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JO-4   Neue Dahme
Infra-red voice transceiver

JO-4 is a covert infra-red-light communication device, also known as a photophone (German: Lichtsprechgerät), developed between 1970 and 1973 by VEB Carl Zeiss Jena in Jena (DDR) for the East-German security service MfS (Stasi). The device was in production from 1974 to 1977 and was used for covert communication across the East-German borders and Berlin's sector borders [2]. It is also known by its project number 17305 and by its codename Neue Dahme. The JO-4 is compatible with the JO-4.02 (Große Dahme) and with its successor, the JO-4.03 (Kleine Dahme).

The kit consists of two optical transceivers, each of which is installed at one end of a free-space communication path in the line-of-sight (LOS).

Each device contains an transmitter and receiver, and uses a patented double-mirror system [4] to guide the narrow parallel infrared beam from one device to the other. As the viewing angle of the mirrors is very narrow (0.38°), the devices must be accurately aligned using the built-in range scope. This way, the device was virtually undetectable and allowed agents to deliver a message without physically crossing the border.
  
JO-4 Lichtsprechgerät

The device was introduced in 1974 as the successor to the earlier devices Dahme I and Dahme II, which in turn were inspired by the American XE-2 that had been confiscated by the Stasi in 1959. The technology was used by the Stasi for cross-border communication with its agents in the free West, and had been improved over the years, to the point where it had a range of several km. In November 1984, a JO-4 was confiscated by the West-German authorities and shown in the press.

  1. The Dahme is a river that flows in the German states of Brandenburg and Berlin. The Stasi commonly used river names for its infrared (IR) communication devices. As Dahme is pronounced the same as the German word Dame (lady), the name was easily transformed into Kleine Dame (little lady).

Two JO-4 units (1 and 2) in leather storage cases
JO-4 stowed in leather storage case
JO-4 Lichtsprechgerät
JO-4 with secondary mirrors in position (bar raised)
Handset - top view
JO-4 on tripod, with handset and external power
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Two JO-4 units (1 and 2) in leather storage cases
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JO-4 stowed in leather storage case
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JO-4 Lichtsprechgerät
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JO-4 with secondary mirrors in position (bar raised)
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Handset - top view
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JO-4 on tripod, with handset and external power

Features
The diagram below shows two different versions of the JO-4, which in this case were part of the same set (i.e. they have the same serial number. At the right is the regular version, which has two large parabolic mirrors — the primary mirrors — and two smaller ones that are mounted on a movable bar — the secondary mirrors. At the left is the lens-version of the device (see below).

Both versions of the JO-4 shown side by side

At the bottom of each device is a 14-pin Amphenol socket to which the handset is connected. The unit is powered by an external 4.5V DC source, that must be connected to the LEMO-socket on the handset. It can be supplied by the PSU (which is missing from our set), or the batteries of a portable flashlight. In the latter case, the supplied power cable must be installed between the LEMO-socket and the E10 fitting of the flashlight (from which the lightbulb has been removed).

At the rear is a small meter. When transmitting, the meter shows the modulation level. In receive mode it shows the battery voltage. To the left of the meter is a volume knob that controls the audio level of the earpiece, and to its right is the eyepiece of the built-in viewfinder.

Handset seen from both sides

Each device is controlled by a handheld remote control unit that must be connected to the 14-pin Amphenol socket at the bottom of each transceiver. The handset has a built-in microphone and a fixed-wired earpiece. At the top is a lever-operated MODE-selector with three positions: receive (centre), transmit & receive (left) and tape input (right). At the bottom of the handset are two sockets: one for connection the 4.5V DC power, and one for connection of external audio devices.

MODE of operation 1
  1. Transmit & receive (microphone & tape player)
  2. Receive only
  3. Transmit & receive (tape player only)
  1. Note that this is different from the modes described in the retrieved documentation [A][B].
    The documentation describes an early prototype, which is different from the final design.

