[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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