On 8/27/2019 6:02 PM, Dick Williams wrote:
As for a 40M and 80M antenna; it depends on what range you are wanting to
maximize your signal (NVIS or DXing with a low angle of radiation). For
NVIS, a low dipole is by far the best choice.
This is an absolute fallacy, although widely believed. See slide 19 in
http://k9yc.com/VertOrHorizontal-Slides.pdf which shows that upward
radiation peaks on 80M at a height of 55 ft, and drops by only 1 dB at
90 ft. These curves are plotted from the preceding vertical patterns.
Divide these heights by 2 for 40M. Also see slides 22-26.
For DXing, ideally you would
like a dipole 1/2 wave length or higher. I read somewhere "the *dipole
should* always be at least 20 feet *higher* than the *height* you were able
to achieve". Since dipoles 1/2 wave length or higher on 80 and 160 are out
of the question for most amateurs, for DXing we default to verticals (or
phased verticals) with there inherent low angle of radiation.
Yes. I've addressed this in considerable detail in this tutorial.
http://k9yc.com/AntennaPlanning.pdf and these slides
http://k9yc.com/VertOrHorizontal-Slides.pdf
The couple of issues with verticals. They need an effective radial system;
2 or 4 tuned elevated, or the most ground radials you can lay out (60 or
more). Unless you are erecting it over saltwater, you will not have very
good results without an effective radial field.
This is not true of all verticals -- some are some form of center-fed
loaded vertical dipoles. These do NOT need (or even benefit from)
radials. But those verticals that are resonant end-fed DO need radials.
The second issue is being
vertically polarized they are noisy, and unless you have a seperate receive
only antenna(s), that may or may not be an issue at your QTH.
A much more important issue with verticals is that they are strongly
dependent on ground conductivity, whereas horizontally polarized
antennas are not. HF verticals also benefit from being installed on a
roof. And unless they are electrically very long (the 43 ft vertical
above 20M), they are low angle radiators.
Verticals are also discussed in that first reference, and in this set of
slides. http://k9yc.com/VerticalHeight.pdf
if you can't erect a descent vertical antenna (full size with 60 or more
1/4 wave radials) go with a dipole as high as you can get it. Am not a
bit surprised by Gedas's experience with a dipole at 70 ft on 40M (about
1/2 wave length above ground) and the short vertica with no really
efficient ground radials. Several years ago, I wanted to play around on
60M. With no place to erect a dipole at a descent height for 60M, I erected
a DX Eng 30M, 1/4 wave length vertical (43 ft).
Actually, 43ft is 0.44 wavelength on 30M. It's 5/8 wavelength on 20M
After laying down about 64
or so 43 ft ground radials, I called it a day. Have to say I have been
quite pleased with its performance.
The 43-ft vertical is discussed here. http://k9yc.com/43FtVertical.pdf
The slide deck also addresses mounting height and the effect of soil
quality.
AD5X has also published some excellent work on the 43 ft vertical, and
it's referenced in the slide deck.
By the way -- all of this work has been peer reviewed by both the
current and retired editors of the ARRL Antenna Book, as well some other
strong engineers.
73, Jim K9YC
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