Unit 1 (lens version) and unit 2 (mirror version) side by side
Handset seen from both sides
Adjustable tripod mount
With open front lid and side panels
JO-4 with secondary mirrors in position (bar raised)
JO-4 ready for use - seen from the rear
Indicator at the rear, shows transmitted signal or battery voltage
Socket for connection of the handset
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Unit 1 (lens version) and unit 2 (mirror version) side by side
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Handset seen from both sides
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Adjustable tripod mount
B
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With open front lid and side panels
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JO-4 with secondary mirrors in position (bar raised)
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JO-4 ready for use - seen from the rear
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Indicator at the rear, shows transmitted signal or battery voltage
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Socket for connection of the handset

Setup
Basic setup
The block diagram below shows the basic setup of the JO-4. A complete system consists of two units known as (1) and (2), each of which is placed at one end of a free-space transmission path. Note that a direct line-of-sight (LOS) between the two units is mandatory. The opening angle is very narrow (0.38°), so use the viewfinders at both ends to ensure that the devices can 'see' each other properly. When correctly adjusted, a distance of 3 kilometres or more should be feasible.

Basic full-duplex setup with flashlight-powered units

Both units are powered externally, as the devices have no provision for interal batteries. In most situations, the 4.5V power was supplied by a 3-battery flashlight that had to be (partly) dis­mantled. Alternatively, the units could be powered by an external mains power supply unit (PSU), but only one such PSU was supplied with the kit (and is missing from the kit in our collection).

Advanced setup
In the advanced setup, the remote system (1) is battery powered, whilst the local system (2) is powered by the mains power supply unit (PSU) (4), via the supplied expansion unit (3). The PSU can also be powered by a 12V DC source. This situation is shown below. Note that the Expansion Unit (3) is connected between remote control unit (2) (the handset) and the local transceiver (2).

Advanced setup with external power and recording facility

In this setup, normal full-duplex voice transmissions are possible, just as in the basic setup. But it is also possible to use the local system (2) as an unmanned auto-recording station. It allows the voice transmissions from the remote station (1) to be recorded onto an external UHER recorder. In this configuration, the local station (2) can be used as an electronic dead letter box (EDLB). It allowed an agent to deliver his message without the need to establish a two-way contact first.

Automatic recording is possible by the virtue of a 16 kHz pilot tone, transmitted by both units. 1 It activates a recorder that is connected to the expansion unit (3). Apart from the auto-recording feature, a tape recorder could be connected to the 5-pin DIN socket of the handset of either unit, either for recording or playback. It allowed instructions and third-party messages to be passed.

  1. Both units transmit a 16 kHz pilot tone that can activate the expansion unit at the other end. Note that this is different from the later JO-4.03 kit, in which only unit number (1) transmits a pilot tone. This was done to accomodate the 70 kHz wideband transfer feature of the JO-4.03.


Versions
  • Mirror version
    This is the basic version of the JO-4.02, in which two double-mirror systems are used: one for the receiver and one for the transmitter. The device shown above is of this type. The three flaps (left, right and top) have to be opened and the mirror bar has to be raised. This version produces a narrow parallel beam of IR light with a very small opening angle.

  • Lens version
    In this version, the two double-mirror systems are replaced by two small lenses that protrude two holes in the front surface of the device. This version is shown below. The beam of this version is wider, as a result of which it has a shorter operational range. It is also known as the wide-angle version (German: Weitwinkel-Dahme) [C].
Mirror version
The basic version of the JO-4 uses two double-mirror systems: one for the receiver and one for the transmitter. Each double-mirror system consists of a large mirror – mounted in a fixed position on the unit – and a small mirror which is mounted on a boom that can be folded down.

The closed device measures just 165 x 115 x 45 mm and weights 1160 grams. At the bottom is an adjustable hinged mount that can be fitted to a tripod. At the front is a large spring-loaded hinged lid, that can be opened to get access to the mirrors. After opening it, the two spring-loaded side panels will unfold themselves.

The image on the right shows the transceiver as seen from the bottom, with its tripod mount extended. The front lid and the side panels are expanded (i.e. open), and form an effective 'light tunnel' to shield the device from direct sunlight.
  
JO-4 with secondary mirrors in position (bar raised)

This is necessary, as sunlight rays consist of multiple wavelengths, including infrared light, that could interfere with the modulated infrared beam from the transceivers. After opening the lid, the secondary mirrors have to be brought in position over the primary mirrors, by raising the metal bar that is normally collapsed. In the image above, it is shown in the raised (operational) position.


The diagram above shows how the patented double-mirror system works [4]. The mirrors consist of a glass body that acts as an infra-red bandpass filter and as a lens. The reflective layer is at the rear of the glass body. The primary mirror is a fixed part of the transceiver, whilst the secon­dary mirror is mounted on a movable bar that can be lowered when the device is stowed. At the centre of the primary mirror is the infrared light source (TX), or the infrared detector (RX).

