"Richard Clark" wrote in message
...
On Tue, 26 Oct 2004 11:51:10 GMT, "Knarf"
wrote:

The difference
between the lumped element and distributed inductor is significant,
although
the gains are almost identical from both models.

Hi Frank,

You've hit the nail on the head (although I've seen it claimed it
makes a 12dB difference!).

Rarely do we get any practical correlation from this "sky is falling"
oops "current is dropping" argument.

73's
Richard Clark, KB7QHC

Hi Richard,

Cannot see where anybody could get a12 dB difference, since you can only
model a lumped element inductance, you could not build it to test the
performance. I have spent many hours this past week modeling short, loaded,
monopoles, over a perfect ground -- triggered by the previous thread -- just
to see what results I could get. An 86.5" vertical, center loaded, with a
lumped element inductor resonating in the 21 MHz range, exhibits an input
impedance of 20.91 Ohms, and a maximum gain of +4.754 dBi. The same antenna
with a distributed 12 turn helix, of 2.5" diameter, and 6" long, has an
input impedance of 18.98 Ohms, and a gain of +4.783 dBi. The helix alone
has a gain of -25 dBi. Transcribing the NEC output file to an Excel spread
sheet produces some very interesting current plots.

73,

Frank