Iff mode 1 code list

Iff mode 1 code list


  • Identification friend or foe
  • Aerospace Acronym and Abbreviation Guide
  • 9 Things You Didn't Know About The History Of The Transponder
  • Identification friend or foe

    Identification, friend or foe IFF is an identification system designed for command and control. It enables military and national civilian air traffic control interrogation systems to identify aircraft, vehicles or forces as friendly and to determine their bearing and range from the interrogator. IFF may be used by both military and civilian aircraft. IFF was first developed during the Second World War , with the arrival of radar , and early friendly fire incidents. Despite the name, IFF can only positively identify friendly targets, not hostile ones.

    There are in addition many reasons that friendly aircraft may not properly reply to IFF. IFF is a tool within the broader military action of Combat Identification CID , "the process of attaining an accurate characterization of detected objects in the operational environment sufficient to support an engagement decision.

    CID not only can reduce friendly fire incidents, but also contributes to overall tactical decision-making. This led to incidents such as the " battle of Barking Creek ", over Britain, [6] [7] [8] and the " air attack on the fortress of Koepenick ", over Germany.

    Robert Watson-Watt had filed patents on such systems in and respectively. By , researchers at Bawdsey Manor began experiments with "reflectors" consisting of a dipole antennas tuned to resonate at the primary frequency of the CH radars.

    When a pulse from the CH transmitter hit the aircraft, the antennas would resonate for a short time, increasing the amount of energy returned to the CH receiver. The antenna was connected to a motorized switch that periodically shorted it out, preventing it from producing a signal.

    This caused the return on the CH set to periodically lengthen and shorten as the antenna was turned on and off. In practice, the system was found to be too unreliable to use; the return was highly dependent on the direction the aircraft was moving relative to the CH station, and often returned little or no additional signal.

    Their aircraft radios were modified to send out a 1 kHz tone for 14 seconds every minute, allowing the tracking stations ample time to measure the aircraft's bearing. Several such stations were assigned to each "sector" of the air defence system, and sent their measurements to a plotting station at sector headquarters, who used triangulation to determine the aircraft's location.

    Known as " pip-squeak ", [12] the system worked but was labour-intensive and did not display its information directly to the radar operators. A system that worked directly with the radar was clearly desirable. On receipt of a signal from the CH radar MHz , an oscillator in the system began to ring with the same frequency. This signal was amplified and sent out an omnidirectional monopole antenna , where it was received by the CH station.

    The oscillator circuit rang only for a short time, causing the signal to quickly disappear again. Since the signal was received at the same time as the original reflection of the CH signal, the result was a distorted "blip" on the CH display which was easily identifiable.

    Mark I was technically complete as the war began, but a lack of sets meant it was not available in quantity and only a small number of RAF aircraft carried it by the time of the Battle of Britain. Pip-squeak was kept in operation during this period, but as the Battle ended, IFF Mark I was quickly put into operation. Pip-squeak was still used for areas over land where CH did not cover, as well as an emergency guidance system.

    If the aircraft moved between CH stations, it had to be manually re-tuned, based on settings read off a card. As the number of radars in British service increased, including new systems deployed by the navy and army , an aircraft might find itself painted by several radars at the same time. This led to the introduction of IFF Mark II, whose primary change was a circuit that automatically changed the tuned frequency, sweeping it through the bands being used by the various radars.

    Each radar would see the IFF returns appear for a short period every few seconds. Even this solution became untenable with the introduction of microwave frequency radars, which dramatically increased the range of frequencies in use. Mark III transponders were designed to respond to specific 'interrogators', rather than replying directly to received radar signals. These interrogators worked on a limited selection of frequencies, no matter what radar they were paired with.

    The system also allowed limited communication to be made, including the ability to transmit a coded ' Mayday ' response. Equivalent sets were manufactured in the US, initially as copies of British sets, so that allied aircraft would be identified upon interrogation by each other's radar. Before flight, the transceiver was set up with a selected day code of ten bits which was dialed into the unit.

