Thanks for keeping me honest.
Bill B.
P-19 #454, Dream Catcher
Nampa, ID
Rich Gort wrote:
>
> The practice of making a feedline a multiple of the working wavelength has
> been around for a long time. Lots of arguements have been heard on both
> sides of the practice. It is usually agreed that it is less important
> when the length of the feedline is long in relation to the operating
> frequency where the match is between the transmitter and the feedline and
> the antenna and the feedline. Having said that, if you wish to follow the
> practice, you must take into account the "velocity factor" of the feedline
> you are using. The formula that you quote is generally used for determing
> the length of an antenna itself and is based on a velocity factor of .95
> which is about right for an 18 ga wire in free space (actual factor for
> a half wavelength is 492 for rf in free space).
>
> Since the velocity factor for coax is much less than .95 (usually around
> .75) you must adjust for it if you want your coax to be a multiple of the
> wavelength. Find the velocity factor for the coax you wish to use and
> then use 492 * K / frequency in MHz for the proper length in ft. ..K being
> the velocity factor for your coax.
>
> Rich Gort (W7JVL)
> WWP19 #202 SAYOKO (Oct, 83)
> Lake Stevens, WA
> Sailing Northern Puget Sound and North Cascades Mountain Lakes