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Opto
Voice
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JO-4.03   Kleine Dahme
Opto-electronic voice transceiver

JO-4.03 is a covert infra-red-light communications device, also known as photophone (German: Lichtsprechgerät), developed between 1985 and 1987 by VEB Carl Zeiss Jena in Jena (DDR) for the East-German security service MfS (Stasi). It is the successor of the original JO-4, introduced in 1974, and was used for covert (agent) communication across the East-German state borders and the sector borders in Berlin. The device is also known as Projekt 17305-1 and was codenamed Kleine Dahme. 1 It is compatible with the JO-4.02 (Große Dahme) and the miniature Finow-I.

The system consists of a local and remote JO-4.03 unit, an expansion unit, a power supply unit (PSU) and various accessories, and was supplied in a large unobtrusive travel suitcase.

The bare (closed) device measures just 170 x 120 x 50 mm and weights 1452 grams. It has three spring-loaded flaps that protects the lenses agains direct sunlight. After opening the largest flap at the front, the two flaps at the sides come out automatically, as shown in the image on the right. At the bottom is a ball-head that allows the device to mounted on a tripod.
  
JO-4.03 ready for use

At the top is an enlarging viewfinder that has the accuracy of a riflescope. It is used to aim the device accurately at the remote station. Once the flaps are opened, a horizontal bar with two small embedded mirrors must be raised before the device can be used. The complete unit, with microphone, earpiece and accessories is packed in a compact black leather storage case. Two such sets are present in the kit. A 45° persicope is provided for adjusting the device from any angle. Normally, an agent would only take one unit in his luggage on a trip to the free West, and use it to pass information to a Stasi station inside the DDR in the direct Line-of-Sight (LOS).

The JO-4.03 was specified for a LOS operational range of up to 3 km [A], but amateur radio operators have meanwhile demonstrated that under good conditions a much longer range is possible [5]. When using the auto-recording and high-speed audio transfer features, the maximum range is restricted to 2 km. Note that only one station transmits a 16 kHz pilot tone.

  1. The Dahme is a river that flows in the German states of Brandenburg and Berlin. The Stasi commonly used river names for its infra-red (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).

Unobtrusive travel suitcase
JO-4.03 inside suitcase
Inside the storage case
JO-4.03 front side with closed optical port
JO-4.03 ready for use
Open optical port with raised mirrors
JO-4.03 with control unit and earpiece
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Unobtrusive travel suitcase
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JO-4.03 inside suitcase
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Inside the storage case
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JO-4.03 front side with closed optical port
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JO-4.03 ready for use
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Open optical port with raised mirrors
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JO-4.03 with control unit and earpiece

Features
A complete system consists of two transceivers (devices 1 and 2) – also known as the main units – an expansion unit (3) and a power supply unit (4). The image below shows one of the main units (device 1), with its control unit and earpiece. The control unit, or handset, holds the batteries (3 x 1.5V AA-size), the microphone, a wired earpiece, the MODE-selector and the volume control with on/off switch. It is connected to the main unit via a 14-pin Amphenol connector.

Click to see more

The main unit is housed in a rectangular black metal enclosure with a ball-head at the bottom for mounting it on a tripod. At a front is a hinged spring-loaded cover that protects the optics. When it is opened, the two spring-loaded side panels will unfold themselves and expose the two large parabolic primary mirrors. Above the mirrors is a bar that holds the two small secondary mirrors.

Raise the bar to bring the secondary mirrors in a locked position above the primary ones. The diagram below shows the result. Note that 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.


Install the device on a tripod and aim it accurately at the other station, using the built-in range­finder (above the hinged cover). Note that the opening angle (2ω) is just 0.14°. At a distance of 2 km, this is equivalent to approx. 10 metres. Turn the device on by turning the volume control knob away from its null-position (click) until a faint noise can be heared. The device is now ready for use. When speaking into the microphone, the signal can be picked up by the other station.

Pilot tone
If necessary, the other station can be called by pressing the red button at the left side of the control unit. This sends a 1000 Hz tone to the other station. Note that transceiver (1) always transmits a 16 kHz pilot tone with the speech. This pilot tone can be used by the other station (2) to start a tape recorder. Note that this reduces the maximum range from 3 km to approx. 2 km.


