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[TowerTalk] 20M Yagi

To: "Towertalk" <>
Subject: [TowerTalk] 20M Yagi
From: "Michael Harris" <>
Date: Fri, 10 Dec 2004 19:46:03 -0300
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I'm currently putting together the material requirements for building a 
three element 20M Yagi based upon the optimised design in the ARRL 
"Antenna Book" 18th edition.

Falklands is a windy place, not particularly high but persistent and a 
real antenna killer due to fatigue.  With this in mind I am planning to 
use the heavy duty element taper schedule.  At present I don't have enough 
thick wall 2" tube for the three element boom but I do for a two element 
of either reflector/driven element or driven/director element combo.  Even 
two elements are better than no elements.

The latter should give a little more gain.  I would assume that either of 
the parasitic element lengths would remain as per the detail in the book 
with just the driven element having to be retuned.  Driven/director with 
the greatest spacing probably least susceptible to change.  Interesting 
that for the optimised designs of the 18th edition the reflector is much 
closer spaced to the driven element than that shown in the 13th edition 

Because of this I can only make a stab at the approximate radiation 
resistance of the driven element for a two element array at somewhere in 
the region of 20 ohms.

Pondering the option of "T" match but not too much information available. 
Does one try and match the 20 ohms or so to 50 ohms with the "T" of go for 
200 ohms and transform it down with a 4:1 balun, this could make for 
rather long arms maybe.  In either case I would be interested in some ball 
park figures for the mechanicals, also the option to do away with the 
series capacitors in the "T" arms by detuning the element on the hf side.

I have a copy of the ARRL "Yagi Antenna Classics" on order but also 
thinking about getting a copy of "Physical design of Yagi Antennas" by 

Now if I could only get the software of the 20th edition without having to 
replace my 18th edition rather earlier than is reasonable.


Mike VP8NO 


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