On 2019-01-20 11:59 AM, VE6WZ_Steve wrote:
Bill, I agree with your analysis and like you I wish there was a
> program like HFTA out there that could handle a vertical radiator.
The issue is that there really isn't any "reflection" with the vertical
radiator - unlike the horizontal radiator. The "beam forming" behavior
is due to "loss in the dirt" for the groundwave and the difference in
propagation (phase) between the groundwave and low angle sky wave.
Any HFTA type program for a vertical would be more sensitive to the
ground constants (resistivity and permitivity). Those values are not
constant, not easily measured and important to a couple of skin depths
(at least).
The biggest contributor to the "enhancement" of verticals on a down
slope (or cliff edge) is simply the height above the lossy soil. Not
only does the loss in the near field decrease because less of the
radiated field penetrates the soil in the near field, the added height
means there are fewer interactions between the radiated fields and the
lossy soil as one moves away from the base of the antenna.
73,
... Joe, W4TV
On 2019-01-20 11:59 AM, VE6WZ_Steve wrote:
Bill, I agree with your analysis and like you I wish there was a program like
HFTA out there that could handle a vertical radiator.
My remote QTH is on a gently sloping hill in all direction and is about 100m
above the surrounding farmland.
Here is a very rudimentary and non-scientific powerpoint which includes a copy of the
“vertical over sloping terrain analysis” from ON4UN’s book. I don't know where
he got this analysis or who did it. Does anyone know??
https://drive.google.com/file/d/1UP45c5MWaWvA0T9no4DHW060FSgC-3Pk/view?usp=sharing
<https://drive.google.com/file/d/1UP45c5MWaWvA0T9no4DHW060FSgC-3Pk/view?usp=sharing>
This analysis of an 80m vertical over sloping ground certainly shows that a
significant low-angle gain benefit of up to 11dB over a flat terrain vertical.
I include a comparison to other plots from Johns book showing how a vertical
over saltwater shows a similar outstanding low-angle response, which we have
all heard in action from various well place DX-peds on the saltwater. I
extrapolate this to 160m.
I can only assume that building a HFTA like program for a vertical is a bit
more complex than a horizontal radiator.
73, de steve ve6wz.
On Jan 20, 2019, at 6:06 AM, Bill via TowerTalk <towertalk@contesting.com>
wrote:
Several people have mentioned the effects of a hill on a vertical or vertical
system.
I also know of no program that allows terrain to be considered for a vertical.
Several people who I consider informed came to the same conclusion I did, it
enhances the signal if it is a downhill slope and is detrimental if is an
uphill slope. For example, if one looks at a Yagi at one wavelength over flat
ground and then at one over sloped terrain, you can see how the angle has
dropped. Likewise, if you look at the flat results and then the print out of
the uphill slope, it is easy to see the low angle has been attenuated.
It's my belief and some antenna gurus, that the steeper the slope, the lower
the angle if down slope, and the more attenuated if up slope.. At my QTH I
have a huge downward slope to EU and NA and a huge up slope to the top of Mauna
Kea (14000 feet) which is LP for EU and SP for VK/ZL. On 80 I have a 4 sq and
on 160 a bent vertical and a very good symmetrical ground system. For the same
conditions and distances I can tell you the signal is much better in the
direction of the down slope than the up slope. Is it a scientific test? No.
However, it does indicate that if one has a big slope (in my case a 1:6 slope
uphill and downhill.) it does affect how a vertical performs. Mine and several
others educated guess? Going downhill at my place probably lowers the angel at
least several degrees. No, I'm not sure if the angle is elevated in the up
hill direction. No doubt though it is attenuated.
Those who have heard me on 80 and 160 in EU and NA will agree that the down
slope helps the signal.
Bill KH7XS/K4XS
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