Setup
The block diagram below shows the basic setup of the JO-4.03. 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 (0.14°), so use the viewfinders at both ends to ensure that the devices can 'see' each other. When correctly adjusted, a distance of several kilometres should be possible.

Basic full-duplex setup with battery-powered units

In the basic configuration, each unit is powered by internal batteries (placed inside the RCUs), or from a 4.5V flashlight, simply by connecting the flashlight cable between the E10 lamp fitting of the flashlight and the small SMC coaxial socket on the remote control unit.

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 unit (1) – that activates a recorder that is connected to the local station (2). Unit (1) is the only unit that generates a pilot tone, so it is important that this unit (1) is used at the remote end. Its serial number has a '1' prefix. When the 16 kHz pilot tone is picked up by the local station, this is confirmed by a continuous 1 kHz tone. After 30 seconds, the recording stops and so does the 1 kHz tone. If the remote signal (1) is lost, the tone becomes intermittent. In the same vain, when configured apropriately, the remote station (1) can also be used to collect pre-recorded messages from the tape recorder at the local station (2).

WARNING — When the external power supply unit (4) is connected to the setup, the batteries have to be removed from the handset (RCU 2) as they will otherwise be damaged. The PSU itself can be powered from the mains, by internal batteries, or by an external 12V DC source, such as the battery of a vehicle.
High speed audio transfer
It is also possible to transfer audio information at high speed from the local station (2) to the remote station (1). It allowed the Stasi to pass long instructions to its agent across the border, whilst minimising the risk that the agent was discovered. In this setup, a recorder at station (2), plays the tape at 2x or 4x the nominal speed. Station (1) can then record this information at 2x or 4x the regular speed and play it back later at nominal speed. This is also known as data mode. It has a bandwidth of 7 - 70 kHz, and requires the BNC sockets on units (1) and (2) to be used.

Setup for high-speed data transfer (data mode)

Note that the data signal can only be sent from unit (2), as unit (1) always transmits a 16 kHz pilot tone. When a second recorder is present at station (2), it can record the voice data transmitted by station (1), whilst station (1) is recording the high speed data from station (2). Note that the local station (2) will automatically start playing its high-speed message when the 16 kHz pilot tone from the remote station (1) is detected.


Parts
Transit case
Leather storage case
IR transceiver
Handheld (remote) control unit
Expansion Unit (XU) - Zusatzgerät (ZG) - Device 3
Mains power supply unit - Device 4
PSU
Viewfinder extension
Tripod for accurately aiming the transceiver
Interconnection cables
Flashlight power cable
Portable light torch
Optional UHER 4000 tape recorder
Transit case
The complete JO-4.03 kit was supplied in the large unobtrusive suitcase shown in the image on the right. It contains two main units – each packed in a leather storage case - an expansion unit, power supply unit, persicope and cables.

The case measures approx. 650 x 430 x 190 mm and is made of printed cardboard. Inside is soft polystyrene foam with a cutout for each component. The cables are stowed in the front left and right corners.

  
JO-4.03 inside suitcase

Storage case
Each of the main units (device 1 & 2) is stowed in a leather storage case that measures 255 x 175 x 110 mm and weights 2785 grams (all items included). Inside the case is a transceiver, a control unit (the handset), a power cable and maintenance tools (cloth and brush).

An agent would normally travel abroad with just this case in his luggage. In most cases, the case would contain device number 1, as this is the only one that transmits a 16 kHz pilot tone.

  
Storage case

Transceiver   1 & 2
The transceiver is the heart of the system. When closed, it measures just 170 x 120 x 50 mm and weights 1455 grams. When the flaps are opened, it measures 170 x 120 x 135 mm. After opening, the secondary mirrors must be brought in position by raising the bar (as shown here).

At the bottom is a ball-head with regular thread to mount it on a tripod. The device has a fixed (grey) cable with a 14-pin Amphenol connector at the end, to which the control unit must be connected.

  
Open optical port with raised mirrors

Handset
The device come with a control unit, or handset, that measures 115 x 62 x 44 mm and weights 350 grams. It has a fixed (black) cable with a 14-pin Amphenol connector at the end that mates with the connector of the transceiver.

