Topband: Are stacked verticals feasible?

[Tom W8JI]

> 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