Front side of collapsed unit
Rear side
JO-4 with open lid and raised mirror
JO-4 with secondary mirrors in position (bar raised)
JO-4 Lichtsprechgerät
JO-4 on tripod, with handset and external power
Primary mirrors
Secondary mirror close-up
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Front side of collapsed unit
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Rear side
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JO-4 with open lid and raised mirror
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JO-4 with secondary mirrors in position (bar raised)
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JO-4 Lichtsprechgerät
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JO-4 on tripod, with handset and external power
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Primary mirrors
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Secondary mirror close-up

Lens version   Weitwinkel-Dahme
For situations in which the remote station – operated by an agent in a hostile area – could not be placed on a tripod and could not be aimed accurately, the Stasi developed a modified version of the basic JO-4, in which the two double-mirror systems were replaced by two miniature lenses.

On this version, the large hinged lid at the front has two holes through which the transmit and receive lenses are directly visible. The device does not have to be opened for operation.

The two smaller flaps at the sides are missing. The image on the right shows this version with the lid open. The two bays for the large mirrors are clearly visible, but the mirrors themselves are missing. The retractable bar with the two smaller mirrors is also missing. The two infrared lenses are visible at the centre of each bay. They protrude the two holes in the hinged front lid.
  
 JO-4.02/II - the lens version

Due to the fact that lenses are used rather than parabolic mirrors, the IR light beam is no longer a parallel beam, as a result of which it can only be used when the distance between the remote station (agent) and the local system (base) is not too large. The advantage however, is that it will still work when the device is not aimed perfectly. This can be useful in situations where the agent has limited time to deploy and clear the setup. In addition, the lack of infrared filtering – caused by the absence of the mirrors – had to be compensated by embedding IR-filters in the lenses.

The lens-version seems to be experimental, and it is currently not known in what situations it was used and whether or not it was widely deployed. The Weitwinkel-Dahme is described in hand-written notes [C] that were found in the Stasi archives (BStU) [2] by Detlev Vreisleben[1].

Rear view
Front side with two lenses protruding the large flap
Close-up of the receiver lens
 JO-4.02/II - the lens version
Two lenses instead of two double-mirrors
Close-up of a single lens
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Rear view
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Front side with two lenses protruding the large flap
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Close-up of the receiver lens
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 JO-4.02/II - the lens version
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Two lenses instead of two double-mirrors
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Close-up of a single lens

Compromise
In November 1984, the West-German authorities arrested MfS-Agent 'J' and confiscated the JO-4 device that he had in his possession. His setup is shown in the image below. The device was powered by a flashlight and was shown in the German weekly magazine Bunte in August 1985.

The article in Bunte caused the alarm bells to go off at Stasi headquarters. Apparently, the JO-4 had been developed at Zeiss at a time when secrecy and confidentiality was not yet an issue. Consequently, many people within Zeiss were aware of the device and its purpose. It prompted Oberstleutnant Schulze – head of Department 31 of the OTS – to brief the Regional Admini­stration for State Security on this delicate matter [3].

In the letter, Schulze confirms unambiguously that the device shown in the article is a JO-4, and that the new JO-4.03 is under development.
  
JO-4 with tripod and flashlight

The device also appeared in 1985 in the annual report of the Bundesamt für Verfassungsschutz (BfV) — the German Federal Office for the Protection of the Constitution — in which photographs of the operational JO-4 device were shown [5]. The image above reflects the confiscated items.


Parts
Leather storage case
JO-4 infra-red transceiver
Remote control unit (handset)
Photographic tripod
Power cable
Portable light torch
Optional UHER 4000 tape recorder
External adjustable attenuator
Expansion unit
Power supply unit
PSU
Storage case
Each of the main units (device 1 & 2) are stowed in a leather storage case that measures 288 x 125 x 57 mm and weights 1510 grams (all items included). Inside the case is a transceiver, a control unit (the handset), a power cable, audio cable and an external volume control unit.

An agent would normally travel abroad with just this case in his luggage, complemented by a tripod and a flashlight.