    To start the identification procedure, the ground operator switched the pulse frequency of his radar from 3, Hz to 5, Hz. The airborne receiver decoded that and started to transmit the day code.

    The radar operator would then see the blip lengthen and shorten in the given code, ensuring it was not being spoofed.

    British military scientists found a way of exploiting this system to the allies advantage. They designed and built their own IFF transmitter called "Perfectos", which was designed to trigger a response from any FuG 25a system in the vicinity. Radar-based aircraft identification is also called secondary radar in both military and civil usage, with primary radar bouncing an RF pulse off of the aircraft to determine position.

    It required the operator to perform several adjustments to the radar receiver to suppress the image of the natural echo on the radar receiver, so that visual examination of the IFF signal would be possible. See also.

    This led to incidents such as the Battle of Barking Creek, over Britain, [7] [8] [9] and the air attack on the fortress of Koepenick over Germany. Robert Watson-Watt had filed patents on such systems in and By , researchers at Bawdsey Manor began experiments with "reflectors" consisting of dipole antennas tuned to resonate to the primary frequency of the CH radars. When a pulse from the CH transmitter hit the aircraft, the antennas would resonate for a short time, increasing the amount of energy returned to the CH receiver.

    The antenna was connected to a motorized switch that periodically shorted it out, preventing it from producing a signal. This caused the return on the CH set to periodically lengthen and shorten as the antenna was turned on and off.

    In practice, the system was found to be too unreliable to use; the return was highly dependent on the direction the aircraft was moving relative to the CH station, and often returned little or no additional signal. When that turned out to be the case, the RAF turned to an entirely different system that was also being planned. Their aircraft radios were modified to send out a 1 kHz tone for 14 seconds every minute, allowing the stations ample time to measure the aircraft's bearing.

    Several such stations were assigned to each "sector" of the air defence system, and sent their measurements to a plotting station at sector headquarters, who used triangulation to determine the aircraft's location.

    Known as "pip-squeak", the system worked, but was labour-intensive and did not display its information directly to the radar operators. A system that worked directly with the radar was clearly desirable.

    This used a regenerative receiver, which fed a small amount of the amplified output back into the input, strongly amplifying even small signals as long as they were of a single frequency like Morse code, but unlike voice transmissions. They were tuned to the signal from the CH radar 20—30 MHz , amplifying it so strongly that it was broadcast back out the aircraft's antenna.

    Since the signal was received at the same time as the original reflection of the CH signal, the result was a lengthened "blip" on the CH display which was easily identifiable.

    In testing, it was found that the unit would often overpower the radar or produce too little signal to be seen, and at the same time, new radars were being introduced using new frequencies. Mark II had a series of separate tuners inside tuned to different radar bands that it stepped through using a motorized switch, while an automatic gain control solved the problem of it sending out too much signal. Mark II was technically complete as the war began, but a lack of sets meant it was not available in quantity and only a small number of RAF aircraft carried it by the time of the Battle of Britain.

    Pip-squeak was still used for areas over land where CH did not cover, as well as an emergency guidance system. By , a number of sub-models were introduced that covered different combinations of radars, common naval ones for instance, or those used by the RAF. But the introduction of radars based on the microwave -frequency cavity magnetron rendered this obsolete; there was simply no way to make a responder operating in this band using contemporary electronics. In , English engineer Freddie Williams had suggested using a single separate frequency for all IFF signals, but at the time there seemed no pressing need to change the existing system.

    This was to become the standard for the Western Allies for most of the war. Mark III transponders were designed to respond to specific 'interrogators', rather than replying directly to received radar signals. These interrogators worked on a limited selection of frequencies, no matter what radar they were paired with.

    The system also allowed limited communication to be made, including the ability to transmit a coded 'Mayday' response. Equivalent sets were manufactured in the US, initially as copies of British sets, so that allied aircraft would be identified upon interrogation by each other's radar. Thus, many of them were wired with explosives in the event the aircrew bailed out or crash landed.

