Radar ST-68U: Identification, Friend or Foe - IFF

Identification, friend or foe (IFF) with Radar ST-68U Tin Shield

For historical information only, do not use for navigation or aviation purposes!

The Soviet/Russian ST-68U is a 3D airspace surveillance radar with a phased array antenna that electronically sweeps the beam in the vertical plane. Special attention was obviously paid to the ability to detect targets at low altitudes, especially cruise missiles (here called wing missiles). In NATO, the radar system is known as the Tin Shield. It was also used by the National People's Army of the former GDR.

The following explanations on the use of the IFF system are taken from the 1988 instruction A 138/1/012 Funkmeßstation ST-68UÄ, Gefechtsarbeit (A 138/1/012 Radio Measuring Station ST-68UÄ, Combat Operations), issued by the East German Air Force (NVA Luftstreitkräfte und Luftverteidigung, LSK/LV), and classified as "Secret" (Vertrauliche Verschlußsache, VVS). In order to better assess the radar in terms of capabilities and use, a few sections with a general description are given first. Then followed by excerpts for the IFF operations.

The sections on the IFF / Identification Friend or Foe are marked by a red margin.

East German instruction A 138/1/012 Radar ST-68UÄ

I. Purpose, inventory and combat capabilities


1. The ST-68UÄ radar is used to detect, identify and track aerial targets, including winged missiles, under the impact of organised (active and passive) jamming, reflections from the earth's surface and meteorological phenomena

2. It ensures:
a) the location of aerial targets and the determination of their coordinates (azimuth, distance, elevation and altitude)
b) the determination of the identification;
c) determining the bearing angles ( and ) to an active jamming carrier.

3. The radar is designed for both non-automated and automated combat operations.


4. To the inventory of the radar belongs:
a) the load semitrailer 6UFÄ (picture 1) with the equipment located in the box body SPP-15, (chassis of type MAZ 938 B);
b) the special trailer 6BP (picture 2) with the electrical station 99Ch6, which is located in the box body KP-10 (chassis of type MAZ 5224 W). Two diesel generators DGM4-60-T0230-Tsch/400 and one converter PSTsch-100 belong to the electric station;
c) the detachable display cabinet 6UF-01Ä.

Radar system ST-68U of the East German National People's Army NVA
Cargo semi-trailer 6UFÄ with antenna (Source: NVA)
Special trailer 6 BP
Special trailer 6 BP (Source: NVA)

Combat capabilities

5. The radar ST-68UÄ ensures the detection of air targets and the determination of their coordinates in the area:
a) Azimuth 360°.
b. Elevation angles from 0° to 6° with a scanning period of 5 s or 10 s and from 0° to 28° with a scanning period of 10 s or 20 s

6. The rotating speed of the antenna is 6 rpm or 12 rpm.

7. The average value of the pulse repetition frequency is 750 Hz (scale 150 km on the display unit) or 1500 Hz (scale 75 km on the display unit)

8. Modes of operation for scanning the airspace:

a) MODE 1: Scanning of the lower detection zone (from -20' to 6°) by four directional diagrams during one antenna rotation

b) MODE 2: scanning of the lower detection zone during two antenna rotations, whereby during the first rotation all radiated energy is concentrated in the two lower directional diagrams (from -20' to 3°) and during the second rotation all energy is concentrated in the two upper directional diagrams (from 3° to 6°)...

c) MODE 3: scanning of the lower and upper detection zones (from -20' to 30°) during two turns of the antenna. During the first antenna rotation, the lower zone (from -20' to 6°) is scanned by four directional patterns and during the second antenna rotation, the upper zone (from 6° to 30°) is scanned by four directional patterns ...

d) MODE 4: Scanning the detection zone from -20' to 3° during one antenna rotation ...

9. The detection distance of a target with an effective reflecting surface σ = 2.5 m² at low heights without jamming:
a) in a height of 50 m: 30 km
b) in a height of 100 m: 45 km
c) in a height of 500 m: 95 km
d) in a height of 1000 m: 120 km.

The maximum detection distance is 150 km.

10. The detection distance of a target with the effective reflecting surface σ = 0.1 m² (wing rocket) without jamming:
a) in a height 50 m: 25 km
b) in a height 100 m: 40 km


13. Protection against active noise jamming is ensured:
a) in the case of jamming via the main lobe, by applying the protection mode PROTECTION OF MAIN LOBE (SeGL);
b) in the case of jamming via the side lobes, by applying the protection mode SIDE LOBE COMPENSATION (KBL);
c) in the case of non-stationary active jamming, by using the protection mode NON-STATIONARY ACTIVE JAMMING (NAP);
d) in the case of impulse response jamming, by applying SIDE LOBE SUPPRESSION (PBO) mode of operation.

14. The radar determines the bearing to an active jamming carrier in azimuth and elevation angle

15. The protection against passive jamming is 1...2 packets/100 m

16. The suppression coefficient of reflections from the earth's surface is at least 45 dB.

17. The FuMS has a protection against anti-radar missiles by changing the pulse repetition frequency, as well as by sector operation and flicker operation of the radiation

18. The identification device of the KREMNIY-2 IFF system belonging to the radar ensures:
a) the identification determination;
b) the determination of coordinates of own aircraft in distress.

