This is an old revision of the document!
An attractive looking unit with some great features however current versions of the module have an altitude limit of 27km. We understand from Adafruit newer versions are on order that have a limit of 40km however these currently aren't on sale. A prototype of this new unit was successfully tested to 38.5km by UKHAS where it worked with no issues. Nothing needs to be set to engage the high altitude mode.
PLEASE BE AWARE ANY MODULES YOU PURCHASE FROM ADAFRUIT AT THIS TIME WILL HAVE A LIMIT OF 27KM
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