Group listening device

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The group listening device was a hydrophone that was used on German ships and submarines during World War II .

development

During the First World War , carbon microphones were still used as noise receivers, similar to those in old telephones. The individual receivers were mostly installed in the front part of the ship along the sides of the hull in order to have enough distance from the own propeller and its noise. The individual microphones were arranged in groups and each one was oriented in a different direction. The individual microphones then had to be unplugged by hand for direction finding. The carbon microphones were not very reliable and so they experimented with other transducers. Dynamic microphones were also discarded. In the end, the piezoelectric principle turned out to be the most suitable. This had already been discovered by Pierre Curie in 1880 . The quartz crystals generate an electrical voltage depending on the pressure acting on them.

In cooperation with the Imperial Navy, Atlaswerke AG in Bremen and Electroacustik ( Elac ) in Kiel began work on piezoelectric transducers and the development of detectors and amplifiers in general.

They experimented with different types of quartz or combinations of several of them. Seignette crystals gave the best result . From 1935, crystal receivers were permanently installed on all submarines.

Modern submarines today use electrostriction and converters made from barium titanate .

Group listening device

The group listening device, abbreviated as “GHG”, consisted of two groups of 24 sensors (one group on each side of the ship) in submarines. Each sensor had a single stage tube preamp. These 48 audio signals were then sent to a switch matrix in the main unit. The sonar guest could use it to set the side of the ship and the exact direction of the sound source. To improve the resolution, there were three switchable crossovers with 1, 3 and 6 kHz center frequency . Due to the side mounting, there was a dead area of ​​40 ° to the bow and to the stern .

  • Range: 20 km against a single driver, 100 km against a convoy
  • Listening range: 2 × 140 °
  • Resolution: <1 ° at 6 kHz, 1.5 ° for 3 kHz, 4 ° for 1 kHz; without crossover 8 °

In May 1942 U 570 was captured by the British. The Elac device installed in the submarine was carefully analyzed; the above resolution values ​​were determined.

Crystal rotary base unit, comparable device from the same period on board the USS Pampanito

Magnetostriction rotary base device

The magnetostriction rotary base unit, abbreviated to "MDB", was a rotatable hydrophone with ferromagnetic sensors, for which no frontal use in submarines is proven, but sensors with magnetostriction were used in the wren (torpedo) .

Crystal rotary base unit

The crystal rotary base unit, abbreviated to “KDB”, was a rotatable hydrophone with piezo sensors. It was very susceptible to depth charges, but without a dead area on the bow. The dead sector aft (due to the screw noise) could not be eliminated with this either.

Balcony device

Balcony device
British soldier in front of two Type XXI boats with balconies under construction

The balcony device was tested for the first time on board the U 194 in February 1943 and was used from 1944. Its 48 hydrophones were attached around the keel. As a result, a greater panoramic view was achieved than with the group listening device only attached to the side.

The deeper installation meant that the hull of the boat covered the sensors and isolated them from surface noise. Now the sonar could also be used when surfaced. The group listening device had to be submerged first, because its sensors were attached above the front depth rudder and therefore very close to the surface; When they emerged, they only received noises from the sea .

This model was standard on all Type XXI boats, but was also installed on Type VII C boats.

S device

The special device for active sound location, abbreviated to "S device", was developed for the detection of mines. It was located on the stem, just above the torpedo hatches. It was introduced during the conversion from VIIb to VIIc, the conversion order dates from October 11, 1940. From 1943 onwards, it was disarmed in favor of more radar warning devices.

Nibelungen device

The Nibelungen device was an addition to the normal group listening device. It was attached to the front of the tower and was used to calculate torpedo data purely acoustically. The target could then be fought blindly by an acoustic torpedo.

The acoustic horizontal plumb line "Nibelung", which could determine the direction, distance and approximate speed of the enemy with just a few impulses, enabled "program shooting" without periscope control. The sound waves were transmitted with 5 kW at around 15  kHz with a pulse length of 20 ms via multiple magnetostrictive oscillators and the echo was processed by a special torpedo lead computer (TVhRe). This analog computer continuously determined the necessary lead using a mechanical arithmetic unit and transferred this value electrically to the torpedoes, whereby position-independent torpedoes (LuTs) from max. 20 meters depth could be shot (the shot from 50 m or 100 m was still being worked on). The transmitter and receiver were housed in the foremost part of the tower without hydrodynamic separation. The plumb range was about 100 degrees from the pre-alignment, the bearing accuracy about 0.5 degrees. Depending on the water conditions, the bearing range was about two to four nautical miles. The recipient worked according to the phase method with sum and difference procedures. The output voltages of the receiver were fed via transformers to the deflection plates of the cathode ray tube DG-9 (Braun's tube), on which an oblique line now appeared, which could be set vertically by turning the base. This “zero” bearing provided the direction and distance of the target with a minimum of three pulses. With the hearing aid, the Doppler effect made it possible to measure the relative speed of the target. There were only a few technical defects that were fixed from January 1945.

Whitefish plant

"Felchen" (named after the fish ) was a system for passive acoustic distance measurement.

Others

Various modern sound measurement techniques are listed under Sonar .

literature

  • The sonar systems of the German submarines , development, testing, use and effect of acoustic detection and deception devices of the German submarines. Bernard & Graefe, September 2006, ISBN 3-7637-6272-8
  • Eberhard Rössler : The German submarines and their shipyards . Bernard & Graefe, 1990, ISBN 3-7637-5879-8
  • Heinrich Stenzel: Guide to the calculation of sound processes . Holt, 1947 pp. 678-679
  • Willem Hackmann: Seek & Strike Sonar, anti-submarine warfare and the Royal Navy 1914–54 . Science Museum, London 1984, ISBN 0-11-290423-8
  • LE Holt: The German Use of Sonic listening , July 1947, US Navy Underwater Sound Laboratory, Fort Trumbull, New London, Connecticut. The Journal of the Acoustical Society of America. Volume 19, number 4, July 1947, doi: 10.1121 / 1.1916561
  • Eberhard Rössler: The sonar systems of the German submarines . Koehler, Herford, 1991, 2nd edition, ISBN 3-7637-6272-8
  • Description of a KDB system for surface ships , Atlas-Werke Aktiengesellschaft (ed.), No. 472, (KDB = crystal turning base = receiver base), Bremen, 1938, half-linen cover, large format, 49 pages, 81 folding tables, attachments, SECRET ,
  • Procedure for determining the direction of sound signals , Reich Patent Office, No. 320/29 in August 1918
  • Blitz und Anker , Volume 2: Information Technology, History & Backgrounds, Volume 2, By Joachim Beckh
  • About hearing sensations in the ultrasound area with bone conduction, Atlas-Werke AG., Bremen 1940

Web links

Individual evidence

  1. USS Witek (DD-848) in the English language Wikipedia