Modeling of proposed specific antennas and stacking combinations is always the
place to start – and then modeling those configurations over your specific
terrain is ESSENTIAL from a hilltop location.
I have literally spent weeks of time modeling every conceivable direction,
height and wave angle from my complex terrain to get the best overall set of
antenna heights/stacking combos to cover the the world and it has been worth
every hour spent! A hilltop location like 403A often requires compromises in
height/stacking combinations in order to get the overall best combination for
the areas of the world and contests that will be worked and that bands that
they will be worked on as well as what part of the sunspot cycle they will be
worked. A non-US station that is optimized for CQWW will not perform as well
in ARRLDX as a station that is optimized for ARRLDX and vice-versa And every
station builder should take this into account.
What is often NOT considered though, is exactly HOW complex topographical
locations (like my qth) antennas/stacking combinations model very differently
than the same antennas/stacking combinations over flat ground.
At my qth on 10, a 37’ 5L Yagi is almost as good on the long haul path to
Japan/Pacific as the top 10 at 100’ which allows me to use the 37’ to find and
work Pacific mults while keeping the top antenna elsewhere. Yet the 109’ 5 L
15 is far better to short haul SA/Carib than the 90’, the 60’ or even a stack
of them! Modeling helps you to see counterintuitive advantages/disadvantages
like this in advance and then plan for them.
Some antennas/stacking combos over complex terrains will also provide very
counter-intuitive and interesting lobes that may appear/disappear in certain
directions because of uneven terrain . For instance, my 109’ top 5 L 15 meter
yagi has a high angle lobe that is very useful toward EU (over flat ground) but
that high angle lobe disappears to the West where it looks down a steep hill.
On 10 meters, the 5L Yagi @ 65’ to SA/Carib is literally in a NULL and
essentially worthless, but is excellent for Northern EU/UA0 and stateside off
the BACK of the antenna! The BEST antenna though for the West coast on 10 is
actually the 5L yagi at 23’ pointed Northeast (NOT West)! Again, it is at the
perfect wave angle over complex terrain to the West even though the lowest
antenna is pointed in the WRONG direction! I am also pretty sure that sporadic
E clouds off the coast of Europe may have something to do with this.
I believe that most hilltop qth’s with complex topography will have unique
counter-intuitive advantages/disadvantages similar in nature to what I have
discovered. And for every hour spent modeling them in advance, it will
probably save 10 – 20 hours of putting antennas up, moving them around, or
taking then down and reinstalling them at different heights later.
Just some thoughts from having yagis at my qth for the past 20 years and going
through the initial build and then two vicious thunderstorm storm caused
rebuilds each time with signal improvements thanks to modeling!
I owe most of this to the K6STI DOS based suite of programs, which I STILL use
on a DOS computer saved for this purpose. THANK YOU BRIAN!
GL Ranko!
73
Bob KQ2M
From: Rich Assarabowski
Sent: Saturday, April 21, 2018 12:47 PM
To: cq-contest@contesting.com
Subject: Re: [CQ-Contest] 4O3A Station rebui
I'll just add to the discussion that there's a HUGE effect of terrain at
Ranko's station, having visited there in 2016 (before the fire). The shot
to the US is off the side of a big dropoff (560m elevation) that drops
non-stop to sea level to the Bay of Kotor and then eventually comes back up
some number of kilometers away across the bay. The closest topography that
I can think of, Ranko, would be Bill KH7XS's on the Big Island, except it is
open water to the horizon in his case. So it's difficult to intuitively
predict what the impact of vertical stacking is. We talked about that at
your station, there was concern by you that HFTA modeling may not give
accurate results when you're skirting a hill instead of directly down a hill
(i.e. following the gradient), which I agree. However, I would still do
the modeling and see what you get. You may be surprised that lower
antennas will outperform high stacks. I'm sure Bill KH7XS could comment
about that, keeping in mind arrival angles from the US at KH7XS are much
lower than they than they are in 4O.
I've heard you many times in contests, Ranko, when you were one of very few
stations coming in from Europe with a very strong signal. But I've also
heard you surprisingly weak when others in Europe were very strong.
I assume the objective of your antennas is to maximize gain vs. F/B (there's
not much to the back of you when you're working the USA). In your
situation with that topography, perhaps horizontal stacking of high-gain
long boom antennas is the way to get gain (vs. vertical stacking), keeping
in mind that you will lose azimuthal beamwidth.
I would try to do some HFTA modeling to at least get a feel for the effect
of antenna height in your very unusual topography and then go from there.
I have a suspicion that you may not need as much tower height as one might
think.
--- Rich K1CC
> When making something big, such as a life time contest project, it is
> better to share and listen for advice. Here we have an experienced group
of
> contesters and maybe someone has something to say that I am not
considering
> at the moment?
>
> I am intending to rebuild the 4O3A station. One of the tasks is to put two
> towers in stack toward USA.
> On each tower I will have a stack of 2L40, together with a tribander
stack.
> The idea is to optimize horizontal distance of towers on 40M and 20M.
Other
> bands can't be optimized, and are not that important.
>
> I am still looking for tribanders designs, either to buy them or to build
> them.
>
> Any advice is welcome.
>
> 73
> Ranko
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