An alternative to dedicated hardware to perform the digital to analog conversion of the digitized packet stream to modulated audio was created by Thomas Sailer, in Germany. It is a Linux kernel module and utilizes a Sound Blaster or a sound card that supports the Windows SoundSystem. Various cable assemblies are presented below and PTT interfacing circuitry between Host and Radio are presented.

Circuit to connect the Serial port  to the PTT line. This is the most common interface and the linux kernel module expects to have it configured this manner
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Circuit to connect the Parallel Port to the PTT line

Circuit to connect the Game Port to the PTT line

Circuit to drive PTT with the right audio channel of the Soundblaster output.