I was not satisfied with my prior results with the APRS testing, so I setup soundmodem in an Ubuntu environment on my trusty netbook and set-off to decode packets. As expected, everything went well – soundmodem was decoding local packets with little trouble. To be sure that the sound card itself was not at fault, I used the same USB sound-card as before.
It appears that my electronics workbench may not be an ideal APRS RX station locale after all – I moved the test setup to the loft of my out-building and was pulling in packets more easily. The next step will be to replicate the setup using a Raspberry Pi in place of the netbook – I just need to configure wireless networking on the Pi before I relegate the hardware to the -20°C temperatures we are experiencing.
Perhaps the received signals were in fact too weak for soundmodem to properly decode before? If this is the case, a good argument for a purpose-built TNC can be made 😉