The fan dipole has a very predictable pattern with no deep lobes that you
can get with loading a random wire. If you have two using separate
feedlines you can have some gain in all directions. I have never built one
so I am not sure how difficult they are to adjust. If you do not mind
using a tuner, and some such as Elecraft's KAT500 are easy to program and
work quite well, than I agree getting the wire lengths close will produce
very good results. This is a great suggestion by Jim for those that are
concerned about tuning multiple wires.
John KK9A
From: jimlux <jimlux@earthlink.net>
Date: Wed, 18 Jul 2018 05:38:27 -0700
So far, in terms of ease and non weird patterns (80m dipole on 15m has a
lot of lobes) is a multiband parallel dipole (like a DX-CC, with parallel
wires spaced 6" apart) fed by a tuner in the shack. Normally the fan or
multiband is a pain to adjust because of the element interactions. You
shorten or lengthen one dipole and the resonance changes on all the other
bands.
However, it doesn't change by much. Maybe the 20m resonance goes to 13.9 MHz.
Well, that's not a huge impedance change, maybe from a nominal 70 ohms to
something like 68-2j. that kind of mismatch isn't going to cause enormous
losses in your coax like you'd see with driving a 40m dipole on 20m (where
the Z is something like 2200 ohms) or driving a 20m dipole on 40m (where
the Z is 14-600j)
So you build the dipole with lengths that are *about* right, hang it in
the air, with an appropriate choke at the feedpoint, run coax, and be
happy.
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|