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Wire tapping
Eavesdropping
LE-40 →
  
LE-35
Wire intercept receiver - this page is a stub

Lauschempfänger (intercept receiver) LE-35 was a sensitive audio amplifier used for covertly eavesdropping on wired analogue telephone communications — also known as wire tapping — developed around 1938 for use by the German Army during WWII. The device was commonly used in combination with Lauschzange (current probe) LZ-35 and was virtually undetectable.

The device is housed in a common panzerholz transport case, and consists of a sensitive three-stage amplifier, built around three RV2 P800 valves (tubes) that are accessible from the front panel for easier maintenance. The amplifier occupies the upper 2/3 of the case, whilst the lower part is taken by the batteries, the spare parts, the cables and the accessories, such as the headphones and the LZ-35 current probe.

Up to 10 analogue telephone lines can be connected simultaneously to the terminals at the left side, one of which is selected for monitoring by means of the switches along the top edge of the front panel. Knobs are available for adjusting the line impedance and the audio volume.

The image on the right was taken from the manual [A]. Around 1940, the device was succeeded by the improved Lauschempfänger LE-40, which had a built-in interference filter.
  

Help wanted
This page currently acts as a placeholder for information about the LE-35. Except for the documentation listed below, no further information about this intercept amplifier is available at present. You can help us to expand this page by providing new or additional information.


Current probe   Lauschzange LZ-35
Lauschzange LZ-35 was a current probe that was mounted around a single wire of the analogue telephone line that had to be monitored, without galvanically touching it. This made the device virtually undetectable, as it did not affect the line in any way by causing a load or a disbalance.

The image on the right was taken from the LZ-35 manual [B], and shows the device intercepting an outdoor telephone line. The device was not small. It measured 120 × 70 × 60 mm and weighted 590 grams. At the bottom of the cylindrical enclosure are two screw terminals for connection to the Lauschempfänger, plus a strain relief ring for the amplifier wires.

Inside the device is a current transformer with a O-shaped core. Part of the core is hinged, to allow it to surround the wire that carries the audio. The transformer picks up the alternating magnetic field that surrounds the wire during a conversation, and feeds it to the amplifier.

The LZ-35 was originally supplied with the intercept amplifier LE-35, but also with the later LE-40. It was also used with the small and portable Drahtlauschempfänger D.L.E. (kl).

  
LZ-35 current probe. Image taken from the manual [B].

Documentation
  1. Der Lauschempfänger LE 35
    Operating instructions (German). D 1060/1. Berlin, 1 March 1938. 1

  2. Die Lauschzange LZ 35
    D 1060/3. Berlin, 11 March 1938. 1
  1. Document kindly supplied by Günter Hütter [1].

References
  1. Günter Hütter, Information about D.L.E. (kl)
    Retrieved July 2017.
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Crypto Museum. Created: Wednesday 02 August 2017. Last changed: Friday, 04 August 2017 - 08:43 CET.
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