Transmit and Receive

The ground causes a reflection of the transmit signal. The receive antenna receives the signal. The RF processor mixes the transmit and receive signals to make a difference frequency. The difference frequency is in proportion to the time it takes the signal to go to the ground and come back. The main processor changes the difference frequency to radio altitude. The radio altitude goes out on two ARINC 429 data buses. The two buses supply radio altitude and status information to these components:

· FCC A or FCC B

· Autothrottle computer

· DEU 1 and DEU 2

· GPWC

· TCAS computer

· FDAU.