The speed of radio signals in a vacuum, for example, is the speed of light, and so the velocity factor of a radio wave in a vacuum is unity, or 100 %.
12.
In a general science and engineering context, these terms would be understood to mean a true speed or velocity in units of distance per time, while " velocity factor " is used for the ratio.
13.
The ratio of the speed of the electromagnetic wave to the speed of light in free space is called the velocity factor, and depends on the electromagnetic properties of the conductor and the insulating materials surrounding it, and on their shape and size.
14.
Their velocity factors thus depend not directly on the permittivity of the circuit board material but on the " effective " permittivity \ epsilon _ \ text { eff } which is often specified for a circuit board material ( or can be calculated ).
15.
For example, at a frequency ? = 20 MHz ( free space wavelength of 15 m ) in a transmission line whose velocity factor is 2 / 3, the guided wavelength ( distance between voltage peaks of the forward wave alone ) would be ? = 10 m.
