GPS WAAS Update (Magellan Sportrak)

Today, we manipulate bits to resurrect a hobbled 15 year old GPS receiver. In the process, I learned about WAAS and s-records to successfully update a client’s  Magellan Sportrak GPS unit.




The first part of this project requires an understanding of the global positioning system (GPS) and the Earth’s atmosphere.

Magellan GPS

The Magellan GPS receiver used older WAAS data. Specifically, INMARSAT 3-F2 (aka. PRN 120) and INMARSAT 3-F4 (aka. PRN 122 AOR-W) were hard coded into the GPS unit. These ceased WAAS service and were not replicated.

You can verify which WAAS satellites are being used by entering the secret [menu][left][right][left][right] 03 menu.


Directly updating the GPS firmware is required.

I created an Excel document to assist the firmware modification process: STPS-v1

A 7z compressed update file for only the Magellan SportTrak is available at: spor534-WAASco


Client’s Response

The client responded with the following

You did it!!  Your update works just fine.  SporTrak now shows WAAS when moving and WAAS AVERAGING when stopped.  I misquoted the # of satellites it is capable of receiving:  the screen shows space for 12 and I got 11 at one time this AM!!   Apparently this version does not show EPE except when it cannot view a WAAS satellite.  But I can tell from the displayed elevation that the precision is greatly improved.


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