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ESK-52   Type 41
German spy radio set

The ESK-52 was a spy radio station, developed by Telefunken in Hannover (Germany) in 1952 for clandestine operations by the French intelligence services. The radio was based on the similar Type 41, which was built for the German intelligence service, the Bundesnachrichtendienst (BND). Like the Type 41, it is actually a post-war replica of the British Type 3 Mk II (B2) spy radio set. For security reasons the ESK-52 was officially described in the documentation as Amateur Radio Set.
 
The radio set is housed inside a large cardboard suitcase and consists of three units, just like the British B2: a power supply unit (PSU) at the right, a receiver (RX) at the front, and a transmitter (TX) at the back. A leather strap at the center keeps the set in place when travelling around.

At the far right is a large storage compartment in which the acessories, such as the morse key, the headphones, the power cables, the antenna and spare valves were kept. The documentation (operators manual, frequency tables, etc.) were stored behind a panel in the top lid of the case.
  
ESK-52 spy radio set

The ESK-52 shown here has a control panel that is labelled in French. It was used for many years during the Cold War by the French intelligence service. Although the radio officially had to be destroyed once it was decommissioned, it has miraculously escaped demolition. It is currently unknown how many ESK-52 sets were produced, but given the low serial number of our set (0059) it is likely that no more than 100 sets were produced. Today they are a very rare find.

A few years after the launch of the ESK-52, in 1954, Telefunken introduced the ESK-632 which was an improved version of the ESK-52. A modulation amplifier was added to the transmitter and a socket for a microphone was added to the front panel. It was also listed as Amateur Radio Set.
 
Suitcase Inside the suitcase ESK-52 spy radioset ESK-52 spy radio set Rear compartment Documents in rear compartment Manuals Frequency tables

 

 
History
Shortly after WWII, in 1950, Telefunken in Hannover (Germany) started building spy radio sets that were 'inspired' by the British WWII Type 3 Mark II (B2). The first radio set that was produced by the HOGA 1 business unit at Telefunken was the B2M, which was actually a 'chinese' copy of the British B2. The front panel layout and the circuit diagram were nearly identical and the only real difference was the use of 'rimlock' type valves in the oscillator circuits of the German B2M [1]. Like the original B2, the B2M consisted of 3 units (combined into a single suitcase version).

In 1952, the ESK-52 and the Type 41 were introduced at the successors to the B2M. The design is based on the B2M, but contains a number of improvements, such as the absence of plug-in coils in the transmitter section. Although the ESK-52 consists of 3 units (RX, TX and PSU), they are mounted together in a single frame (and wired internally) that is built inside the suitcase.

As the transmitter of the ESK-52 can only be used for CW (morse), an improved version, known as the ESK-632 was released in 1954. A modulation amplifier was added to the transmitter, allowing the connection of a crystal microphone in order to produce Amplitude Modulation (AM).
 
  1. At the time, the HOGA business unit of Telefunken Werk-Hannover, was responsible for the production of the ESK-52 radio set and the earlier B2M. It is currently unknown what the abbreviation 'HOGA' stands for. If you have further information, please let us know.

Parts
Transmitter
TX
Receiver
RX
Power Supply Unit
PSU
Morse key Headphones Accessories and spare parts Operating and Technical Manuals Frequency tables

 
Transmitter
The transmitter (TX) is built around two valves (tubes): a 6AG7 for the crystal-based oscillator (CO) and a 6L6 for the RF power amplifier (PA). It covers a frequency range of 3 to 16 MHz and produces an output power of 20W.

The transmitter is suitable for CW only.
  
Transmitter

 
Receiver
The superheterodyne receiver is built around four valves: 2 x ECH12 and 2 x EAF12. It has the same frequency span as the transmitter (3 to 16 MHz), divided over three ranges (3-5.5, 5.5-7 and 7-16 MHz). The IF frequency is at 470 kHz.   
Receiver

 
Power supply unit
The Power Supply Unit (PSU) is mounted to the right of the transmitter and receiver and is internally wired to the other two units.

It is suitable for a wide range of AC mains voltages (90 - 230V), but can also be operated by a 6V DC battery. In the latter case an electromechanical vibrator is used to convert the 6V DC into the LT and HT voltages needed by the set.
  
Power Supply Unit (PSU)

 
Morse key
The ESK-52 was usually supplied with a good quality morse key such as the bakelite Wehrmacht key shown here, which was actually a leftover from WWII. Note the special connector with the narrow pitch that is used for connected to the transmitter.   
Wehrmacht morse key

 
Headphones
The ESK-52 is suitable for connection of any high-impedance pair of headphones. It was commonly supplied with the Telefunken headphones shown here, which was actually a leftover from WWII.   
Telefunken headphones

 
Accessories
The suitcase has a large storage compartment to the right of the radio set, in which all accessories, such as the morse key, the headphones and the antenna wires are kept.

Also in this compartment are the spare values, fuses, a mains lamp adapter, etc.
  
Accessories

 
Manuals
The ESK-52 was supplied with typed instruction in French. For service personnel, there was also a technical manual with circuit descriptions and circuit diagrams. In the latter manual, the radio was identified as 'Amateur Radio Set' in order to hide its true purpose.

The documents were usually stored inside the rear compartment, inside the top lid of the suitcase.
  
Manuals

 
Frequency tables
In an operational context, the ESK-52 was supplied with a frequency table that was used by the operator to determine which channel to use on certain days and times. The image on the right shows an original frequency table that was found with the radio set featured here.

Several blank frequency tables were provided for 'future' use by the operator. The tables were supplied in a transparent plastic 1 sleeve.
  
Frequency tables

 
  1. The plastic sheet has been removed from the tables shown here, as it contains acetate which produces toxic fumes that can potentially damage the documents.

Rear compartment Rear compartment with documents Manuals Close-up of the instructions Disguised as 'Amateur Radio Set' Plastic sleeve with frequency tables Frequency tables

 
References
  1. Helmut 'Jim' Meyer, HS0ZHK, My way to Ham - Radio and beyond
    Website QRZ.COM. Personal correspondence. Retrieved May 2014.

  2. Louis Meulstee, Wireless for the Warrior, volume 4
    ISBN 0952063-36-0, September 2004

Further information

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Crypto Museum. Created: Sunday 05 February 2017. Last changed: Sunday, 05 February 2017 - 17:50 CET.
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