Definition 1 of 2
Definition
A single electronic unit that both transmits radio signals and receives the returning signals, housed together so they can share antennas, timing circuits, and processing electronics. In a radio altimeter, the receiver-transmitter sends a signal downward toward the ground and measures the returning signal to calculate height above the terrain.
Plain English
One box that does two jobs — it sends out a radio signal and listens for it to come back. Combining both functions in the same unit lets the system compare what was sent with what was received and work out a useful answer, such as how high the aircraft is above the ground.
Context Anchor
Seen in radio altimeter diagrams, where the receiver-transmitter is connected to the antennas and the cockpit height indication.
Derivation
Built from two ordinary words: 'receiver' (something that receives) and 'transmitter' (something that transmits). The hyphenated form signals that both functions live in one piece of equipment rather than two separate boxes.
Why Pilots Care
Provides the precise above-ground-level height data required for safe low-altitude flight and instrument approaches when visual references are unavailable.
Intuition Check
Do not assume a receiver-transmitter is only a voice radio. In this context, it is the measuring unit in the radio altimeter system.
Example Sentence 1
The radio altimeter's receiver-transmitter sends a signal to the ground and uses the returning signal to display height above the terrain.
Example Sentence 2
During the low approach the pilot cross-checked the altitude displayed from the receiver-transmitter against the published minimums.