I am considering a horizontal loop antenna that would be "squarish"
(depending on tree locations) and about 400' in circumference. My
(automatic) tuner is located in my garage (with 100' of coax going to
the shack in the house). The lead wires for the antenna and ground
are short and direct through the garage wall - I don't envision any
feedline from tuner to the wire loop. I don't want to use a balun
since there isn't really any feedline to balance and the impedances
presented to the balun would be all over the (Smith) chart. Would it
make sense to feed one end of the loop from the tuner and connect the
other loop end to the ground connection near the tuner or just leave
it open (essentially a square longwire antenna)? I would also have
three counterpoise wires following the loop lying on the surface of
the ground. The articles that I can find all use openwire feedlines
and balanced tuners (or baluns) but that arrangement doesn't fit my
situation. Thanks W0BF

On Sat, 09 Feb 2008 17:16:07 -0600, Bruce W. Ellis
wrote:

I am considering a horizontal loop antenna that would be "squarish"
(depending on tree locations) and about 400' in circumference. My
(automatic) tuner is located in my garage (with 100' of coax going to
the shack in the house). The lead wires for the antenna and ground
are short and direct through the garage wall - I don't envision any
feedline from tuner to the wire loop. I don't want to use a balun
since there isn't really any feedline to balance and the impedances
presented to the balun would be all over the (Smith) chart.

Hi Bruce,

Well, in fact you have described a feedline - the one going to the
automatic tuner. This one has every need for choking as any line that
left the tuner (which is, by and large, not recommended by most
automatic tuner vendors). You probably also have DC power or control
lines going to that tuner as well. They need choking too.

However, given you also mention a 100 run, then this presumably means
along or under ground. Ground proximity would probably snub any
Common Mode currents which would then reduce your specific need for
choking.

Would it
make sense to feed one end of the loop from the tuner and connect the
other loop end to the ground connection near the tuner or just leave
it open (essentially a square longwire antenna)?

You might want to make it switchable.

I would also have
three counterpoise wires following the loop lying on the surface of
the ground.

This technique falls outside of the canon of most lore, but not
without its benefits. However, three wires will not provide much
efficiency gain. On the plus side, it could make a difference for
NVIS.

You don't mention much about frequencies of operation nor about
directionality.

The articles that I can find all use openwire feedlines
and balanced tuners (or baluns) but that arrangement doesn't fit my
situation. Thanks W0BF

You have enough to work with as it is. As for openwire or coax
feedlines; to my knowledge, autotuners are built to feed unbalanced
antennas directly (at the feedpoint) rather than as traditional hand
adjusted tuners being used away from the antenna. This is, perhaps, a
bias from seeing too many SGCs. Anyway, I don't see a downside to
your plan.

73's
Richard Clark, KB7QHC

Try it...
Maybe you will like it...
And if you don't, THEN we will say you should have known better in the
first place

denny / k8do

On Feb 9, 5:16*pm, Bruce W. Ellis wrote:
I am considering a horizontal loop antenna that would be "squarish"
(depending on tree locations) and about 400' in circumference. *My
(automatic) tuner is located in my garage (with 100' of coax going to
the shack in the house). *The lead wires for the antenna and ground
are short and direct through the garage wall - I don't envision any
feedline from tuner to the wire loop. *I don't want to use a balun
since there isn't really any feedline *to balance and the impedances
presented to the balun would be all over the (Smith) chart. *Would it
make sense to feed one end of the loop from the tuner and connect the
other loop end to the ground connection near the tuner or just leave
it open (essentially a square longwire antenna)? *I would also have
three counterpoise wires following the loop lying on the surface of
the ground. *The articles that I can find all use openwire feedlines
and balanced tuners (or baluns) but that arrangement doesn't fit my
situation. *Thanks * W0BF

Greetings,

I had a horizontal loop antenna up for several years prior to my
moving to Texas. It was cut for 80 meters and was about 30 feet up in
a square configuration.

I fed it with coax to one corner, however I had a homebrew choke at
the connection point. I used a 10" long piece of 6 inch pvc pipe with
about 10 turns of coax around it.

The antenna worked fairly well and by virtue of the design loops are
pretty quiet.

You mention 400 feet on your loop. The formula I used was 1005/
frequency = feet in loop.

There is a yahoo group devoted to skywire loop antennas and some good
info can be found there.

At the present time I'm getting ready to erect an 80 meter loop, but
this one will be fed with 600 ohm homebrewed ladder line into a
Palstar balanced wire tuner. I'm anxious to get this on the air.