The identification zone covers the detection zone of the radar in all operating modes of the identification device.

19. The identification device ensures the identification request in SINGLE CHANNEL OPERATION as well as the operation in VECTORING and VALVE OPERATION modes.

The VECTORING operation mode is used to direct your own aircraft to targets.

With VALVE operation, the identification signals are only passed to the panoramic display unit (RSG) of the radar if an echo signal from the target is also present.

20) The transition periods to higher levels of readiness when using the ST-68UÄ radar shall be determined by order of the Deputy Minister and Chief of Air Force and Air Defence through the On-Duty System. They are as follows for the radar company / radar post
a) from standby level 2 to standby level 1: 3.5 min;
b) from service level 2 to service level 1: 8.5 min;
When supplied by the aggregate, the standard time is increased by 2 min.

21. the standard times for deployments are
a) From the time a command is given to prepare to march to the time the marching readiness is established, 120 minutes;
b) from the time the command is given to establish combat readiness from march until the first air situation report 120 min.
The standard times refer to deployments without command post visual display and without imitator.

22. The power supply of the radar is provided by three-phase alternating current with a voltage of 220 V; 400 Hz. The maximum power consumption of the radar is 45 kW.

23. The radar set is operational under the following conditions:
a) at ambient temperatures from -40 °C to +50 °C;
b) at a relative humidity of up to 98 %;
c) at altitudes up to 1000 m above sea level;
d) at wind speeds of up to 20 m/s;
e) at icing up to a thickness of 8 mm.

24. the permitted transport speed is
a) on asphalt roads 62 km/h
b) on roads (unpaved) 35 km/h
c) in rought terrain 8 km/h.

25. To haul the radar in motor vehicle transport, two motor vehicles are needed:
a) Tractor unit KrAZ 255 W: to transport the 6UFÄ cargo semi-trailer
b) truck KrAZ 255 B: for transport of electric station 99Ch6.
Containers and packing cases are transported on the loading area of the truck KrAZ 255 B.
The total length of the vehicles (tractor unit KrAZ 255 W with cargo semi-trailer 6UFÄ) is 18.57 m. The turning radius is at least 13.5 m (front wheel track axle) or 14.5 m (front wheel mudguard).

26. Two panel wagons are required for the transport of the radar system by rail.
The external dimensions and the dimensions of the transport units of the FMS in marching order are summarised in table 3.

Table 3: External dimensions and dimensions of the transport units of the radar system

Trailer 6UFÄ:
mass: 20,8 t
length: 13.825 m
width: 2.890 m
height: 3.325 m

Trailer 6BP:
mass: 14.3 t
length: 7,500 m
width: 2,860 m
height: 3.296 m

27. To increase the detection distance of targets at low and extremely low altitudes, the semi-trailer shall be deployed on a hill of at least 6...8 m height. The hill must have a 4 m wide driveway, the angle of inclination must not exceed 17°, and a horizontal flat space measuring 6.5 m x 10.5 m. If the mounting space is equipped with special supports made of concrete or other materials for the lateral support arms of the semi-trailer, the required minimum dimensions of the mounting space are reduced to 4.0 m x 10.5 m.

II. Combat operations

Organisation of combat operation and functional duties of the members of the combat crew


29. Combat operation of the radar is conducted by both the combat crew and the duty crew.

30. Belonging to the combat crew:
a) Station commander: workstation at remote visual display unit 195RR01E;
b) a radar operator: workstation in the compartment of the 6UFÄ cargo semi-trailer at the display unit of the cabinet 195RR01Ä
and a radio observer: on the remote display unit on the command post (GS);
c) an electrician/military driver: workplace in the electric station.

Allocation of work places:
In the semi-trailer, the workstation of the station commander is located on the left screen of the display unit and the workstation of a radar operator is located on the right screen of the display unit.
In the command post, the workstation of the radar operator is located on the left screen of the remote display unit.

31. Belonging to the duty crew:
a) a radar operator: workstation at the visual display unit in the cargo semi-trailer;
b) an electrician/military driver: workplace in the electric station.

Allocation of work places:
In the duty crew, the radar operator has his workstation at the display unit of the semi-trailer. The duty crew may be reinforced by a second radar operator in the event of high tension, on the order of the commander of the unit or, in his absence, of the officer on duty (hereinafter the unit commander/OoD). In this case, each screen of the display unit is occupied by a radar operator.

32. The control of the radar operating modes is carried out from the semi-trailer. Technically possible is also such a variant of combat operations, in which the control is carried out from the remote display cabinet.

Modes of operation:


Operation modes of the radar station
In combat operation - working mode 1. In case of special air situation on the order of the uni commander/OoD - working mode 2 and 3. Working mode 4 may be used only with the permission of the Chief of Radar Troops.

Rotation speed of the antenna:
For combat operation and combat training: 6 rpm. Short-term operation at 12 rpm is permitted after detecting air targets at extremely low altitudes or targets with a small reflecting surface.

