Posted by
Mike Morrow-3 on
May 15, 2011; 11:28pm
URL: http://elecraft.85.s1.nabble.com/KX1-We-need-to-develop-the-ideal-antenna-tp6366906.html
Bob/AB5N wrote:
> I guess I have come to the conclusion that nobody has really run the gamut
> trying antenna designs for the KX-1.
And I guess I'd contest that statement. Testing portable HF antennas for
field and backpack use has been my principal ham interest for more than 30
years (but for general HF use, not just for the KX1).
> Its requirements are unique (the tuner etc).
I don't see anything unique about the KX1 application that doesn't apply
to any other HF rig. I usually operate a K1 with the KAT1 auto tuner, but
sometimes I go over to the dark side and use a mobile general coverage HF
transceiver. I use the same antenna for either, out in the field.
> OK, I'll "run the gamut"... with my goal being to fulfill the above
> criteria.
Thanks. I have a write-up for a very simple design that meets all your
criteria, plus is inexpensive and quick to home brew.
Erik/K7TV wrote:
> ...I have settled on a dipole with jumpers, and this is the best configuration
> yet. KK5F beat me to suggesting it here, but I am chiming in because the subject
> is interesting, and details are worth discussing.
As long as the antenna may be quickly accessed to alter the jumpers around the
insulators, and as long as some sort of support can be found or erected for the
ends and center, it is inarguably the very best approach for a dipole antenna.
The "insulator+jumper" approach used on my multi-band dipole performs better than
my permanently-installed home trap dipole.
> 1. My insulators are rectangular pieces of Lexan sheet, cut to about
> 0.25" x 0.5" x 1.75".
The insulator in my design is a 1.25-inch piece of 3/8-inch-OD PVC tubing,
with .125-inch holes drilled through it .25 inches from the ends. Only a
drill and a tubing cutter are required to completely fabricate one in a
matter of minutes. The 2.5-inch jumper around an insulator is permanently
affixed (soldered) on the down-leg side of the insulator, and utilzes a
1.5-inch alligator clip on the other end to close the jumper around the
insulator. I've never suffered a failure of any PVC insulator, which are
now 15 years old.
> 2. The wire I use is the extremely lightweight copperclad available
> from The Wireman...
My dipole assembly has been in service for 15 years, but I have used many
wire antennas in my experiments. The ***ONLY*** wire that I've ever used
that NEVER failed anywhere or anyhow is Flexweave-tm, also available from
Wireman (items 542 through 549) and other sources. It'll cost at least
$.21/foot (100 feet or more), but it is worth several times that, IMHO.
I use 14 ga. Flexweave, which consists of 168 fine strands that create a
wire that is extrememly flexible, durable, and a real joy to work.
> 3. My feedline is RG-58 from my Buddipole, which includes a lightweight
> balun using beads.
I prefer RG-8X, which is negligibly larger in diameter. I've used a balun
in earlier designs, and found it to be superflous for all practical purposes
in a temporary field installation. I do use a balun on my home dipole.
> 4. The configuration is inverted-vee, supported at up to 22 ft or so.
I tie the ends of my dipole off somewhere around eight feet above ground,
and use a set of dome tent replacement support rods to push the center
insulator up about nine feet above ground. It still works well, even this
low.
> 5. I store the antenna with feedline detached on two "Halo Winder"
> type spools designed for kite string.
I connect the jumpers around the 12 insulators, disconnect the coax at the
center conductor (which has a SO-239 connector), and roll the antenna up in
a one-foot diameter coil. I do the same for the coax. The 14 ga. Flexweave
is resistant to unspiraling into a complex jumble the way all other antenna
wire does when such a roll-up is attempted. It's all a very small volume
and weight for the backpack, and no sharp edges on anything!
> ...it turned out the wire had broken right at a solder joint.
Flexweave-tm will eliminate that possibility of failure. In fact, if some
Flexweave-type of wire is not used, failure due to wire fatigue is a
certainty...probably sooner than later...with such wire antennas.
If anyone is interested in a detailed description with photos of my seven-band
(10 through 40 meters) dipole, I can send a pdf file on request. It claims
no innovation and may be freely distributed, if desired. I have just revised
it to clarify some of the text and to add discussion of extending it for 80/75
and 60 meters. If any of the 60 or so list members that have received earlier
versions over the past decade want the update (Revision 3), just let me know.
73,
Mike / KK5F
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