[Antennas] Elevated Vertical-sloping radials

Wed Mar 23 13:51:18 EST 2005

Ed wrote about the perfect match:
> This concept has some measure of truth to it, but is not always true.
The
> circumstance where it is true is the case of a 1/4 wave monopole over
perfect
> ground. The theoretical radiation resistance is 37 ohms, giving a
mismatch to
> a 50 ohm feed. Losses in series with the radiation resistance would
> increase the total resistance, thus giving a better match, but with poorer
radiation
> efficiency.
> In other cases, such as a horizontal or vertical dipole, this argument is
not
> true.
> Ed
>
Thanks Ed. I was thinking that when we measure swr, or a tuner makes
adjustments in series with that measurement, we do so for the effect of
impedance mismatch to the transmitter that the whole antenna and
transmission line(s) caused. Therefore if 37 ohms was the felt impedance
(including transmission line), then that would never be a 1:1 swr until the
tuner had absorbed the mismatch felt at that point. Those are the losses in
series with the radiation resistance of which you speak, I assume.
I also believe I create that same situation with a horizontal dipole when I
use the tuner to match great impedance differences caused when operating
significantly above it's resonant frequencies, right? In that case, every
adjustment below what the transmitter is capable of dealing with ( assume
3:1, no fold-back, etc) is actually decreasing the amount of radiation
emitting from the antenna.
In the case of my horizontal dipole, the resonant frequency matters little
if we "tune" it by trimming or adding in order to create a perfect match and
1:1 swr at the transmitter, thereby achieving maximum efficiency at the
desired frequencies.
Are these assumptions correct?
73,
Jack Painter
Virginia Beach, Virginia