Topband: Are stacked verticals feasible?

[Tom W8JI]

> If I am reading the question correctly, aren't we talking about something 
> that is done at VHF/UHF with great regularity?  Stacked vertical elements, 
> stacked vertically polarized beams and all manner of stacked vertical 
> "anything" are done there all of the time to avoid cross polarization loss 
> when the other stations (especially mobile) are the main users.
>

Stacking compresses beamwidth in the plane of the stacking. It's nothing but 
a collinear antenna placed vertical.

Stacking gain depends on individual element directivity and spacing between 
radiation areas (which are the current maximum areas).

Much of the stuff with VHF or UHF Ham antennas is just a gimmick with 
completely false gain claims. This is because Hams have a false idea that 
two antennas have 3 dB more gain than one antenna. If we really look at it, 
spacing has to be pretty wide (typically almost 3/4 wave) with broad pattern 
antennas like verticals to get near 3 dB, and that would be with zero 
feedline loss in the stack. It takes a commercial 150 MHz antenna about 20 
feet to make 5 dBd gain. It takes a Ham manufacturer less than ten feet to 
make 6 dB gain. Someone is clearly misleading people, and I doubt it is the 
commercial people.

Directional antennas like Yagi's are even worse. The more directive each 
stacked cell is, the wider spacing has to be to get near 3 dB gain. In 
practice, peak stacking gain is rarely over 2 dB. This is especially true if 
ground gain already compresses the pattern in the same plane as stacking. My 
40M stack of two 3-element full size Yagis, spaced optimally with a height 
limitation of 200-feet, only has about 2 dB stacking gain. That's a lot of 
work for 2 dB. Adding a third antenna, even going over 300 feet limit, adds 
even less gain.

What mostly makes my 40 meter system work is location and propagation, not 
the big antennas on a 200 ft tower. Because I'm in a rural location, I can 
hear and work DX that people with very similar antennas just 20 miles away 
near populated areas have no hope at all of hearing. I could probably outdo 
a Yagi stack located in a nearby city area with a regular dipole.

Now imagine those quad people who "think" two half size Yagi's stacked 1/4 
wave apart (that's all a quad is) have 2 dB gain! The truth is, the gain is 
zero to 1 dB depending on height.

Gain is all about the spacing between high current areas, and the initial 
pattern.  But results are mostly all about location and local environment.

> So understanding that it is done at those frequencies, the answer to the 
> original question of "can it be done," so to speak, is a resounding YES. 
> I just don't have any idea how you could extrapolate that to MF (160 
> meters)...... It would be a monstrously tall structure..... he he he. 
> Actually, I have a set of stacked vertical beams that I use for a 
> point-to-point link with a marginal repeater from my cabin up in the high 
> country on the Mogollon Rim in AZ...... It is an incredibly effective 
> antenna that was much less so with a single vertical beam..... Hopefully I 
> didn't just waste everyone's time by misinterpreting the question..... :) 
> :)
>

The system described can be done, but the gain would be near zero. The gain 
could also easily be negative, and with the described scenario, would never 
be noticeably more than just a regular old vertical dipole. It's a 
complicated picture, especially when at VHF with multipath. Things often are 
not what we imagine.


73 Tom