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KF 4-2
Krypto-Fernsprecher

KF 4-2, also known as 103K-47-F, was an analogue voice terminal, manufactured in the early 1980s by Gelma Industrie-elektronik in Bonn (Germany) for use by NATO. It consists of a grey telephone set with a green handset, and was probably used as part of an underground Cold War NATO communications system. It is als known by its stock number NSN 5805-12-183-3784.

The basic device is a grey German analogue 1 FeTAp-612 desktop telephone set, of which the dial has been replaced by a blank panel. These telephones were made by a variety of German manufacturers, including Siemens and Hagenuk.

The device is fitted with a green handset, that probably indicates that it was used on a secured (encrypted) line. Strangely, the device is a hybrid, as the handset is from a Dutch T-65 telephone, rather than a FeTAp-61 2 as one would expect. It has an integrated push-button near the speaker, and is fitted with a noise-cancelling microphone.
  
KF 4-2 voice terminal

Due to the fact that the noise-cancelling microphone is thicker than a regular one, the handset is not fully seated in the cradle when it is placed on-hook. The device is connected to the local exchange, or PABX, via a standard 4-wire cable that has a 5-pin male XLR plug fitted at the end. At the front right is a ground-button that was probably used for calling the exchange. At the front of the device is a DYMO label with the number 4, which indicates that this was extension 4.

  1. FeTAp = Fernsprech Tisch Apparat (Remote Speech Table Device).
  2. The German FeTAp-61 and the Dutch T-65 are very similar and are nearly identical in size, which is why the Dutch handset fits the German telephone set. The reason for using the T-65 handset might be related to the presence of the push-button and the noise-cancelling microphone.

KF 4-2 voice terminal Front view Green T65 handset with push-button and noise cancelling micriphone Green T65 handset with push-button near speaker Special noise cancelling microphone Gap between handset and cradle, caused by presence of noise-cancelling microphone Bottom side
A
×
A
1 / 8
KF 4-2 voice terminal
A
2 / 8
Front view
A
3 / 8
3 / 8
A
4 / 8
Green T65 handset with push-button and noise cancelling micriphone
A
5 / 8
Green T65 handset with push-button near speaker
A
6 / 8
Special noise cancelling microphone
A
7 / 8
Gap between handset and cradle, caused by presence of noise-cancelling microphone
A
8 / 8
Bottom side

Help required
At present we have no further information about this device, or the communications system to which is was connected. According to a former owner, it was found in the underground bunker of a large Dutch facility. If you have any information about the use of this telephone set, or about the system to which is was connected, please contact us.

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Interior
Bottom side Connections and label at the bottom Disassembled KF 4-2 Interior PCB with telephone circuit Ground button assembly Ground button contacts 5-pin XLR plug
B
×
B
1 / 8
Bottom side
B
2 / 8
Connections and label at the bottom
B
3 / 8
Disassembled KF 4-2
B
4 / 8
Interior
B
5 / 8
PCB with telephone circuit
B
6 / 8
Ground button assembly
B
7 / 8
Ground button contacts
B
8 / 8
5-pin XLR plug

Connections
Handset
  1. Yellow
    Fa
    Speaker (1)
  2. Green
    Fb
    Speaker (2)
  3. White
    Ma
    Microphone (1)
  4. Brown
    Mb
    Microphone (2)
  5. Grey
    ?
    Button (1) 1
  6. Pink
    ?
    Button (2)
  7. -
    ?
    not connected
  1. THis is a normally closed switch.

Line
  1. White
    La
    Line (A)
  2. Brown
    Lb
    Line (B)
  3. Green
    W
    Extra bell
  4. Yellow
    E
    Ground
Wall socket
The device is fitted with a regular 4-wire telephone cable, with a 5-pin XLR socket at the end that was proably fitted to a wall socket or directly to a (secure) communications device. Below is the pinout of the XLR connector, when looking into the female socket in which the plug is seated.

  1. Green
    W
  2. Yellow
    E
  3. Brown
    Lb
    Line (B)
  4. White
    La
    Line (A)
  5. not connected
References
  1. Wikipedia (Germany),
    Retrieved March 2020.

  2. Arwin, Grey Mice: what's the difference between a T65 and FeTAp 61?
    25 November 2018.
Further information
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Crypto Museum. Created: Sunday 01 March 2020. Last changed: Sunday, 01 March 2020 - 19:37 CET.
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