Weather radars have two main parts: the transmitter and the receiver.
The transmitter sends out short, controlled pulses of microwaves in to the air.
These pulses spread out as they travel, covering a wider and wider area.
When the waves hit the raindrops, part of the pulse is echoed back to the machine.
The receiver is the part of the radar that records the echo.
The longer the gap between a pulse and its echo, the farther away the object is.