Garmin GPS - Legend HCx and WAAS

Author

Legend HCx and WAAS

Scott Nelson

2008-02-14, 4:33 am

I just received the Legend HCx and am wondering about WAAS. Are there
any benefits/drawbacks to leaving it on all the time? In the setup you
can toggle it on or off. I was under the impression that it increased
accuracy. Why would you choose to shut it off. The default setting
seems to be off.

Thanks.
Scott

Roarmeister

2008-02-14, 10:33 am

On Thu, 14 Feb 2008 00:21:48 -0600, Scott Nelson
< treasuredude62@nospa
myahoo.com> wrote:

>I just received the Legend HCx and am wondering about WAAS. Are there
>any benefits/drawbacks to leaving it on all the time? In the setup you
>can toggle it on or off. I was under the impression that it increased
>accuracy. Why would you choose to shut it off. The default setting
>seems to be off.

Perhaps to save battery life?

James Robinson

2008-02-14, 10:33 am

Scott Nelson < treasuredude62@nospa
myahoo.com> wrote:

> I just received the Legend HCx and am wondering about WAAS. Are there
> any benefits/drawbacks to leaving it on all the time? In the setup you
> can toggle it on or off. I was under the impression that it increased
> accuracy. Why would you choose to shut it off. The default setting
> seems to be off.

The WAAS signal requires that the GPS be powered up all the time, since
there is a significant amount of digital information transmitted. To save
energy, a GPS will often alternately power down the receiver for several
seconds, then power up to capture a GPS signal, and to on. That will
extend battery life. When WAAS is enabled, it remains on all the time.

WAAS doesn't necessarily improve accuracy. There are conditions where it
will, and conditions where it won't. There are several signals that WAAS
uses, some from satellites, and some from ground stations. The greatest
benefit is when the GPS is near one of the ground transmitters, but if you
are far from a ground station, or don't receive the ground transmitter
signal, the WAAS signals from the satellites can actually reduce accuracy.
Thus WAAS isn't useful in places like South America without the ground
stations.

ben brugman

2008-02-14, 3:33 pm

> are far from a ground station, or don't receive the ground transmitter
> signal, the WAAS signals from the satellites can actually reduce accuracy.
> Thus WAAS isn't useful in places like South America without the ground
> stations.

Normally waas systems do increase accuracy and not reduce is.

A few years ago when in Europe Waas was still experimental it was better
to have the Waas switched of, results then would be more consistend.

A GPS with Waas switched on does not receive from ground stations,
satellites only. Using waas on some units (Garmin) for example, uses
two channels for the Waas satellites leaving only 10 for 'normal' satelites.

Because more satellites are tracked with the waas on, in some circumstances,
you could be using more power. (But this is very limited).

And I have never seen a GPS unit which is switched on all the time when
using
waas and is intermittendly switched on and of using 'normal' mode. It takes
more
time to get a fix on a waas satellite, but switching on/off is not normal
for
GPS units.

ben

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