73

KI4BUN / AAV6TP TX

On Mon, 18 Feb 2008 13:47:22 -0800 (PST), wrote:

There is a yahoo group devoted to skywire loop antennas and some good
info can be found there.

There is also an article on pg. 56 of the March 2008 QST on this
topic. The author used ferrite on the coax/power cable to the auto
tuner to isolate it an make it act as a balanced tuner. The loop in
the article was fed directly and not with a feedline from the tuner to
the loop.

S.T.W.

Sum Ting Wong wrote:
On Mon, 18 Feb 2008 13:47:22 -0800 (PST), wrote:

There is a yahoo group devoted to skywire loop antennas and some good
info can be found there.

There is also an article on pg. 56 of the March 2008 QST on this
topic. The author used ferrite on the coax/power cable to the auto
tuner to isolate it an make it act as a balanced tuner. The loop in
the article was fed directly and not with a feedline from the tuner to
the loop.

S.T.W.

I once thought that would work, and even helped a little with an Antenna
Compendium article promoting it a long time ago. But I came to realize
that it doesn't matter at all whether the balun is at the input or
output of the tuner -- the balun is just as effective one place as the
other. The reason is that what counts is the common mode impedance,
which is the impedance to ground seen looking along the outside of the
coax toward the antenna, and this is the same on both sides of the tuner
(except, of course, for the difference due to the short distance between
the two points). Putting the balun the input has the disadvantage of
making the tuner chassis hot.

I'm sorry to see that QST's article review process still isn't working.

Roy Lewallen, W7EL

I'm sorry to see that QST's article review process still isn't working.

Roy Lewallen, W7EL

Heck Roy, if it worked, Nov-Dec QEX would have been 14 pages shorter. (And a
better rag for it as well!)

W4ZCB

Bruce W. Ellis wrote:
"I am considering a horizontal loop antenna that would be "squarish"
(depending on the tree locations) and about 400` in circumference."

If you had more trees (octagonalish) would enclose more area with the
same wire. Radiation is a function of loop area.

Tesonant loops are often one wavelength in perimeter. 400` is about 122
meters. 160 meters = 525 feet. 80 meters = 262 meters. What band do you
prefer? If a loop`s perimewter is a little too short for resonance, it`s
inductive and can be tuned with a low-loss variable capacitor.

The 20th edition of the ARRL Antenna Book has a horizontal loop
"skywire" (squarish) on page 5-20. A 7 MHz loop at 40 ft. elevation has
about the same radiation as a 7 MHz dipole at 30 ft. elevation for
various azimuths. It might be worthwhile reading the Antenna Book
article before construction.

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:

If you had more trees (octagonalish) would enclose more area with the
same wire. Radiation is a function of loop area.

Can you please explain that a little more? If you put 100 watts into a
400 foot circumference loop and it radiates 95 watts, will an 800 foot
loop radiate four times that, or 380 watts? Then can you feed back 100
to put back into the loop, and have 280 left over to run your
refrigerator to keep your beer cold?

Or if the 800 foot loop radiates 95 of your 100 watts, does the 400 foot
loop radiate only 23.75 watts? If that's what happens, where does the
rest of the power go?

Is the radiation pattern the same for a long skinny loop as for a round
one, as long as the enclosed area is the same?

. . .

Puzzled,

Roy Lewallen, W7EL

Roy Lewallen, W7EL wrote:
"Can you please explain that a little more? (Radiation is a function of
loop area.)"

Not being a typist, I`ll refer you to "TV And Other Receiving Antennas"
by Arnold Bailey. On pages 407 and 408 Bailey gives two formulas for
computing the antenna resistance for a loop antenna.

On page 408, Bailey has Fig. 8-14 which plots radiation resistance (the
stuff we build antennas for) versus the loop perimeter in wavelengths.
For a square closed loop of one wavelength perimeter, the graph
indicates about 50 ohms.

Bill Orr, W6SAI in "All About Cubical Quad Antennas" gives the full-wave
vertical loop antenna an impedance of 125 ohms on page 15.

On page 14, Orr writes:
"For purposes of illustration, the two wire folded dipole may be "pulled
open" to a diamond-shaped loop fed at the bottom point. If this
distortion of the loop is continued the antenna will become a shorted
transmission line."

A perfect circle is the geometric shape enclosing the most area for a
given perimeter. The more corners a closed figure has, the more closely
it usually approximates a circle. That is why I commented on an octagon
versus a square.

Best regards, Richard Harrison, KB5WZI