On Mon,8/18/2014 10:16 PM, Rick - DJ0IP / NJ0IP wrote:
Jim, I didn't understand the point on slides 4 and 5.
I concur with everything you wrote.
Perhaps you mean where you wrote 130 ft. height for a horizontal antenna is
"low" on 160m.
Well, remember that these slides accompany my talk, and also this talk
was to the Pacificon Antenna Forum, which draws folks a somewhat above
average knowledge of antennas. Ya hadda be there. :)
The fundamental principle at work is that a horizontal antenna that is
low as a fraction of a wavelength is an inefficient antenna, both
because of ground losses and because all the energy goes more or less
straight up. I'd call any horizontal antenna lower than a quarter
wavelength low. Most of us are stuck with low antennas for 40M and below.
But what is is about the line "Verticals RULE on 160M" that you don't
understand? To me, that says don't even consider a horizontal antenna.
Further, the fact that the rest of the talk covers only vertical
antennas (with various forms of counterpoise) should tell you SOMETHING. :)
Well my main point is, we have good dB numbers shown for different vertical
solutions, but there are no dB numbers shown comparing a low dipole at a
typical height one would have in a city - say 50 ft. max, to anything
vertical.
You're right -- I almost never see that sort of comparison, which is
what I did in the other link I gave. It compares vertical and horizontal
antennas at various heights on 80, 40, and 20. The 80M plots are easily
scaled for 160M. Simply double the heights shown on the horizontal axis.
So a resonant horizontal dipole at 80ft on 160 would behave like a
resonant 80M dipole at 40 ft on 80M.
Also, both of those presentations are 1 hour talks, and especially with
the 160M talk, I had to have my roller skates on to get through it in
that time. :)
There the difference is larger (in dB) than the difference between a good
vertical and a great vertical.
Yes. And the primary difference between a mediocre vertical and a great
one is the counterpoise/radial system.
Another tutorial you might find interesting is this one.
http://k9yc.com/VerticalHeight.pdf It doesn't address 160M, but it
clearly shows the effects of the quality of the soil on a vertical
antenna, and also the value of mounting vertical antennas higher.
73, Jim K9YC
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