On 5/3/14 9:43 AM, "Drax Felton" <draxfelton@gmail.com> wrote:
> You don't want a resonant antenna. You want one that presents a 50 ohm non
> reactive load to the feed line if that's what the feed line is.
>
> Otherwise you use a matching network.
>
> Right?
Not quite. A dummy load presents a 50-ohm non-reactive load.
A resonant quarter-wave monopole over a decent ground might have an
impedance of about 12 ohms. You can probably play with the length of the
antenna to get to 50 ohms, but at that point it will be neither ideal nor
non-reactive.
Would be better to just accept the 12 ohms and design a feed system around
that, such as a 4:1 transformer (with the 1 side on the antenna and the 4
side on the feedline). In this case, the fact the math comes up 2 ohms shy
of 50 ohms is ignored.
In all the designs I've read about, the objective has almost always been
resonance with an associated matching network being a way to cope with the
antenna's natural impedance at resonance, rather than trying to make up for
a mismatch by detuning the antenna.
73, kelly
ve4xt
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