Topband: Are stacked verticals feasible?

[Carl]

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 at aol.com>
To: "Tom W8JI" <w8ji at w8ji.com>
Cc: <topband at 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 at 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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