Tom,
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.
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.
Again, in my own case, stacking/phasing 4 fairly long beams allowed comms that
any other configuration, including a single long boom yagi, did not allow at
the same quality level. I never measured the actual gain, but I do know that a
single beam didn't cut it..... Yes, I could communicate, but with alot of noise
into the repeater...... When I stacked them, it became full quieting which is a
fairly big difference in "quality." I know it wouldn't take much actual gain to
make happen, but it does indicate "some" gain :) :) By the way, it allows me
to go simplex into Phoenix from that location on the Rim, as well, with great
signals according to the guys I've spoken with. A few tests with a single beam
versus a combination of phased beams (2 or 4 beams) indicated the same basic
thing according to the folks on the other end. I won't quote what they said
concerning "s-meter" readings because that is pretty meaningless...... BUT,
full quieting vs "noisy signal" does indicate a
reasonable gain, even if I don't know the exact numbers.
Oh, one thing I didn't mention is that the beams are all homebrew using
aluminum booms and elements (plumbers delight construction) and were phased
using the proper impedance for the phasing lines..... with a large amount of
time spent ensuring as little untoward beam coupling as possible (of the type
that, as you know, causes real problems when trying to get the impedances and
phasing lines to be correct). Basically, I followed some moonbounce array
designs from handbooks of the past, with more of today's understanding of
proper phasing, if you will. Seems to work well and all indications are that
it does, indeed, have fairly significant gain (which is not actually a measured
gain, so I cannot speak to "how much" with any degree of accuracy, as I
mentioned above). WHEW, this is more of a book than I intended..... LOL LOL.
Mike AB7ZU
Kuhi no ka lima, hele no ka maka
On Sep 6, 2013, at 7:01, "Tom W8JI" <w8ji@w8ji.com> wrote:
>> 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
> _________________
> Topband Reflector
_________________
Topband Reflector
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