Radar start-up time

​The component that transmits radar energy is called a magnetron and is similar to that which is in your microwave oven, but much more powerful.  This is a tube, which will be damaged if the filament isn't heated to a proper temperature.  Therefore, radars have a timing circuit – typically 2 or 3 minutes – which disables the magnetron from transmitting until the filament is sufficiently heated. This protects the magnetron from being damaged.