bobby49 wrote: ↑Sat Mar 09, 2019 3:13 pmI can't give you a complete answer, since I don't use any Spot devices. Geographical coverage depends on (1) which satellite system is in use, (2) the altitude of that satellite system, (3) the power transmitted from the device up to the bird, and (4) the power transmitted down from the bird. That gets into all sorts of messy technicalities. The digital length of the message dictates how long the link has to stay good to get a confirmed signal transfer, and for the birds in low earth orbit the overhead time is only 30-60 seconds for each pass. Geosynchronous satellites are all in high earth orbit, appearing to hover in one spot in the sky, so coverage tends to stay more constant, but those aren't generally used for messaging. Also, some devices use only the satellite signals that are above a certain mask angle above the horizon, since low angle satellite signals get unreliable. Believe me, we've only scratched the technical surface of this stuff, and I used to teach GPS classes.
That wasn't even a partial answer. :-)
I found a blog where it was mentioned that there was a need to upgrade the ground stations in Asia and Australia before 2-way messaging would work in those regions. That seems to be one of the bugaboos with the Spot technology.
Given my own disappointing experience with 1-way Spot messaging I wonder how well the 2-way messaging works. At least with 2-way you'll get feedback (or a lack thereof).