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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