[SixClub] vertical antenna

[Gabriel Sierra]

Hi,

There are a couple things going on into an antenna
design. The capacitive reactance (Xc) and Inductive
reactance (Xl) play a big role. Without getting to
much into the details, one thing for sure is true:
antenna length is not a linear figure. On antenna
books, they often use a factor in addition to the good
ol' 3x10E8/f. This factor changes depending on the
size of the antenna you are going to build. The
factors has the net effect to shorten the antenna a
bit to correct for Xl and XC influences. The other
thing going on into an antenna is impedance at the
feedpoint. What it means is that as you change the
length, the impedance of the antenna also changes. It
changes in cycles and multiples of wavelength. There
are points of minimum impedance while there are points
of maximum impedance. This impedance resembles a sine
wave. For instance, a 1/4 wave antenna has as little
as 36 ohms impedance while a full wavelength has a
1000 ohms impedance. I have a very good european book
called "Las Antenas" which was originally published in
France and has been translated to various languages.
Mine is in Spanish. I wish I remember where I put it
in my shack. As soon as I find it, I will post the
formulas and the ISBN.

Cheers,

Gabriel Sierra, WP3BM

--- "Richard J. Fiero II W5TFW" <w5tfw at cox.net> wrote:

> if you build a Vertical antenna at 1/4 wave and it
> is x amount tall cant you 
> just double the lenght to get 1/2 wave ? or is the
> some formula that tells 
> you how that works?
> 
>                                                     
>                         
>                                           Thanks, 
> Joey
> Richard J. Fiero II  W5TFW
> QSL Manager USS KIDD DD-661
> http://members.cox.net/w5tfw/my%20web%20page.htm 
> 
>
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Gabriel Sierra
Moondancer Recording Studios
moonrec at prtc.net
http://www.moondancer.freeservers.com