On AREDN nodes with USB, uses an attached GPS device (such as the VK-162 USB GPS Dongle) to update the time and location of the node every 10 minutes.
AREDN nodes without a local GPS device with automatically look for DtD connected nodes with WhereAndWhen (with attached GPS) installed and will sync time and location from them. This allows the use of a single GPS dongle per site with all nodes benefiting.
NOTE: If you have devices connected via DtD but at physically different location (perhaps using a non-AREDN radio to connect them), make sure to disable GPS on those remote devices so they don't "move" to the GPS location.
Particularly handy for nodes being used at different locations in the field.
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GlobalSat BU-353N : https://www.amazon.com/GlobalSat-BU-353N-GNSS-Receiver-Black/dp/B0BLF7DSRY/