[Antennaware] Multiband antennas

[Paul Decker]

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)