Many of us use 1 wl horizontal loops configured in a square or rectangular
shape. When these loops are operated at frequencies greater than the
fundamental, the horizontal pattern changes from a nearly circular pattern
to one with lobes & nulls.

For example, if I operate a 60' high, 1 wl, side fed, square, 80 meter
horizontal loop on 40 meters, the horizontal pattern is that of a
4 leaf clover with four fairly broad lobes and four nulls.

Now this is great if you intend to QSO with a station in the
direction of a lobe but not so great if your target is in the
direction of a null.

Now if I move the feed point to an adjacent side of the square, the
lobes become nulls & the nulls become lobes. In essence, I have "rotated"
the pattern by
moving the feed point.

I have attempted to take advantage of this shift in pattern by
erecting a 160 meter loop that "floats" in pulleys at the corners. I
then tried to physically drag the loop wire through their supporting
pulleys & move the entire antenna wire until the feed point was where
I wanted it. This was a really stupid idea & did not work out due to the
weight of the
wire, binding at the pulleys, mechanical problems, the hassel of "rotation"
, etc., etc. & I have
abandoned this idea.

I'm thinking now that I should just add a second feed line on a side
adjacent to the original fed side and simply select the feed line
(and pattern) that suits my operating needs. Like this:


********************************** *
* *
* *
* *
* *
* *
* *
* *
X *
Feed (1) *
X *
* *
* *
* *
* *
* *
***************XFX******************
e
e
d
(2)

My problem is that I'm not sure of the effect of adding that second
feed line. Should the unused feed line be grounded or simply left
unconnected at the transmitter? Or should I use relays at the
feedpoints to "jumper" the unused feedline? I use 450 ohm "window" type
ladder line.

Or, as another ham has suggested, put up a second loop, spaced a few feet
down from the first loop, & feed it where I like.

My goal is an antenna that covers 160- 17 meters, & has some capability to
steer the "gain" on the
frequencies greater than 2.0 mc.

Any help/comments will be appreciated.

I've successfully used two feedlines for a single antenna (my "Field Day
Special", for reversing the direction) by making the feedlines an
electrical wavelength long and leaving the unused one open. In my case,
I wanted an open at the unused feedpoint, rather than a short as you do.
Also, you don't need that much length. Either of these should work for
your antenna, producing a short circuit at the connection point of the
unused feedline:

1. Make the feedlines an electrical quarter wavelength long and leave
the unused one open circuited.
2. Make the feedlines an electrical half wavelength long and short
circuit the unused one.

Whichever one you choose, don't "ground" the unused feedline or connect
it to anything else.

Anyone else trying this method should be aware that even a small amount
of feedline loss translates into a poor open or short at the antenna, so
loss usually has to be considered. In this particular case it won't be a
problem.

Roy Lewallen, W7EL

T.E.O wrote:

. . .
My problem is that I'm not sure of the effect of adding that second
feed line. Should the unused feed line be grounded or simply left
unconnected at the transmitter? Or should I use relays at the
feedpoints to "jumper" the unused feedline? I use 450 ohm "window" type
ladder line.

. . .

Roy

Tnx for the reply. Is the 1/4 or 1/2 wl feed line you desribe measured using
the fundamental (1wl) freq. of the loop or the operating freq.?

Terry
W8EJO


"Roy Lewallen" wrote in message
...
I've successfully used two feedlines for a single antenna (my "Field Day
Special", for reversing the direction) by making the feedlines an
electrical wavelength long and leaving the unused one open. In my case,
I wanted an open at the unused feedpoint, rather than a short as you do.
Also, you don't need that much length. Either of these should work for
your antenna, producing a short circuit at the connection point of the
unused feedline:

1. Make the feedlines an electrical quarter wavelength long and leave
the unused one open circuited.
2. Make the feedlines an electrical half wavelength long and short
circuit the unused one.

Whichever one you choose, don't "ground" the unused feedline or connect
it to anything else.

Anyone else trying this method should be aware that even a small amount
of feedline loss translates into a poor open or short at the antenna, so
loss usually has to be considered. In this particular case it won't be a
problem.

Roy Lewallen, W7EL

T.E.O wrote:

. . .
My problem is that I'm not sure of the effect of adding that second
feed line. Should the unused feed line be grounded or simply left
unconnected at the transmitter? Or should I use relays at the
feedpoints to "jumper" the unused feedline? I use 450 ohm "window" type
ladder line.

. . .

The operating frequency. It should work adequately over a single band,
but not multiple bands. At frequencies near, but not exactly at, the
frequency you've cut the feedlines for, the effect will be that a little
reactance will appear at the point where the unused feedline connects.
This will make the antenna tune a little differently, but have no other
significant effect. Far away from that frequency, though, as on another
band, you can have some wild impedances at the second feedline
connection point, resulting in a very different pattern and impedance at
the active feedpoint.

Roy Lewallen, W7EL

T.E.O wrote:
Roy

Tnx for the reply. Is the 1/4 or 1/2 wl feed line you desribe measured using
the fundamental (1wl) freq. of the loop or the operating freq.?

Terry
W8EJO

on another
band, you can have some wild impedances at the second feedline
connection point, resulting in a very different pattern

Roy Lewallen, W7EL

============================

But who cares - the sole objective is to change the radiation pattern away
from nulls. ;o)
----
Reg, G4FGQ

On Thu, 08 Apr 2004 20:04:12 GMT, T.E.O hath writ:
Many of us use 1 wl horizontal loops configured in a square or rectangular
shape. When these loops are operated at frequencies greater than the
fundamental, the horizontal pattern changes from a nearly circular pattern
to one with lobes & nulls.

For example, if I operate a 60' high, 1 wl, side fed, square, 80 meter
horizontal loop on 40 meters, the horizontal pattern is that of a
4 leaf clover with four fairly broad lobes and four nulls.

Now this is great if you intend to QSO with a station in the
direction of a lobe but not so great if your target is in the
direction of a null.

Now if I move the feed point to an adjacent side of the square, the
lobes become nulls & the nulls become lobes. In essence, I have "rotated"
the pattern by moving the feed point.

There was a feller in north Denver a couple hundert years ago that
had a rotatable rhombic. He had a circular track in place for ore
carts -- he had four ore carts with telephones poles installed in
them (with concrete, or the somesuch.) This was *LONG* before
(affordable) digital electronics and I am unsure how he co-ordinated
and synchronised travel of all 4 ore carts.
I know for sure that he had a lot of acreage, _and_ a very
understanding wife...


73
Jonesy
--
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