"Cecil Moore" wrote in message
...
Knarf wrote:
Could not get it to work. Below is my NEC2 code ( heavily segmented as
it is easier to figure out where to place the source and load). What am
I doing wrong? Resonant on 7.25 MHz before extending the antenna.
Approaches resonance on 22 MHz, when extended, with very high series L.
A 40 m dipole is resonant on the 3rd harmonic anyway so all you are doing
is isolating the extra 1/4 wave by placing a very high impedance at the
quarter wave point. I guess I missed something, be interested in any
comments.

The lumped point inductance will definitely not give the correct results.
The coil needs to use the helix feature of EZNEC+ 4.0. I constructed an
8-sided coil out of segments in EZNEC 2.0 and the results can be viewed
at:

http://www.qsl.net/w5dxp/octcoil2.gif

The dimensions and inductance are not perfect but the idea is perfectly
clear. There's 0.11 amp at the bottom of the coil and 0.57 amps at the
top of the coil. By playing with lengths of wire and frequency, I've seen
the current at the bottom of the coil as low as 0.005 amps while the
current at the top of the coil was about 0.6 amps.
--
73, Cecil http://www.qsl.net/w5dxp


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Sorry that was really dumb, did not think before I posted the response. I
was certainly aware that the currents in, and out, of a lumped element
inductor are the same. I had recently modeled a short monopole with a
physical, octagonal, helix (Now I learn about the GH card!). The difference
between the lumped element and distributed inductor is significant, although
the gains are almost identical from both models.

73,

Frank