I'm trying to design an antenna, actually combine two already designed antennas
to use a common feeder. The 40 meter antenna would be fed from a short 6"
length of feedline from the 20 meter antenna.
I have a 20 and 40 meter extended double zepp, both fed with 600 Ohm open wire
line. When I combine the antenna's together, of course, it changes the
characteristics. The combined antenna models fine for 40 meters, but changes
wildly for 20. I was thinking that adding a low pass filter or "trap" to the
feedline which feeds the 40 meter antenna, the idea being to cut it out of the
picture.
So the modeling question is this, how do i model a trap, I thought it would
simply be a parallel load with some RLC value, but this doesn't appear to work
correctly for me.
My second question is, does anyone have any ideas on how to make this work?
The antenna's are modeled like this:
Wires:
1 W3E1 -3, 0, 780 -528, 0, 780
#14 200 1 0
2 W4E1 3, 0, 780 528, 0, 780
#14 200 1 0
3 W6E1 -3, 0, 780 W5E1 -3, 0, 125
#14 50 1 0
4 W7E1 3, 0, 780 W5E2 3, 0, 125
#14 50 1 0
5 W3E2 -3, 0, 125 W4E2 3, 0, 125
#14 1 1 0
6 W1E1 -3, 0, 780 W8E1 -3, 0, 786
#14 10 1 0
7 W2E1 3, 0, 780 W9E1 3, 0, 786
#14 10 1 0
8 W6E2 -3, 0, 786 -1056, 0, 786
#14 200 1 0
9 W7E2 3, 0, 786 1056, 0, 786
#14 200 1 0
Loads:
1 8 33.00 32.75 66 Short
Short 12 0 Ser
2 9 33.00 32.75 66 Short
Short 12 0 Ser
3 1 33.00 32.75 66 Short Short
6 0 Ser
4 2 33.00 32.75 66 Short Short
6 0 Ser
5 6 0.00 5.00 1 150 3.5
152 0 Trap
6 7 0.00 5.00 1 150 3.5
152 0 Trap
Source:
1 5 50.00 50.00 1 1 0 I
By the way, individually, these antennas perform great in real world tests!
73,
Paul (KG7HF)
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