Definition
A method of sending several independent signals over a single communication channel at the same time by assigning each signal its own separate frequency band within that channel.
Plain English
A way of carrying many signals down one wire or radio link at once by giving each signal its own slice of the frequency range, so they don't interfere with each other.
Context Anchor
Seen in aviation communication, navigation, and equipment descriptions when explaining how a system carries more than one signal on the same link.
Derivation
Frequency refers to how fast a wave cycles. Division means splitting something into parts. Multiplexing comes from the Latin multi (many) and plex (folded together), meaning to combine many things into one. Put together: many signals folded into one channel by dividing it into separate frequency slices.
Why Pilots Care
Pilots usually do not operate FDM directly, but understanding the term helps when reading avionics descriptions, equipment manuals, or technical explanations of communication and navigation systems.
Analogy
Think of a radio dial. Many stations broadcast at the same time, but each one sits on a different frequency, so your radio can pick out just one without the others bleeding through. FDM does the same thing inside a single communication line.
Intuition Check
FDM does not mean one signal is being sent faster. It means several separate signals are being kept apart by placing them in different frequency ranges.
Example Sentence 1
Older avionics systems used frequency division multiplexing to carry several voice and data channels over one cable.
Example Sentence 2
Maintenance crews check the FDM setup to ensure each navigation signal stays within its assigned frequency band.