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Old May 11th 05, 04:56 PM
 
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Interesting.
One respondent says position is a factor and the
other says it is not according to Kraus ,who may
well have been directing his comments at a Yagi
model So I changed the feed point on my model,
which is not a Yagi, to other elements to see if
they lagging or leading.
Surprise !
Some of the other elements were resonant also
thus they could be fed in one or more places
at the same time
Since with the initial design they are not all
directly fed these apparently do not fall into any
catagory.
I suppose literature in general can only apply
definitions to that which is known by the author
at the particular time
Regards
Art


"Richard Harrison" wrote in message
...
Art Unwin wrote:
"When modeling close spaced element antenna assemblies it is possible
that some elements are physically longer than the "driven" element. Is
the length of an element sufficient to declare a "reflector" or are
there other caveats involved (i.e. phase)?"

Art answered his own question. The element doesn`t care how it gets a
leading (capacitive) current, or a lagging (inductive) current.

In our broadcast curtain antenna arrays, we used an RCA WM-30A phase
monitor for the current angle in the ibnductive parasitic reflectors.
Phase was adjusted to spec with a short-circuit stub connected to where
the feedpoint would be if it were a driven element.

Kraus is unequivocal on page 245 of edition no. 3 of "Antennas":
"When the halfwave parasitic element is inductive (longer than its
resonant length) it acts as a reflector. When it is capacitive (shorter
than its resonant length) it acts as a director."

Best regards, Richard Harrison, KB5WZI



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