# Characteristic Description

The impedance that a transmission line of infinite length exhibits at a specified frequency. Composed of distributed parameters resistance (R), inductance (L), capacitance (C), and conductance (G). Measurement Unit: Ohms.

${Z_0} = \sqrt {\frac{{R + jwL}}{{G + jwC}}}$

Capacitance (C)

Properties of two electrodes (conductors) which builds up a charge caused by a difference of potential (voltage). Capacitance serves as a "leakage pathway" in cables and therefore should be minimized.
Measurement Unit: Picofarads per Foot (ns/Ft.)

Resistance (R)

Opposition to current flow. Can be direct current measurement (aka DCR) or alternating current measurement, at a specified frequency. At higher frequencies, conductor resistance increases due to skin effect.
Measurement Unit: Ohms

Dielectic Constant

The ratio of the absolute permittivity of a given dielectric to that of free space. The lowest dielectric constant is that of free space (1.0)

Time Delay (Td)

The speed at which a signal travels through a transmission line. Measured in nanoseconds per Foot (ns/Ft.)

Velocity of Propagation (Vp)

The ratio of the speed of signal in a given material to the speed of a signal in free space, at a given frequency. Measurement Unit: Percent (%) The ratio of the speed of signal in a given material to the speed of a signal in free space, at a given frequency.
Measurement Unit: Percent (%)

Crosstalk

The undesirable coupling of signals from one transmission path (i.e. twisted pair) into another at a given range of frequencies. Near End Crosstalk (NEXT) is the power input to the disturbing (excited) pair as compared to the power output coupled into the disturbed (listening) pair at the end of the cable which included the disturbing source. NEXT is typically specified in decibels (dB).

Far end Crosstalk (FEXT) is the same measurement as NEXT except that the measurement of input power and output power are performed on opposite ends of the cable. FEXT is typically measured in decibels per unit length (dB/1000 Ft.)

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