<I'm going to look at the arrl articles Rick listed>
Jim asked "When you say open sleeve, do you basically mean something where the
apparent diameter of the conductor is larger (e.g. like cage dipoles,
bowties, biconicals, and to a lesser extent, fan dipoles)?"
I use "open sleeve" in terms of a second single, parallel parasitic dipole
element, shorter than than the dipole
driven element, and parallel to it, but not one cut for another band. In terms
of whether you should call
it "loading" ..I think not, since it's not physically in the driven element,
like normal L we talk about for the
driven element. I also don't think that the abstraction of saying it's an
apparent larger diameter is right.
(next we'll argue about how a folded dipole with 6" separation "acts" ! :)
This definition of "open sleeve" is a reduction of the original dual parallel
wires, or coax, incarnations, but
commonly described with the same words.
Side note: I was reading Tom Schiller's (Force12) patents on open-sleeve feeds
for 20/15/10 tribanders.
He calls his patent "No loss, multi-band, adaptable antenna"
The "no-loss" might get some eyebrow-raising :)
Curiously, he mentions 1.14x as an interesting minimum frequency delta for the
parasitic element. Don't know how
he came up with that.
"17. A low loss antenna comprising:
a driven element resonant at a first frequency, not resonant at a second
frequency, and not resonant at a third
a first adjacent element adjacent to the driven element on a first side of the
driven element, said first adjacent
element spaced apart from the driven element and resonant at the second
frequency, not resonant at the first
frequency, and not resonant at the third frequency; and
a second adjacent element adjacent to the driven element on a second side of
the driven element, said second
adjacent element spaced apart from the driven element and resonant at the third
frequency, not resonant at the
first frequency, and not resonant at the second frequency; and
a common feed point located at the driven element for coupling to a feedline
for feeding signal energy to the
where the second frequency is at least 1.14 times the first frequency, the
third frequency is at least 1.14 times
the second frequency, and the third frequency is less than two and one-half
times the first frequency."
"24. The low loss antenna as set forth in claim 17, wherein the electrical
length of the first adjacent element is
at least 14% greater than the electrical length of the second adjacent element."
Now the elements here are fatter, and shorter for a 20/15/10 tribander than
what I'm talking about.. So maybe the
losses aren't as interesting?
Or just part of a tradeoff
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