The handset contains a microphone, a mode-selector, a volume indicator (LED bar) and a call button, and has a fixed earpiece. It allows full-duplex voice conversations. When pressing the call button, a 1000 Hz tone can be heared at the other end. All audio signals are also available on a 5-pin DIN socket at the bottom.

  
Control unit with cable and earpiece

Expansion box   3
Although both devices can be used stand-alone (transceiver + handset), device number 2 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.

The device is designated device number 3. The cables are wired for connection of an UHER Report 4000 audio tape recorder.

 Look inside this unit

  
Expansion box (Device 3)

Power supply unit   4
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.

The device must always be connected to the transceiver via the expansion unit (device 3) by means of a special power cable that was supplied as part of the kit.

 Look inside this unit

  
Mains power supply unit (Device 4)

Periscope
If the eyepiece is unreachable, the periscope shown in the image on the right can be used to aim the device at the counterpart station. It should be mounted instead of the existing eyepiece – for which a suitable tool is provided – and can be used at any angle of rotation.

Instructions on how to mount the periscope, are given in chapter 6 of the user manual [A].

  
45º Periscope and lens mounting tool

Tripod
The JO-4.03 has an opening angle (2ω) of just 0.14°, 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 10 metre cone.

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

  
Tripod with photograph thread

Cables
The JO-4.03 was supplied with a collection of cables, such as a mains power cable, a cable for connection to the 12C battery of a car, an inter­connection cable used between device (3) and (4) and one or more DIN cables for connecting the (optional) UHER tape recorder(s).

These cables are all intended for use at the local station. In addition, each station comes with a special power cable (see below).

  
Cables

Power cable
In addition to the above cables, each unit was supplied with a special power cable that allows the device to be powered by a 4.5V flashlight, rather than by its internal batteries.

The cable has a small connector, which should be fitted to the SMC coaxial socket on the hand device (RCU), whilst the other end is installed in the lamp fitting of the flashlight.

  
Flashlight power cable

Flashlight
The JO-4.03 can powered by an external 4.5V DC source, that must be connected to the SMC-socket at the bottom of the handset. In most cases, an existing portable flashlight was used for this, such as the Artas Focus 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-4.03 was used in the advanced or high-speed configuration, an UHER 4000 tape recorder could be connected to station (2) 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

Unobtrusive travel suitcase
JO-4.03 inside suitcase
Storage case
Inside the storage case
Contents
JO-4.03 front side with closed optical port
JO-4.03 rear side with viewfinder
Open optical port, with collapsed mirrors
Open optical port with raised mirrors
JO-4.03 ready for use
Expansion box (Device 3)
Expansion box (Device 3)
Mains power supply unit (Device 4)
Control unit with cable and earpiece
Control unit with red call button
Control unit seen from the bottom
Leather wallet with 45º periscope
45º Periscope and lens mounting tool
45º Periscope detail
Storage case with tripod
Tripod with photograph thread
Cables
Flashlight power cable
JO-4 power cable connected to the flashlight
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Unobtrusive travel suitcase
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JO-4.03 inside suitcase
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Storage case
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Inside the storage case
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Contents
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JO-4.03 front side with closed optical port
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JO-4.03 rear side with viewfinder
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Open optical port, with collapsed mirrors
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Open optical port with raised mirrors
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JO-4.03 ready for use
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Expansion box (Device 3)
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Expansion box (Device 3)
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Mains power supply unit (Device 4)
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Control unit with cable and earpiece
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Control unit with red call button
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Control unit seen from the bottom
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Leather wallet with 45º periscope
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45º Periscope and lens mounting tool
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45º Periscope detail
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Storage case with tripod
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Tripod with photograph thread
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Cables
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Flashlight power cable
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JO-4 power cable connected to the flashlight

Interior
Due to the compact and sensitive nature of the optical parts, we have decided not to open the transceiver. As the unit is fully operational, there is currently no need to disassemble it. Below are several images of device 3 (expansion unit) and device 4 (PSU) that were taken during their repair.

