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Reference
Main Menu: GPS Tab
WAAS Capability
The GPSMAP 178C is capable of receiving WAAS (Wide Area Augmentation System) satellite sig-
nals. WAAS is an FAA (Federal Aviation Administration) funded project to improve the overall accuracy
and integrity of the GPS signal for aviation use, but land/sea based users may also benefi t from this
system. At this time, the system is still in the development stage and is not fully operational. There are
currently two WAAS satellites that can be received in the U.S.A., one over the Atlantic Ocean and one
over the Pacifi c Ocean, in a geo-stationary orbit over the equator. Effective use of the WAAS satellite
signal may be limited by your geographic location in relation to those satellites, now in developmental
service. WAAS satellite signal reception requires an absolute clear view of the sky and works best when
there are no nearby obstructions such as buildings, mountains, etc. WAAS satellites are numbered 33
or higher when viewing the sky view on your GPSMAP 178C. Initial reception of the WAAS signal may
take up to 15-20 minutes, then 1-2 minutes afterwards. When WAAS differential correction has been
received for GPS satellites (numbers 32 or below), a ‘D’ appears in the signal bar of the sky view and
‘2D or 3D Differential’ appears in the receiver status. To learn more about the WAAS system, its satellite
positions and current state of development, visit the FAA web site (http://gps.faa.gov). Since WAAS
requires CPU resources of the GPSMAP 178C to search for and track the satellites, you may disable the
WAAS feature to improve unit performance if WAAS reception is not available in your area.
To disable/enable WAAS capability:
1. From the GPS tab, press MENU, then use the ARROW KEYPAD to highlight ‘WAAS Off’ or ‘WAAS
On’ and press ENTER.
Receiver Status and Accuracy
Receiver status is indicated at the top fi eld of the page, with the current Accuracy and Dilution Of
Precision (DOP) to the right of the sky view. Accuracy uses DOP and other factors to calculate horizon-
tal position accuracy in feet or meters.
Highlight ‘WAAS Off’ and press ENTER
to disable the WAAS capabilities.
GPSMAP178CManual.indd 69 3/19/2004, 3:10:37 PM