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

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

I wrote:
"A circle of 16 ft peroimeter has a diameter of 6.09 ft."

My eyesight needs correction. It should have been 5.09 ft.

The area of a 16-ft circumference circle is 30.37 sq ft, not 20.13 sq
ft.

30.37 sq ft is more than 16 sq ft, so the circle radiates more than the
square for the same length of wire.

Best regards, Richard Harrison, Kb5WZI

Just a question

In microwave we talk about aperature as a determing factor of antennas.

To what extent does this apply to HF ??

--
Caveat Lecter

Richard Harrison wrote:
I wrote:
"A circle of 16 ft peroimeter has a diameter of 6.09 ft."

My eyesight needs correction. It should have been 5.09 ft.

The area of a 16-ft circumference circle is 30.37 sq ft, not 20.13 sq
ft.

30.37 sq ft is more than 16 sq ft, so the circle radiates more than the
square for the same length of wire.

With the same power input? If I apply 100 watts to the square and get
(very nearly) 100 watts radiated, how much do I get from the circle?
Let's see, 30.37/16 * 100 = 190 watts. If I could capture that in a
screen room with another antenna, I could feed 100 watts back to the
transmit antenna and have 90 watts left over to run the refrigerator to
cool my beer. . .

Roy Lewallen, W7EL

Richard Harrison wrote:
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. . .

That's almost correct, but not quite. Except for loss, a triangular
loop, square loop, folded dipole, or round loop radiate equal amounts
*regardless of their enclosed areas* -- the amount of power that's
applied to them. The round loop doesn't radiate any more than any of the
others. None is one more "effective" than another, except that the
patterns will be different, so one might be more effective than another
at communicating in a particular direction -- but the round loop won't
necessarily always be the winner.

The statements you made earlier about a round loop radiating more, and
the continuing hangup about enclosed area, are based on the assumption
that the loop is small and is driven by a constant current source. For a
given amount of wire, the round loop has the highest radiation
resistance, and therefore if fed with a constant current, it consumes
and therefore radiates the most power of any loop made with the same
length of wire. This is a set of conditions often used by textbook
authors to illustrate some basic principles, but it isn't representative
of amateur (or commercial, for that matter) antenna use. It's necessary
to read and understand the qualifications given by the authors before
quoting their conclusions.

For a given length of wire, you'll get the most efficiency from a round
loop for a given length of wire. But unless the loop is electrically
very small, the efficiency will be high enough that this won't make any
noticeable difference. Making a large loop round -- or increasing its
enclosed area -- won't make it "radiate better" or be "more effective".

Roy Lewallen, W7EL