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The antenna system of a typical air traffic control radar, the ASR-9. The curved reflector antenna on the bottom is the primary surveillance radar (PSR), and the flat antenna on top of it is the secondary surveillance radar (SSR). In operation the antenna rotates about a vertical axis, sweeping a vertical fan-shaped beam of microwaves around ...
Military aircraft also use a dedicated UHF-AM band from 225.0 to 399.95 MHz for air-to-air and air-to-ground, including air traffic control communication. This band has a designated emergency and guard channel of 243.0 MHz. [2] [8] Radio aeronautical navigation aids use other frequencies.
The aircraft emergency frequency (also known in the USA as Guard) is a frequency used on the aircraft band reserved for emergency communications for aircraft in distress.The frequencies are 121.5 MHz for civilian, also known as International Air Distress (IAD), International Aeronautical Emergency Frequency, [1] or VHF Guard, [1] and 243.0 MHz—the second harmonic of VHF guard—for military ...
SSR antenna of Deutsche Flugsicherung at Neubrandenburg, in Mecklenburg/Western Pomerania Transponder in a private aircraft squawking 2000. Secondary surveillance radar (SSR) [1] is a radar system used in air traffic control (ATC), that unlike primary radar systems that measure the bearing and distance of targets using the detected reflections of radio signals, relies on targets equipped with ...
(VFR squawk code for airspace 5,000 feet (1,500 m) and below prior to 15 March 2007 when replaced by the international 7000 code for VFR traffic.) [5] 0022 Germany (VFR squawk code for airspace above 5,000 feet (1,500 m) – prior to 15 March 2007 when replaced by the international 7000 code for VFR traffic.) [5] 0025 Germany
This information is displayed on the radar screen beside the aircraft's icon for use by the air traffic controller. The transponder code is assigned to the aircraft by the air traffic controller before takeoff. Controllers use the term "squawk" when they are assigning a transponder code, e.g., "Squawk 7421".
Provides 2-digit 5-bit mission code (cockpit selectable) [1] 2: Provides 4-digit octal unit code (set on ground for fighters, can be changed in flight by transport aircraft) [1] 3: A: Provides a 4-digit octal identification code for the aircraft, set in the cockpit but assigned by the air traffic controller. Mode 3/A is often combined with Mode ...
A discrete transponder code (often called a squawk code) is assigned by air traffic controllers to identify an aircraft uniquely in a flight information region (FIR). This allows easy identification of aircraft on radar. [6] [7] Codes are made of four octal digits; the dials on a transponder read from zero to seven, inclusive. Four octal digits ...