On Jul 1, 8:16*am, "-.-. --.-" wrote:
if a half wave end-fed *monopole* antenna have the following primary
characteristics (if IIRC):

- High Z at the feedpoint (voltage maximum and current node);
- very small counterpoise lenght compared to the resonant wavelenght of the
antenna (typical 0.1-0.2 lambda)

can i mantain the same characteristics shortening the antenna in any way ??

With proper design you can maintain the resonance characteristic with
that short antenna, but not its characteristics of SWR bandwidth,
exact radiation pattern (directivity), or radiation resistance.

For a single frequency the only important difference will be radiation
resistance, unless the short radiator is used with a virtually perfect
(zero loss) ground plane.

A typical r-f ground loss even in a set of 120 each, 1/4-wave-long
buried radials is on the order of two ohms. So referencing the
example in the link to Kraus that I posted earlier, the radiation
efficiency of that helically-loaded monopole system with a two ohm r-f
ground would be about 0.6/2.6 = 23%, approximately.

The loss of a radial system using 0.1-0.2 lambda conductors would be
significantly higher, so the antenna system radiation efficiency then
would be significantly less than 23%.

A naturally-resonant, unloaded monopole about 1/4-wave high has a
radiation resistance of around 34 ohms. When it is used with a two
ohm r-f ground, the radiation efficiency of the antenna system is
about 34/36 = 94%.

RF