Enter your Wire Diameter, Wire Separation, and Substrate Dielectric Constant into the Twisted Pair Cable Calculator to find the Characteristic Impedance of your cable, along with Propagation Delay, Inductance per inch, and Capacitance per inch.
Characteristic Impedance
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Propagation Delay
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Inductance per inch
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Capacitance per inch
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Characteristic impedance is the impedance that an infinite length of cable would present to a source. It's the ratio of voltage to current for a wave traveling down the cable and is crucial for matching source and load impedances to prevent reflections.
Twisting pairs of wires together reduces electromagnetic interference (EMI) by ensuring that both wires in the pair experience similar interference, which can then be canceled out by differential signaling. It also reduces crosstalk between adjacent pairs.
Larger wire diameter decreases the characteristic impedance of the twisted pair. This is because thicker wires have lower inductance and higher capacitance per unit length, both of which reduce impedance.
Common twisted pair cables have characteristic impedances of 100Ω (Cat5/Cat6 Ethernet cables) or 120Ω (telephone cables). The specific value depends on the wire gauge, spacing, and dielectric material.
Higher dielectric constant increases capacitance and decreases both impedance and propagation speed. Materials with lower dielectric constants (like air or foam) result in faster signals and higher impedance.
Propagation delay is the time it takes for a signal to travel through a unit length of cable. It's inversely related to the speed of light in the medium and increases with higher dielectric constants.