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CardinalNSB(at)aol.com
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 Posted: Thu Jan 04, 2007 10:38 am Post subject: WAAS |
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I thought the WAAS signal was generated from the ground, am I wrong? Skip
[quote][b]
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ainut(at)hiwaay.net
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| Posted: Thu Jan 04, 2007 12:02 pm Post subject: WAAS |
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It's origins begin on the ground then the corrrections are uplinked to the sats which are then broadcast to us.
CardinalNSB(at)aol.com (CardinalNSB(at)aol.com) wrote:
[quote] I thought the WAAS signal was generated from the ground, am I wrong? Skip
[b]
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bakerocb
Joined: 15 Jan 2006
Posts: 727
Location: FAIRFAX VA
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| Posted: Fri Jan 05, 2007 5:21 am Post subject: WAAS |
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1/5/2007
Skip wrote: "I thought the WAAS signal was generated from the ground, am I
wrong?"
Hello Skip, How WAAS works is a bit complex. Here is a brief description
from a US govt web site http://gps.faa.gov/programs/index.htm.
------------------------- BRIEF WAAS DESCRIPTION
BEGINS -----------------------------
"How It Works
Unlike traditional ground-based navigation aids, the WAAS covers nearly all
of the National Airspace System (NAS). The WAAS provides augmentation
information to GPS receivers to enhance the accuracy and reliability of
position estimates.
The signals from GPS satellites are received across the NAS at many
widely-spaced Wide Area Reference Stations (WRS) sites. The WRS locations
are precisely surveyed so that any errors in the received GPS signals can be
detected.
The GPS information collected by the WRS sites is forwarded to the WAAS
Master Station (WMS) via a terrestrial communications network. At the WMS,
the WAAS augmentation messages are generated. These messages contain
information that allows GPS receivers to remove errors in the GPS signal,
allowing for a significant increase in location accuracy and reliability.
The augmentation messages are sent from the WMS to uplink stations to be
transmitted to navigation payloads on Geostationary communications
satellites.
The navigation payloads broadcast the augmentation messages on a GPS-like
signal. The GPS/WAAS receiver processes the WAAS augmentation message as
part of estimating position. The GPS-like signal from the navigation
transponder can also be used by the receiver as an additional source for
calculation of the user's position.
WAAS also provides indications to GPS/WAAS receivers of where the GPS system
is unusable due to system errors or other effects. Further, the WAAS system
was designed to the strictest of safety standards - users are notified
within six seconds of any issuance of hazardously misleading information
that would cause an error in the GPS position estimate."
------------------------------- BRIEF WAAS DESCRIPTION
ENDS --------------------------------
One significant point that I want to make is that while WAAS is not
considered a "ground based system" by the US Govt it still involves "ground
facilities" and 91.205 (d) (2) reads "Two way radio communications system
and navigational equipment appropriate to the ground facilities to be used".
My position is that an ABEA (Amateur Built Experimental Aircraft) equipped
with TSO C146a Gamma-3 certification WAAS avionics complies with 91.205 (d)
(2).
OC -- The best investment we will ever make is in gathering knowledge.
Time: 10:38:28 AM PST US
From: CardinalNSB(at)aol.com
Subject: Avionics-List: WAAS
I thought the WAAS signal was generated from the ground, am I wrong? Skip
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