Expansion Unit interior
Expansion Unit interior (upper board removed
Expansion Unit lower board
Expansion Unit upper board
PSU interior
PSU interior
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Expansion Unit interior
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Expansion Unit interior (upper board removed
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Expansion Unit lower board
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Expansion Unit upper board
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PSU interior
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PSU interior

Restoration
When we obtained a complete set of two JO-4.03 devices in November 2021, they were both in working condition, with the exception of the power supply unit (4) and the expansion unit (3). In both devices the internal fuse holder was corroded to the point where it no longer conducted. After replacing the silver-plated fuse holders, the devices were tested and no further anomalies were found. Nevertheless we replaced all electrolytic capacitors as a precaution.

Surprisingly, the soft polystyrene foam inside the suitcase was still in very good condition, which is not trivial after so many years of storage. Testing of the two transceivers is possible by setting them up with the secondary mirror collapsed (i.e. not raised) at a distance of 2 metres. This is equivalent to a distance of 2000 metres with the mirrors in place. Everything worked as expected. Apart from a little background noise, the audio quality and the speech legibility is excellent.

Fixed
  • Units superficially cleaned
  • Leather case treated with leather grease
  • Expansion unit (3) internal fuse holder replaced
  • PSU (4) internal fuse holder replaced
  • PSU (4) all electrolytic capacitors replaced
  • Battery cable correct (polarity was reversed)
Corroded fuse holder inside the expansion unit
PSU interior
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Corroded fuse holder inside the expansion unit
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PSU interior

Video footage
In this video, German collector Karsten Hansky shows how the 16 kHz pilot tone from transmitter (1) can be used to activate a recorder, by connecting the expansion unit (3). This is described in the advanced setup. Note the 1 kHz confirmation tone that is returned by transmitter (2) as long as the recording runs. This way, the agent knows that the message is being received. After 30 seconds, the recording (and the 1 kHz tone) is stopped automatically. When the pilot tone is lost, transmitter (2) sends an intermittent tone for 30 seconds, so that the agent is informed of this.


Using the JO-4.03 as an electronic dead letter box (EDLB). © Karsten Hansky [6].



Connections
Power
For connection of the DC power, a rectangular 6-pin receptacle is available on the power supply unit (PSU). Only the outer 4 contacts are used and they are cross-wired, to that the cable can be inserted either way. Below is the pinout when looking into the receptacle on the PSU (device 4).



External audio
At the bottom of the handset is a 5-pin 180° DIN socket on which all audio signals are available. 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.
Cable 1
For playing back a pre-recorded message via the local transmitter, the tape recorder must be connected to the DIN 5/180 socket on the expansion box (3). That is the socket that is marked with an input symbol. A suitable cable was supplied with the JO-4.03. It has a DIN 5/180 plug at one end that that must be fitted to the DIN 5/180 socket on the expansion box (3).




At the other end of the cable are two further DIN connectors: a 3-pin one that carries the audio signal and should be connected to the audio output of the tape recorder, and a DIN 5/360 that carries the signal for starting the playback. It is currently unclear for what type of tape recorder this cable was intended, as the standard issue UHER 4000 does not have a socket for the latter.

 More about DIN connectors and standard wiring

Cable 2
For recording a received message, the tape recorder must be connected to the DIN 6/240 socket on the expansion box (3). That is the socket that is marked with an output symbol. A suitable cable was supplied with the JO-4.03. It has a DIN 6/240 plug at one end that that must be fitted to the DIN 6/240 socket on the expansion box (3). A possible wiring layout is shown here.


At the other end of the cable are two further DIN connectors: a 3-pin one that carries the audio signal and should be connected to the audio output of the tape recorder, and a DIN 5/360 that carries the signal for starting the playback. It is currently unclear for what type of tape recorder this cable was intended, as the standard issue UHER 4000 does not have a socket for the latter.

 More about DIN connectors and standard wiring

External volume control
With some units, an external volume control unit was supplied. It is used to adjust the audio level into the tape recorder. It is currently unclear how this cable was used, but it is likely that the DIN 5/180 plug at the left was connected to the 5-pin DIN socket on the handset of the JO-4.03.



