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Opto
Voice
ZEISS
Stasi
  
JO-4.03 →
← JO-4.01
  
JO-4.02   Große Dahme
Opto-electronic voice transceiver

JO-4.02 is a covert infra-red-light communication device, also known as photophone (German: Lichtsprechgerät), developed between 1979 and 1986 by VEB Carl Zeiss Jena in Jena (DDR) for the East-German security service MfS (Stasi). It is the more powerful 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 of Berlin. The device is also known as project 17304 and as Große Dahme, 1 and is compatible with the smaller JO-4.03 and the miniature modular FINOW.

The device has an oval-shaped enclosure that measures 315 x 240 x 120 mm and weights 4346 grams, batteries not included. Most of the space is taken by the two large double-mirrors; one for the transmitter and one for the receiver.

If two identical units are used, communication over a distance of 5 km 2 should be feasible. In practice however, the JO-4.02 was often used as a base station, with a smaller portable unit, such as the JO-4, JO-4.03 or FINOW, at the other end. Stasi (MfS) agents used the devices to exchange messages without physically crossing the border.
  
JO-4.02 infra-red full-duplex transceiver

The device has a opening angle of just 0.18°. At a distance of 1 km this is equivalent to 3 metres. For this reason, the devices at both ends of the transmission path have to be aligned accurately, using the built-in range scope (viewfinder) and the mechanical adjustments of the tripod mount at the bottom. A wideband version of the device — suitable for the reception of black and white video signals (CCTV) transmitted by the JO-4.05 — was known as JO-4.06.

 Listen to the JO-4.02

  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 Große Dame (big lady).
  2. In practice, much larger distances are possible. In recent years, amateur radio operators were able to cover a distance of 14 km [5] and in one case even 24 km [7].

Leather storage caes
JO-4.02 with protective caps
JO-4.02 infra-red full-duplex transceiver
JO-4.02 infra-red full-duplex transceiver
Rear side with viewfinder
JO-4.02 with handset and earpiece
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Leather storage caes
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JO-4.02 with protective caps
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JO-4.02 infra-red full-duplex transceiver
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JO-4.02 infra-red full-duplex transceiver
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Rear side with viewfinder
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JO-4.02 with handset and earpiece

HELP PLEASE — We are currently looking for the complete circuit diagram of the JO-4.02. From the Stasi archives (BStU), we have obtained the circuit diagram of the later handset and mechanical drawings of the main unit, but unfortunately the circuit diagram of the main unit is still missing [B].  Contact us
Features
The image below provides a quick overview of features of the JO-4.02. At the right is the device, which is here lying on its rear side. The two double mirror systems are facing upwards, When in transit, these mirrors are covered by aluminium caps. At the rear is a curved overhead cap, that can be moved forward to protect the device against direct incoming sunlight. This is necessary, as sunlight contains infrared rays that may interfere with the faint infrared signal of the JO-4.02.

Click to see more

At the bottom of the main device is a 14-pin Amphenol socket to which the handset must be connected. The handset has a built-in microhone and a fixed-wired earpiece. At the bottom of the handset is a 5-pin DIN socket for connected of external audio equipment, such as a tape recorder. The unit is powered by internal batteries, or by an external 4.5V DC source (e.g. from a portable flashlight) that is connected at the bottom of the handset, using the supplied E10 cable.


The diagram above shows how the patented double-mirror system works [9]. 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 an embedded part of the transceiver, whilst the secon­dary mirror is mounted on a fixed frame that is located over the primary mirror. At the centre of the primary mirror is the infrared light source (TX), or the infrared detector (RX).

Mode of operation
  1. Transmit & receive (microphone & tape player)
  2. Receive only
  3. Transmit & receive (tape player only)
Applications
The JO-4.02 was suitable for the following applications, provided that there was a direct line-of-sight between the two stations:

  • Duplex speech with another JO-4.02 over distances up to 5 km
  • Transfer of wideband (high-speed) tape recordings over distances of at least 3 km
  • Duplex speech with the portable JO-4.03 over a distance of > 3 km
  • Duplex speech and data transfer with covert FINOW device > 1.5 km
  • Duplex speech with JO-4 over a distance of > 3 km
  • Duplex speech with JO-4.01 over a distance of 500 m
Older type handset
Handset and fixed-wired earpiece
JO-4.02 with handset and earpiece
Close-up of the double mirror
Viewfinder (range scope)
Adjustable head
Battery compartment
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Older type handset
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Handset and fixed-wired earpiece
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JO-4.02 with handset and earpiece
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Close-up of the double mirror
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Viewfinder (range scope)
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Adjustable head
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Battery compartment

Sound samples
On 17 August 2014, three German Amateur Radio Operators — DL3HRT, DL2HSX and DL2AWT — carried out several experiments with two JO-4.02 devices and one homemade Lichtsprechgerät — the AATiS AS802 ELiSE 1 — over a distance of no less than 14 km. The test results are available (in German) here [5]. Below are two audio clips that were recorded during the experiments [4].

