One could point out that placing a small inductance to ground in series with
the ungrounded radiator and feeding the junction of the two is quite similar
to tapping up the grounded radiating element to attain a match.
Practically speaking, people have been using 1/4 wave whips on vehicles and
ground planes successfully for probably more than seventy years now with few
ill effects caused by SWR. The problem of the 36 ohm theoretical impedance
of the infinitesimally thin radiator seems to have been mitigated by
reality.
I believe this thread has run its course. Thanks to the moderator for his
patience.
73,
Al, K9SI
Re: Ground plane yada yada
Posted by: "allan crites" [email protected] wa9zzu
Date: Wed Feb 24, 2010 10:49 am ((PST))
In the gnd plane example the feed point is in series with the driven
element, and in the example in which you are referring there is a tap up the
driven element understandably to get to a higher impedance and the feed is
in parallel to the driven element (as in a tap up an inductor in a resonant
circuit) with with a series inductor, resonated with the series capacitor.
There's a difference. One is series fed and the other is parallel fed. There
is no doubt that the method you espouse is valid, but your comparison to a
series fed element is not. One could also run a short section of coax in
parallel with but spaced away from the driven element with the center
conductor of the coax connecting to the tap on the element, and achieve a
wider operating bandwidth. The coax feed can be shown on a Smith Chart to be
the equivalent to the series LC for impedance matching purposes.
WA9ZZU
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