Topband: 2-element loop antenna for 160m

[Steve Ireland]

At 05:33 PM 6/08/2003 -0700, you wrote:
W4EDS wrote
> 
>Has anyone ever done analysis on a full wave or larger loop with two
wires; electrically tuning one of the wires either higher or lower to
create a 2 element antenna that might possibly have a lower angle of
radiation and maybe some gain? I can get to a height of around 80 feet but
that is too low for 160.
> 

VK6VZ replied:

G'day all

For the last two months I have been trialling a fixed 2-element delta loop
array for 160m (roughly three-quarters of a wavelength in circumference,
fed as a vertical array and using about a quarter wave of linear loading in
the base section of each element, in the voltage sections). 

In its cardioid configuration (driving one element, with the other tuned as
a reflector) this antenna shows gain and front-to-back over a single
element, with a couple of 'S' units f/b on VK6HD's signals and 20dB-plus
f/b on DX.  Most of my noise here comes from the south and when I beam
north (towards Europe/North America) I can hear signals at Q5 that are lost
in the noise on the single element configuration.  Each element slopes at
about 30 degrees, off the top of a 90' mast and away from the base.

The antenna shows a 'Z' of 80 to 90 ohms on my Autek RF-1 and each element
is fed with a half wave of coaxial line, made up of a quarter wave of 75
ohm followed by a quarter wave of 50 ohm.  This goes to a switching/phasing
unit, which places a series-tuned LC network in the designated reflector
element. 

A couple of days ago I was listening just below 1824KHz and could hear
JA3KZR at 449, with heavy QSB, with the antenna beaming at him.  On the
single element and figure-8 patterns (and off the back of the beam)
JA3KZR's signals were completely inaudible - not even a trace of his
signals could be heard.

It is the most fun 160m antenna I have ever had - and I suspect when the
conditions improve, probably the most effective.  The next step is to build
a simple relay switching unit to feed the designated driven element as a
horizontally polarised one - i.e. to switch the antenna between horizontal
and vertical polarisation.

I should add that the antenna has an eighth-wave radius ground screen under
most of it.

Jim K1PX has done some EZNEC modelling on the antenna and while its pattern
isn't ideal, this shows the addition of the other element drops the
radiation angle and gives some front-to-back (although not as much as I
actually 
seem to experience, in practice).

Incidentally, my family and I have all got influenza, so would appreciate
if any questions were kept to a minimum right now - this e-mail took a lot
of time and effort to write.  Thanks, gang.

Vy 73

Steve, VK6VZ