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ZEISS
Stasi
  
JO-4.02 →
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JO-4.01   17303
Passive infrared communication device - wanted item

JO-4.01 was a passive infrared covert speech communication device, introduced around 1983 by VEB Carl Zeiss Jena in Jena (DDR), for the repressive security service of the former DDR (East-Germany) — Ministerium für Staatssicherheit (MfS), better known as the Stasi. The device has wide-angle characteristics and was intended for the transmission of speech and pre-recorded (high-speed) messages over distances < 1 km. It can be used in three different configurations.

The device consists of three basic elements: a triple mirror unit, a voice amplifier (transmitter) and a infrared receiver. It is called a passive device, as it does not actively radiate infrared light itself. Instead, it has to be illuminated by an infrared beam from the outside — typically a JO-4.02 or JO-4.03 that could be placed up to 1 km away, as long as it was in the line-of-sight (LOS).

The core of the device is the triple-mirror, which comprises a prism and a membrane-mirror, as shown in the image on the right. The membrane is excited by the audio (speech) of the operator.
  
Prism and membrane mirror used at the core of the triple-mirror. Photograph by Detlev Vreisleben [1].

The triple-mirror system is housed in a trapezoidal enclosure with an infrared (IR) filter at the front. In the simplest configuration, the triple mirror is used as a stand-alone device, without any additional active components. The performance can be enhanced by using a Sennheiser MM-23 microphone and an audio amplifier, to assist the membrane-mirror. If two-way communication was required, an infrared receiver could be added to the setup. The device was supplied in the most complete configuration, so that it could be used for all three possible configurations [A].

Due to the wide-angle nature of the device, it should not be placed behind regular window glass (reflection) or above a heater (turbulence), and the active area (i.e. the input port) should not be obscured in any way. The device was developed at Carl Zeiss Jena (CZJ) in Jena (DDR) between 1976 and 1979. Production started around 1983 and lasted until at least 1989, just before the fall of the Berlin Wall. A spin-off from the JO-4.01 development, is the Rostock infrared bug.

Complete JO-4.01 system with triple-mirror, transmission amplifier, receiver, microphone and earpiece. Photograph by Detlev Vreisleben [1].
Triple-mirror (passive unit). Photograph by Detlev Vreisleben [1].
Prism and membrane mirror used at the core of the triple-mirror. Photograph by Detlev Vreisleben [1].
Sennheiser MM-23 buttonhole microphone
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A
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Complete JO-4.01 system with triple-mirror, transmission amplifier, receiver, microphone and earpiece. Photograph by Detlev Vreisleben [1].
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Triple-mirror (passive unit). Photograph by Detlev Vreisleben [1].
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Prism and membrane mirror used at the core of the triple-mirror. Photograph by Detlev Vreisleben [1].
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Sennheiser MM-23 buttonhole microphone

Setup
JO-4.01 consists of three basic elements: a triple mirror, an audio amplifier (transmitter) and an infrared receiver. Depending on the application, one, two or all three of these items are used. The device can be used in three different configurations that are further explained below:

  1. Passive mode
  2. Assisted mode
  3. Duplex mode
1. Passive mode
In this configuration, only the triple mirror unit is used. It consists of a triangular glass body with one fixed mirror, and a reflecting membrane that acts as the second mirror. The two mirrors are placed at a 90° angle, in such a way that they reflect an incoming (unmodulated) infrared beam.

JO-4.01 in passive mode

At the right is the opposite station, which in most cases was a JO-4.02 (Große Dahme). In this configuration the JO-4.02 acts as an activation device. It illuminates the triple mirror with an unmodulated infrared beam. The membrane-mirror is excited by the operator's voice and modulates the reflected infrared beam, which is then picked up by the receiver of the JO-4.02. This is the only purely passive mode. It requires a person to speak close to the membrane.

2. Assisted mode
The membrane in the above configuration can be assisted by adding an miniature lapel microphone, an audio amplifier and a miniature speaker (bascially an earpiece). By placing the speaker in the vicinity of the membrane-mirror, the amplified audio excites the membrane.

JO-4.01 in assisted (simplex) mode

This mode is known as the assisted or active mode. It is a one-way system that is activated (illuminated) by an unmodulated infrared beam from the JO-4.02 at the other end. Although the amplifier is dubbed transmitter, the device only transmits when it is actively being illuminated.

