I hope I'm not speaking too soon, but I think I finally have a working APRS IGate running on the Eee PC! After recompiling soundmodem to cure an apparent problem with the audio, as I wrote yesterday, I ended up with a worse problem: the diagnostic 'scope display froze when I used it. I was on the point of giving up, but on the basis of "nothing ventured, nothing gained" I ran the soundmodem software anyway, started Xastir and lo and behold, received a position beacon from my VX-8E!
There was still a lot of Googling, tinkering and tearing out of hair to get from there to where I am now, and I probably can't even remember half of it. I won't even start to describe my abortive attempt to set up aprsd to work as a gateway without the mapping interface of xastir which I don't like very much. If any aprsd wizards read this and would like to offer their advice I'd still like to try it, though.
One problem I noticed when using soundmodem as a kernel mode driver (which isn't necessary for xastir, but is for aprsd) was that at start-up it spewed out a long burst of what sounded like packet but actually wasn't. Google (however did we manage without it?) turned up a few snippets about this, with the generic advice that soundmodem was being treated as a network device and you needed to stop your network daemons binding with address 0.0.0.0. This was Greek to me. I was hoping for help along the lines of "click here, uncheck that check box" and so on. Eventually I discovered that the rogue daemon was the avahi-daemon service. In Ubuntu you can disable it from System / Administration / Services, then restart and no long transmission when soundmodem starts. It's simple when you know how!
Next I found that APRS messages addressed to my VX-8E (G4ILO-7) and received by xastir were not being transmitted over the air so it could receive them. I had made all the necessary settings, or so it appeared, but there is an additional step: you have to create a file in $HOME/.xastir/data called nws-stations.txt containing a list of calls whose messages you wish to send over the air. The first time I tried it, it didn't seem to work, and I posted a question about this on the xastir mailing list. The post was spotted by John, EI7IG, who sent me an APRS message that appeared on the VX-8E! Why it didn't work the first time I have no idea.
I think everything is now working as it should be. I'm using my FT-817ND on the RF side, for the simple reason that I already have the cabling for it. I'll probably try using my TH-F7E later on, but I don't have the necessary cabling for it.
So now I can be tracked as I move about the local area, and can send and receive text messages via amateur radio. I've already had a few exchanges with EI7IG and I can tell you, I wish Yaesu had implemented predictive text on the VX-8E! If you have APRS too please send a message to G4ILO-7 to say hello. But check my current location page first to see if G4ILO-7 is shown, because APRS text messages aren't stored and sent later if the recipient's current location isn't known.