How GPS works on meshtastic?

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  1. The GPS antennas that come with the t-beam are not great. You need to make sure they properly face the sky and even then they could use an upgrade. Have a look at this thread.
  2. Depending on the GPS chip (NEO-M6 / NEO-M8N) you can use only GPS sattelites (NEO-6M) or also sattelites from other systems e.g. Galileo, Baidu, GLONASS (NEO-M8N). However this has to be configured. I used a serial passthrough sketch and the official u-center software to configure mine to use GPS, Galileo and GLONASS, however I do not know if Meshtastic overrides that setting. Maybe @geeksville can clarify and / or make a change that does for everyone using a NEO-M8N.

Update: I looked at the code and the GPS is reset to factory defaults. Section 1.5 of the datasheet quotes:

The NEO-M8 GNSS modules are concurrent GNSS receivers which can receive and track multiple
GNSS systems: GPS, Galileo, GLONASS and BeiDou. Owing to the dual-frequency RF front-end
architecture, either GLONASS or BeiDou can be processed concurrently with GPS and Galileo signals providing reception of three GNSS systems. By default the M8 receivers are configured for concurrent GPS and GLONASS, including SBAS and QZSS reception. If power consumption is a key factor, the receiver should be configured for a single GNSS operation using GPS, Galileo, GLONASS or BeiDou and disabling QZSS and SBAS.

So for nodes connected to the power grid it might be an option to enable GPS + Galileo + GLONASS or GPS + Galileo + BeiDou and for mobile usage it might be an option to use only a single GNSS to save power.

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