Hi Gary,
I suggest you model it with Xnec2 or Nec2 or other decent modeling
program. There are likely to be some interactions. If you don't want
to do that, you may be better off with an antenna that will do all
bands. The designers should have done their work on the interaction
issue, and it can be tricky getting all those bands to play right
together on the same boom. Another option is to feed the boom on your
tribander. See K4RO's web page:
http://www.k4ro.net/k4ro/station_tour/40boom.html
I did something similar. I put two fiberglass poles to extend the boom
and suspended a 40 meter dipole below it. I found I had to tune it
because it interacted with the beam, but I could also tune it on all the
others bands including 80 meters and the 20 meter beam was unaffected
both in simulation and experimentally. You can see a photo on my
qrz.com page (KL7NA). It was really nice to be able to rotate the
dipole and I could see nulls and peaks on all frequencies.
73,
Rob, KL7NA
On Sat, 2008-02-02 at 07:10 -0800, Gary Slagel wrote:
> I want to have gain antennas for 10/15/20/40 on top of
> my tower and am trying to decide between a 4 band
> antenna like the Force 12 C4XSL or a tribander and a
> separate 40m yagi on the same mast. Struggling with
> which is worse, interaction from having the 40M
> elements interlaced on the same yagi or interaction
> from having the two antennas stacked vertically.
>
> I'm leaning toward two separate antennas separated by
> about 10 feet and one oriented perpendicular to the
> other.
>
> Does anyone have any opinions?
>
> Thanks,
> Gary
>
>
> Gary Slagel/N0SXX
> Lakewood, CO
> http://marina.fortunecity.com/sanpedro/351
>
>
>
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