IFF
Identification Friend or Foe
It is important, in general, to know whether an echo on
the display tube of a radar equipment comes from a friendly or from a hostile
aircraft. To assist the
identification of responses from friendly aircraft, a system of recognition
known as FF has been adopted. In
essence this system permits the echo from a friendly aircraft to be given some
distinguishing feature such as a periodic increase in size, or an associated
mark or set of marks which appears on the display tube.
In the Mark II system,
friendly aircraft carried a receiver/transmitter which received the pulses
transmitted from the radar station and re-radiated them from the aircraft with
inappreciable delay and with enhanced strength. Since the IFF set was
periodically swept through the tuning band of the radar station the echo on the
display was seen periodically to increase in size thus affording a means of
identification.
This system which was suitable for the early needs of ground radar proved
inadequate for later developments and was replaced by the IFF Mark III system.
In this system the aircraft still carries a receiver/transmitter which is
however not stimulated by the actual normal pulses transmitted from the radar
station. Instead, at the radar stations special interrogator transmitters and
receivers working on a frequency different from the radar detection frequency
can be operated at will to excite the airborne receiver/transmitter and to
receive responses from it. Since
the pulse recurrence frequency of the interrogator usually bears some simple
relation to that of the radar station itself; the IFF responses can be displayed
on the display tube along with the normal aircraft echoes that they serve to
identify. Sometimes a separate IFF display is used.
Some form of coding is generally adopted.
RAF Designation | US AAF Designation | US Navy Designation |
IFF Mk I | ||
IFF Mk II | ||
IFF Mk IIE | ||
IFF Mk IIG British | ||
IFF Mk IIG American | SCR 535 | ABE |
IFF Mk IIN British | ||
IFF Mk IIN | ABD | |
IFF Mk III | SCR 595 | ABK |
IFF Mk III Lightweight | ||
IFF Mk IIIG | SCR 695 | ABF |
IFF Mk IIIGR | ||
IFF Mk III Q | ||
IFF Mk IV | ||
IFF Mk V | ||
SCR-515 | ABA |
Frequency range | 20-30 MHz | ||
RAF | US | US Navy | |
Designation | |||
Responds to | CH | ||
Main Items | |||
Transponder | |||
Power unit | |||
Test equipment |
1939
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Frequency range | |||
RAF | US | US Navy | |
Designation | ARI 5000 | ||
Responds to | RAF - CH,
MRU/TRU Royal Navy - 70, 279, 280 Army - GL Mk I, II |
||
Main Items | |||
Transponder | R 3002 (12V), R3082 (Tropical 12V) R 3003 (24V), R 3083 (tropical 24V) |
||
Power unit | |||
Control unit | type 17, 18 | ||
Aerial system | type 90, 93 | ||
Test equipment |
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Frequency range | |||
RAF | US | US Navy | |
Designation | ARI 5027 | ||
Responds to | Main Chain Home as well as other ground radar stations. | ||
Main Items | |||
Transponder | R 3060, R 3061 | ||
Power unit | |||
Control unit | type 17, 18 | ||
Aerial system | |||
Test equipment |
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Frequency range | 40-50 MHz / 60-70 MHz | ||
RAF | US | US Navy | |
Designation | ARI 5010 | ||
Responds to | RAF - CHL, GCI, AI Mk IV, V, VI Royal Navy - 280 Army - GL Mk I, II |
SCR 268, 516, 527, 588, 627 | CXAM, SA, SC SK (part of band) |
Main Items | |||
Transponder | R 3077 (12V) R 3078 (24V) |
||
Power unit | type 110, 111 | ||
Control unit | type 82, 83 | ||
Aerial system | |||
Test equipment |
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Frequency range | 100-116 & 175-225 MHz, 0.5-1.5 W, | ||
RAF | US | US Navy | |
Designation | SCR-535-AZ
(12Volt) SCR-535-A (24Volt) |
ABE (12Volt) ABE-1 (24Volt) |
|
Responds to | RAF - CHL, GCI, AI Mk IV, V,
VI, ASV Mk II Navy - 268 Army - SLC, CD, LW, AA No.5 |
SCR 268, 516, 270, 217, 602, 521, 527, 588, 627. | SK, ASE, ASVC |
Main Items | |||
Receiver | BC-647A | CPR-43AAP | |
Indicator | BC-767 | ||
Control assembly | BC-648-A | ||
Switch assembly | BC - 649 - A | ||
socket | SO-158A | ||
Power switch | B-54, AN-3015 | ||
Switch box |
BC-706 | ||
Test equipment | IE-16-A IE-45-A |
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IFF Mk IIN British |
Frequency range | |||
RAF | US | US Navy | |
Designation | ARI 5036 | ||
Responds to | RAF - CHL, GCI, MRU/TRU Navy - 79, 29, 286 Army - SLC, CD, LW AA No.5 |
SCR 268, 527, 588, 627, 602, 516 | CXAM SA (part of band) |
Main Items | |||
Transponder | R 3108 (12Volt) R 3109 (24Volt) |
||
Power unit | |||
Control unit | type 108, 109 | ||
Aerial system | |||
Test equipment |
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Frequency range | 38-52 & 195(175)-225 MHz, 0.5-1.5 W | ||
RAF | US | US Navy | |
Designation | ABD (12Volt) ABD-1 (24Volt) |
||
Responds to | RAF - CHL, GCI, MRU/TRU, AI Mk IV, V, VI,