  
JO-4 stowed in leather storage case

Transceiver   JO-4
The transceiver is the heart of the system. When closed, it measures just 165 x 115 x 45 mm and weights 1160 grams. When the flaps are opened, it measures 165 x 115 x 135 mm. After opening, the secondary mirrors must be brought in position by raising the bar (as shown here).

At the bottom is an adjustable tripod mount. Also at the bottom is a 14-pin Amphenol socket to which the control unit must be connected.

  
JO-4 with secondary mirrors in position (bar raised)

Handset
The device is operated with an external remote control unit, or handset, that must be connected to the 14-pin Amphenol socket at the bottom.

The handset contains a microphone and has a fixed wired earpiece. At the top is the MODE-selector. In the middle position (rest) the receiver is enabled. Pushing the lever to the left enables the transmitter and the receiver (duplex). At the top is a red button. When pushed, the device transmits a tone to 'wake' the other party.

  
Handset

Tripod
The JO-4 has an opening angle (2ω) of just 0.38°, which means that both devices must be aligned accurately to achieve a proper and reliable communication path. At a distance of 2 km, it illuminates just a 13 metre area.

For a proper and stable link, it is therefore mandatory to mount each device on a tripod, such as the one shown in the image on the right.

  
Tripod with photograph thread

Power cable
The JO-4 has no provisions for fitting internal batteries. Instead, it must be powered by means of the special power cable shown in the image on the right. The cable has a coaxial LEMO-connector at one end – that must be fitted to the socket at the bottom of the handset – and an E10 lamp thread at the other end.

The E10 thread can be fitted to the E10 socket of a portable flashlight – it replaces the lightbulb – such as the one shown below. Alternatively, an external power cable could be used.

  
Power cable

Portable flashlight
The JO-4 is powered by an external 4.5V DC source, that must be connected to the LEMO-socket at the bottom of the handset. In most cases, an existing portable flashlight was used for this, such as the Narva Artas 9480 shown in the image on the right. It uses three 1.5V D-type batteries (mono cells) which are sufficient for many hours of uninterrupted operation.

The reflector must be removed from the flash­light and the light bulb has to be taken out of its E10 socket. Next, one end of the power cable is screwed into the E10 socket.

  
Narva Artas 9480 flashlight

Recorder
When the JO-4 was used in the advanced configuration, an UHER 4000 tape recorder could be connected to either station via expansion box (3), using the supplied cables.

Depending on the configuration, the UHER 4000 was used for recording or playback. Although UHER was a West-German brand, their recorders were available in East-Germany (DDR) as well.

 More information

  
UHER 4000 Report-S

Volume adjuster
Each unit came with an adjustable attenuator that could be connected between the handset and a tape recorder. It allows the level of the input signal – which varies with the distance to the opposite station – to be adjusted manually.

The device consists of a rectangular metal enclosure with a recessed thumb-operated potentiometer. It has two fixed wires: one that terminates in a 5-pin DIN plug, and one with a 3-pin DIN-plug at the end.

  
Handheld volume adjustment for tape recorder

Expansion unit
Although both devices can be used stand-alone (transceiver + handset), one device was usually connected to the expansion unit shown in the image on the right. It can be connected to the power supply unit (4) (see below) and has sockets for connection of an external recorder.

This device is missing from the JO-4 kit in our collection, but is similar to the one supplied with the later JO-4.03.

 Check out the JO-4.03

  
Expansion box (Device 3)

Power supply unit
The device could be powered from the AC mains by means of the supplied power supply unit (PSU) shown in the image on the right. It is designated device number 4 and is suitable for the 200-250V AC mains only.

This device is missing from the JO-4 kit in our collection, but is similar to the one supplied with the later JO-4.03.

 Check out the JO-4.03

  
Mains power supply unit (Device 4)

Two JO-4 units (1 and 2) in leather storage cases
JO-4 stowed in leather storage case
JO-4 with open lid and raised mirror
Storage case with tripod
Tripod with photograph thread
Handset with earpiece and cables
Handset
Handset - bottom view
Handset - top view
Earpiece
Power cable
External power cable
Audio cable
Volume adjustmet unit
Handheld volume adjustment for tape recorder
Volume adjuster
Narva Artas 9480 flashlight
JO-4 with tripod and flashlight
JO-4 power cable connected to the flashlight
Powering the JO-4 from a Narva Artas 9480 portable flashlight
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Two JO-4 units (1 and 2) in leather storage cases
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JO-4 stowed in leather storage case
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JO-4 with open lid and raised mirror
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Storage case with tripod
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Tripod with photograph thread
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Handset with earpiece and cables
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Handset
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Handset - bottom view
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Handset - top view
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Earpiece
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Power cable
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External power cable
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Audio cable
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Volume adjustmet unit
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Handheld volume adjustment for tape recorder
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Volume adjuster
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Narva Artas 9480 flashlight
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JO-4 with tripod and flashlight
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JO-4 power cable connected to the flashlight
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Powering the JO-4 from a Narva Artas 9480 portable flashlight

