Crosstalk is a form of interference caused by signals in nearby conductors. The most common example is hearing an unwanted conversation on the telephone. Crosstalk can also occur in radios, televisions, networking equipment, and even electric guitars.
Causes of Crosstalk
Crosstalk is caused by coupling, the transfer of electrical energy between conductors. The three main types of coupling are capacitive, inductive, and conductive. Capacitive coupling occurs when two separate conductors are close enough together to act as a capacitor. Inductive coupling occurs when the current in one conductor induced a similar current in another conductor. Conductive coupling occurs when there is physical contact between conductors.
Capacitive coupling is reduced by spacing the conductors apart, or by increasing the insulation between them. It is impractical to increase the spacing in cables that contain hundreds of separate wires, so better insulation is preferred.
Inductive capacitance is reduced by twisting two wires around each other to create a twisted pair. This reduces most of the electromagnetic interference by creating a smaller cross-section for the field to act on.
Conductive capacitance is easily eliminated through adequate insulation between conductors. Crosstalk in telephone wires often happens when rainwater seeps into the terminals.
Digital signals are not affected by interference as much as analogue signals. This is because digital uses either high voltage or zero voltage, not the continuous voltage range of an analogue signal. Only the most severe crosstalk will disrupt a digital signal.
There are many categories of electrical cable used for telecommunications, each with different specifications for crosstalk. Category one is the most prone to crosstalk and is used for telephone cable. Category seven has the strictest specifications and is the least prone to crosstalk, which makes it ideal for high speed networking.