so ive been running APRS for about 3 months now with a TM-D710G and a garmin puck GPS plugged into the back, mostly works fine but lately my position on aprs.fi is showing me about 2 miles southeast of where i actually am. the GPS itself shows the right coordinates when i look at the display, so its not the GPS lying to me. beacon interval is set to smart beaconing and ive double checked the NMEA sentence config, its outputting GGA and RMC.

what gets me is it was working perfectly up until like two weeks ago and i havent changed anything. well i did update the firmware but that was after the problem started so i dont think thats it. also the symbol and SSID are showing up correctly, its just the lat/lon thats off. anyone run into this before or have any idea what to check next

might sound dumb but check if there's another station with a similar callsign or if someone near you has a digipeater that's doing something weird with your packets. sometimes aprs.fi will latch onto an older cached position for a bit. try pulling up the raw packet decode on aprs.fi — click your callsign and look at the actual raw data coming through. if the raw packet has the right coords then its somewhere in the display chain. if the raw packet itself is showing wrong coords then the issue is between the GPS and the radio.

also worth checking the datum setting on the garmin. some of them default to something other than WGS84 and that can throw position off by exactly the kind of amount you're describing.

yeah the datum thing is real, had that bite me once on a trip when i borrowed a friends GPS unit. but also — two miles SE is a pretty specific error. that kind of consistent offset sometimes points to a coordinate conversion issue in how the radio is parsing the NMEA string. the D710 has had some quirks with certain GPS firmware versions where it gets confused between decimal degrees and degrees/decimal minutes and just silently does it wrong. its not common but it happens.

honestly id just try a different GPS if you have one laying around, even a cheap phone running APRSDroid over bluetooth just to see if the position problem follows the radio or stays with the garmin. that'll at least narrow it down fast.