Phantom circuit

Under phantom circuit is understood in communications technology, a method of increasing the number of voice channels in remote cables. The process of the phantom circuit is usually used between exchanges of the telephone network.

Today, the process is no longer used. It has been superseded by the carrier frequency method and later by compressed and digitally encoded transmission. With these methods can be transmitted with a much more additional cable channels.

Overview

In the method the speech currents of the phantom circle in addition, the so-called trunks transferred to the wire pairs. The separation of the voice channels is performed by the use of high quality low-frequency transmission transducer at the ends of the transmission line. There is ever a phantom circuit ( called quad) from two tribes won ( = two pairs ), from four strains a rollercoaster, etc.

Due to the low accrued gains on other channels ( one roller only creates another potential channel ) can be used for voice channels only trunk and quad. Add to that a perfectly symmetrical structure of the transfer arrangements is difficult to achieve in more consolidated tribes.

In June 2008 it was announced that the Fraunhofer Institute for Communication Systems ESK by using phantom circuits could successfully improve DSL data rates and ranges. The data throughput of an additional phantom line was about 70 % of each normal DSL speeds of the two underlying Side - Channels. Alternatively, the range to increase by almost 20 % succeeded.

Function

By feeding the phantom speech currents in the secondary centers of the line transformer is achieved as to cancel the magnetic effects and induce the phantom currents on the primary side of the strains no voltage. Providing a high degree of symmetry of the arrangement, there is no mutual interference of the channels.

Thus, the roller with only four line pairs seven speech channels are transmitted, the symmetry and the potential isolation from each other and remain received from the ground.

The transformer windings have a winding sense, so that:

  • The channels 1, 3, 5 and 7 transmitted symmetrically via the two lines of the four strains
  • Channels 2 and 6 are transmitted symmetrically over each two lines of stem 1 and 2 or 3 and 4
  • Channel 4 is transferred symmetrically on each every four lines of stem 1, 2 and 3, 4
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