[Elecraft] RE: Effective Antennas for use with K2 ATU

[Ron D'Eau Claire]

I'll second Stewart's recommendation whole-heartedly, Nicholas. I also have
a very small garden and use a doublet fed with open wire line. The doublet
is a total of 45 feet long overall, which works FB down through 40 meters
(the effectiveness of a center fed wire doesn't drop appreciably until it
gets almost to 1/4 wavelength overall - or about 33 feet on 40 meters). 

I arranged a 25 foot support pole just outside my shack window to hold it up
in the center. One end drops down to a support about 10 feet high and the
other end runs almost horizontally across to a point at the peak of my roof.

That combination works FB on 20 through 10 meters gaining me all the DX I
can hear - and that's a great deal when the bands are open. That length
makes the antenna an "extended double Zepp" on 10 meters, which is the
longest antenna one can use on 10 meters without getting into high-angle
radiation lobes. Of course, with the diminishing sunspot cycle 10 meters
won't be such a big issue except for those 10 meter enthusiasts who watch
for and enjoy the openings that occur all the way through the minimum.
They're there. They're just a lot less frequent than in the recent past. 

As Stuart said, horizontal antennas are much more efficient than a vertical
because they don't have the ground losses that verticals have. That isn't
just losses due to a ground connection, but includes losses caused by
induction of ground currents some distance from a vertical that don't occur
with a horizontal. 

But to provide low angle radiation for DX operations with a horizontal
antenna, you need to have it up close to 1/2 wavelength, at least, above the
ground. Lower heights will give you great high-angle radiation for
short-skip/local contacts out to perhaps 600 miles or so. That's what is
often called a NVIS (near vertical incidence system) today. So, for good DX
effectiveness on 40 meters you need to have your dipole up about 50 or 60
feet at least. For many ops, including myself in my present QTH, that's out
of reach. In that case, for contacts out beyond 1000 mi., a vertical, with
its inherent low angle radiation, can produce much better results in spite
of the ground losses. 

What I do is to feed one half of my doublet - the half running almost 30
feet straight up the pole and then horizontally about 25 feet to the peak of
my roof, as an end-fed "Inverted L" on 40 and 80 meters. A 1/4 wave
counterpoise wire makes a good RF ground to load the "L" against (I used an
elevated counterpoise with a 'tuner' to resonate it for the band  I'm
using). That places the current peak of my antenna at the bend on 40, which
produces a heavy mix of vertical and horizontal polarization. Stations
within 1000 miles can't tell the difference between the "L" and my doublet.
Stations much past 1000 miles can't hear me on the doublet while they copy
me Q5 on the "L".

It also works on 80, although its short length really limits its efficiency
there. Still, I often work stations out to 1,000 mi on 80 running 100 watts
CW.   

I used the same technique Stuart mentioned to bring the wires into the shack
where I have a sash window by the operating desk. I cut a strip of expanded
foam about 1 inch high and as wide as the sash to fit tightly under the
window. A stick cut to length goes from the top of the sash to the top of
the window frame where it wedges to hold the window tightly down against the
foam (and keep the window from being opened from the outside). I picked up
some 1/4 inch plastic tubing at Tap Plastics that I poked through the foam
to provide "feed throughs" for the feeder and counterpoise wires. The tubing
is stiff and protects the foam from being cut and torn by the movement of
the wires. If I get too many holes from making too many changes, I just
replace the foam with a new strip. Very little air can slip through the
tubing with the wires in them. You can always add a dab of silicon grout or
a wrap of tape to completely seal them if desired. That results in very
little insulation efficiency loss with the thick strip of foam filling the
gap. 

Like every antenna in every station, this one is a compromise. Perhaps mine
is more of a compromise than many, but it's less than many others have to
live with. And it works very well. 

Ron AC7AC