"chuck" a écrit dans le message de news:
...

André, you might find this interesting:

http://www.cebik.com/gp/gp3.html
On Ground Planes


fine this page on ground planes Chuck

I thank you and everybody who tried to help me in understanding the
phenomenons with ground plane antennas.

with GPA = a vertical pole and four radials, it appears that:

-the vertical patern of a vertical dipole is not quite identical; it is
difficult to see on the graphs, but it is different, so the gains are
slightly different
-four radials are not a perfect plane (not a surprise!)
-the radiation resistance is low, 22 Ohms in free space, consequently the
losses with a real ground are greater than with 36 or 72 Ohms
-with my 40m GPA, the efficiency falls to 56% at the ground level (half the
power to warm the ground...);
to reach 90% the antenna must be ten meter above the ground, or use a
multitude of radials.

very pleased with this newsgroup, despite the difficulty, for me, with
english.

73

André F5AD
http://www.youtube.com/watch?v=Do11t0Btrpw