I'm wiring up a new radio and intercom system on my plane. The installation manual suggests:
5.10.3 Audio wiring
For any wires carrying an audio signal, a screened twisted pair should be used to avoid any unwanted signals interfering with the radio installation. Unscreened wires can act as small antennas and transmissions from other avionics on the aircraft could be picked up by the radio and heard as interference in the connected headsets. For example, Mode S transponder transmissions can be audible as clicking sounds in the headset and cause an annoying distraction to the pilot.
Correctly terminated screened wiring will limit any unwanted transmissions being picked up by the radio and should be used on the MIC and PHONE lines.
All makes sense, however:
Is it sufficient to combine the headphone and microphone signals into a single screened cable, or should I route two separate cables?