3. Duplex mode
In the most complete configuration, an infrared receiver is added to the setup. It is mounted close to the triple mirror, so that it 'sees' part of the the infrared beam from the base station. It enables full duplex communication. If necessary, the receiver could also be detached and used elsewhere.

JO-4.01 in full-duplex mode

In this mode, the illumination beam from the base station – which activates the transmitter – can be modulated with the speech from the operator at the base station. Note however, that in that case, the reflected beam contains the voice data from both ends of the link.


Specifications
Triple mirror
  • Type
    Acoustic-optical modulator [3]
  • Purpose
    Covert cross-border agent communication
  • User
    MfS (Stasi)
  • Manufacturer
    Carl Zeiss Jena
  • Angle (2ω)
    20°
  • Bandwidth
    300 Hz - 4 kHz
  • Active area
    48 x 22 mm (i.e. the size of the IR-filter)
  • Dimensions
    63 x 42 x 40 mm
  • Temperature
    -20 to +45°C
Transmitter
  • Type
    AF audio amplifier (electro-acoustic amplifier)
  • Power
    2 to 3V DC
  • Current
    < 1 mA
  • Max. level
    80dB
  • Impedance
    200 - 2000 Ω (microphone)
  • Bandwidth
    300 Hz - 3 kHz
  • Power
    2 to 3V DC
  • Current
    < 1 mA
  • Batteries
    2 x LR-6 Alkaline (sufficient for 2 months)
  • Dimensions
    104 x 63 x 40 mm
  • Temperature
    -20 to +45°C
Receiver
  • Type
    Infrared receiver
  • Power
    2 to 3V DC
  • Current
    < 1.5 mA
  • Angle (2ω)
    12°
  • Active area
    10 mm Ø
  • Impedance
    600 - 1000 Ω (earpiece)
  • Dimensions
    104 x 40 x 23 mm
  • Temperature
    -20 to +45°C
Parts
  • Acoustic-optical modulator
  • Electro-acoustic amplifier (transmitter)
  • Infrared receiver
  • Earpiece
  • Lapel microphone Sennheiser MM-23
  • IR notch filter
  • External power cable (short and long)
  • Receiver power cable
  • 2 dummy batteries
  • Set of screws
  • Screwdriver
  • Lint-free cloth
  • Leather storage case
Nomenclature
  • JO-4.01
  • 17303
Documents
  1. JO-4.01 - Development planning 1
    MfS/CZJ, 1976, 1977, 1978.

  2. JO-4.01 - Development phase A1, Final Report (German) 1
    Bestätigungsbeleg zum Entscheidungsprotokoll der Verteidigung: A1.
    CZJ, 28 October 1977 (signed 28 November 1977).

  3. JO-4.01 - Development phase A4, Template (German) 1
    CZJ, 27 August 1979.

  4. JO-4.01 - Development phase A4, Progress Report (German) 1
    CZJ, 30 August 1979.

  5. JO-4.01 - Development pahse A4, Test Results (German) 1
    CZJ, 12 September 1979.

  6. JO-4.01 - Development phase A4, Final Report (German) 1
    CZJ, 25 September 1979.

  7. Test and adjustment aids for JO-4.01 (German) 1
    Justier- und Prüfmittel. CZJ, May 1982.

  8. JO-4.01 test result 1983, 1985 1
    CZJ, Handwritten documents (German).
  1. Document obtained from BStU [2] and kindly supplied by Detlev Vreisleben [1].

Documentation
  1. JO-401 - Datasheet (German) 1
    Kennblatt passive Technik 17 303. Information 14/86 Aufgabe B.
    VVS-MfS o035-721/86. 1986.

  2. JO-4.01 - Operating Instructions (German) 1
    Bedienungsanleitung für das Gerät 17303.
    VVS-o052, MfS-Nr. B224/25. Version 2. 6 pages.

  3. JO-4.01 - Block Diagram 1
    MfS, 3 September 1979.
  1. Document obtained from BStU [2] and kindly supplied by Detlev Vreisleben [1].

References
  1. Detlev Vreisleben, Personal correspondence
    November 2021.

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

  3. DDR Patent DD299778, Akusto-optischer Modulator hoher Brennweite
    CZJ, 29 March 1983.

  4. DDR Patent DD292553, Akusto-optischer Modulator
    14 March 1990.
  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: Thursday 16 December 2021. Last changed: Monday, 20 December 2021 - 10:01 CET.
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