PS should I have used an actual helix? Very tedious to structure with code,
although have done it in other models. Noticed that the current in and out
of the coil is vastly different when compared with using the lumped element
model.
Frank
"Knarf" wrote in message
news:Z4jfd.743$VA5.640@clgrps13...
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.
Regards,
Frank
Code:
CM free space dipole antenna
CE
GW 1 99 -33 0 0 66 0 0 0.0026706
GS 0 0 .3048
GE 0
EX 0 1 33 0 1 0
LD 4 1 67 67 1200 0
LD 5 1 1 99 5.8001E7
FR 0 31 0 0 20 0.1
RP 0 181 1 1000 -90 90 1 1
EN
"Cecil Moore" wrote in message
...
The results of the measurement of current at the bottom and top of the
coil
in an off-center-fed dipole configuration should leave no room for doubt.
------1/4WL------FP------1/4WL------
Start out with a 1/2WL dipole. Measure the resonant fundamental
frequency.
Then, to one end, add a coil and another 1/4WL of wire
------1/4WL------FP------1/4WL------//////------1/4WL------
Adjust the coil inductance so the antenna is resonant on three times
the fundamental frequency of the original dipole.
Measure the current at the left(bottom) of the coil and measure the
current at the right(top) of the coil.
The current at the left of the coil will be nearly zero. The current
at the right of the coil will be approximately the same as the feedpoint
current, somewhere around 1-2 amps for 100w input. This can probably be
demonstrated using the helix feature of EZNEC.
--
73, Cecil http://www.qsl.net/w5dxp
"The current and voltage distributions on open-ended wire antennas are
similar to the standing wave patterns on open-ended transmission lines
...
Standing wave antennas, such as the dipole, can be analyzed as traveling
wave antennas with waves propagating in opposite directions (forward and
backward) and represented by traveling wave currents If and Ib ..."
_Antenna_Theory_, Balanis, Second Edition, Chapter 10, page 488 & 489
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