Crosstalk (electronics)
Crosstalk, or crosstalk, crosstalk English name, abbreviated XT, is a term used in telephony and originally referred to an effect by which one can listen quietly having another conversation on the phone - hence the name. Today, the term in communications technology is commonly used for the unwanted interference actually independent signal channels. The strength of cross-talk between channels is indicated in decibels (dB).
Electrical crosstalk
The electrical crosstalk (English crosstalk or X - Talk) is a simple physical process based on: a pair provides an electrical resonant circuit is and can therefore be used both as a transmitter and as a receiver of electric fields. Will be an electrical signal such as the speech signal transmitted through a wire pair, which is controlled jointly with a number of other pairs of wires in a cable, this signal is coupled to other pairs of wires. The coupling is inductive, capacitive or electrically, with the injected signal level is very low. One speaks of crosstalk attenuation, Eng. crosstalk attenuation.
In full -duplex data transmission differentiates between two types of undesirable disturbance: near-end crosstalk and far end cross talk, see below.
Various techniques are applied to reduce the crosstalk: Twisting and shielding of wires, use of coaxial cables, use of optical fiber cables. Fiber optic cables are immune to crosstalk between the individual glass fibers.
For certain modulation method crosstalk occurs between the individual channels in the medium (for example, WDM in fiber optics).
Near-end crosstalk
As a near-end crosstalk or NEXT (near end crosstalk, NEXT ) refers to the interference signal, which is at the near end, ie on the side of the transmitter is received. The level of the interfering signal is greater than the FEXT.
Transmitter side, the receiver side Signal A → ========================== → Signal A - attenuation losses | | | | | :: VV V V v v v NEXT ( A) ← → ========================== FEXT (A) Remote crosstalk
The far end cross talk or far-end crosstalk (far end crosstalk FEXT ) is received at the remote end, ie on the side of the receiver. Since adding inductive and capacitive coupling in the reverse direction ( to transmitter), tends to extinguish in the forward direction but that FEXT is much smaller than the NEXT.
Alien crosstalk
The alien crosstalk (Alien crosstalk, AX ) is caused by signal coupling rather than by the lines of a common wiring harness, but by other nearby cables laid. These couplings appear uncorrelated to the desired signal and can be equally difficult to filter out as noise. The alien crosstalk is also subdivided, if it is observed at the near or the far end.
- Fremdnahübersprechen: ( alien near end crosstalk, ANEXT )
- Foreign far end cross talk ( alien far end crosstalk, AFEXT )
Icon crosstalk
Icon crosstalk is in contrast to other types of crosstalk represents a temporal cross-talk on the same channel and can occur in the transmission of digitally encoded information. It is the interaction between (not necessarily immediately ) consecutive symbols in the transmission technology.
Acoustic crosstalk
In the sound we also speak at the undesired sound recording from adjacent sound sources by microphones when recording or transmission with multiple microphones (main microphone and spot microphones ) of crosstalk. More specifically, this is an acoustic crosstalk (English: leakage, spillage or bleeding ). Musical Instruments talk about acoustic, such as the hi-hat on the snare mic. This " bleed" as crosstalk is generally undesirable, but is also used for sound design in space design; see here the three-to -one rule ( 3:1 rule ).
Crosstalk in the consumer electronics
Even for devices in consumer electronics occurs electrical crosstalk, and this usually happens between the two stereo channels. Amplifiers are less affected, more the phenomenon in analog sources such as turntables, tape decks and tape recorders is pronounced. In the 1960s, the crosstalk was still so high in records that, to achieve a stereo effect, half of the instruments and vocals were recorded almost exclusively on one of the channels. In digital signal processing, such as in a CD player or MP3 files, the phenomenon is no longer (or only negligible) occurs.