Sea clock (radar)

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Radio measuring device FuMG 38G Seetakt on the Admiral Graf Spee

The radio measuring device FuMG 38G Seetakt was an early ship radar of the German Navy during World War II . It was developed in the 1930s.

development

In the German Reich, Hans Erich Hollmann began work in the field of microwaves in the late 1920s , which would later form the basis of most radar systems around the world. During this time he was particularly interested in the use of microwaves for communications technology, but he and his partner Hans-Karl von Willisen were also active in the field of radar-like systems.

In 1934 Hollmann, von Willisen and Paul-Günther Erbslöh founded the company GEMA (Society for Electroacoustic and Mechanical Apparatus). In autumn 1934, GEMA built the first radar for locating ships. It worked on the wavelength of 50 cm and could detect ships up to 10 km away. The system was similar to the development by Christian Hülsmeyer , it could not display any distance information either.

On behalf of the Navy, a pulse radar was developed with which they could record the light cruiser Königsberg at a distance of 8 km with an accuracy of 50 m in the summer of 1935 . That was good enough for fire control on ships. The same system was also able to detect an aircraft 28 km away and 500 m altitude. The military benefits were not neglected during this period. A land-based version was developed under the name Freya , while the sea-based version was developed under the name Seetakt . For the navy, the focus of development was first on distance measurement, the perception of targets and obstacles at night and in bad weather was the next item on the priority list. Its use as a target radar, for which the Würzburg radar device was developed for the Wehrmacht, was initially secondary for the Navy.

The first prototypes still used the wavelength of 50 cm or 600 MHz. However, since these frequencies were still difficult to control at that time and GEMA still had little experience in series production, especially for rough use on ships, the first device from the production series worked at 60 cm or 500 MHz and was January 1938 installed on the ironclad Admiral Graf Spee . The sea clock radar of Graf Spee was able to locate ship targets at a distance of 25 km. As a result of the initiative of some forward-looking officers, the Navy, like the Royal Navy with its Type 79 and the US Navy with the CXAM, had individual functional radar devices on their ships. Further development was delayed because neither the Kriegsmarine nor GEMA gave the project a high priority. In addition, for reasons of confidentiality, only a few people were informed and detailed documents for troubleshooting (e.g. circuit diagrams) were not on board. In the years after 1939, numerous German ships were equipped with sea clock devices.

technology

Later devices (e.g. FMG 41gU or FuMO 29) were then operated at 82 cm to 77 cm or 368 MHz to 390 MHz. With a peak power of 8 kW, a pulse length of three microseconds and a pulse frequency of 500 Hz, targets the size of a ship at sea could be detected at a distance of up to 220 hm (22 km) on good days  , but normally the maximum detection distance was only at 110 m. The accuracy was about 70 m and an angle of three degrees.

About 200 maritime clock devices were manufactured and used on surface ships, submarines and - in large numbers - on land for coastal defense. On submarines, the range was far below 7 km due to the lower antenna structure, and the detection range was also limited to 60 degrees.

discovery

At the end of 1939, due to the development obstacles and the still low reliability, only four marine clock units were in use, one of which had been of great use on the pirate voyage from September to December 1939 of the armored ship Admiral Graf Spee . On December 13, 1939, she was involved in a sea battle off Montevideo, in which she was so damaged that the port of Montevideo in neutral Uruguay had to be called. Since there was a threat of internment and the damage could not be repaired sufficiently to be able to continue the operation, the Admiral Graf Spee was self- sunk after three days in port outside the Uruguayan territorial waters. The crew had previously disembarked and were interned. But the ship had not sunk very deep and its upper parts were not completely covered by water. This is why the antenna of the marine clock was still sticking out of the water and was mentioned in its report to the home service after an inspection by the Royal Navy. Very few took note of the report, with the exception of Reginald Victor Jones , a scientific expert in the British military secret service, for whom this report was very informative: the antenna dimensions alone allow conclusions to be drawn about the frequency ranges used.

In the autumn of 1940, when the Royal Navy , which knew nothing about German radar equipment, suspected a system comparable to the British chain home system on the German side due to targeted attacks on night ship convoys in the canal area , NE Davis, a communications engineer, became a communications engineer the Marconi Company , commissioned with further investigation. With a broadband receiver he succeeded in recording the sea clock broadcasts and in February 1941 six jammers were installed on these frequencies near Dover on the Channel coast: the radar war began.

See also

Web links

swell

  1. ↑ Earth observation portal, including the history of earth observation (Kramer), Chapter 1.2 Overview by decades, p. 81 (PDF; 19.8 MB) (English) ( Memento from July 28, 2007 in the Internet Archive )
  2. ↑ Radio measurement technology in Germany from a lecture by Dr. Wolfgang Holpp, EADS, 2004, on www.100-jahre-radar.de
  3. ↑ a b ORIGINS OF GERMAN RADAR: SEETAKT, FREYA, WUERZBURG , an open source source for this text on vectorsite.net, Greg Goebel (English)
  4. ↑ FGAN-FHR celebrates 100 years of RADAR. Retrieved March 6, 2019 .
  5. ↑ Dr.-Ing. Wolfgang Holpp: The century of the radar. 2004, accessed March 6, 2019 .
  6. ↑ Some pictures of the power levels of Seetakt devices from A. O. Bauer on www.xs4all.nl
  7. ↑ Radar history , presentation by John Schneider, Lockheed Martin, September 2, 2003, therein p. 21, on math.la.asu.edu (PDF; 4.8 MB) (English)
  8. ↑ Radar unit FMG41 PDO on Emmanuel Gustin's submarine
  9. ↑ see also The Radar War (PDF; 137 kB) by Gerhard Hepcke, on Radar World