Monday, September 07, 2009

Eee I'm getting nowhere

Developments on the APRS front have been moving on faster than I can write about them. A couple of days ago I had an email from someone who was running an APRS IGate on an Asus router. I thought this was a good idea - better and more economical than leaving a PC on all the time - but one to consider for some time in the future. Then I remembered that I had an Asus Eee PC 2G Surf sitting unused on a shelf. If I could install the Linux equivalent of UI-View, Xastir, on this, I would have a standalone low power consumption APRS IGate at no extra cost!

The first thing I did was install Xastir-Eebuntu 3.0 from the live CD available in the Xastir Wiki to the Eee PC. It was time to vape the Xandros OS that came with the Eee PC as it was too old to run the latest ham software and failed with errors when many of them tried to use the soundcard anyway.

Because I don't have a TNC I needed soundmodem, which is the Linux equivalent of the SV2AGW Packet Engine. I downloaded that from the Ubuntu repository and then configured it according to the excellent HowTo: SoundModem instructions in the Xastir wiki. Xastir worked just fine, and I could even hear what sounded like packet coming out of the speaker. But no matter how I adjusted the input audio levels I could not decode a single packet transmitted by my VX-8 radio.

Eventually I found that the soundmodem configuration utility has a diagnostic tool. When using the oscilloscope I saw horizontal lines in the waveform - exactly the problem described here and shown in the screenshot on the right.

While wondering what to do about that I had an email from Gareth, GW4KJW, who suggested running UI-View32 under wine, the Linux Windows emulator. This seemed like a good idea, so I installed wine from the Ubuntu reporitory and then extracted the AGWPE archive into a folder and ran it. This appeared to work OK. I then installed UI-View32 from its installer. Ui-View ran, but the map display went black a fraction of a second after the map was displayed. I also got a run-time error message when trying to load a different map.

After more Googling I found that this problem had been encountered before. I tried the recommended solution of downloading and running the winetricks script. This worked, after installing some CAB extractor utility it needed, and UI-View looked fine. But it still did not decode any packets.

Using the AGWPE soundcard test utility I found that audio was being received by the software. However there was a delay of a few seconds between changing the audio level and seeing a response on the oscilloscope display. Presumably some delay was occuring getting the audio from Linux to wine to AGWPE. Perhaps the Eee PC is just too underpowered for this application. The audio looked normal - no horizontal lines - but I could not get anything to decode, so I decided to give Xastir one more try.

First I had to fix the problem with the breaks in the audio. I downloaded the source code for soundmodem (version 0.14), and after downloading and installing a couple of libraries I was able to compile the source code. However when running the diagnostic tool I noticed that the oscilloscope display froze after a second or two. Thinking it was just a glitch, I went ahead anyway and made the changes mentioned in the linux.hams posting mentioned above. This changes the sample rate from 9600Hz (which soundmodem tries to use and which is probably not supported by the Eee PC hardware) to 11025Hz. I then recompiled and tried again. Unfortunately the display still freezes, so I am no further forward.

If you ever wondered why hams who use Linux are hardly ever on the air, I think you have here a very good example of the reason! I suppose the next stage is to try and find some appropriate groups to post the above findings to in the hope that someone more knowledgeable than me will have the answer. But it's all so time-consuming and frustrating that I'm running out of enthusiasm.
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