    Jerry Proc reports: Alongside the switch to turn on the unit was the IFF destruct switch to prevent its capture by the enemy. Many a pilot chose the wrong switch and blew up his IFF unit. The thud of a contained explosion and the acrid smell of burning insulation in the cockpit did not deter many pilots from destroying IFF units time and time again.

    Eventually, the self destruct switch was secured by a thin wire to prevent its accidental use. Before a flight, the transceiver was set up with a selected day code of ten bits which was dialed into the unit. To start the identification procedure, the ground operator switched the pulse frequency of his radar from 3, Hz to 5, Hz. The airborne receiver decoded that and started to transmit the day code. The radar operator would then see the blip lengthen and shorten in the given code, ensuring it was not being spoofed.

    The system included a way for ground controllers to determine whether an aircraft had the right code or not but it did not include a way for the transponder to reject signals from other sources. British military scientists found a way of exploiting this by building their own IFF transmitter called Perfectos, which were designed to trigger a response from any FuG 25a system in the vicinity.

    IV radar , which originally operated at MHz. By comparing the strength of the signal on different antennas the direction to the target could be determined. It used a single interrogation frequency, like the Mark III, but differed in that it used a separate responder frequency. Responding on a different frequency has several practical advantages, most notably that the response from one IFF cannot trigger another IFF on another aircraft.

    But it requires a complete transmitter for the responder side of the circuitry, in contrast to the greatly simplified regenerative system used in the British designs. This technique is now known as a cross-band transponder. When the Mark II was revealed in during the Tizard Mission , it was decided to use it and take the time to further improve their experimental system. The main difference between this and earlier models is that it worked on higher frequencies, around MHz, which allowed much smaller antennas.

    This would immediately reveal the IFF's operational frequencies. This moved to still higher frequencies around 1 GHz but operational testing was not complete when the war ended.

    By the time testing was finished in , the much improved Mark X was beginning its testing and Mark V was abandoned. As development continued it was decided to introduce an encoding system known as the "Selective Identification Feature", or SIF.

    SIF allowed the return signal to contain up to 12 pulses, representing four octal digits of 3 bits each. Depending on the timing of the interrogation signal, SIF would respond in several ways. Mode 1 indicated the type of aircraft or its mission cargo or bomber, for instance while Mode 2 returned a tail code.

    Mark X began to be introduced in the early s. This was during a period of great expansion of the civilian air transport system, and it was decided to use slightly modified Mark X sets for these aircraft as well.

    These sets included a new military Mode 3 which was essentially identical to Mode 2, returning a four-digit code, but used a different interrogation pulse, allowing the aircraft to identify if the query was from a military or civilian radar. Several new modes were also introduced during this process. Civilian modes B and D were defined, but never used. Mode C responded with a bit number encoded using Gillham code , which represented the altitude as that number x feet - Radar systems can easily locate an aircraft in two dimensions, but measuring altitude is a more complex problem and, especially in the s, added significantly to the cost of the radar system.

    By placing this function on the IFF, the same information could be returned for little additional cost, essentially that of adding a digitizer to the aircraft's altimeter. This works on the same frequencies as Mark X, and supports all of its military and civilian modes. It had long been considered a problem that the IFF responses could be triggered by any properly formed interrogation, and those signals were simply two short pulses of a single frequency.

    This allowed enemy transmitters to trigger the response, and using triangulation , an enemy could determine the location of the transponder. There are two key differences, however. One is that the Interrogation pulse is followed by a bit code similar to the ones sent back by the Mark 3 transponders.

    The encoded number changes day-to-day. When the number is received and decoded in the aircraft transponder, a further cryptographic encoding is applied. If the result of that operation matches the value dialled into the IFF in the aircraft, the transponder replies with a Mode 3 response as before.

