What got my attention was seeing what appears to be stacked groundplanes at
the Manchester NH airport.
I dont want a collinear or vertical dipole.
The basic ollinears are 2 half wave elements fed at the center either
vertical or horizontal and go back to the 30's for SWBC and some ham use. In
the late 40's and 50's collinear VHF/UHF ham arrays in either polarization
were very popular and with reflectors were called bedspring or curtain
antennas.
I had a 16el 6M, 8 driven and 8 reflectors, collinear up for about 10 years
strapped to the side of a tower and aimed at Europe. It consistently
outperformed a 7/7 modified Hi Gain stack (24' booms) in signal reports but
was noiser on receive due to the broad lobe and poor F/B.
There are several 40 and 80M curtains in use and also used on other bands
when designed and fed properly. Great for a narrow sector coverage or trying
to play king of the hill to EU, VK, etc.
Hopefully Ive explained myself sufficiently by now to get some constructive
suggestions.
----- Original Message -----
From: "Mike Armstrong" <armstrmj@aol.com>
To: "Tom W8JI" <w8ji@w8ji.com>
Cc: <topband@contesting.com>
Sent: Friday, September 06, 2013 11:16 AM
Subject: Re: Topband: Are stacked verticals feasible?
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
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