A reasonable approximation for the signal speed in 100 ohm balanced twisted pair cable is __________, where c is the velocity of light in free space.

Question

Quizplus · Accepted Answer

The signal speed in a balanced twisted pair cable is slower compared to free space due to the dielectric material surrounding the wires. The dielectric material in a twisted pair cable is typically plastic or rubber, with a relative permittivity (εr) of around 2.2-2.7. The velocity factor (VF) is the ratio of the speed of the signal in the cable to the speed of light in free space, and is given by VF = 1/√(εr). For a cable with an εr of 2.5 (typical for twisted pair cables), the VF is approximately 0.8. Therefore, the signal speed in the cable is 0.8 times the speed of light in free space (c), which gives a reasonable approximation of 0.6c.

A Reasonable Approximation for the Signal Speed in 100 Ohm