Phantom circuit
Under phantom circuit is meant in communications technology, a method for increasing the number of speech channels in long-distance cables . The phantom switching procedure was mostly used between exchanges in the telephone network.
With this method, several channels in addition to the number of wire pairs can be transmitted using one cable. However, it has been replaced by the carrier frequency method and later by compressed and digitally coded transmission.
overview
In the process, the speech streams of the phantom circles are also transmitted in the twin wires , the so-called trunks . The speech circuits are separated by using high-quality LF long-distance line transformers at the ends of the transmission path. A phantom circle (called a four ) is obtained from two trunks (= two double veins), an eight from four trunks , etc.
Due to the small gain in additional channels (an eight only creates one additional possible channel), only trunk and fours are used for speech channels. In addition, a completely symmetrical structure of the transmission arrangements is more difficult to achieve with more trunks involved.
In June 2008 it was announced that the Fraunhofer Institute for Communication Systems ESK successfully with the help of phantom circuits DSL - data transfer rates could improve and ranges. The data throughput of an additional phantom line was about 70% of each normal DSL speed of the two underlying side channels . Alternatively, it was possible to increase the range by almost 20%.
function
By feeding the phantom voice currents into the secondary centers of the line transformer it is achieved that the magnetic effects cancel each other out and the phantom currents do not induce any voltage on the primary sides of the trunks. Provided that the arrangement is highly symmetrical , there is no mutual influencing of the channels.
With the figure eight, seven speech channels can be transmitted with only four line pairs, whereby the symmetry and the potential separation from one another and from the earth potential are retained.
The transformer windings have a winding sense so that:
- the channels 1, 3, 5 and 7 are transmitted symmetrically over the two lines of the four trunks
- channels 2 and 6 are transmitted symmetrically over both lines from trunk 1 and 2 or 3 and 4
- channel 4 is transmitted symmetrically over all four lines from trunk 1, 2 and 3, 4
literature
- Günther Oberdorfer: Lexicon of electrical engineering. Springer Verlag, Vienna 1951.
- Harald Schumny: Signal transmission. Textbook of communications engineering with remote data processing, 2nd revised edition, Friedrich Vieweg & Sohn Verlag, Braunschweig 1987, ISBN 3-528-14072-0 .
- M. Schleicher: The electrical remote monitoring and remote control for high-voltage systems and power plants. Published by Julius Springer, Berlin 1932.
- Julius Wallot: Introduction to the theory of weak current technology. Springer Verlag, Berlin / Heidelberg 1932.