A High-Performance Sound-Card AX.25 Modem

My APRS RF-to-internet gateway (iGate) had been running  a sound-card modem called soundmodem by Thomas Sailer. The software modem caused various problems and I have not found a suitable replacement. Eventually, I decided to try to implement my own sound-card-based software modem. The results have been very good, in spite of the fact that I do not have much background in digital signal processing.

I’ve been using the modem for many months now in my iGate. The modem is run is a component of javAPRSsrvr, not as a separate program. It’s working reliable non-stop.

An article that I wrote for QEX explains how the modem works and how I designed and optimized it. It is also available on my university web site.