You can make any kind of telemetry link you like. APM will need it to interface as a standard serial port. An audio link may not provide sufficient bandwidth depending on how much telemetry you want to transmit. The APM firmware has configurable baud rates for the telemetry, but keep in mind if your link is too slow you will either bog down the autopilot or loose data.
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In the SVN I can't find a doug.h needed to compile the latest svn code.
Earl