so ive been messing around with APRS for about a year now and generally love it but i keep running into this frustrating situation where my mobile beacon just disappears from aprs.fi for stretches of like 10-15 minutes when im driving through the valley areas around here. im running a TM-D710G with the internal TNC and using WIDE1-1,WIDE2-1 paths which should be pretty standard right?

the weird thing is it's not like im in a complete RF dead zone, i can still hit a couple repeaters in those areas no problem. but the APRS packets just aren't making it through. my best guess is the digi coverage just has holes that happen to line up with the repeater footprints in a weird way. i pulled up the digipeater map on aprs.fi and there does seem to be a gap but its hard to tell exactly what the coverage should look like from just that.

anybody dealt with this before? i was thinking about building a fill-in digi but i dont really know where to start with siting one, or whether it'd even be worth the effort if nobody else is using APRS much around here anyway

yeah hilly terrain is basically the nemesis of APRS, the digis are usually sited for wide coverage which means flat high spots and valleys just fall through the cracks. your path choice sounds fine for most areas but if youre hitting coverage gaps you could try temporarily switching to WIDE1-1 only and see if theres a wide1 fill-in digi already out there that you didnt know about - sometimes those show up as WIDn-N on the map but they're actually functioning as fill-ins.

as for building one, its honestly not that complicated if you have a linux box lying around. direwolf as the TNC software, a cheap radio, and a decent antenna up high is basically all you need. the harder part is finding a site with power that actually has line of sight to cover the gap. i spent about three months coordinating with a local business owner to get one on their roof before it all fell through. if you go that route just make sure you're coordinating with your regional APRS frequency coordinator if there is one.

I had something similar going on with my setup, turned out one of the digis I thought was covering me had been off the air for like six months and nobody noticed because APRS traffic in the area was pretty thin. You can check last heard times on aprs.fi for each digi in your expected path and sometimes thats the culprit right there - digi just sitting there technically on the map but not actually running.

also the TM-D710 is a solid radio for this but double check your power output setting, i had mine accidentally set to low power at some point and didnt realize for weeks