Loading coil#Krarup cable

As Krarupkabel a special, historical construction for coil-loaded transmission lines of communications engineering from the period starting from 1900 is called. It is named after the Danish Civil Carl Emil Krarup.

History

1893 Englishman Oliver Heaviside had discovered through investigation, the possibility of reducing the artificial increase in the inductance of the telephone cable attenuation. The Frenchman Aimé Vaschy had come independently to the same results. Around the same time with the Mihajlo Pupin attempts in America to realize these ideas through spot-on insertion of inductors ( coils) in the remote cable, you also took in Germany on these thoughts. The occasion was the intention of linking Sweden and Norway with the German telephone network. Karl Strecker suggested experiments that were carried out in the cable plant Reydt. Here, the copper wires were wrapped with a fine iron band. The tests were successful, so plans were made to build the new Scandinavia cable according to this principle. The Danish postal administration took part in further experiments, which were carried out at the University of Würzburg. Carl, Emil Krarup developed where the final form of construction, in which the copper wires were wound with a thin steel wire. 1903, named after Krarup cable between Fehmarn and Laaland was designed, it lived up to all expectations. That same year, the voice traffic with Sweden and Norway was recorded.

Krarupkabel were also used later ( on March 4, 1927, a Krarup cable, the transatlantic telephone cable between Emden and New York (via Horta / Azores ) put into operation.

Pros and cons of Krarupkabel

Advantages: In Krarupkabel the increase of the line inductance looked completely evenly over the line length. The Krarupkabel had in contrast to Pupinkabel no distinct cutoff frequency. A later extension or relocation presented in contrast to Pupinkabel not a big problem Represents the cable had (as opposed to Pupinkabel with its coils boxes) a homogeneous mechanical structure. This was particularly advantageous in the installation as a submarine.

Cons: The extra inductance was set in cable production and could not be changed later. It could not be reached so high inductance values ​​as in Pupinkabel.

Technical Background

In the signal transmission over long lines impedance matching is performed to the line impedance, which is calculated according to the following formula:

• ZLtg ... line impedance
• R ' ... resistance coating, resistance per unit length
• C ' ... capacitance
• L ' ... inductance

• G ' ... conductance per unit length
• ω ... angular frequency 2 · π · f

At low frequency, low inductance and conductance per unit length is considered negligible:

Thus, a large part of the transmitted signal energy is lost due to ohmic losses in the resistor pad. Through the magnetic material in the sheath of the line increases the inductance of the line and stored in the magnetic field energy is converted into heat instead carried on. This results in the equation:

Simply put, increase the line impedance and for the same power more voltage but less current is required, so that the power loss is reduced.