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

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

Caveat Lecter wrote:
"To what extent does this (aperture) apply to HF?"

To the fullest extent of the concept. See the 3rd edition of Kraus`
"Antennas", Section 2-11, The Radio Communications Link, beginning on
page 336.

Radio antennas scale to wavelength. Microwave antennas may be
impracticably large when scaled to longer wavelengths, but if built work
exactly like their higher frequency models.

Best regards, Richard Harrison, KB5WZI

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

It applies just as well. However, while the aperture of a parabolic
reflector is about the area of the reflector, this isn't at all true of
simple wire antennas like a dipole. For example, a half wave dipole's
aperture is just slightly larger than a dipole of infinitesimally short
length, and about equal to that of a loop. The aperture of a loop stays
almost constant as the loop size is increased, until it gets big enough
for the pattern to appreciably change.

Aperture is the same as directional gain (not numerically, but when one
is greater so is the other), which is the same as gain when loss is
neglected. Since aperture has no direct or obvious connection to
physical size or dimension of most wire antennas, gain is usually used
at HF as a descriptive measure rather than aperture. Note that the gain
of all but an isotropic antenna is different in different directions,
and therefore so is the aperture.

People with a weak understanding of the principles involved often fall
into the trap of thinking that a larger antenna must have a larger
"aperture" or, as amateurs like to call it, "capture area". That
mistaken notion leads to all sorts of false conclusions. But the general
misunderstanding of the terms are a real boon to antenna charlatans.

Roy Lewallen, W7EL

Also, the aperture is different in different directions.

Caveat Lector wrote:
Just a question

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

To what extent does this apply to HF ??

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

Ed wrote:
How would a three sided loop work?"

ON4UN`s "Low-Band DXing" says:
"---the delta loop can be called the poor man`s quad loop."

However the patterns and performance with various options are presented
because it requirea only one tall support and is easy to erect.

ON4UN`s book is published by ARRL.

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:
[...] Pythagoras who found the approximate value of pi by [...]
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.

He should have measured the diameter instead, which is easier than
measuring the radius (and would have given him the correct answer).

Just yanking your chain. Good discussion.

73,
kz1o

Thank you Roy - excellent as usual.

I recall a RADAR range equation where aperture (capture area) was one of the
terms

--
Caveat Lecter (a RADAR tech)



"Roy Lewallen" wrote in message
...
It applies just as well. However, while the aperture of a parabolic
reflector is about the area of the reflector, this isn't at all true of
simple wire antennas like a dipole. For example, a half wave dipole's
aperture is just slightly larger than a dipole of infinitesimally short
length, and about equal to that of a loop. The aperture of a loop stays
almost constant as the loop size is increased, until it gets big enough
for the pattern to appreciably change.

Aperture is the same as directional gain (not numerically, but when one is
greater so is the other), which is the same as gain when loss is
neglected. Since aperture has no direct or obvious connection to physical
size or dimension of most wire antennas, gain is usually used at HF as a
descriptive measure rather than aperture. Note that the gain of all but an
isotropic antenna is different in different directions, and therefore so
is the aperture.

People with a weak understanding of the principles involved often fall
into the trap of thinking that a larger antenna must have a larger
"aperture" or, as amateurs like to call it, "capture area". That mistaken
notion leads to all sorts of false conclusions. But the general
misunderstanding of the terms are a real boon to antenna charlatans.

Roy Lewallen, W7EL

Also, the aperture is different in different directions.

Caveat Lector wrote:
Just a question

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

To what extent does this apply to HF ??

Dave wrote:
"He should have measured the diameter instead, which is easier than
measuring the radius (and should have given him the correct answer)."

Dave is correct. The circumference is pi times the diameter. The radius
is only 1/2 the diameter. I miswrote.

Best regards, Richard Harrison, KB5WZI

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.

Roy Lewallen, W7EL


Yea, if you put them in the metal jar and measure number of electrons (or
whatever trons), including with dummy load, they will "radiate equal amounts "
..

Loops - delta, quad or circular have some advantage (gain) over folded dipole
or dummy load, due to some stacking effect and pattern forming properties. This
is what we are interested in and what was the point of asking the question.
Just stick the folded dipole and quad or other loop in the EZNEC and you will
see if there is any advantage or gain from particular configuration. Just like
two phased verticals produce more radiation in particular direction, the same
applies to loop vs. dipole. If one wants to nit pick, you could find that most
signal (radiation) in particular direction would be coming from circular loop,
followed by square, triangular, folded dipole, dummy load, in that order.

Making a large loop round -- or increasing its
enclosed area -- won't make it "radiate better" or be "more effective".

Stick it in EZNEC and see what you get in favorite direction.

73 + MX Yuri, K3BU.us

On 17 Dec 2004 22:26:56 GMT, oUsama (Yuri Blanarovich)
wrote:
[snip]

|Stick it in EZNEC and see what you get in favorite direction.

Prehaps a return to the original question is in order. Ed asked:

" 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?"

The man asked a simple question about what I believe is a horizontal
loop and you bozos started telling him it would work better (be more
efficient) if it was round.

Roy is too nice a guy to put it this way, but I'm not; It won't make a
rat's ass difference whether it's a triangle, a square, a circle or
anything in between. Unless it's 100'+ above ground, it's pretty much
going to radiate straight up; which in this case is its "favorite
direction."