Oh Tom, I FULLY agree that it would be VERY difficult and not very practical,
especially considering we are talking 160...... In fact, the price/performance
ratio simply wouldn't be worth it, in my own humble opinion..... no doubt about
that.
There are certainly better ways to get ALOT more gain and probably for alot
less money. Real Estate being the real limiter here.... LOL
Mike AB7ZU
Kuhi no ka lima, hele no ka maka
On Sep 6, 2013, at 9:25, "Tom W8JI" <w8ji@w8ji.com> wrote:
>> Fully understood. I wasn't referring to the usual collinear antennas sold
>> by "comet" or anything of that nature. I am referring to the stacking
>> arrangements used for ops like moonbounce, etc. As far as the design theory
>> (and practical application) goes, I have a reasonable amount of schooling
>> and experience (been active since 1966..... he he he). Just so you realize
>> I am not referring to the often (always?) false gain claims made by
>> manufacturers for their antenna designs.
>
> ........but this is verticals, and not a narrow BW like a long Yagi. The
> narrower the pattern of a cell in the stack, the wider minimum useful
> stacking distance becomes.
>
> Also, for 160, antennas are near earth. Earth spoils everything. A 160
> antenna at 260 feet is like a two meter antenna at 3.25 feet above ground.
>
>
>> All I was saying was, "yes, it is possible and is done" when speaking to
>> vertical stacking. As far as stacking what we would call "ground plane"
>> antennas (quarter wave vertical element against elevated radials), the only
>> example I have seen with any regularity is done aboard some Naval vessels
>> (stacked/phased, if you will, horizontally on a yard arm). I "think" I have
>> seen the same thing at airports, but I cannot tell for certain that they are
>> phased arrays or just happen to "look" like they are related. Understand
>> that in all cases to which I refer, including my own, I am speaking of
>> phased arrays, which I believe is what we are talking about as well. I may
>> have misinterpreted the question to some degree.
>
> This is 160. The distance ratio for the same behavior on two meters is 80:1.
> If we look at: http://www.w8ji.com/stacking_broadside_collinear.htm
>
> we see **freespace** short dipole stacking distances, between current
> maximums, is 0.35 WL for 1 dB stacking gain. This is for freespace. That
> means the current maximums have to be .35*160 = 56 meters apart **if** the
> elements are in freespace. They have to be even further apart if near earth,
> because the earth reflection already compresses the vertical pattern. I'd
> guess, for 1 dB stacking gain over a ground mounted vertical (ignoring ground
> losses), we could move the lower current maximum to about 50 meters above
> earth and eliminate the upper element. That would pretty much be a vertical
> dipole. If we wanted to get 2-3 dB gain, we'd probably need 300 feet of
> height and an inverted groundplane at the top.
>
> For 160, is it is a useless endeavor at normal heights.
>
> Making matters worse, 5/8th wave verticals are dogs on 160. Been there, done
> that, used them. A 1/4 wave vertical, or something up to maybe 200 feet, is
> actually better. They have never worked well here, they never worked when I
> used broadcast towers, and when W8LT used them in 160 contests they were also
> pretty weak.
>
> The whole thing is a waste of time on 160. Even if someone could run a
> vertical collinear with useful gain, it would just kill their signal by
> focusing it at too low an angle for 160, while nulling more useful angles.
>
> 73 Tom
>
>
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Topband Reflector
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