  1. AS802 ELiSE is a homemade infrared communication device that is compatible with the Stasi's JO-4.02 and similar devices. It is available from the German amateur radio club AATiS as self-build kit AS802 ELiSE [6].

Setup
The diagram below shows a typical setup with the JO-4.02 (Große Dahme) as the local station (2). At the left is the remote station (1), which can be any infrared communication device from the JO-4.xx series. When this is another JO-4.02, it should be possible to cover a range of 5 km or more.


Each of the devices can have a tape recorder connected to the handset, which can be used for recording or playback. At the JO-4.02 side, it can be used for high-speed audio recording or playback, typically at 2x or 4x the regular speed, as it has a bandwith of 16 kHz. Some other models also support high-speed data transfer. Check the relevant pages for further information.

Advanced and high-speed setup
In the advanced setup, the JO-4.02 was commonly used as the base station, with a much smaller portable device, such as the JO-4 or the JO-4.03 at the other end. By connecting an expansion unit and a mains power supply unit to the JO-4.02, the base station could be converted into an unmanned automatic-recording station. This configuration is shown in the diagram below.

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). For this to work, unit (1) has to be either a JO-4 (Neue Dahme), or a JO-4.03 (Kleine Dahme) of which the serial number starts with '1' (e.g. 1 302). 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).

The expansion unit and the PSU are currently missing from the JO-4.02 kit in our collection. They are very similar though, to the expansion unit and the PSU of the JO-4.03 (Kleine Dahme). Follow the link below for other possible configurations when used in combination with the JO-4.03.

 Check out the JO-4.03



Complete JO-4.02 kit (newer model) [8]

Parts
Leather storage case
JO-4.02 infrared transceiver
Remote control unit (handset)
Photographic tripod
Power cable
External adjustable attenuator
Portable light torch
Maintenance tools
Optional UHER 4000 tape recorder
Carrying case
When unused, the main unit can be stowed, together with the handset, the cables and the maintenance tools, in the brown leather storage case shown in the image on the right.

The case measures 330 x 250 x 140 mm and weight approx. 5875 grams, all items included. Inside the case is room for the main device, the handset, the maintenance tools and any cables.
  
Leather storage caes

Transceiver   JO-4.02
The transceiver is the heart of the system. With the sunlight cap retracted, it measures 315 x 240 x 120 mm and weights 4346 grams.

At the bottom is an adjustment mechanism with photographic thread, suitable for mounting it on a regular tripod. The device has a 14-pin Amphenol socket at the bottom, to which the handset must be connected.

  
JO-4.02 infra-red full-duplex transceiver

Handset   old model
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 left is the MODE-selector and the volume control which also acts as the ON/OFF switch. Pushing the black button at the front, transmits a 1000 Hz tone to 'wake' the other party. The meter in the upper right corner shows audio level or battery power.

  
Older type handset

Handset   new model
The grey metal handset shown above was later replaced with a black plastic one, in which the analogue meter was replaced by a LED-bar.

In addition, the MODE-selector has moved from the left side of the handset to the front, whilst the external power socket has been replaced by a more secure SMC connector.

  
New type handset with LED-bar

Tripod
The JO-4.02 has an opening angle (2ω) of just 0.18°, 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 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-4.02 is normally powered by internal batteries, but can also be powered externally from a regular 3-battery flashlight, using the special power cable shown in the image on the right. It is installed instead of the lightbulb.

In addition, cables are present for the connection of an UHER tape recorder, and (optionally) for the connection of an alternative power source.

  
Power cable for flashlight

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

Flashlight
If necessary, the JO-4.02 can be powered externally by a 4.5V DC source — typically a 3-battery flashlight like the Narva Artas 9480 shown in the image on the right — using the supplied E10 power cable.

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. Move the mouse over the image to see how this works.

  
Narva Artas 9480 flashlight

Maintenance tools
For a good and reliable connection over a range of several kilometres, it is important that the optical parts of the device are kept as clean as possible and free from dust. When the device is not in use, the black aluminium caps should be placed over the mirrors.

To remove any dust or dirt from the mirrors, a piece of lint-free cloth and a small brush was supplied with every kit.

  
Maintenance cloth and brush

Recorder
When the JO-4.02 was used in the advanced or high-speed configuration, an UHER 4000 tape recorder could be connected to either station via expansion box, 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

Complete kit with newer type handset
Leather storage caes
Inside the leather case
JO-4.02 with accessories in leather case
JO-4.02 infra-red full-duplex transceiver
JO-4.02 infra-red full-duplex transceiver
Close-up of the double mirror
Power cable for flashlight
Handset and fixed-wired earpiece
Older type handset
New type handset with LED-bar
Audio cable
Volume adjustmet unit
Handheld volume adjustment for tape recorder
Volume adjuster
Maintenance cloth and brush
Narva Artas 9480 flashlight
Power cable connected to the E10 fitting of the flashlight
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Complete kit with newer type handset
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Leather storage caes
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Inside the leather case
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JO-4.02 with accessories in leather case
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JO-4.02 infra-red full-duplex transceiver
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JO-4.02 infra-red full-duplex transceiver
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Close-up of the double mirror
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Power cable for flashlight
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Handset and fixed-wired earpiece
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Older type handset
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New type handset with LED-bar
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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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Maintenance cloth and brush
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Narva Artas 9480 flashlight
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Power cable connected to the E10 fitting of the flashlight

Click to see more

Interior
The interior of the JO-4.02 is easily accessible. First, the light shielding cap has to be removed. It is held in place with two screws; one on each side. Next, the viewfinder adjustment ring has to be removed (one miniature screw), followed by four screws around the edges of the outer case shell.

