Van,
> 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
performance.
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
pounds.
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."
73,
... Joe, K4IK
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