Jorge,
One of the benefits of a stack is to reduce or eliminate the higher angle lobes
for receive. From the middle of the USA where I am located, it can make a big
difference in reducing the QRM from everything between here and the East Coast
toward Europe. The difference in the level of a signal from W8, for example,
may be as much as 20 dB at times.
The difference in the signals from Europe with both antennas and just the high
one may not be noticeable and is never really significant. While there are some
times that the lower one is stronger to Europe than the two together, I would
have to think long and hard about doing it again if there was not the benefit
on receive.
I am referring to my observation of 8/8 on 20m, 114 foot (35 meter) booms,
fixed on Europe at about 75 and 150 feet.
It occurs to me that there is little need for you to minimize the strength of
your signal to any location between you and either USA or Europe. In fact
anyone who calls is someone who gives you points.
A lot of the enjoyment is spending time dreaming and planning what to do. All
I am saying is that 18 Yagi antennas and the associated switching to cover
20/15/10 in two fixed directions is a lot of work.
73...Stan, K5GO
Sent from my iPad
On Feb 25, 2014, at 5:12 AM, "Jorge Diez - CX6VM" <cx6vm.jorge@gmail.com> wrote:
> Hi Stan
>
> Or maybe a better idea is to have two 200 ft tower, one for Europe and other
> for USA each one with 3 x 10 mts + 3 x 15 mts + 3 x 20 mts beam at the
> appropriate height?
>
> 73,
> Jorge
>
>
> De: Stan Stockton [mailto:wa5rtg@gmail.com]
> Enviado el: lunes, 24 de febrero de 2014 10:00 p.m.
> Para: Jorge Diez - CX6VM; TowerTalk@contesting.com
> Asunto: Re: [TowerTalk] multiple antennas on same tower
>
> Jorge,
>
> I took a six element 15 design I had and put three of them with 50 foot
> spacing in EZNEC Pro.
>
> In free space the SWR was as follows, driving all three:
>
> 21.000. 1.035
> 21.225. 1.028
> 21.450. 1.290
>
> The free space gain at 21.200 was 15.65 dBi and front to back 39.02 dB.
>
> Then I put three more down six feet from the first three and turned them 75
> degrees and just drove the original stack of three.
>
> The SWR was:
>
> 21.000 1.45
> 21.225. 1.49
> 21.450. 1.95
>
> The free space gain at 21.200 was 14.15 dBi and the front to back with a
> skewed pattern was 19.95 dB.
>
> Different antennas may react differently - better or worse and obviously
> there could be something done to improve the detrimental interaction. You
> will definitely see a difference when you go from EU to USA but you will be
> putting up a lot of antennas to have the overall performance degraded by
> enough that I would not do it.
>
> 73...Stan, K5GO
>
> Sent from my iPad
>
> On Feb 24, 2014, at 5:20 PM, Stan Stockton <wa5rtg@gmail.com> wrote:
>
> Big problems with that, Jorge. Even if 90 degrees off and I think you won't
> be positioning them that far off (more like 70 degrees or so?) with only 6
> feet of separation (your example used two feet but even with 6 feet) your SWR
> will likely be higher than you want to see, you will lose gain and the
> patterns will be disturbed.
>
> Stan, K5GO
>
>
> On Mon, Feb 24, 2014 at 3:40 PM, Jorge Diez - CX6VM <cx6vm.jorge@gmail.com>
> wrote:
> Hello
>
>
>
> Thinking on fixed antennas to avoid rotor problems, I have a question/doubt.
>
>
>
> if I have a stack of 3 antennas (15 mts monobanders) on the same tower, how
> worst will be to add a second stack of 3 antennas on the same tower at 6 ft
> of separation each one?
>
>
>
> For example, a stack fixed to Europe at 50/100/150 ft. Then I add a stack
> fixed to USA at 48/98/148
>
>
>
> This is possible or will damage the performance?
>
>
>
> Will use any combination, each stack at a given time for quick switch
> between Europe and USA and also will want to use both stacks at the same
> time
>
>
>
> Thanks,
>
> Jorge
>
> CX6VM/CW5W
>
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>
>
>
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