Influences on satellite locks

[Guest CapnGadget]

I have noticed that my eTrex basic has worked GREAT under extremely heavy, tall tree cover on one day and just plain crappy on another...

I have also noticed that the earlier in the day it is the more it seems to be able to keep a good lock to the point that I search caches as early in the day as can and will plant my next cache early as well.

The only clue I've had that it might be time related other than the lock/no lock is that in the "advanced" page you can see that the unit has locked on to satellites that are almost in a straight line as if they were "hiding" behind each other. Hence the unit would have trouble triangulating. Have only noticed that in the evening and I'm wondering if it is a function of my general area which is eastern canada...are the satellites harder to "see" for the unit the farther north one goes?

Has any other eTrex owners noticed this sort of thing?

[Guest k2dave]

is that moisture absords the gps signal. Early in the day the earth is heating up and the amount of water the air can hold increases. so water on leaves and such evaporate leaving them dry - and the gps signal easy to receive. when the temop stablizes transpiration (water leaving the leaves) doesn't evaporate as fast and absorbs the gps signal.

 

but that just a guess

[Guest k2dave]

post repeated -

 

[This message has been edited by k2dave (edited 16 August 2001).]

[Guest Bob Bowter]

Satellite geometry most definitely has an effect on the likelihood of getting and keeping lock. Under arboreal cover the birds close to the horizon are particularly difficult to receive. This is only made worse if the GPS receiver's antenna is of the patch variety.

 

There seems at be a some correlation between poor satellite geometry and arrival at a cache site. The probability of poor geometry also increases if one is about to get the coordinates for a cache that is being hidden.

 

Like the weather, just wait a while and the geometry will improve. Typically, I have found that a bad geometry lasts for about 20-30 minutes. Uses the time to enjoy the woods.

[Guest jbwcpa]

quote:

---

Originally posted by k2dave:

My wag is that moisture absords the gps signal....

 

but that just a guess

---

 

I found a nice web site that explains error correction for the above conditions along with some other stuff I didn't know, like how my GPSR knows what time it is and why its clock is so accurate. Thank Trimble for it.

 

ERROR CORRECTION CLICK HERE

 

Montana State and the University of Colorado at Boulder also has a couple of nice GPS sites that do a good job of explaining the technology. The Colorado site allows you to go into more technical detail thru submenus. Also, check out the slide shows on Montana's web site.

 

COLORADO GPS

MONTANA GPS

 

[This message has been edited by jbwcpa (edited 16 August 2001).]