Definition
The simultaneous transmission or reception of two signals using a single antenna, made possible by a device called a diplexer that separates the signals by frequency so they do not interfere with each other.
Plain English
Using one antenna to handle two different radio signals at the same time, with a small filter unit that keeps the two signals from getting in each other's way.
Context Anchor
Seen in aircraft radio and avionics discussions, especially when one antenna or cable path is used by more than one radio function.
Derivation
From the Latin 'duplex,' meaning 'twofold' or 'double.' The 'di-' prefix in 'diplex' carries the same sense of two. The word signals that two things are sharing one path.
Why Pilots Care
Allows multiple radio functions without extra antennas, reducing weight and space on the aircraft.
Analogy
It is like two people using the same doorway to enter different rooms, with a guide at the door sending each person the right way. The doorway is shared, but the paths stay separate.
Intuition Check
Do not confuse diplex with duplex. Duplex is about two-way communication; diplex is about two radio signals sharing one antenna or signal path while being kept separate.
Example Sentence 1
The aircraft uses diplex operation so a single antenna handles both the VHF communication radio and the navigation receiver.
Example Sentence 2
Diplex operation in the navigation receiver lets the system monitor two signals through a single antenna connection.