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RE: [TowerTalk] 40 meter Steppir

To: "'Van Fair'" <>, <>
Subject: RE: [TowerTalk] 40 meter Steppir
From: "Joe Subich, K4IK" <>
Date: Sun, 22 Feb 2004 23:14:26 -0500
List-post: <>

> A choice of three different element spacings available on the 
> 4 element should provide one acceptable for a 2 element 40 
> and even a rotatable dipole on 30 would be an upgrade if no 
> spacing would suit 30 meters.  Another  thought is to offer a 
> long driven element for 40 and 30 meters with the other 2 or 
> 3 elements remaining as they are now, to give a rotatable 
> dipole on 30 and 40. 6 meters would probably also have to go 
> to solve mechanical problems but for the next 6 years 6 
> meters will not attract much attention anyway. 

SteppIR (Fluidmotion) yagis are set for a 22 Ohm feed impedance 
and use a special balun/matching transformer to match 50 Ohms. 
One would need at least a two element, close spaced yagi to 
reach the 22 Ohm feed impedance to match the other bands. 

The element spacing on the current four element design is not 
conducive to replacing just two elements with longer ones.  
Replacing the reflector and driven element would create a 
mechanically unbalanced antenna (a problem for rotors and masts). 
Replacing the reflector and second director creates a wide 
spaced array with matching problems.  

It might be possible to replace the driven element and first 
director ... creating a two element DE/Dir antenna with modest 

Six meters is a non-issue ... it's essentially "free" due 
to the adjustable elements.  For those who want performance 
on six meters Fludimotion offer additional fixed length 
six meter elements. 

> Maybe price of this approach could be a more realistic $2000 
> to 2500.  Two elements on 40 and 30  would satisfy the most 
> number of potential customers. 

Based on the price difference between the BigIR and SmallIR 
verticals, the cost difference between long and short elements 
should be on the order of $100 per element.  Thus the "saving" 
in a design that offers only two elements on 30 and 40 meters 
would be minor (even at twice the price).   

For those who want 30 and 40 meter capability, if Fluidmotion 
do design a longer dipole element, I see two approaches: 

For those with limited space and/or resources, a rotary  
dipole that would cover 6.9 to 55 MHz could be mounted above 
and parallel to the boom of a two or three element SteppIR 
design yagi.  

For those who want higher performance, and have the ability 
to support it, five elements on a 32 foot boom.  The five 
element design would have three "big elements" and two "small 
elements."  They would be used to create a three element 30/40 
meter antenna using the full 32 foot boom, a four element 
20/17/15 meter antenna using all 32 feet of boom and a four 
element antenna for 15/12/10 meters using 24 or 26 feet of 
boom and, optionally, a six element six meter antenna using 
two additional fixed length directors.

Such a design would have essentially the same gain as the 
current 4 element SteppIR on 20/17/15/12/10 meters but would 
maintain its pattern (front to rear) at greater than 22 dB 
across the entire range.  In addition, the 30 and 40 meter 
performance would be equivalent to the 20 and 17 meter 
performance of current three element SteppIR.  

Making an educated guess based on a comparison of specs 
of the other Fluidmotion products, I would expect something 
like that to have a turning radius of slightly less than 40' 
a surface area of about 18 ft^2 and weigh in at about 120

I do not work for or speak for Fluidmotion ... this is from 
my own modeling based on some speculating on what could be 
done "if the parts were available." 


   ... Joe, K4IK 


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