    If the values do not match, it does not respond. This solves the problem of the aircraft transponder replying to false interrogations, but does not completely solve the problem of locating the aircraft through triangulation. To solve this problem, a delay is added to the response signal that varies based on the code sent from the interrogator.

    When received by an enemy that does not see the interrogation pulse, which is generally the case as they are often below the radar horizon , this causes a random displacement of the return signal with every pulse. Locating the aircraft within the set of returns is a difficult process. Mode S During the s, a new civilian mode, Mode S, was added that allowed greatly increased amounts of data to be encoded in the returned signal. This was used to encode the location of the aircraft from the navigation system.

    This is a basic part of the traffic collision avoidance system TCAS , which allows commercial aircraft to know the location of other aircraft in the area and avoid them without the need for ground operators. The basic concepts from Mode S were then militarized as Mode 5, which is simply a cryptographically encoded version of the Mode S data. Radar-based aircraft identification is also called secondary surveillance radar in both military and civil usage, with primary radar bouncing an RF pulse off of the aircraft to determine position.

    It required the operator to perform several adjustments to the radar receiver to suppress the image of the natural echo on the radar receiver, so that visual examination of the IFF signal would be possible. Commonly referred to as a squawk code.

    See also.

    The radar operator would then see the blip lengthen and shorten in the given code, ensuring it was not being spoofed. The system included a way for ground controllers to determine whether an aircraft had the right code or not but it did not include a way for the transponder to reject signals from other sources.

    British military scientists found a way of exploiting this by building their own IFF transmitter called Perfectoswhich were designed to trigger a response from any FuG 25a system in the vicinity. IV radarwhich originally operated at MHz. By comparing the strength of the signal on different antennas the direction to the target could be determined. It used a single interrogation frequency, like the Mark III, but differed in that it used a separate responder frequency.

    Responding on a different frequency has several practical advantages, most notably that the response from one IFF cannot trigger another IFF on another aircraft. But it requires a complete transmitter for the responder side of the circuitry, in contrast to the greatly simplified regenerative system used in the British designs.

    This technique is now known as a cross-band transponder. When the Mark II was revealed in during the Tizard Missionit was decided to use it and take the time to further improve their experimental system. The main difference between this and earlier models is that it worked on higher frequencies, around MHz, which allowed much smaller antennas.

    This would immediately reveal the IFF's operational frequencies. This moved to still higher frequencies around 1 GHz but operational testing was 8 week ultrasound complete when the war ended.

    By the time testing was finished inthe much improved Mark X was beginning its testing and Mark V was abandoned. As development continued it was decided to introduce an encoding system known as the "Selective Identification Feature", or SIF. SIF allowed the return signal to contain up to 12 pulses, representing four octal digits of 3 bits each. Depending on the timing of the interrogation signal, SIF would respond in several ways. Mode 1 indicated the type of aircraft or its mission cargo or bomber, for instance while Mode 2 returned a tail code.

    Mark X began to be introduced in the early s. This was during a period of great expansion of the civilian air transport system, and it was decided to use slightly modified Mark X sets for these aircraft as well. These sets included a new military Mode 3 which was essentially identical to Mode 2, returning a four-digit code, but used a different interrogation pulse, allowing the aircraft to identify if the query was from a military or civilian radar.

    Several new modes were also introduced during this process. Civilian modes B and D were defined, but never used. Mode C responded with a bit number encoded using Gillham codewhich represented the altitude as that number x feet - Radar systems can easily locate an aircraft in two dimensions, but measuring altitude is a more complex problem and, especially in the s, added significantly to the cost of the radar system.

    By placing this function on the IFF, the same information could be returned for little additional cost, essentially that of adding a digitizer to the aircraft's altimeter.

    Aerospace Acronym and Abbreviation Guide

    This works on the same frequencies as Mark X, and supports all of its military and civilian modes. This allowed enemy transmitters to trigger the response, and using triangulationan enemy could determine the location of the transponder. There are two key differences, however. One is that the Interrogation pulse is followed by a bit code similar to the ones sent back by the Mark 3 transponders. The encoded number changes day-to-day.

