Huh? A folded dipole is a LOOP. It radiates the same amount of RF as a
circular loop. No more, no less. Just in a different direction and more in
the favored direction. Pythagoras who?

--
Steve N4LQ
"Richard Harrison" wrote in message
...
Roy, W7EL wrote:
"In what way is the effectiveness of a circular loop decreased by
changing its shape?"

There is an old story about the kid who tells his dad about learning in
school that pi r sguare. Dad replied that what school taught him was
dumb. All the world knew pie are round. Cornbread are square.

Maybe it was Pythagoras who found the approximate value of pi by
constructing ever more equilateral sided figures inside and outside of a
circle until there was no significant difference in the lengths making
up the sides of the interior and exterior figures. He could measure
straight lengths. He found the value to be 3.1416 for the approximate
value of pi which multiplied by the radius would equal the perimeter of
the circle. Also, pi times the radius squared gave the enclosed area.

The figure which encloses the most area for a given perimeter is a
perfect circle. Distorting a circle reduces the area it encloses.

Radiation from any loop depends on its enclosed area. This is intuitive
from transmission line behavior. It`s often observed that the wider the
spacing between the wires, the more the line radiates. As we increase
the area of a loop, the distance between the wires increases. Like the
transmission line, iits radiation increases.

An antenna of any configuration radiates. Efficiency is determined by
the ratio of radiation resistance to loss resistance. The antenna with
minimum perimeter for a particular radiation resistance will also have
minimum loss with other parameters being equal.

Best regards, Richard Harrison, KB5WZI

On Wed, 15 Dec 2004 07:54:05 -0500, "N4LQ" wrote:

Huh? A folded dipole is a LOOP.

Hi Steve,

Richard is right, but to answer your Huh? then it could be argued
that a standard dipole is an open loop or an unfolded dipole.

Classic radiation resistance formulas that are the basis of antenna
theory introduction are composed at small sizes such that the dipole
or the loop are no where near standard sizes. Their accuracy extends
between roughly a tenth wavelength to a quarter wavelength or more in
the greatest (not perimeter) physical dimension. This is often the
same range of size employed by the Ham in the HF regions.

It radiates the same amount of RF as a circular loop. No more, no less.

Typically, yes, but to ignore the lesson of Rr may lead some to ignore
the importance of Ohmic loss in small radiators. That is to say,
offering the sobriquet that wire has negligible loss must have some
objective correlative: in comparison to what is it negligible?

One Ohm compared to 100 Ohms is trivial, whereas one Ohm in comparison
to 10 mOhms is warmed over death. Same wire, same loop (or dipole),
but far different results for different frequencies that yield
different radiation resistances.

Just in a different direction and more in
the favored direction. Pythagoras who?

Yahoo Pythagoras, an Australian red-headed actor wasn't it?

73's
Richard Clark, KB7QHC