What is the term for the ratio of the actual velocity at which a signal travels through a transmission line to the speed of light in a vacuum?

The velocity factor (VF) is the precise term used to describe how fast a radio frequency signal travels through a transmission line compared to the speed of light in a vacuum. It is usually expressed as a decimal or a percentage. Because no signal can travel faster than the speed of light in a vacuum, the velocity factor of any physical cable is always less than 1.0. The other options are incorrect because they measure different properties. Standing wave ratio (SWR) evaluates reflected power due to impedance mismatches. Surge impedance and characteristic impedance both refer to the ratio of voltage to current in the line, not the propagation speed of the signal.