What is the nominal impedance per pair for UTP conductors?

What is the nominal impedance per pair for UTP conductors?

• A. 50 Ohms
• B. 100 Ohms
• C. 75 Ohms
• D. 120 Ohms

Answer: (B)

In data networking, twisted-pair cables have a characteristic impedance that the signal “sees” as it travels along the pair. For unshielded twisted pair (UTP) used in Ethernet, that impedance is designed to be about 100 ohms per pair. This differential impedance between the two conductors is what the transceivers expect and terminate into, which helps minimize reflections and maintain signal integrity at high speeds. Why 100 ohms fits well here is because Ethernet standards such as 100BASE-TX and 1000BASE-T use 100-ohm differential signaling on each twisted pair. The cable geometry (twist rate, conductor size, and dielectric) is chosen to achieve this target impedance, while keeping crosstalk and insertion loss within specified limits. The impedance is treated as nominal because real cables vary a bit along their length and with bending, but they’re specified to be around 100 ohms. Other impedance values correspond to different media (for example, coax often uses 50 or 75 ohms) and aren’t the standard for UTP Ethernet cables. So the best answer is 100 ohms.

In data networking, twisted-pair cables have a characteristic impedance that the signal “sees” as it travels along the pair. For unshielded twisted pair (UTP) used in Ethernet, that impedance is designed to be about 100 ohms per pair. This differential impedance between the two conductors is what the transceivers expect and terminate into, which helps minimize reflections and maintain signal integrity at high speeds.

Why 100 ohms fits well here is because Ethernet standards such as 100BASE-TX and 1000BASE-T use 100-ohm differential signaling on each twisted pair. The cable geometry (twist rate, conductor size, and dielectric) is chosen to achieve this target impedance, while keeping crosstalk and insertion loss within specified limits. The impedance is treated as nominal because real cables vary a bit along their length and with bending, but they’re specified to be around 100 ohms.

Other impedance values correspond to different media (for example, coax often uses 50 or 75 ohms) and aren’t the standard for UTP Ethernet cables. So the best answer is 100 ohms.