A dipole mounted on the roof of a tall building presents a complex
situation. The feedpoint impedance will likely be determined by
the height of the dipole above the roof (and conducting steel support
beams etc). The ground reflection will depend on how high and
close the the edge of the roof the antenna is placed.
If the antenna is mounted close to the edge, the ground reflection
in that direction will be from the earth below. If the roof is wide, the
reflection across the roof will be from the roof (high angle).
de Tom N4KG
............................
On Fri, 12 Sep 1997 16:44:16 -0300 "Carlos Augusto S. Pereira"
<py1cas@ax.apc.org> writes:
>Dear friends,
>
>We all know that the height of a dipole over the ground deeply
>influences the take-off angle of a horizontaly polarized antenna. With
>a
>higher antenna we should expect a lower radiation angle. Right?
>
>Well, we also know that for 80m we need at least 1/2 wavelenght in
>order
>to obtain a 30 degrees angle. For that we need a very high tower! But
>if
>we install a dipole for 80 meters on the top of a very tall building?
>What happens? Can we expect a low angle or not, or there are more
>parameters involved on it?
>
>Thanks in advance,
>
>Carlos - PY1CAS
>E-mail: py1cas@ax.apc.org
>
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