"Wes Stewart" wrote in message
...
On Sat, 19 Mar 2005 23:23:30 GMT, "Frank"
wrote:

[snip]

The following code produces Zin = 0.117 - j2717 ohms at 1.9 MHz. What did
I do wrong? Note the high segmentation to place the feed-point near the
base of the antenna.

Frank

CM 9 ft monopole
CE
GW 1 108 0 0 0 0 0 108 0.25
GS 0 0 0.025400
GE 1
GN 1
EX 0 1 1 00 1 0
LD 5 1 1 108 5.8001E7
FR 0 9 0 0 1.8 0.025
RP 0 181 1 1000 -90 0 1.00000 1.00000
EN

My bad. I hate it when that happens. A typo on the length on my
part. 101 instead of 108.

It's more like 0.12 -j2890 in EZNEC. I'm not real fluent in NEC decks
but I think you are using too many segments.

A more realistic analysis than above, with the following structure, produces
some interesting results:
9ft monopole, segmented in 12" lengths, mounted above a 6' x 6' wire grid
model, also 12" segments, (All wires # 10 AWG). 5 ft above a
Sommerfeld/Norton average ground (Er = 13, Sigma = 5 mS/m). Frequency 1.9
MHz.

Zin = 1.23 - j3059, max gain = -8.3 dBi at 25 deg. elevation. (surface
wave not computed). Structure
efficiency 98.7%.

A suitable matching network, assuming an inductor Q of 300, consists of a
shunt "L" (161uH) followed by a
series C (16.2 pF). The network loss is 11.5 dB and 28 kV RMS at the base
with 1.5 kW in.

With an inductor Q of 1000, the component values become: L = 193.5 uH, and C
= 8.88 pF.
Loss = 6.3 dB, and 51 kV RMS.

Frank

Edited code follows:

CM 9 ft monopole above 6ft X 6ft wire grid gp
CE
GW 1 9 0 0 14 0 0 5 0.0509449
GW 2 1 -3 -3 5 -2 -3 5 0.0509449
|
|
GW 85 1 3 2 5 3 3 5 0.0509449
GS 0 0 0.304800
GE 1
GN 2 0 0 0 13.0000 0.0050
EX 0 1 9 0 1 0
LD 5 1 1 9 5.8001E7
LD 5 2 1 1 5.8001E7
|
|
LD 5 85 1 1 5.8001E7
FR 0 9 0 0 1.8 0.025
RP 0 181 1 1000 -90 0 1 1
EN