Garmin 76CSx position error observed a few days ago

My recently purchased GPSMAP 76CSx experienced a weird behavior on May
18th while I was driving home from work. I was driving N on my
regularly traveled route and the position indicator showed me on a
parallel path roughly 375-500 feet west of my actual location. I have
reviewed the track log to confirm this. During this time my reported
elevation was roughly -390 ft.

At geocaching.com I discovered that several other users have
experienced similar behavior on the same day. some with 76CSx and some
with 60CSx. Nobody else has chimed in with other GPSr types.

Any clue as to what is going on?

At all other times this unit has shown me traveling right down the
center of the lanes.

Thanks,

geokitebuggy

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George Cameron wrote:

Your receiver could have been in a 2D mode with the wrong elevation.
Having an external antenna on the top of your vehicle will help
tremendously.

That was the first thing I checked. It was seeing about 8 sats at the
time with high signal strength on most. WAAS enabled, too. EPE +/-
20 ft. or so. 3D fix...

I got home, put in fresh batteries, went out in the front yard with
good open sky view and it said I was several hundred feet from where I
knew myself to be.

At 4:20 PM PDT I was trying to find a geocache and all was well. I
turned the GPSr off until 5:29 PM at which time the error was present.
The error went away at 5:49 PM. I have looked at my track log more
closely and the error is roughly 0.2 mi with a bearing of 340 deg
true.

Weird, huh?


wrote:

George Cameron wrote:
[rearranged to bottom posting ;]

The U.S. Coast Guard collects reports of GPS anomalies
http://www.navcen.uscg.gov/gps/gpsuserinput.htm


What is your approximate location?
I'm interested in GPS error and have been collecting data from various
CORS stations and plotting. I'd like to plot errors for 2 or 3 stations
in your vicinity.

[My initial goal is good understanding of the periodic errors. Eventual
goal is anomalies due to tropospheric effects -- possible correlation to
major &/or intense storm systems.
Error sources http://edu-observatory.org/gps/gps.html
More error sources http://users.erols.com/dlwilson/gps.htm
GPS & Water Vapor http://www.etl.noaa.gov/technology/archive/gps/ ]

Location here: N38* 02.3xx W121* 15.9xx

I observed the errors within approx. 3 miles of this loc.


On Mon, 21 May 2007 07:33:39 -0500, Richard Owlett