    When the number is received and decoded in the aircraft transponder, a further cryptographic encoding is applied. If the result of that operation matches the value dialled into the IFF in the aircraft, the transponder replies with a Mode 3 response as before.

    If the values do not match, it does not respond. This solves the problem of the aircraft transponder replying to false interrogations, but does not completely solve the problem of locating the aircraft through triangulation. To solve this problem, a delay is added to the response signal that varies based on the code sent from the interrogator. When received by an enemy that does not see the interrogation pulse, which is generally the case as they are often below the radar horizonthis causes a random displacement of the return signal with every pulse.

    Locating the aircraft within the set of returns is a difficult process. During the s, a new civilian mode, Mode S, was added that allowed greatly increased amounts of data to be encoded in the returned signal. This was used to encode the location of the aircraft from the navigation system.

    This is a basic part of the traffic collision avoidance system TCASwhich allows commercial aircraft to know the location of other aircraft in the area and avoid them without the need for ground operators. The basic concepts from Mode S were then militarized as Mode 5, which is simply a cryptographically encoded version of the Mode S data.

    Radar-based aircraft identification is also called secondary surveillance radar in both military and civil usage, with primary radar bouncing an RF pulse off of the aircraft to determine position.

    It required the operator to perform several adjustments to the radar receiver to suppress the image of the natural echo on the radar receiver, so that visual examination of the IFF signal would be possible. This led to incidents such as the " battle of Barking Creek ", over Britain, [6] [7] [8] and the " air attack on the fortress of Koepenick ", over Germany. Robert Watson-Watt had filed patents on such systems in and respectively. Byresearchers at Bawdsey Manor began experiments with "reflectors" consisting of a dipole antennas tuned to resonate at the primary frequency of the CH radars.

    When a pulse from the CH transmitter hit the aircraft, the antennas would resonate for a short time, increasing the amount of energy returned to the CH receiver.

    The antenna was connected to a motorized switch that periodically shorted it out, preventing it from producing a signal. This caused the return on the CH set to periodically lengthen and shorten as the antenna was turned on and off.

    In practice, the system was found to be too unreliable to use; the return was highly dependent on the direction the aircraft was moving relative to the CH station, and often returned little or no additional signal. Their aircraft radios were modified to send out a 1 kHz tone for 14 seconds every minute, allowing the tracking stations ample time to measure the aircraft's bearing.

    Several such stations were assigned to each "sector" of the air defence system, and sent their measurements to a plotting station at sector headquarters, who used triangulation to determine the aircraft's location.

    9 Things You Didn't Know About The History Of The Transponder

    Known as " pip-squeak ", [12] the system worked but was labour-intensive and did not display its information directly to the radar operators. A system that worked directly with the radar was clearly desirable. On receipt of a signal from the CH radar MHzan oscillator in the system began to ring with the same frequency. This signal was amplified and sent out an omnidirectional monopole antennawhere it was received by the CH station. The oscillator circuit rang only for a short time, causing the signal to quickly disappear again.

    Since the signal was received at the same time as the original reflection of the CH signal, the result was a distorted "blip" on the CH display which was easily identifiable. Mark I was technically complete as the war began, but a lack of sets meant it was not available in quantity and only a small number of RAF aircraft carried it by the time of the Battle of Britain.

    Pip-squeak was kept in operation during this period, but as the Battle ended, IFF Mark I was quickly put into operation.

    Pip-squeak was still used for areas over land where CH did not cover, as well as an emergency guidance system. If the aircraft moved between CH stations, it had to be manually re-tuned, based on settings read off a card. As the number of radars in British service increased, including new systems deployed by the navy and armyan aircraft might find itself painted by several radars at the same time.

    This led to the introduction of IFF Mark II, whose primary change was a circuit that automatically changed the tuned frequency, sweeping it through the bands being used by the various radars. Each radar would see the IFF returns appear for a short period every few seconds.


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