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marker beacon[′märk·ər ‚bē·kən]
A low-power radio beacon transmitting a signal to designate a small area, as an aid to navigation.
arrays produce a circular pattern that appears elongated at right angles to the runway because of the directional characteristics of aircraft receiving the antenna. The station-location, or Z, marker gives a positive position for aircraft operating under instrument flight conditions to show the pilots when they are passing directly over a low-frequency navigational aid. There are three marker beacons: the outer marker, which is sited 4 to 5 NM from the touchdown and transmits two low-pitched dashes per s; the middle marker, which is located ¼ to ½ NM from the touchdown and transmits high-pitched dots and dashes alternately; and the inner marker, which is located at the runway threshold and transmits six high-pitched dots per second. Normally, the inner marker is not installed. The signals from the marker are beamed vertically upward in a fan shape and can be heard in the aircraft only when it is directly above the beacons.