Here are some radio things I have accumulated and/or created. Various things are listed on the left.
Below is a soundcard interface I made to connect my Puxing PX-777+ to my computer's soundcard for packet mode operation. The top circuit links the radio receiver to the computer's microphone jack. This drops the voltage down by a factor of 10 and isolates the different grounds. The output is mono; therefore, I use a mono plug for that end. The computer end is a stereo plug, but the middle channel is unused. In theory, one could connect another radio to that end, since the soundcard TNC I use is channel selective. Both cables are shielded. The PX-777 uses a 2.5mm plug for the speaker.
The bottom circuit connects the radio transmit to the computer's speaker. Note that the PTT is connected to the ground of the radio speaker. The tip of the transmit plug is not used. This appears to remain at +5V dc. A capacitor is added to filter DC voltages. As always, be careful of the polarization of the capacitor.
A full description of the process can be found here.