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An attractive looking unit with some great features however early versions of the module had an altitude limit of 27km. We understand newer versions have a limit of 40km however this has not been proven or disproven at the time of writing. A new unit was successfully tested to 38.5km where it worked with no issues. Nothing needs to be set to engage the high altitude mode.
To test if your module has the 40km firmware on it issue the command $PMTK604*6D (or $PMTK605*31) to the module i.e :
The module will respond with its firmware :
5223 = 40km firmware
5153 = 27km firmware
Weight : 7g
External link : Adafruit Ultimate GPS Breakout