Transmission power:
For combat operation, 50% of the transmission power must be used. In the event of active radar jamming, switch over to 100 % of the transmission power

33 The radar operator determines the locations of the targets on the screen of the display unit in the coordinate system azimuth-distance. If necessary, it is possible to determine and report the coordinates according to the flight reporting grid.

34. The tactical lines shall be displayed on the screens of the display units in accordance with the provisions of DV 138/0/001 (formerly DV 103/0/001) Combat Operations of the Air Force and Air Defence Radar Forces, Radar Battalion and Radar Company and by order of the Deputy Minister and Chief of the Air Force and Air Defence on the System on Duty. The defined tactical lines shall be plotted on the left screen of the display unit at a scale of 75 km and on the right screen of the display unit at a scale of 150 km.

35. Commands (orders) and target assignments to targets shall be transmitted by the command post via intercom or telephone (radio) channels to the workstations of the members of the combat crew of the radar. Messages are transmitted via telephone or radio channels.

36. In order to check the primary air situation objectively, the screen is photographed and the information (messages) transmitted via the communication channels are recorded on a tape recorder. The structural or auxiliary equipment shall be used to photograph the screen. The additional equipment shall be so fitted that the left-hand screen of the semi-trailer's display unit can be photographed. The station commander shall be responsible for objective control.

37. The station commander reports to the unit commander/OoD. He is responsible for the continuous operational readiness of the radar and structural communication assets, for the organisation and conduct of combat operation with the radar in the On-duty System (DHS) and in combat, for the integrity of the crew and for compliance with safety, health, labour and fire regulations.
He has to:
a) conduct station operational checks and report the results to the OoD
b) upon receipt of tasks to detect and track targets, to determine the station's modes of operation
c) ensure the timely identification and monitoring of targets
d) determine the operating modes of the display cabinet 195RR01Ä
e) report to the command post the use of radar jamming measurements and initiate suppression measures
f) to specify the target characteristics on the order of the OoD
g) ensure that radar operators comply with the ordered information period
h) to ensure the filter change at the IFF device at the specified times
i) monitor the functioning of the station and take measures to remedy any disturbances

38. The radar operator is subordinate to the station commander/OoD. He is responsible for the timely detection of targets and for the quality of the reported target data.
He has to:
(a) upon commencement of service at DHS (On-duty System), perform a functional check of the station and communication equipment, familiarise himself with the air situation and report to the station commander/OoD that service has commenced
b) to switch the station on or off on command of the OoD
c) continuously monitor the appearance of targets on the screen and report newly emerging targets to the command post immediately
d) report data on targets with the ordered information period
e) report to the command post the excursion of targets out of the station's detection range and the interference to work caused by radio jamming measurements and the nature of the interference
f) to take measures to eliminate any malfunctions (defects) that have occurred.

39. The electrician/military driver is subordinate to the station commander and is responsible for the technical condition and the timely switching on or off of the electric station.
He has to:
a) carry out a functional check of the electric station when starting work at DHS (On-duty System)
b) to notify the commencement of service at DHS
c) constantly check the fuel, oil and coolant levels
d) switch the electric station on or off in time
e) to take measures to remedy any malfunctions that have occurred.
Depending on the local conditions and commands concerning the power supply, specifications of the above functional obligations may be made.

Identification request

70. The IFF request is carried out according to the specifications in DV 138/0/001 (previously DV 103/0/001).

71. The identification interrogation is carried out by briefly pressing the MANIP key on the console 195UF03, at the moment when the deflection line has approached 10° to the target sign

72. The main operating mode of the IFF device at the identification interrogation is the single-channel operation (the switch DWUCHKAN.-ODNOKAN.) of the block 2U1Ä of the cabinet 2M1-F1Ä must be permanently switched to position ODNOKAN. (SINGLE CHANNEL OPERATION). In case of SINGLE CHANNEL operation of the identification interrogation, the identification reply signals appear on the display screens of the radar as arc-shaped marks behind the respective target, i.e. they are located on the same azimuth as the echo signal of the target, but at a greater distance. In azimuth, the identification mark is wider than the target sign.

73. If own aircraft outside the detection distances of the radar are to be detected by the IFF signals and their co-ordinates determined, the type of identification VECTOR must be used. For this purpose, the switch NAWED - K2 of the block 2U1Ä must be set to the position NAWED (VECTOR). The VECTOR mode of operation shall also be switched on on command of the command post to direct own aircraft to targets.

74. VALVE OPERATIONS. To determine the belonging of targets, press the KL (VALVE) button on the console 195UF03.
This mode is used in the following cases:
a) when a target is less than 40 km away from the station
b) to increase the resolution of identification interrogation of targets at the same distance from and in slightly different azimuths to the station
c) to prevent the influence of asynchronous pulse emissions on the identification channel.

Title image: Radar ST-68U Tin Shield at the Soviet Wachstedt early warning site, East Germany / GDR, on 26 November 1985. Source: Unit History US Military Liaison Mission (USMLM) to the Commander in Chief Group of Soviet Forces in Germany,


Soviet IFF (Identification, friend or foe) systems