ASV Mk II Navy - 79, 279, 286 Army - SLC, CD, LW, AA No.5 |
SCR 268, 516, 527, 588, 627, 602, 521 | CXAM, SA, SC, SK, ASE, ASVC |
Main Items | |||
Transponder | CPR-42AAH CPR-43AAH |
||
Power unit | |||
Control unit | CPR-23ABE | ||
Aerial system | |||
Test equipment |
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IFF Mk III |
Frequency range | 157-187 MHz, I Band | ||
RAF | US | US Navy | |
Designation | ARI 5025 / ARI 5640 | SCR 595AZ (12Volt) SCR 595A (24Volt) |
ABK, ABK-2,-4,-6 (12Volt) ABK-1, -3,-5, -7 (24Volt) |
Responds to | All Radars with auxiliary interrogators | BLx Interrogators | |
Main Items | |||
Transponder | R 3067 (12Volt) R 3090 (24Volt) |
CHZ-A3AAXory | |
Power unit | |||
Control unit | Type 1 (include type 89 and 90) | BC 958, 965 | CHZ-23ABG |
Aerial system | Type 90 (for aircraft having a
speed of 350 m.p.h. or over) Type 93 (all other aircraft) |
CHZ-66AAV | |
Type of Wave | Pulse-modulated | ||
Frequency range | 157 to 187 Mc/s
continuously swept in 2.5 seconds. Flyback time less than 0.5 second (HT is switched of during this time) |
||
Pulse widths | Narrow - 5 to 9 uS
(3/4 mile) Wide - 17 to 35 uS (2,5 mile) Distress - 60 to 100 uS |
||
Test equipment | Signal Generator 22 Test set type 74 |
TS 52 (power) TS 163 TS 164 (pulse) TS 172A (respons) |
U/W RC-127,136,148,150,151,184
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Frequency range | 157-187 MHz, P Band | ||
RAF | US | US Navy | |
Designation | ARI 5253 | ||
Responds to | RAF - All Radars with auxiliary interrogators Navy - BLx Interrogators |
||
Main Items | |||
Transponder | R 3211 (12Volt) R 3212 (24Volt) |
||
Power unit | |||
Control unit | |||
Aerial system | |||
Test equipment |
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IFF Mk IIIG
|
Frequency range | I-Band 157-187 Mhz G-Band, 200 Mhz |
||
RAF | US | US Navy | |
Designation | ARI 5628 | SCR 695AZ (12Volt) SCR 695A (24Volt) |
ABF (12Volt) ABF-1 (24Volt) |
Responds to | All radars with auxiliary interrogators, Special GCI frequency | ||
Main Items | |||
Transponder | R 3598 | BC 966 | |
Power unit | |||
Control unit | BC 958, 965 | ||
Aerial system | |||
Impact switch |
BC 765 | ||
Detonator warning unit |
BC 767 | ||
Production | Stewart Warner Corp. | ||
Type of Wave | Pulse-modulated | ||
Frequency range | 157 to 187 Mc/s
continuously swept in 2.5 seconds. Flyback time less than 0.5 second (HT is switched of during this time) |
||
Pulse widths | Narrow - 4 to 9 uS
(3/4 mile) Wide - 15 to 35 uS (2,5 mile) Distress - 60 to 100 uS |
||
Test equipment | Test set type 74 & 163 Wavemeter W1310 or 1432 Testmeter type F & D |
IE-45-A IE-46-A |
|
Remarks | American version of Mk IIIG. It possesses a second channel for CGI. Modified in Europe to avoid interference with Lucero. |
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IFF Mk IIIGR
|
Frequency range | I-Band 157-187 Mhz G-Band, 200 Mhz |
||
RAF | US | US Navy | |
Designation | ARI 5131 | ||
Responds to | All radars with auxiliary interrogators, Special GCI frequency | ||
Main Items | |||
Transponder | R 3120 (12Volt) R 3121 (24Volt) |
||
Power unit | type 356, 357 | ||
Control unit | Type 1 (include type 89 and 90) | ||
Aerial system | Type 90 (for aircraft having a
speed of 350 m.p.h. or over) Type 93 (all other aircraft) |
||
Impact switch |
|||
Detonator warning unit |
|||
Production | |||
Type of Wave | Pulse-modulated | ||
Frequency range | 157 to 187 Mc/s
continuously swept in 2.5 seconds. Flyback time less than 0.5 second (HT is switched of during this time) |
||
Pulse widths | Narrow - 4 to 9 uS
(3/4 mile) Wide - 15 to 35 uS (2,5 mile) Distress - 60 to 100 uS |
||
Test equipment | Test set type 74 & 163 Wavemeter W1310 or 1432 Testmeter type F & D |
IE-45-A IE-46-A |
|
Remarks | Similar to Mk III but possesses a second frequency channel permitting it to give identification to GCI and CHL stations. The channel may be adapted to provide "Rooster" facilities. (Airborne beacon) |
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Frequency range | |||
RAF | US | US Navy | |
Designation | ARI 5640 | ||
Responds to | |||
Main Items | |||
Remarks | Greater flexibility and security. |
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Frequency range | 435-500Mc | ||
RAF | US | US Navy | |
Designation | MGRI 5298 | SCR-515? | ABA? |
Responds to | |||
Main Items | |||
BC 645 | |||
BC 646 | |||
AN 40, 80 | |||
Test equipment |
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Frequency range | |||
RAF | US | US Navy | |
Designation | ARI 5717 | ||
Responds to | |||
Main Items | |||
Test equipment |
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Similar to | Navy ABA |
Used with | |
Frequency range | |
Main Items | Transponder BC 645 |
BC 706 | |
Control box BC 646 | |
BC 705 | |
BC 727 | |
Test equipment |
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