Posted by
Craig Smith on
Mar 16, 2009; 1:39am
URL: http://elecraft.85.s1.nabble.com/43-Vertical-and-the-K2-tuner-tp2481408p2483733.html
Hi Roy ...
Congratulations on your new 40 meter vertical project. It should provide
you with some improved DX capability as compared with a dipole at modest
heights.
I can offer a couple of pieces of advice, based on my own experience that
may streamline your quest.
If you are using radials that are in the ground or on the ground forget
about "tuning". The coupling to ground will detune them substantially.
Please see the recent work by Rudy Severns N6LF both on his website and in
the recent issues of QEX.
Both in/on ground radials and elevated radials can work well. I have used
both here and have been quite happy with the results.
If you are using radials on/in the ground for 40 meters, you can expect
reasonably good results with 32 radials between 20 and 30 feet each. Don't
worry about the exact length. The DX Engineering radial plate is a joy to
work with and will make your task much less onerous.
I have also had good success with elevated radials on 40. Since I can't put
up any permanent antennas, I use a 40 ft fiberglas Spiderbeam pole as a mast
that puts the feedpoint at about 6 feet. I used the following tuning
technique. I wish I could remember where I saw it first, but can't. So I
can't give the original author his/her proper credit, but can verify that it
works well.
Make a low 40 meter dipole at the feedpoint level (about 6 or 7 feet in my
case). Tune it to resonance at your desired frequency as you would any
dipole. I use the AIM4170 analyzer set up to cancel out the coax feedline
effects. Then put this dipole on the ground and put up and tune a second
dipole oriented 90 degrees from the first one. These two "dipoles" will
become your four element ground plane for the vertical.
Now start with about a 33 ft vertical element with the four element ground
plane tied to the coax shield. Tune the vertical element to best
resonance/SWR using the previously tuned ground plane elements. If you have
enough height, you can tweak the SWR by raising/lowering the feedpoint
height. The result will be a very efficient 40 meter ground plane
vertical.
If your interest is in only one band and you have the height and ability to
erect a permanent antenna, the elevated radial approach is probably better.
If you want to do multiple bands and/or need to have an antenna that can be
put up and taken down frequently, the better approach is probably to use
ground radials. One radial field can cover ALL the HF bands. And by
putting a remote tuner at the base, you can use one vertical element (such
as the presently in-vogue 43 ft) vertical element to cover several bands.
73
.... Craig AC0DS
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