+rrules Posted July 26, 2011 Share Posted July 26, 2011 I have heard mixed reviews. I don,t seems to get much help when I turn it on. Quote Link to comment
+ky.m.guy Posted July 26, 2011 Share Posted July 26, 2011 Wikipedia article says it does. Quote Link to comment
7rxc Posted July 26, 2011 Share Posted July 26, 2011 I think part of the discussion yes/no originates during the early days of WAAS when the information was broadcast from ground stations along the US coastline and some inland. Canada didn't have m/any of those. Once the geostationary sats came online, things changed. Obviously one has to be able to hear the transmissions, so the closer to the equator, the better. One reason it seems not to work by much, is that today's GPSrs are much better at hearing and processing the GPS sats. I'm not sure if it was first implemented before high sensitivity receivers, but I seem to recall some of the regular variety had WAAS but not the high sensitivity part. All do better than pre WAAS GPSrs. I'll touch up this if my memory proves incorrect, I promise. I use WAAS on most of the time, but I find in my location the difference on open ground is about 1 metre at most. It does help in marginal coverage areas. Doug 7rxc Quote Link to comment
+Avernar Posted July 26, 2011 Share Posted July 26, 2011 I think part of the discussion yes/no originates during the early days of WAAS when the information was broadcast from ground stations along the US coastline and some inland. Canada didn't have m/any of those. Once the geostationary sats came online, things changed. WAAS has always been broadcast from orbit. Differential GPS (DGPS) is broadcast from the ground and is not wide area. DGPS also needs a separate radio receiver hooked up to the GPSr. Quote Link to comment
+Westacular Posted July 26, 2011 Share Posted July 26, 2011 I think part of the discussion yes/no originates during the early days of WAAS when the information was broadcast from ground stations along the US coastline and some inland. Canada didn't have m/any of those. Once the geostationary sats came online, things changed. WAAS has always been broadcast from orbit. Differential GPS (DGPS) is broadcast from the ground and is not wide area. DGPS also needs a separate radio receiver hooked up to the GPSr. True. Doug mixed up the details, however: 1) WAAS relies on ground-based reference stations to provide relevant correction data for different regions. There weren't any active in Canada until 2007. Prior to that, much of northern and eastern Canada effectively weren't covered. 2) Geostationary satellites necessarily orbit above the equator. As you move north, the apparent elevation of the satellite gets closer to the horizon, and the signal becomes harder to receive (and, if you're not in a plane, more likely to be blocked by local terrain). Compared to the original two satellites, the current ones (2 became active in 2007 and a third in 2010) have stronger signals, and are positioned at better longitudes for covering Canada. The conclusion stands: In Canada, the general usefulness of WAAS is much better now than it was pre-2007. Useful links: "WASS IN CANADA" The FAA's WAAS Test Team Website, which has a number of interesting real-time maps and graphs like the one ky.m.guy posted. Quote Link to comment
Andronicus Posted July 27, 2011 Share Posted July 27, 2011 I think part of the discussion yes/no originates during the early days of WAAS when the information was broadcast from ground stations along the US coastline and some inland. Canada didn't have m/any of those. Once the geostationary sats came online, things changed. Obviously one has to be able to hear the transmissions, so the closer to the equator, the better. One reason it seems not to work by much, is that today's GPSrs are much better at hearing and processing the GPS sats. I'm not sure if it was first implemented before high sensitivity receivers, but I seem to recall some of the regular variety had WAAS but not the high sensitivity part. All do better than pre WAAS GPSrs. I'll touch up this if my memory proves incorrect, I promise. I use WAAS on most of the time, but I find in my location the difference on open ground is about 1 metre at most. It does help in marginal coverage areas. Doug 7rxc Don't mix up sensitivity with accuracy. WAAS has nothing to do with sensitivity. WAAS helps to correct for atmosphiric distortion. Without that correction GPS accuracy has a theoretical maximum accuracy of about 15m. Sensitivity allows you to 'hear' the satalittes even during thick cloud and trees and buildings etc. are in the way. Accuracy units are ±m (eg. ±15m or ±2.7m) Sensitivity units are dBm (or W or mW or µW) (eg. -165dBm or -155dBm) Quote Link to comment
7rxc Posted July 28, 2011 Share Posted July 28, 2011 (edited) I didn't mix anything up, I still believe that I read about ground stations transmitting on WAAS frequencies before the satellites were enabled in that sense, but it was limited to marine use areas and was short lived. I'm trying to track down the reference. It was to enable use of marine navigation GPS early... It was not intended for the Aviation market at that time. In effect it was a DGPS system using the new WAAS hardware. Either way it was there, unless I'm nuts, a definite possiblity. edit: Memory seems to have been fuzzy... just missed something on the US NDGPS system... they used longwave radio receivers for the DGPS info, not the WAAS frequencies. Perhaps they tried them on a smaller scale. I'm still looking though. Just busy with something else right now. As for accuracy, precision and the sensitivity thing, I believe I was clear... there were low sensitivity GPSrs with WAAS. I know the regular Legend was in that bunch. Now they have H versions. The WAAS really helps on the legend, but would not show on the H versions so much simply due to the better reception. Low sensitivity receivers will accept more multi path (reflection) signals and that can degrade the coordinate since it can affect the path lengths in the mountains for example. Any way the OP only asked about the debate re did it work or not and the fact remains that it works, and depending on the GPSr it works to different amounts to improve the results... My Map60cx usually gives 1 metre difference at most times. Doug 7rxc Edited July 28, 2011 by 7rxc Quote Link to comment
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