Remote cable

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Pattern from the Rhineland Cable

As remote cable or wide power cord in to Telecommunications Cable referred that in contrast to the local cable handling the message traffic between different exchanges serve in wide area. The umbrella term is wide-area cable. Wide-area cables are long-distance cables (Fk), main office cables (Hk), node office cables (Kk). Long-distance cables go from main office to main office and in interstate traffic. Main office cables go from the main office to the node office or from node office to node office. Node-office cables go from the node-office to the end-office or from end-office to end-office. According to a precise definition, trunk cables connect the main exchanges (HVSt). The old name for main exchange is main office.

Long-distance telephone connections in Germany were implemented almost exclusively via overhead lines until 1912 . In the winter of 1909, extreme weather conditions (freezing snow and storms) resulted in the rods and masts of long-distance lines breaking in rows around Berlin and Magdeburg. Despite great efforts, it took months to repair the damage. This event is considered to be the trigger for plans to accelerate the laying of long-distance cables in the earth. In the meantime one had enough experience how to reduce the attenuation of long-distance connections by means of pupinization or Krarup cables . The crosstalk between individual lines could be controlled by a suitable stranding .

Sectional drawing of the Rhineland cable, section Berlin-Hanover

In July 1912, Siemens & Halske received the order to lay the so-called Rhineland Cable , which was initially relocated from Berlin to Hanover in 1913/1914. Since line amplifiers had existed since 1912, but had not yet been tested, the Rhineland cable was initially constructed in such a way that speech communication from Berlin to the Rhineland would have been possible without amplification by amplifier offices. When work on the cable line resumed after the First World War , the possibility of switching on amplifiers was of course taken into account.

As early as 1914, the constantly increasing demand for voice channels had led to attempts to route several channels over one line using the carrier frequency method . Since 1917, the Army Intelligence Force has been promoting attempts to make better use of the existing ones instead of building new overhead lines by transmitting an additional carrier-frequency voice channel above the frequency band normally used. Phantom circuits made it possible to use the transmission paths multiple times with minimal technical effort, both on crossed overhead lines and on twin-core long-distance cables. The simultaneous connection for the simultaneous transmission of telephone calls and telegrams on the same line, which had been tried and tested before 1914, was increasingly introduced. The two fundamental technical innovations of the wartime, the amplifier and the hybrid circuit , were particularly suitable for overcoming long distances. Since 1916, improved amplifiers, the high vacuum tubes, were mass-produced. With the development of the electron tube in 1918, it was possible to bridge up to 100 km on overhead lines using the carrier frequency method. The first German high frequency offices were established in Berlin, Hamburg, Munich and other cities in 1920/1921.

Hybrid circuits were important assemblies in the analog transmission network. Due to the attenuation of the signal, amplifiers had to be inserted into the long-distance lines at regular intervals. Since amplifiers can only amplify the signal in one direction, the directions of conversation had to be separated by a hybrid circuit in front of the amplifiers on a two-wire line. The signals were then amplified separately for each direction by two amplifiers and then merged again to form a two-wire line behind the amplifier. Because of the safety against whistling, however, in practice no more than three amplifiers could be looped into a two-wire line, otherwise the line would become unstable. It was only through the use of four-wire lines that almost any number of amplifiers could be connected in series, thus enabling clear communication over large distances.

It would be ten years before it was possible to implement carrier-frequency telephony over long-distance cables in 1932. Here the decision from the past turned out to be particularly farsighted, to give preference to the Pupin cables over the Krarup cables.

Long-distance cable spool box from 1937

For the use of low frequency amplifiers in cable cores, the winding of the cores had to be reduced and completely removed for carrier frequency operation. Since the coil elements were housed in special coil boxes along the cable route, this was possible without any problems.

The long-distance cable network had been laid and maintained since 1921 by the Deutsche Fernkabel Gesellschaft , a joint venture between the Post Office and cable suppliers. The local exchanges were automated, the long-distance network cabled and thus shielded from the weather, and the transmission ranges extended with amplifiers. For better utilization, the cables not only transmitted telephone calls, but also telegrams and broadcast radio programs from the central broadcasting studios in Berlin to the decentralized transmitters throughout the Reich. After the connection of the national long-distance cable networks, which were growing throughout Western and Northern Europe, and after the start of radio telephony overseas in 1927, the telephone prevailed over the telegraph worldwide.

In the early 1930s the development of broadband coaxial cables (for example type 21a) began. The first broadband coaxial cable from DRP, the cable FK501 Berlin-Trebnitz-Leipzig, went into operation on March 1, 1936 at the opening of the Leipziger Messe. The FK502 for telephony and television as well as for video telephony was connected on July 12, 1938 on the Trebnitz-Munich route. By 1944 these cables reached Hamburg, Vienna, Frankfurt and Cologne. In addition to broadband cables, special carrier frequency cables (e.g. type 24b) have also been developed. These cables were primarily used in close proximity.

To minimize crosstalk between transmission directions, trunk cables can physically consist of two cables laid side by side, one for direction A – B and the other for direction B – A. In the course of the digitization of communication networks, the transition to fiber optic cables took place in the long-distance cable sector .

literature

  • Krauskopf: Article "Fernkabel" in: Manual dictionary of electrical telecommunications , hv Ernst Feyerabend et al., Vol. 1, Berlin: Springer 1929, pp. 395-400.
  • European Telephone Service, 1921–1943.
  • Country maps of the European telephone network . Special issues of the "European Telephony Service", ed. P. Craemer and A. Franke. Berlin: European telephone service, 1928 ff. (With own network maps for all countries)
  • Thomas, Frank: Telephoning in Germany. organizational, technical and spatial development of a large-scale technical system . Frankfurt a. M .: Campus 1995, pp. 228-252.

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