Connections
Power socket
The device is powered by an external 3.5 to 4.5V DC source, that must be connected to the LEMO-socket at the bottom of the handset. This coaxial connector has the (+) terminal connected to the contact at the centre.

  1. +3.5 to 4.5V DC
  2. Ground
    Wiring of the LEMO-socket at the bottom of the handset
Audio socket
At the bottom of the handset is a 5-pin 180° DIN socket to which external audio devices, such as a tape recorder, can be connected. Below is the pinout when looking into the socket.

  1. Line in (from tape recorder)
  2. Ground
  3. Line out (to tape recorder)
  4. Microphone in (2kΩ)
  5. Earphone out
    5-pin 180° DIN socket at the bottom of the handset, when looking into the socket.
Specifications
  • Type
    Line-of-sight (LOS) light-based communication device
  • Purpose
    Covert cross-border agent communication
  • User
    MfS (Stasi)
  • Manufacturer
    Carl Zeiss Jena
  • Frequency
    317 THz (940 nm) - infrared
  • Modulation
    AM
  • Operation
    Full duplex
  • Bandwidth
    400 - 3000 Hz (narrowband)
    250 - 16000 Hz (wideband)
  • Angle (2ω)
    0.38° (transmitter)
    0.28° (receiver)
  • Power
    3.5 - 4.5V DC
  • Batteries
    3 x 1.5 D-size (external)
  • Viewfinder
    Γ = 5.5x, viewingle angle (2ω) = 8°
  • Range
    3 km (2 km when using wideband option)
  • Call tone
    1050 Hz ±100 Hz
  • Pilot tone
    16 kHz (crystal)
  • Dimensions
    165 x 115 x 45 mm (collapsed)
  • Weight
    1160 g
Nomenclature
  • JO-4
  • 17305
  • Neue Dahme
Known serial numbers
  • 1 0067 1
    2 0067
    Crypto Museum (Netherlands)
  1. This is the rare wide-angle variant (Weitwinkel-Dahme).

Documentation
  1. JO-4 description (German) 1
    Pflichtenheft für das Thema JO-4. 1973.
    Based on functional specification of 13 September 1971.

  2. JO-4 technical description (German) 1
    MfS/Carl Zeiss Jena, 1972. BStU, MfS-OTS Nr. 1238.

  3. Wide-angle version (technical notes in German) 1
    Weitwinkel-Dahme. MfS, 30 June 1978.

  4. BPX65 Silicon PIN Photodiode, datasheet
    Osram, 23 December 2015, Version 1.3.
  1. Document obtained from BStU [2] and kindly supplied by Detlev Vreisleben [1].

References
  1. Detlev Vreisleben, Personal communication
    November 2021.

  2. Bundesbeauftragte für die Stasi-Unterlagen (BStU) 1
    Federal Commissioner for the Stasi-Records.

  3. Ob.Lt. Schultze, Information zum Produktionsthema JO 4
    MfS, 21 October 1985. 2

  4. German Patent DD265972, Mangin-Zweispiegelsysteme
    Filed 5 November 1987.

  5. BfV, Nachrichtendienstlichte Hilfsmittel/Nahbereichskommunikation
    Bundesamt für Verfassungschutz, annual report 1985.
    Verfassungsschutzbericht 1985. pp. 229-230.
  1. Full name: Bundesbeauftragte für die Unterlagen des Staatssicherheitsdienstes der ehemaligen Deutschen Demokratischen Republik (DDR) — Federal Commissioner for the Records of the State Security Service of the former German Democratic Republic (GDR) — officially abbreviated to BStU.
  2. Document obtained from BStU [2] and kindly supplied by Detlev Vreisleben [1].

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© Crypto Museum. Created: Sunday 21 November 2021. Last changed: Monday, 20 December 2021 - 09:32 CET.
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