What type of encoding is utilized in an aircraft's mode C transponder transmission?

In an aircraft's Mode C transponder transmission, pulse position modulation (PPM) is used. PPM is a method of transmitting data where the information is conveyed by changing the position of the pulses in the time domain. This is particularly effective in the context of aircraft transponders since it allows for precise transmission of information, such as altitude, with minimal bandwidth usage.

The decision to utilize PPM in Mode C transponders stems from the need for efficient and reliable communication in airspace, where clarity and accuracy are paramount. This modulation technique helps ensure that the transponder's signal containing altitude and identification information can be decoded accurately by air traffic control radar.

Other modulation types like frequency modulation, amplitude modulation, and phase modulation aren't suitable for this application due to various reasons, such as susceptibility to interference or the complexity of their signal structures, which can hinder the straightforward, robust communication required in aviation.