> have a question from my radio club,
>
>We have a Hygain 4 element 20m monoband yagi (204) and a Cushcraft 40-2cd.
>We would like to put them on the same boom.
>Something like a EF-420/240 from force12.
>
>Ideally we want to keep as much of the existing hardware as possible (Ie keep
>the hygain boom)
>
>Have you done this (or similar)? Can it be done ? If so what changes need to
>made ?
I have both a EF-420 and an EF-420/240, so I can provide a little input:
The 20m antenna in the EF-420/240 is identical to the plain EF-420, so no
changes to the 20m dimensions were needed to interlace the 40m. I think the
EF-420/240 does lose a fraction of a DB in gain on 20m compared to the EF-420.
The 40m reflector is between the 20m reflector and driven element, and the 40m
driven element is between 20m directors #1 and #2. They are placed
approximately in the center of the gaps between the 20m elements. I'm not sure
about changes in the 40m elements lengths...for the F12 shortened elements
those had to be tuned anyway.
You really do need to model it though. I tried it a while back, and such a
combination is fairly insensitive to dimensions. However, it might be a little
more sensitive if your 20m has a shorter boom (the EF-420 boom is about 30
feet).
Tor
N4OGW
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