>I ran some EZNEC simulations of ~1/4 wave monopoles over perfect
>ground. According to the program, if you shorten the monopole just
>enough to achieve resonance, the impedance is 36.0 ohms, independent
>of diameter for a range of diameters from 0.00001 to .02 wavelengths.
>This doesn't agree with any textbooks on the subject that I have read.
>Are the textbooks all wrong, or is this an NEC-2 limitation (or did I
>goof up somewhere). I tried various numbers of segments and it
>doesn't seem to affect the results.
>
>Rick Karlquist N6RK
>rick_at_area.com
Rick,
In my paper presented at the ACES Conference 1999, I discuss
methodology to predict antenna impedance that agrees with measurement,
for MF broadcast antennas where the tower is thick, thick with respect
to the wire that feeds it.
For a detailed comparison with measurement one must also includes the
insulated guys which support the tower.
An example which you can try. For a 1 MHz antenna, no guys, fed by a
piece of wire 1 metre long, wire gage #10, I calculate as follows:
Tower diameter Ra Tower height for resonance*
(mm) (ohms) (metres)
10 36.96 71.84
100 39.12 70.78
1000 46.28 68.6
* Tower is sitting on an insulator 1 metre high, feed wire length 1 m
connects to ground. Source on feed wire. Number of segments 70.
73, Jack, VE2CV
_____________________________________________
John S. (Jack) Belrose, PhD Cantab, VE2CV
Senior Radioscientist
Radio Sciences Branch
Communications Research Centre
PO Box 11490 Stn. H
OTTAWA ON K2H 8S2
CANADA
TEL 613-998-2779
FAX 613-998-4077
e-mail <john.belrose_at_crc.ca>
_____________________________________________
Received on Wed Oct 13 1999 - 20:06:53 EDT
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