Specifications
  • Type
    Line-of-sight (LOS) light-based communication device
  • Purpose
    Covert cross-border agent communication
    Speech, recorded audio, wideband data (7-70 kHz)
  • Usage
    Indoor (limited outdoor usage)
  • User
    MfS (Stasi)
  • Manufacturer
    Carl Zeiss Jena
  • Frequency
    317 THz (940 nm) - infrared
  • Range
    ≤ 3 km
  • Automatic
    ≤ 2 km
  • Microphone
    250 - 6000 Hz, 0.25 mW into 5 kΩ
  • Earpiece
    250 - 3200 Hz
  • Input
    150 Hz - 16 kHz, 0.2 - 2V into 10 kΩ (from tape recorder)
  • Output
    700 mW into 10 kΩ
  • Data
    7 - 70 kHz, 700 mV into 300Ω
  • Power
    3 x 1.5V AA-size (in handset)
    Mains 220V AC+ (by connecting device 4 PSU)
    Battery pack (inside device 4 PSU)
  • Temperature
    -0°C to 45°C (device 3 and 4)
Transceiver   1, 2
  • Power
    3.5 - 4.5V DC
  • Current
    25 mA (RX), 120 mA (TX)
  • Angle (2ω)
    0.14°
  • Viewfinder
    Γ = 5.5x, viewingle angle (2ω) = 7°
  • Temperature
    -20°C to +45°C (0°C to 45°C for device 3 and 4)
  • Dimensions
    170 x 120 x 50 mm
  • Weight
    1452 g
Checklist
  1. Optical transceiver (remote station)
  2. Optical transceiver (location station)
  3. Expansion unit
  4. Power supply unit
  • Suitcase
  • 45° Periscope in leather wallet
  • 2 x Control unit (for 1 and 2)
  • 6-pin DIN cable
  • Mains cable
  • Battery cable with large crocodile clips
Nomenclature
The device is known by the following designators:

  • JO-4.03
  • 17305-1
  • Kleine Dahme
  • Palme
Known serial numbers
The serial number of a JO-4.03 consists of three digits, prefixed with the number of the device. For example: if the serial number is 302, the primary transceiver has the serial number 1 302, the secondary transceiver has 2 302, the expansion unit has 3 302 and the PSU has 4 302.

Below is a non-exhaustive list of known serial numbers:

  • 1 224
    2 238
    3 453
    4 536
    Private Collector, Germany
  • 1 228
    2 216
    ?
    ?
    Mike Prichard Collection, Australia
  • 1 302
    2 302
    3 302
    4 302
    Crypto Museum, Netherlands
  • 1 316
    2 316
    3 316
    4 316
    Private collector, Austria
  • 1 425
    2 425
    3 425
    4 425
    Private collector, Netherlands
  • 1 225
    2 240
    3 455
    4 550
    Private collector, Germany
Documentation
  1. JO-4.03 operating instructions (German) 1
    Bedienungsanleitung für das Gerät 17 305-1 (JO-4.03)
    Undated.

  2. JO-4.03 original circuit diagram
    Extracted from [D].

  3. JO-4.03 functional description (German) 1
    MfS, Abt. 26/4. Info.Nr. 5/87 - Aufgabe B, Kennblatt 17 305-1. 1987.

  4. JO-4.03 final report (German) 1
    Abschluß-Bericht zur Studie JO-4.03.
    VEB Carl Zeis Jena, 6 April 1983.

  5. Stasi case file about the JO-4.03 1
    Collection of documents and diagrams related to the JO-4.03.
    MfS/CZJ, 1983-1987.

  6. German Patent DD265972, Mangin-Zweispiegelsysteme
    Filed 5 November 1987.
  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. Ob.Lt. Schultze, Information zum Produktionsthema JO 4
    MfS, 21 October 1985. 2

  4. Günter Hütter, Personal correspondence
    September 2021.

  5. Peter Greil (DL7UHU), www.lichtsprechen.de
    Visited 22 November 2021.

  6. Karsten Hansky, Stasi JO-4.03 opto-electric voive transceiver as electronic dead letter box
    16 February 2022.
  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: Wednesday 17 November 2021. Last changed: Monday, 07 March 2022 - 21:38 CET.
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