so ive been running APRS for a few months now with a TM-D710G and a byonics GPS puck mounted on the dash. works great most of the time but every now and then my position on aprs.fi shows me like 12 miles south of where I actually am, sometimes in the middle of a lake which is obviously wrong. the weird thing is it doesn't happen consistently, could be fine for days then suddenly show up wrong for a few beacons then fix itself.

my NMEA feed looks correct when i monitor it through the radio's display, shows the right lat/lon, so im not sure if its a digipeater thing or what. using WIDE1-1,WIDE2-1 path which i figured was pretty standard. anybody seen this kind of thing before or have a idea what might cause it

that sounds like it could be a corrupt packet getting through without triggering a checksum failure, or possibly a different station's packet getting attributed to your callsign somehow. does aprs.fi show the path info on those bad position reports? if you click on the packet detail it'll show you which digipeaters touched it and that might give you a clue. also worth checking if your SSID is unique, ive seen cases where someone nearby is running the same callsign-SSID combo which causes all kinds of weirdness on the network.

the 12 miles off thing is suspicious though, that's too consistent to be pure noise. could be a NMEA sentence getting parsed wrong, like if the GPS occasionally spits out a position from before it had a solid fix and the radio is just blindly forwarding it. some of those cheaper pucks will output a technically valid NMEA sentence with old coordinates right after powerup before they reacquire. might be worth looking at what time of day the bad beacons happen and see if it correlates with when you start the car.

yeah the startup thing is almost certainly it. my mobilinkd had the same deal when i was running it with a garmin that took a while to get a solid fix. the radio doesnt know the GPS hasnt settled yet, just sees valid NMEA and fires a beacon. i just added a small delay before the radio starts transmitting after power on, think there's a setting for that in the TM-D710 menu somewhere, beacon delay or something like that. been ages since i configured mine so dont quote me on the exact menu location