I am attempting to model a shunt-fed tower for 160 meters. The tower is 97
feet tall and has three yagis on it, for a total of about 104 feet, of
which 6 is tubing mast.
I have tried the shunt feed at a variety of locations -- at 34 feet, EZNEC
has clearly gone crazy, because the radiation pattern is spherical at a
field level of -99.9 dBi. At 64 and 95 feet, the patterns look more like
they should, but the gains (>6 and >20 dBi, respectibely) are clearly off
the wall. Moreover, the source impedances look plain nutty.
I've attached the wire table below, and will be happy to send the .EZ file
to anyone who would like to wrestle with it. There must be something
simple I'm doing wrong, but I can't see it.
In the wire table, wires 1-3 are the tower, wire 4 is the mast, wires 5-10
are the booms of the yagis (which have insulated elements), wire 11 is the
shunt arm, and wire 12 is the shunt wire. The source is as close to the
end of wire 12 as the program will permit.
I have also tried it with the shunt wire (W12) connected to ground and the
feedpoint in the middle of the first segment above ground (as in the
ungrounded case), and a different set of loony values results.
Thanks for any advice.
Pete, N4ZR
Wire Conn. --- End 1 (x,y,z : ft) Conn. --- End 2 (x,y,z : ft) Dia(in) Segs
1 G 0.000, 0.000, 0.000 W2E1 0.000, 0.000, 69.000 1.20E+01 10
2 W5E2 0.000, 0.000, 69.000 W3E1 0.000, 0.000, 95.000 1.20E+01 2
3 W11E1 0.000, 0.000, 95.000 W4E1 0.000, 0.000, 98.000 1.20E+01 1
4 W6E2 0.000, 0.000, 98.000 W7E2 0.000, 0.000,104.000 2.00E+00 10
5 -9.000, 0.000, 69.000 W8E2 0.000, 0.000, 69.000 2.50E+00 10
6 -9.000, 0.000, 98.000 W9E2 0.000, 0.000, 98.000 2.50E+00 10
7 -9.000, 0.000,104.000 W10E2 0.000, 0.000,104.000 2.50E+00 10
8 9.000, 0.000, 69.000 W1E2 0.000, 0.000, 69.000 2.50E+00 10
9 9.000, 0.000, 98.000 W3E2 0.000, 0.000, 98.000 2.50E+00 10
10 9.000, 0.000,104.000 W4E2 0.000, 0.000,104.000 2.50E+00 10
11 W2E2 0.000, 0.000, 95.000 W12E1 0.000, 3.000, 95.000 1.00E+00 10
12 W11E2 0.000, 3.000, 95.000 0.000, 3.000, 1.000 # 14 10
73, Pete N4ZR
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