The case shell can now be removed by pulling it towards the rear of the device. This reveals the interior as shown in the image above. At the centre is the printed circuit board (PCB) of which the solder side is visible. The PCB has three large curved cut-outs: one for the viewfinder, one for the VQ120 IR-LED of the transmitter, and one for the SP211 IR photo-transistor of the receiver.

The PCB isheld in place with four screws. After removing these screws the PCB can be tilted outwards, as shown in the image on the right, but be careful not to damage the delicate wiring.
  
Loosened PCB

Compared to the handset [B], the circuit of the main device is relatively simple. At the left is the receiver, whilst the transmitter circuit is at the right. At the far end of the board is the wiring to the 14-pin Amphenol connector. The two flying wires go to the IR LED and IR photo-transistor.

Interior
JO-4.02 with removed case shell
PCB inside theJO-4.02
IR-detector wiring detail
Viewfinder
Loosened PCB
PCB detail
PCB with replaced electrolytic capacitors
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Interior
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JO-4.02 with removed case shell
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PCB inside theJO-4.02
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IR-detector wiring detail
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Viewfinder
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Loosened PCB
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PCB detail
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PCB with replaced electrolytic capacitors

Restoration
As the electrolytic capacitors had almost certainly degraded after all these years, we decided to replace all of them. To make this a bit easier, we temporarily desoldered the yellow and black wires to the IR LED and the IR photo-transistor. This allows the PCB to be placed horizontally.

Once all electrolytic capacitors were replaced, the wiring was restored and the PCB was mounted back in place. Finally the case shell was put on again and the device was ready for use. Testing it against a known good JO-4 unit revealed that the audio quality had improved as a result of the restoration. Checking the removed capacitors with an LCR-meter, confirmed that indeed their capacity had approximately halved, whilst the ESR had more than doubled.


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
  • Angle (2ω)
    0.18° (transmitter)
  • IR output
    1 mW
  • Range
    5 km (duplex speech)
    3 km (wideband tape)
    1.5 km (against FINOW)
    500 m (against JO-4.01)
  • Power
    3.5-4.5V DC
  • Battery
    3 x R6 1.5V
  • External
    From 3 x R20 in flashlight
  • Current
    35 mA (receive)
    150 mA (transmit)
  • Bandwidth
    250 Hz - 3200 Hz (earpiece)
    250 Hz - 6000 Hz (microphone)
    250 Hz - 16 kHz (tape recorder)
  • Input
    0.25 mW into 2 kΩ
  • Output
    0.7V into 10 kΩ
  • Range scope
    5.5 × enlargement, 2ω = 7°
  • Temperature
    -20°C to +45°C
  • Dimensions
    315 x 240 x 120 mm
  • Weight
    4346 g (without batteries)
Checklist
  • Main unit (transmitter, receiver, range scope, tripod-mount and battery holder)
  • Control unit (earpiece, microphone, control cable and power cable)
  • Leather storage case with carrying strap
Options
  • Expansion unit for auto-recording
  • Mains power supply unit
Nomenclature
  • JO-4.02
  • 17304
  • Große Dahme
Known serial numbers
  • 108
    Crypto Museum, Netherlands
  • 101062
    Private collector, Austria
Connections
Power socket
The device is powered by an external 3.5 to 4.5V DC source, that must be connected to the power 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 power 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 (≤ 70dB)
  2. Ground
  3. Line out (16 kHz bandwidth) (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.
Datasheets
  1. VQ120 infrared LED - datasheet
    Undated.

  2. SP211 photo-transistor - datasheet
    Undated.
Documentation
  1. JO-4.02 description (German) 1
    Undated.

  2. JO-4.02 technical drawings and circuit diagram 1
    June 1979 — August 1986 (incomplete).

  3. Lumofon advert 1
    Selectronic, LED und Laser-Kommunikationsanlagen, Undated.
  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. Karsten Hansky, Personal correspondence
    December 2021.

  5. Karsten Hansky et al., Lichsprechversuche am 17. August 2014...
    Experiments with JO-4.02 and homemade device over 14 km (German).
    DL3HRT, DL2HSX & DL2AWT, 17 August 2014.

  6. AATiS, AS802 Simple light transceiver (self-build kit)
    AS802 Einfacher Licht-Sende-Empfänger (ELiSE).
    Retrieved December 2021.

  7. Peter Greil (DL7UHU), www.lichtsprechen.de
    15 January 2005. p. 4.

  8. Günter Hütter, Personal correspondence
    September 2021.

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

Further information
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© Crypto Museum. Created: Sunday 21 November 2021. Last changed: Monday, 20 December 2021 - 12:51 CET.
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