I have frequently seen postings to this group from people who have just acquired or built a new KX1 / K1 / KX3
and are looking for a portable end fed wire antenna length that can be matched on some combination
of bands, using the internal tuner of their Elecraft Rig.
The simple answer is, you need to stay away from multiples of a half-wavelength on the bands
that you wish to use the antenna on.
Going through some of my antenna bookmarks in my web browser I found a couple of links that
I will share that should make this a lot easier to figure out a wire length that will work
(i.e. load with a usable SWR) for your particular choice of bands :
http://www.hamuniverse.com/randomwireantennalengths.htmland
http://udel.edu/~mm/ham/randomWire/(Note that in the last figure on this second link, it is lengths with "white space" under the corresponding
lettered band combinations that you want to use for an antenna length that will work on that combination of bands.)
I hope that this is helpful.
Michael VE3WMB
P.S. For end fed wires (not halfwaves) I have always had good luck erecting them as inverted vees or inverted-Ls
and using a few ground radials that are a minimum of 1/8 wavelength long at my lowest planned operating frequency.
(ie. usually 16 ft). There was a study done that shows that unless you are deploying more than about 20 radial wires
making them any longer than 1/8 wave on the lowest band doesn't really improve antenna efficiency by very much.
As usual it is a tradeoff between reasonable antenna efficiency and convenience (i.e. I think that few portable operators
have the patience to lay down 20+ radials).
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