UPDATE July 2018.
About a year or so ago I went to Direwolf on my pi to run as an igate. It has been stable and very easy to use and monitor. I recommend it before futzing with this stuff below.
After putzing with an APRS receiver in my plane, I decided I would try and provide some service to the APRS community by setting up an I-gate. APRS iGate is an application that listens to APRS packets heard by a radio receiver(144.390Mhz in the US), and relays them to the APRS-IS network on the internet.
There are different ways to accomplish this. My method uses UI-View and AGWPE applications.
AGWPE is the packet engine that listens to your sound card and functions as a terminal node controller to the receiving application, in this case UI-View. Simply put, you hook up a receiver (I used a simple Rat Shack hand held scanner) output to your sound card. AGWPE listens to that on the card and converts the sound to digital packets the application can understand,
UI-View is an APRS application for 32 bit Windows. Its simple job in my case is to take the packets from the packet controller program above, and put them on the internet.
So with an antenna in my attic, connected to a scanner, connected to a computer I can "Gate" from RF(radio frequency) to the internet.
Here is my I-gate and the heard locations, and a view on a map
I went through a couple of weeks of madness trying to get my i-gate set up.
First problem was I could not get my hardware to keep the soundcard drivers active. Turned out to be that when using RDP to control the remote server, the sound gets selected from the controlling computer, disabling the card on the controlled computer. ARGH!!!!! Once I told RDP to leave the sound on the host, wallah, the sound card stayed alive on the server. Most folks would not run into this problem. Most admins like me never care about sound over RDP. But this time was different. Took me many many hours of debugging.
Next item was connecting to the aprs server. I found the key to be downloading the proper list. However I could not get the list to d/l through the menu selection on UI-View. I found that the default location to get the list is no longer active. You should put in france.aprs2.net/APRServe2.txt
This allowed the current list to be downloaded. I found several helpful hits on setup here.
Which ARPS server you gate to is up to you. I use this one.
Some good screenshots of the UI-view setup can be found here. Plus that link has good discussions overall about APRS related topics.
Your receiver matters.
While listening to the APRS freq and watching the igate log, I realized that I was receiving way more signals rf than I was decoding and gating. I decided to try another receiver. And bam, I went from gating ~200/hr to over 1500/hr. Wow! Big difference. So the moral of the story is, a good receiver puts a cleaner signal to the soundcard for decoding and gating.
I had a rat shack portable receiver and went to a rat shack desktop model I had. Good find. Funny how Im watching the area gates for who is getting what. Tracerts allow me to find the fastest routes to market on the gate.