Having walked down the path you're on right now, I can sympathize with how challenging it is to learn about APRS. I'm not sure if it's intentionally cryptic (because the 2-meter system really can't handle too many concurrent users) or not, but it took me months to find out about it and even then, I couldn't be sure I had it right because much of the information is conflicting. Then you get "helpful" people who tell you to "go figure it out" and "you can really wreak havoc if you don't set it up right," yet offer no help or pointers to where you might actually learn how to do that. APRS is one area that definitely needs some friendlier Elmering because, one bad transmitter can really ruin it for a large area.
[end rant]
[begin Elmering
]
1) you want your 857 set to FM to receive the APRS packets
2) you should probably set up a receive-only iGate until you know what you're doing and what's going on around you.
3) APRS covers a range of technologies so you need to understand all of them in order to make the best use of it and not make a lot of enemies. For example, radio propagation, antenna gain, capture effect, packet addressing, packet encoding, the APRS protocols, etc.
4) Bob Bruninga's site is comprehensive, but it's not written for the novice. There's lots of information out there, but it's hard to tell what's current and what's obsolete. (If it suggests using "RELAY," for example, that's an old page.)
Remember, APRS shares a very limited resource (it's single frequency) that must be used sparingly for it to work for everyone. The more packets that get transmitted needlessly (People who beacon their position every 10 seconds and unnecessary digipeaters that echo packets everyone has already heard, for example) reduce what's available for everyone else to use.
Good luck and have fun!
