[Elecraft] KX1 - We need to develop the ideal antenna

[Erik Basilier]

After using a 26 ft wire with counterpoise as well as vertical and
horizontal Buddipole configurations, for the past year or so 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. Here are some details of
mine:

 

1.       My insulators are rectangular pieces of Lexan sheet, cut to about
0.25" x 0.5" x 1.75". Each insulator has a row of 6 holes. The holes are
just wide enough to pass  the male and female connectors, which are Molex
pins with added shrink-wrap tubing to avoid wire breakage. The wire from
each side is passed through 3 holes in a zig-zag fashion, and the connectors
are joined hanging in the air, forming a loop of about 1.5" diameter.  This
arrangement is easy to disassemble in the field, yet holds the wire securely
without placing stress on the connection itself. It depends on the friction
created between the shoulders of the holes and the wire insulation. The
ability to disassemble without tools helps me when I want to remove the 80 m
sections, or make repairs or replacements.

2.       The wire I use is the extremely lightweight copperclad available
from The Wireman, which is strong and has a tough insulation which is happy
to be subjected to the sharp edges of the insulator. It is also stiffer than
some other kinds of wire. I find that the insulators hold securely even with
softer wire, and I don't expect regular pvc insulation to be a problem, as I
never put much mechanical tension on the wire. I do think the copperclad is
more efficient than tinned copper which should have more rf resistance.
Don't know how large this effect is in practice, but every little bit helps
with qrp.

3.       My feedline is RG-58 from my Buddipole, which includes a
lightweight balun using beads. This can be purchased as a separate item.

4.       The configuration is inverted-vee, supported at up to 22 ft or so.
At the bottom is the tripod plus short mast from the Buddipole, which is
light enough to be carried in the field for shorter trips. This is from a
few years ago. I understand that Buddipole currently only makes a heavier
model tripod that is intended to support a small beam. In any case, my
tripod is the heaviest part of the setup, and for a longer trip on foot I
would leave it at home and use whatever I can find to support the pole. The
tripod with Buddipole short mast provides about 8 of the 22 ft. The rest of
the height comes from a Cabela's Crappie Pole which is quite a bargain at
$20 or so, and extremely light. If I remember right it is a 16 ft model, but
with the top section removed. (It will remove itself the first time the
antenna falls over!). I had to make a custom piece to connect the crappie
pole to the Buddipole mast.

5.       I store the antenna with feedline detached on two "Halo Winder"
type spools designed for kite string. I don't remember which vendor I bought
them from, but they were available in a variety of sizes, without string,
easy to find on the net. I use the 5" diameter model which leaves room to
spare with wire for all bands including 80 m.  Each spool with wire and
insulators weighs about 5 oz. My center insulator is similar to the other
insulators, and I detach the wire by unthreading the 3 holes on each side
for transportation. A hole in the middle slips right over the crappie pole,
and stops because the pole sections are conical. At first I used Buddipole's
mini banana connections for the feedline, but the plugs were damaged when
the antenna fell, so now the feedline is soldered and bolted to the
insulator, with pigtails for Molex pin connection to the antenna wire. (I
got a new feedline from Buddipole, since I still like to use the complete
Buddipole in some situations where weight is not an issue.)

 

Before I took this antenna into the field, I tried flexing the soldered
copperclad to see if it would break. It would not. The steel core seemed
very hard to break. Then, first time in the field, the KX1 ATU wouldn't find
a good match, and it turned out the wire had broken right at a solder joint.
That's when I slightly enlarged the insulator holes and added shrinkwrap
tubing around the solder joints. It turned out that the wire still locked
very securely in the holes. 

 

The Molex pins tend to get loose with use. Not a big deal, as they can
easily be adjusted in the field with a knife and maybe a rock. Nevertheless,
I still want to find better pins. I dream about gold-plated machined pins
such as those found in some expensive military connectors or maybe top
quality IC connectors/chip carriers. The ideal solution would include both
the female and male parts, available without cannibalizing a multipin
connector; the overall diameter should be small (1/8" or less) to slip
through insulator holes, and the the pair should have enough spring
force/friction to stick together when used without a connector shell. Anyone
know a source?

 

I have long toyed with the idea of trying traps, especially for the 20/30
switch point, where the trap should be very light and not have all that much
reactance to influence the bandwidth at, say, 80.

 

Overall I like this antenna so much that I have toyed with the idea of
making them for sale. Just kidding.

 

73,

Erik K7TV

 

 

KK5F wrote:

 

The approach that I found worked best for me was an antenna that was a
full-length 40m dipole (66 feet), with each leg broken in six places with a
home-made PCV tubing insulator with integral jumper and clip so that the
appropriate length dipole can be established for all seven HF bands between
10m and 40m.  I built the antenna for all these bands for use with any rig,
not just the limited coverage of a K1 or KX1.  It works better than any
other antenna I've ever used in a field environment.  It typically takes
less than a minute to alter insulator jumper configuration to switch to
another band.  It meets *all* of the desired criteria listed by Bob, to
which I would add "5.  Is very inexpensive and quick to home-brew."  (I have
a pdf file with construction details, diagrams, and photos that I'll e-mail
to anyone on request.)  I use the technique that you suggest of attaching a
33-foot segment to each leg for 80m operation, which is rare for me.