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Upon interrogation, Mode S transponders transmit information about the aircraft to the SSR system, to TCAS receivers on board aircraft and to the ADS-B SSR system. This information includes the call sign of the aircraft and/or the aircraft's permanent ICAO 24-bit address (which is represented for human interface purposes as six hexadecimal ...
An SSR ground station transmits interrogation pulses on 1030 MHz (continuously in Modes A, C and selectively, in Mode S) as its antenna rotates, or is electronically scanned, in space. An aircraft transponder within line-of-sight range 'listens' for the SSR interrogation signal and transmits a reply on 1090 MHz that provides aircraft information.
The original design had three such "modes", Mode 1 was triggered by the interrogator by sending the two pulses 3 μs apart (±0.2 μs), Mode 2 was 5 μs and Mode 3 was 8 μs. [ 10 ] The response to these interrogations remained simple; a successful interrogation on Mode 1 or 3 caused a single pulse to be sent in reply, very shortly after the ...
The basic concepts from Mode S were then militarized as Mode 5, which is simply a cryptographically encoded version of the Mode S data. The IFF of World War II and Soviet military systems (1946 to 1991) used coded radar signals (called cross-band interrogation, or CBI) to automatically trigger the aircraft's transponder in an aircraft ...
Primary radar determines range and bearing to a target with reasonably high fidelity, but it cannot determine target elevation (altitude) reliably except at close range. SSR uses an active transponder (beacon) to transmit a response to an interrogation by a secondary radar.
Mode C uses a spacing of 21 μs, and requests the aircraft's pressure altitude, provided by the altitude encoder. Mode 2 uses a spacing of 5 μs and requests the aircraft to transmit its Military identification code. The latter is only assigned to Military aircraft and so only a small percentage of aircraft actually reply to a mode 2 interrogation.
The time difference between interrogation and reply minus the 50 microsecond ground transponder delay, and the pulse spacing of the reply pulses (12 microseconds in X mode and 30 microseconds in Y mode), is measured by the interrogator's timing circuitry and converted to a distance measurement (slant range), in nautical miles, then displayed on ...
Jaylynik 16:18, 19 June 2006 (UTC) IFF is not a seperate interrogation system, and it works just fine without a KIT or a KIR. You don't need Crytpo for IFF as a whole, only for the secure mode, mode 4. Modes 1, 2, 3/A and C are all considered modes of IFF. It just so happens that 3/A and C are also Civilian/SSR modes.