Changes in WAAS

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There have been a few recent changes in the FAA's satellite-based augmentation system (SBAS) known as WAAS or wide-area augmentation system. Three satellites are now available for the WAAS signals-in-space corrections. Listing the satellites from East to West, they are:

Satellite Name / MNEA Number / PRN Number / Orbital Position

INMARSAT-4F3 NMEA-46 PRN-133 98°W

ANIK F1R NMEA-51 PRN-138 107.3°W

GALAXY-15 NMEA-48 PRN-135 133°W

See Wide Area Augmentation System - Wikipedia, the free encyclopedia

I have been looking for a source of information on the date from which PRN-133 was operational. It seems like the onset of service from PRN-133 was earlier this year (2011), and the signal has been available for quite a while.

I have a fairly new GPS receiver (internal to a Lowrance HDS-8), but it seems to be ignorant of PRN-133, the newest signal source. For my location (in the Great Lakes) the PRN-133 signal would be preferred due to its higher look angle. My GPSr always uses PRN-138.

I am interested to learn if other GPS receivers in the Eastern USA are aware of and making use of PRN-133 for WAAS precision fixes.

[GordMay]

On April 2010, WAAS satellite PRN 135 lost control of its navigation computer – the system that keeps the satellite stationary over the equator. Normally PRN 135 is at longitude 133º West. With no navigation computer, the satellite drifted slowly to the East. In December 2010, it had drifted to 93ºW, when finally the navigation computer was back online. In January 2011, work began to bring the satellite back online and move it back to 133ºW.

While on the move back to 133ºW, PRN 135 will be in test mode. Receivers on the ground may be selecting PRN 135 as the primary WAAS satellite to use, based on where it is in the sky. If only test messages are available on the receiver’s primary WAAS satellite, the receivers wait to see if full messages will be coming. Unfortunately this prevents the receiver from using the valid signals that are currently transmitting from PRN 133 and 138.

To ensure uninterrupted WAAS performance, users should manually tune their receivers to use PRN’s 133 and 138 until PRN 135 arrives back at its home at 133ºW, later in 2011.

More ➥ WAAS User Information - Hemisphere GPS

And ➥ Welcome to the WAAS Test Team Website

Hope this helps,
Gord

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Originally Posted by GordMay

On April 2010, WAAS satellite PRN 135 lost control of its navigation computer – the system that keeps the satellite stationary over the equator. Normally PRN 135 is at longitude 133º West. With no navigation computer, the satellite drifted slowly to the East. In December 2010, it had drifted to 93ºW, when finally the navigation computer was back online. In January 2011, work began to bring the satellite back online and move it back to 133ºW.

While on the move back to 133ºW, PRN 135 will be in test mode. Receivers on the ground may be selecting PRN 135 as the primary WAAS satellite to use, based on where it is in the sky. If only test messages are available on the receiver’s primary WAAS satellite, the receivers wait to see if full messages will be coming. Unfortunately this prevents the receiver from using the valid signals that are currently transmitting from PRN 133 and 138.

To ensure uninterrupted WAAS performance, users should manually tune their receivers to use PRN’s 133 and 138 until PRN 135 arrives back at its home at 133ºW, later in 2011.

More ➥ WAAS User Information - Hemisphere GPS

And ➥ Welcome to the WAAS Test Team Website

Hope this helps,
Gord

Hi Gord. Thanks for the reply, but it did not help. I was aware of the problems that affected the GALAXY 15 satellite. It is an interesting story, but because GALAXY 15 was so far West, it was never a useable signal for me, and probably not for most boaters in the Eastern USA.

My GPS receiver is integral to my multi-function SONAR and chart plotter, (an HDS-8) and I am afraid I cannot control what signal it prefers for WAAS.

From what I have read, including the links mentioned above, it appears to me that PRN-133 is operational, and it should be possible to receive it and make us of it with a WAAS capable GPSr. I am most curious to see if there are other users in the Eastern USA who can make use of the new satellite, sending PRN-133.

ASIDE: there is potential for some confusion because the "133" is both the longitude of one of the satellites and the psuedo-random noise code number of another. However, the two are not correlated.

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I have received (via another channel) one report of a GARMIN GPS receiver (located near New Orleans, Louisiana) showing it was acquiring a signal from PRN-133, but that signal was not being used for the precision fix.

Any other reports of reception of PRN-133 from North American GPS receivers?

[barnakiel]

Outside USA I tried to switch the WAAS on a couple of times. Each time, the accuracy dropped. Garmin units.

Hope it works fine in the US.

b.

[goboatingnow]

Originally Posted by barnakiel

Outside USA I tried to switch the WAAS on a couple of times. Each time, the accuracy dropped. Garmin units.

Hope it works fine in the US.

b.

I have several Garmin units, they all work fine on EGNOS

Dave

[barnakiel]

Originally Posted by goboatingnow

I have several Garmin units, they all work fine on EGNOS

Dave

As I said, it works BUT accuracy drops.

Or at least this is what the units report.

b.

[Hud3]

Garmin advises that you not activate the WAAS feature if you're not in an area with WAAS coverage for that very reason--the accuracy degrades.

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Thanks to all for the several new topics added to the discussion.

I am really most interested to know if anyone is seeing PRN-133 being received on their GPS receivers when in North American, and particularly when in the Eastern half of the USA. The signal from PRN-133 should be preferred in the Eastern half of the USA over the other two sources.

So far no reports of PRN-133. Anyone have a report of reception of PRN-133?

[barnakiel]

Originally Posted by Hud3

Garmin advises that you not activate the WAAS feature if you're not in an area with WAAS coverage for that very reason--the accuracy degrades.

Bang on. THX. Exactly as we observed.

Treat the word 'coverage' with caution - you can still see the satellites!

b.

[continuouswave]

These comments about using WAAS for a precision fix in areas that are far outside of its coverage area are interesting, but they are nothing new. While WAAS is a "wide area" it is not useful on a global basis. The FAA makes quite clear what the coverage area is.

The only recent change in WAAS has been the addition of a new signal source with PRN-133. I am interested to learn if anyone in North America is able to receive PRN-133 on their GPS receiver and use it for WAAS.

The signal from PRN-133 has been available for about a year. I am surprised that no one is reporting that they are able to receive it. Are all of our marine GPS receivers this badly made that they can't receive PRN-133?

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I am pleased to report that my Lowrance HDS-8 GPS receiver has finally found PRN-133. It showed up this morning when I had the receiver on the work bench. Yesterday I had moved the receiver around the house and back yard trying to coax it into finding PRN-133 without success. This morning it showed up by surprise.

[fairbank56]

I checked the Naval Academy Navy 44's last week, Furuno BBWGPS to NavNet Vx2, and they are showing PRN 133 with good signal strength.

Eric