Loop Antenna as Triangle?
 

I would like to put up a 160 meter loop, fed with 450ohm ladderline.
Although I have enought room, the existing trees would only provide three
supports, pretty much in the shaped of a equalaterral triangle. How well
would a three sided loop work? Should I feed it in the center of one side?


Ed

I would like to put up a 160 meter loop, fed with 450ohm ladderline.
Although I have enought room, the existing trees would only provide three
supports, pretty much in the shaped of a equalaterral triangle. How well
would a three sided loop work? Should I feed it in the center of one
side?

Ed
--------------------------------------------------------------------

An approximately equilateral trianglular loop, of the same perimeter, will
not work greatly different from an approximately square loop.

The tuner settings will change a little. The radiation pattern will not
noticeably change unless actually measured. Radiating efficiency will be
slightly but not very noticeably less. Connect the feedline wherever it is
convenient. The radiation pattern will change from being crudely
omni-directional to another crudely omni-directional shape.

Reg.

Hi Ed

The IDEAL loop skywire is a perfect circle!

Any deviation from that reduces it's affectiveness, but not very
appreciatively that you would notice enough for it to warrant worrying
about it.

I've had loop skywires that resembled the letters M, R and even close
to the letter V all closed loops of course, and I saw no difference in
their performance.

TTUL
Gary

That's interesting. In what way is the "effectiveness" of a circular
loop decreased by changing its shape?

Roy Lewallen, W7EL

Gary V. Deutschmann, Sr. wrote:
Hi Ed

The IDEAL loop skywire is a perfect circle!

Any deviation from that reduces it's affectiveness, but not very
appreciatively that you would notice enough for it to warrant worrying
about it.

I've had loop skywires that resembled the letters M, R and even close
to the letter V all closed loops of course, and I saw no difference in
their performance.

TTUL
Gary

Hi Roy

That's interesting. In what way is the "effectiveness" of a circular
loop decreased by changing its shape?

I ducked class that day!

TTUL
Gary

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

Richard Harrison wrote:
. . .
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.
. . .

Ok, let's start with a triangular loop with negligible loss. We feed 100
watts to it. Since it has negligible loss, 100 watts must be radiated.

You've said that the radiation must increase as we round out the
triangle. So how much more radiation can we expect from a round loop fed
with 100 watts? 120 watts? 150?

Roy Lewallen, W7EL

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

Roy, W7EL wrote:
'Ok, let`s start with a triangular loop with negligible loss."

"Negligible loss" eliminates the differences between loops of most
shapes with the same enclosed areas. Area of a triangle is 1/2 its base
times its altitude, if I remember.

I`d rather use 16 ft of wire to make a square loop with 4-ft sides. Side
squared makes an area of 16 sq ft.

A circle of 16 ft perimeter has a diameter of 6.09 ft. Radius is 3.049
ft. Squared, it`s 9,27. and times pi it`s 20.13 sq ft.

Clearly the circle has the greater area for the same wire. Loss is based
on the resistance of the wire which is the same in both cases.

For more enclosed area, you get more radiation for the same wire and
loss.

As a short cut, I`ll quote Terman on page 907 of his 1955 edition:
"The radiation resistance of a loop antenna is less the smaller the loop
area."

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