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

 


IFF Mk I

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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IFF Mk II

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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IFF Mk IIE

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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IFF Mk IIG British

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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IFF Mk IIG American

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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IFF Mk IIN

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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IFF Mk III Lightweight

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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IFF Mk III Q

Frequency range  
       
  RAF US US Navy
Designation ARI 5640    
       
Responds to      
       
Main Items      
       
Remarks Greater flexibility and security.

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IFF Mk IV

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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IFF Mk V

Frequency range  
       
  RAF US US Navy
Designation ARI 5717    
       
Responds to      
       
Main Items      
       
       
       
       
Test equipment      

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SCR 515

   
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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