[TowerTalk] Fixed Quads
K7GCO@aol.com
K7GCO@aol.com
Sat, 29 Jan 2000 17:08:16 EST
In a message dated 29.01.00 07:13:32 Pacific Standard Time, KI7WX@aol.com
writes:
<<
For folks interested in wire antennas and using natural supports, I could
use
a bit of advice.
In preparation for the upcoming contest events I'm looking at erecting
some
fixed quad loop "beams". The loops will be hung from a catenary line
running
(length wise) NE/SW -> e.g. Europe. I have about 50 feet of length to play
with and the height measures out at 85 feet above ground. That's pretty
spiffy as it'll place the center of 20M diamond shaped loops at around 1
wavelength and 40M about 1/2 wavelength which should be decent for both
bands. It will get higher with time as the trees grow .... ..
With that setting, I want to suspend loops for both 40 and 20M from this
line. Looking at a driven element and reflector with ~20' spacing for 40M
and probably 4L on 20M using 10 feet between elements (30' total). Two
questions for the group:
(1) Does shape of the loop matter much? From my reading it appears that
cubes (diamonds) are credited with very slightly more gain than equilateral
triangles. I'll probably do the pragmatic thing and use what ever shape is
easiest, but curious what experience teaches here. It probably doesn't
matter
except on paper.
(2) For rotatable quads it's obviously possible to build multiband arrays
by
nesting the loops for higher bands within the loops for the lower bands.
It's not immediately obvious to me why interaction is not a problem, but I
accept the results. For my situation, erecting "nested" elements will not
be
too practical and would likely result in a twisted mass of wire and much
frustration.
Taking a page from the yagi book, I have pondered "interlacing" the
elements
to take better advantage of the available catenary length. For example, the
40M outer elements could surround the 20M elements to give a larger spacing
on 40. Alternatively I could add a couple 10M loops inside of the 40M loops.
Stuff like that. Has anyone played with this type of arrangement that can
offer practical advice?
Cheers,
Mark KI7WX/4
>>
Mark, you did a great job of preliminary design and have good questions.
You are a prime candidate for the next step that you should do and will
thoroughly enjoy. Learn how to use Eznec and try many variations. When you
come up with what looks good, try it and you will realize a rare satisfaction
not many in Ham Radio ever enjoy. When it works great you will take pictures
of it and brag about it to all your friends--on and on. Then try and improve
it with what the (S)Nit Pickers tell you won't work. I usually do them first
as 90% of the time they work great--in antennas, guns, internal & external
ballistics, photography and other technical areas.
Getting advice is a crap shoot and bad advice doesn't cost them any
wasted money or time--it will you with no refunds. Few will intentionally
mislead you. Antennas are very complex and simple at the same time. You will
get a lot of honest bad advice. Even though I still consult a lot of others
constantly, you will learn to sort them out--and their advice.
If you decide to get and learn Eznec, call me and I'll give you the K7GCO
Short Course on how to shorten your get up to speed time. It will make it a
powerful working tool that more on TT should also use before giving advice.
You are so very close to Ham Heaven, open the door and walk in and join the
fun deriving information you can bet money on and not lose. Deriving antenna
information on test ranges in the past was a very very expensive process in
time and money. So far every yagi or quad I've built that I designed or
massaged in Eznec, has worked exactly like I had expected--the first time. I
don't build prototypes anymore. I build the final model the first time. I
may change it later but I don't have any maintenance on it due to a quick
build. I have a mill, lathe, a lot of aluminum and that speeds up my
construction and quality of the antenna.
Although I have all the aluminum I'll ever need, I'm switching to mostly
quads except for yagi's (and quads) with 2 or more driven elements. They
develop more gain, F/B and maintain it over the band. Yagi's do not. Yagi's
gain and F/B elements have to be a "certain spacing and length"--real
close--and peaked in the middle of the band. That's why it was called a
"Parasitic Beam". Except for the DE, the gain and F/B elements are "Total
Parasites." Their hand is in the DE's and other elements "Pocket Field" all
the time. They sponge off the DE for their existence and their "Total
Performance Potential" is seldom ever reached. These elements (just like
people) are on "welfare" with liberal joints (working minds) that go bad
unless properly treated.
In "Driven-Arrays", the amplitude and phase are controlled, optimized and
spacing is not as critical. It has been discovered that "other beneficial
factors result"--even patentable. When properly designed, one can get more
of everything over a "Parasitic Welfare Yagi" over the whole band--not just
in a narrow range of frequency. W4GL was the first to show that in the 40's
with a 3 element All-Driven Array. I'm still doing research on his original
design. It was somewhat a victim of "Nontechnical Political Correctness"
also and TT wasn't even around then.
Yagi's peaked for the higher gains, fall off faster and Driven Arrays of
even less gain will beat them when the yagi's are out of their "Welfare
Office." Few hams consider "Whole Band Performance" when evaluating a beam.
This is why the Driven Arrays in the year 2000 should be very strongly
considered for getting the most out of your money. Some Mfgs. already have a
running start. I hope this is not too advanced thinking for "Past Century
Thinking." Too many have to be dragged kicking and screaming into the next
Century, let alone the next hour or minute. I'd like to suggest a more open
minded attitude for TT'ers. Advancing the State of the Antenna Art should
not be a Mortal Sin and should be "Politically and Technically Correct."
Even Prof.Yagi and Uda should have got a Nobel Prize for Antennas or
Something but their antenna has seen better days.
Mark, you have a simple wire antenna and can find and master all you want
to know all by yourself in a short period of time and know it's the optimum.
Take the next step, master Eznec (I'll help you) and you will never regret
it. My most enjoyable research and development hours in ham radio have been
on Eznec (several thousand)--yours can be also.
K7GCO
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