Re: Electrically length

thejim wrote:
What do we mean by saying "electrical length" of an antenna?

It usually means the length as measured in units of wavelength at a particular frequency and at the propagation speed of light in that medium.

For instance, a quarter wavelength long whip (one who's electrical length is 1/4 wave) is a vertical antenna that is a quarter of a wavelength long at one operating frequency, and at the slightly less than free space speed of light for RF energy traveling attached to that diameter conductor. This also has lots of uses when you are using specific length of transmission line to perform impedance matching functions, since all the calculations of what length is needed for a particular effect are calculated in electrical length or specific number of waves or fraction of waves that are stored in that length (based on the speed of propagation along the line, and the operating frequency), not the external physical length. But to cut the cable you have to convert electrical length to physical length. This is why every transmission line specification includes propagation speed relative to free space.
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