Picture taken June 24, 2005
View from the bridge. The radar antenna actually consists of two parts. The bottom part, large and parabolically shaped, is the combined primary radar transmitter and receiver. It sweeps a high-power narrow pulse beam around, and listens for radio echoes in between the pulses. These echoes are transformed into the familiar radar blips on the controller's screen. The top part of the antenna assembly (like a bar) is the secondary radar transmitter and receiver. This one broadcasts transponder 'pings,' to which all planes equipped with a transponder reply with a 'pong'. This reply signal offers three advantages over the primary radar echo: it is very clearly defined (not a bounce, but a clear transmission), it contains a unique ID number for the plane (the squawk code), and it contains the current pressure altitude of the plane. The secondary radar data is usually fed to the computer which creates the data tags for the controller's radar display.
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