?

Answer: No. What is affecting your GPS signal reception is the fact that the wipers running back and forth across your windshield is intermittently blocking reception and making it difficult for your GPS to get a complete navigation data string. Turning off your wipers until the signal locks will speed the initial lock.

 

3) Sometimes my GPS gets a thick coating of water on it and it does not receive as well. Does this not prove that rain can cause signal degradation?

Answer: No. A coating of water, even a fairly thin one is NOT the same as raindrops. The GPS signal frequency of about 1575mhz was chosen expressly because it is a "window" in the weather as far as signal propagation is concerned.

 

4) This all sounds good, but do you have a reference that supports these statements?

Answer: Yes.

See: Ref: http://www.navcen.uscg.gov/pubs/gps/sigspec/default.htm (Courtesy of Sam Wormley)

 

Cloud, Rain, Snow, weather in general does NOT attenuate the GPS signals enough to effect accuracy. As can be seen below, the total atmospheric loss (from all causes including rain, clouds, snow, fog, etc.) is but 2db. This is small compared with other variables.

 

L1 and L2 Navigation satellite Signal Power Budget

 

Parameter L1 P-Code L1 C/A-Code L2 P-Code

-----------------------------------------------------------------------------------------------------

User minimum received power -163.0 dBw -160.0 dBw -166.0 dBw

Users linear antenna gain 3.0 dB 3.0 dB 3.0 dB

Free-space propagation loss 184.4 dB 184.4 dB 182.3 dB

Total atmospheric loss 2.0 dB 2.0 dB 2.0 dB

Polarization mismatch loss 3.4 dB 3.4 dB 4.4 dB

Required satellite EIRP +23.8 dBw +26.8 dBw +19.7 dBw

Satellite Antenna gain at 14.3° 13.5 dB 13.4 dB 11.5 dB

worst case Block II off-axis angle

Required minimum satellite antenna +10.3 dBw +13.4 dBw +8.2 dBw

Input power 10.72W 21.88W 6.61W

 

5) Ok then, can I use my GPS underwater?

Answer: No. Just a few millimeters of "solid" water will severely attenuate the GPS signal.

 

Joe Mehaffey

[+RVA_Scooter_Girl & Matty Syxx]

Wow. Thanks for all the answers guys.

 

Could it possibly be time of day then?

 

Again, I'm still learning how everything works...I took it out today about mid-day on a clear sunfilled day and had absolutely no problems until I got under heavy foliage cover...which was expected. The numerous times that I wondered if it was cloud cover (thanks for clearing that up) was in the early evening..out in the open...

[+Tahoe Skier5000]

You should connect that GPS to your scooter.

[peter]

Could it possibly be time of day then?

...

The numerous times that I wondered if it was cloud cover (thanks for clearing that up) was in the early evening..out in the open...

Reception should be fine in the evening although accuracy will be marginally better at night when the troposphere is less affected by solar radiation.

 

However, the GPS satellites have orbital periods of about 12 hours. So if you go out on successive days at the same time you'll get just about the same satellite configuration. It's possible that in your location you had a relatively poor arrangement of satellites overhead during that time. Check the satellite page to see where in the sky the sats are located and which ones your unit is receiving. Doing this with my eMap I can almost always identify why a specific satellite is not being received - i.e. which hill, building, person, tree trunk, etc. is blocking the reception.

[+Go JayBee]

Take it out of your pocket! Hold it in your hand, antennae side up...

I have had both eTrex Legend and Vista...they both seem to react the same way. You gotta hold them just right.

 

Hope this helps,

JayBee

 

edit for spelling error

Edited June 28, 2004 by Go JayBee

[+RVA_Scooter_Girl & Matty Syxx]

You should connect that GPS to your scooter.

*grin* That's my plan....