John Ferrell wrote:
On 19 Apr 2007 12:17:00 -0700, wrote:
Hello,
Just joined the group and I have a question about constructing a multi-
band dipole.
I plan to construct a 80/40/20/15 band multi-element dipole using
separate dipole wires for each band,
but a single feedpoint. My question is: how important is the spacing
BETWEEN the
individual band wires. I understand that they can't/shouldn't touch,
but is there any distance
that is optimal? or is just keeping them from touching enough?
Thanks,
Mike
KD7VRG
There is a picture in most ARRL antenna books that shows a fan dipole
made from twin lead that just don't work!
Other than that, my experience with fans has been good. They are easy
to adapt to any environment. The same tactics adapt to a vertical
quarter wave as well.
I find that trying to prune/tune a multiwire antenna (like a fan) is an
exercise in frustration because of the strong interactions among the
elements, aggravated by the fact that most people install antennas in
places other than a vacuum. there's wind blowing (which changes the
spacing), trees, other stuff, etc.
So, I figure that if you get it "reasonably close", and then use an
autotuner to deal with the rest. If you want to obssess about loss in
the feedline, then put the tuner at the feedpoint.
Yes, the tuner costs some money, but it's a one time investment, and
makes playing with wire antennas much more pleasant and fast. Once
you've got that tuner, you can literally build decent antennas in 10
minutes with parts from the grocery store.
If you get a tuner that has a computer interface, then you can use it to
measure the Z of the antenna, if you feel compelled to prune.