T&T: Garmin 76 and 3D Differential

[Peter Bennett]

Monday, August 6, 2007, 8:56:48 AM, bv wrote:

b> Hello

b> I have a 4 or 5 years old GPS Garmin 76. In the last months, I noticed that
b> it does not show anymore the option "3D Differential", but only "2D GPS
b> Location" or "3D GPS location" (in Lake Champlain, Vermont and NY State)

b> Was there a change in the GPS network ? Is my Garmin 76 getting too old ?

Recently (July 1?), two of the older WAAS satellites have been turned
off - this may affect WAAS differential corrections on older
receivers, if they can't find the new WAAS satellites.

b> Secondly, can somebody remind me what is the WAAS Enabled or disabled option
b> in the Menu ? I can't see any noticeable difference.

WAAS is a satellite-based differential correction system which should
slightly improve the accuracy.  However, the uncorrected accuracy is
now in the 30 ft range, I believe, so I don't think the WAAS
improvement is really worthwhile for most of us.

I have experienced a problem with a Garmin 168 when using WAAS - if
the WAAS satellite hides behind an island (not uncommon here in the
PNW), the GPS spends so much time trying to get the WAAS data that it
doesn't have time to properly handle the NMEA-0183 output to my
autopilot, so the pilot starts complaining about "No data".  As a
result, I leave WAAS off.

b> All the Best

b> Bryan

-- 
Peter Bennett, VE7CEI    Vancouver, B.C., Canada
Ennos 31 "Honeycomb"
GPS and NMEA info: http://vancouver-webpages.com/peter 
Vancouver Power Squadron: http://vancouver.powersquadron.ca