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I've seen the term velocity factor applied to feedlines and antenna. What is the "velocity factor"? |
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Basically, the velocity of an RF signal in a wire is not the same as the velocity of that same RF signal in the vacuum of space. When reduced to equivalent terms of wavelength, it means that one cycle of a particular frequency will not travel as far in the wire as it does in space. Thus, a signal that's exactly 40-meters wavelength in free space will be 40*0.95 or 38-meters in a wire that has a 95% velocity factor. |
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Velocity factor is the multiplier applied to the speed of light to give the speed of a radio signal inside of a material. Basically Speed_material = VF * C Velocity factor always has to be between 0 and 1. |
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In a real transmission line, the energy actually travels somewhat slower, then the speed of light-from 63 to 97% of light speed,depending primarily on the dielectic properties of the insulating materials used in the construction of the line.The fraction of the speed of propagation in a transmission line compared to the speed of light in Free Space is called the Velocity Factor(VF) of the line.The velocity causes the lines electrical wavelength to be shorter than the wavelenth in space. wavelenght,in ft = 983.6 f= freq in Mhz. VF=velocity factor _ x VF |
