Definition
An electronic unit that both sends out (transmits) and detects returning (receives) radio signals through the same housing. In a radio altimeter, the RT generates the signal that is sent down toward the ground from the transmit antenna and processes the reflected signal picked up by the receive antenna, then calculates the height above terrain from the time delay between the two.
Plain English
The box that does both jobs in one unit — it sends a radio signal out and listens for it to bounce back. In a radio altimeter, that bounce-back is what tells the airplane how high it is above the ground.
Context Anchor
Seen in radio altimeter diagrams, especially where the system components are labeled between the antenna and the cockpit display.
Derivation
A straight combination of receiver (the part that picks up incoming signals) and transmitter (the part that sends signals out). Combining them into one unit saves weight, wiring, and panel space — which is why almost all aircraft radios are built this way.
Why Pilots Care
It supplies the actual altitude-above-ground readings used during low-level flight, instrument approaches, and terrain clearance.
Intuition Check
RT does not mean a ground radio station here. In this context, it means the aircraft’s radio altimeter unit that both sends and receives the height-measuring signal.
Example Sentence 1
The radio altimeter RT is mounted in the avionics bay and wired to two small antennas on the belly of the aircraft.
Example Sentence 2
Before flight the technician checks that the RT is transmitting at the correct power and receiving clear reflections.