If I upgrade my yellow etrex to a waas unit, will I get better performance under foliage?

WAAS is iffy at best in the typical geocaching environment. The augmentation comes from ONE satellite, which is typically closer to the horizon rather than overhead. One good obstacle in that direction and WAAS becomes useless.

The additional processing overhead due to processing the WAAS augmentation data also tends to slow down the responses of most consumer GPS's. My GPS V has WAAS ... I keep it turned off except when I'm using the unit in the air or on water.

Scott

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Scott Johnson (ScottJ)

Short answer no.

Long answer of why not.

The way a GPS calculates where it is, is by knowing where the GPS satellites are and calculating the distance from them. The way it calculates distance is by timing how long the radio signal from satellites takes to arrive and then multiply by the speed of the radio signal. The problem is that while a radio signal travels at the speed of light in a vacuum, which is constant however part of the time it is traveling in the earth’s atmosphere. The speed in the atmosphere varies depending on many things like pressure, amount of water vapor and so on. The GPS receiver guesses at these effects and does a fairly good job. What WAAS does is have 25 stations with GPS receivers. The location of these stations are know with high accuracy. The computers there calculate how long a signals from the satellites should take, and measure how long it really took. This information is transmitted to the WAAS satellites. A GPS receiver with WAAS capablility then can receive this information and adjust the time figures it got to a more correct figure. It still can't be fully correct since there is only 25 stations. What the GPS receiver does is figure which of the stations it is close to, and if station 1 says the satellite signals are 3% slow and station 2 says 1% slow it will assume the actual delay is somewhere in between. What figure is uses depends on which station is the closest.

Now the since the problem with foliage is that it blocks part of the signals from the satellites, it doesn't change the timing so WAAS can't help. In fact since there are only 2 WAAS satellites, and we in the east can only pick up one of them. Furthermore they are low in the sky, and tend to be blocked in the woods while at least some of the GPS satellites may be high and have less foliage blocking them.

So WAAS is not helping in the woods.

I understand your explanations. I assumed that additional WAAS sats had been deployed by now. I guess the only thing for it then is a GPS76, and a loooong pole to carry the antenna on.

quote:

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Originally posted by Hostetter Family:
I guess the only thing for it then is a GPS76, and a loooong pole to carry the antenna on.

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Actually, based on my experience with my GPS76, you don't need the pole. It will maintain a sat lock even under trees. I agree with the other comments, WAAS will not help a GPS unit maintain sat lock under trees, that is mainly a function of the GPS antenna and how the unit is held. WAAS really helps where you have pretty good reception, and no major obstructions to the southeast, where the WAAS sat #35 lives.

FWIW,
CharlieP