Topband: Grounded Half Loop Antennas for 160...

[David Sinclair]

Ed Swynar wrote:

> Hello All, I recently developed an infatuation of sorts for the
> grounded half loop antenna, & ended-up putting TWO of them in
> the air---one oriented north-south (like an inverted "V"), the
> other east-west (like an inverted "U")...
 >
> I'm curious as to the experiences of others who may now be using,
> or have used in the past, anything similar on Top Band, be it for
> DX, close-in QSOs, whatever...
> 
> BTW, they are GREAT harmonically-operated antennas!
> 
> ~73~ Eddy VE3CUI - VE3XZ
>
Hi, Eddy-
I had some good success with "U" antennas.
At one time, I had two 80 meter half squares set up perpendicular
to one another. The horizontal wire in one ran NNE/SSW and the other
ran WNW/ESE. They were very close, i.e. the vertical wires at one end
came down within 5 feet of each other. Note that the vertical wires
at the far ends were NOT grounded! I tried voltage-feeding one end
of the NNE/SSW "U" on 160 meters using a resonant L/C with link coup-
ling. That antenna worked great into Europe from MD on the US east
coast. It compared very favorably to my full wave, vertically-fed
loop on my 120ft tower. I usually could not see any difference
on signals from EU. Occasionally, the full size loop was up to 1
S-unit better. This was all quite a surprise. BTW the horizontal
wires in both 80 half squares had considerable sag, probably being
about 70ft at each end and only about 35-40ft in the middle.

For comparison's sake, visualize my full size loop as follows:
imagine my property is perfectly square, and I erect a full wave
horizontal loop around my perimeter at about 15ft average height
over ground. Imagine my 120ft tower perfectly centered in the
middle of the square, so that any diagonal line you draw from
opposite corners cuts through the center of my tower. Now fold
the loop along a diagonal line and rotate half of the loop, a
triangle shape, up 90 degrees to vertical. That is what I had,
and it performed very well on top band. I managed to work S9SS
using that loop despite his very high interference (QRN) level.
I fed that loop slightly up one of the sloping vertical sides,
a quarter wave down from the apex (vertical polarization).

If you draw an 80 half square and label the current directions
in each half wave of wire, you see how the vertical wires are
in phase and are additive. The horizontal wire has currents in
opposing phases which should cancel. But if you draw the same
half square and label it for current on 160m, you see the current
should all be in phase over the entire length of the wire. This
implies that the currents should be in opposing phases in the
vertical wires and should cancel, and the current in the hori-
zontal section is all in phase, so that wire should radiate.
The center wire slopes considerably, however. On paper, it looks
like it should not be a very good antenna on top band, but I found
it was very good indeed. Of course, I may have had quite a lot of
interaction between my full size loop and these two 80m half
squares. Who knows how this mess would model!  73, David K3KY