On Sat, 15 Nov 2014 21:38:10 -0000, wrote:

The following shows the effect on elevation pattern for a 1/2 wave
dipole antenna over ground at various heights for perfect, very good,
average, and extremely ground.

The important value to note is the elevation angle for the main lobe.

Generally for DX an elevation angle at or below 30 degrees is desirable
and for NVIS an angle above 60 degrees.

The elevation angles apply to any dipole type antenna, such as a G5RV,
OCF dipole, etc. but the absolute gain values will be quite different.

Also some types of dipoles have more lobes than the two of the 1/2
wave dipole; those lobes will still be elevated.

Perfect V good Avg Ext poor
Height gain @ elev gain @ elev gain @ elev gain @ elev
0.10 8.6 90 6.3 90 4.4 90 3.1 90
0.15 8.4 90 7.1 90 5.8 90 4.3 90
0.20 8.0 90 7.1 90 6.1 90 4.6 66
0.25 7.4 90 6.7 68 5.9 61 4.8 50
0.30 6.9 56 6.4 51 5.9 48 5.1 41
0.35 6.8 45 6.5 42 6.1 40 5.4 35
0.40 7.1 39 6.9 36 6.5 35 5.8 31
0.45 7.7 33 7.5 32 7.0 31 6.3 28
0.50 8.3 30 8.1 29 7.6 28 6.7 25
0.55 8.9 27 8.5 26 7.9 25 6.9 23
0.60 9.1 25 8.6 24 8.0 23 6.9 21
0.65 8.9 23 8.4 22 7.8 21 6.9 20
0.70 8.5 21 8.0 20 7.6 20 6.8 18
0.75 8.0 19 7.7 19 7.3 18 6.7 17
0.80 7.6 18 7.4 18 7.2 17 6.7 16
0.85 7.5 17 7.4 17 7.2 16 6.7 15
0.90 7.6 16 7.5 16 7.3 15 6.9 15
0.95 7.8 15 7.7 15 7.5 15 7.1 14


Special note:

Most people understand that the results of an antenna analysis program
reflect the material used to construct the antenna and the type of
ground, if any, used for the analysis, are an approximation, and are
not accurate to 27 decimal places.

Further, most people also understand that absent them being a part of
the model used for the analysis, objects in the near field of the antenna,
such as, but not limited to, 20 foot prision walls, blimp hangers,
skyscrapers, a deluge of biblical proportions, giant sequoia trees,
hovering 2 mile wide alien spacecraft, hords of locusts, large gold
deposits under the antenna, battles between Autobots and Decepticons,
beached aircraft carriers, and stadium domes may well effect the
actual antenna perfomance.

Your mileage may vary, void where prohibited.

Any spelling mistakes in this article are all entirly my fault. Any grammer
errors spotted in this article were put there because I could.


I have seen people talking about NVIS antennas for DX.

w.

Helmut Wabnig [email protected] --- -.dotat wrote:

snip

I have seen people talking about NVIS antennas for DX.

w.

Which makes no sense as NVIS stands for Near Vertical Incidence Skywave,
which means most of the power goes near vertical so the maximum
communication range of that mode is around 400 miles.

This is a short article that talks about NVIS antennas:

http://en.wikipedia.org/wiki/Near_ve...idence_skywave


--
Jim Pennino

On Sun, 16 Nov 2014 21:11:49 +0100, Helmut Wabnig [email protected] ---
-.dotat wrote:

I have seen people talking about NVIS antennas for DX.
w.

They may actually have a point. The problem is the assumption that
when bouncing RF off the ionosphere, the angle of incidence is equal
to the angle of refraction. In other words, to do DX, you need a low
angle of incidence.

I got the clue long ago, when I noticed that spinning a beam (yagi)
antenna, often resulted in little or no change in signal strength. It
wasn't all the time, but it did happen often enough for me to notice.
The explanation offered by Eric Nichols, KL7AJ is that sometimes, the
signal appears to be coming from directly overhead. I've uploaded a
copy of his Dec 2010 QST article (and added a text layer to make it
searchable):
"HP Ionospheric propagation may not happen the way you think it does"
http://802.11junk.com/jeffl/HF-Circular-Polarization/
http://802.11junk.com/jeffl/HF-Circular-Polarization/QST_Dec_2010_p33-37.pdf
"The answer is rather simple, once one recognizes that those
signals are circularly polarized. Actually it’s coming from
straight overhead."

I built a copy of his setup using junk parts and tested it with WWV
15MHz. I would agree that the signal is certainly circular polarized,
but I'm not 100.0% sure that it's always arriving from directly
overhead.

Please note that NVIS is limited by the maximum usable frequency of
the F layer and is usually used only on 80 and 40 meters during the
day, and 160 and 80 meters at night:
http://en.wikipedia.org/wiki/Near_vertical_incidence_skywave

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558