Definition Of Terms

Address The unique code to which a Mode S transponder replies. This is not be confused with the "4096" code used for identifying ATCRBS transponders. The address of a Mode S transponder is not alterable by the pilot or crew.

Altitude the pressure of the aircraft as transmitted by a ATCRBS of Mode S transponder. This information is obtained is obtaine from an external sensor and transmitted to the transponder.

ATCRBS Air Trafic Control Radar Beacon Syatem. The original non-selective secondary radar beacon system usig the usual two-pulse interrogation and an auxiliary SLS pulse.

DPSK Differential phase shift keting. the method of modulation used for the selective Mode S uplink interrogation.

DF downlink format. the format included in a Mode S transponder reply to an interrogation or squitter message that indicates the type of message.

Mode S A secondary radar system where transponders can e individually interrogated or selected (the s in Mode S), so that the ammount of interference or garble can be reduced to a minimum.

Reply A transmittedresponse, from the airbone transponder, to an interrogation.

SLS Side Lobe Suppression. A pulse transmitted from an omni-directional antenna used as reference level to prevent replies to interrogations received from the secondary radar antenna sidelobes.

Squitter The self generated transmission made by a Mode S transponder, not in reply to an interrogation, for the use of collision avoidance systems.

Surveillance alt. An interrogation that causes only the addressed Mode S transponder to reply with its altitude.

Surveillance ID. An interrogation that causes only the addressed Mode S transponder to reply with its "4096" code.

"4096" code This refers to the octal number dialed into either a ATCRBS or Mode S transponder by the pilot or other crew member.