Hi Branco
I can only echo Bob and Rich.
At ZM4T we are 320 m asl with steep (~45 degrees) down sloping terrain down to
80 m asl, followed by some hilly area up to 120 m again before it ends in the
Ocean.
The location is classified as Extreme High Wind Zone. Everything has to be
designed for 200 km/h+ wind. We have >100 km/h every month, often every week.
So we also had a painful learning of what survives and what doesn't.
Due to the terrain we spent endless nights with HFTA and focussed entirely on
optimising antenna heights for dedicated directions.
We don't have big towers available to manage vertically optimised stacks so
focus was on using up to 20 m hight (free standing towers) and single yagis at
dedicated heights per main direction.
TOA's need to be below 10-15 degrees here as we barely have any higher angles
contributing. Optimum height for a 10m beam towards US here is 6-7 m above
ground. We get max gain at 1 degree. For 15m it is 9-10m height etc. When
installed higher performance degrades at lower TOA's but gets often better at
some higher TOA's (depending on terrain). Today we have identical tribander on
one tower at 9m and 18m. On 10 & 15 m the lower beam always wins.
In steep sloping terrain antennas can be too high!
On the other hand I found from simulations that you need much less vertical
stacking distance in steep sloping vs. flat terrain. But so far I could not
confirm this by own experiments/installations.
73 Holger, ZL3IO/ZM4T
> Date: Mon, 23 Apr 2018 10:27:29 -0400
> From: "Bob Shohet, KQ2M" <kq2m@kq2m.com>
> To: "Rich Assarabowski" <konecc@snet.net>, <cq-contest@contesting.com>
> Subject: Re: [CQ-Contest] 4O3A Station rebui
> Message-ID: <5C9E3531CD3B451C820721B2295339D8@BOBWINPC1PC>
> Content-Type: text/plain; charset="UTF-8"
>
> 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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