W5VX wrote:
>I'm not trying to pick a fight and I know that I am going to regret asking
t>his question but...
A rational discussion about interesting antenna issues is the point of this
reflector, isn't it? A bit of honest disagreement is a feature, not a bug.
>How can a 4 element multiband yagi with a compromised boom length deliver
>gain approximating that of a well designed 5 element monobander?
I think the answer basically boils down to this: boom length is a key
contributor to gain.
The SteppIR design removes the constraint to solve for "acceptable"
bandwidth. This allows the antenna to be configured for "optimal" gain at a
given frequency with a fixed feed impedance of 22 ohms. It turns out that
if you get to optimize the elements for gain absent a requirement for
bandwidth, and you have four elements on a 32 foot boom, you get pretty
close to the optimal amount of gain possible from a 32 foot boom.
The SteppIR also doesn't try to deliver excellent F/B. The removal of this
constraint also improves its ability to deliver gain. Since I don't care
about F/B, this isn't an issue for me.
The "big" monobanders that I studied on 10 and 15 meters have booms of 32
feet or less, and they have to solve for bandwidth in addition to other
factors, so they can't get much better gain than the SteppIR on its 32 foot
boom. If you removed the constraints of bandwidth and F/B, you could do
better with 5 elements spaced as you please than the SteppIR can with 4
fixed elements, but with those constraints in place, you pretty much can't.
On 20 meters, where the "big" antennae have 48 foot booms, the SteppIR can't
compete. But it isn't the lack of elements, it is mostly the lack of boom
length.
***dan, K6IF
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