I thought I would share with this group how I matched a 30 meter loop I
made
to use with my Omni VII and Orion.
I made a full wave delta loop for 10.1 mhz. I used 14 gauge wire and
erected the delta as an equilateral triangle with a flat side on top and
the
point of the triangle directly at the bottom. The triangle is 33 feet on
a
side for 10.1 mhz. I have the top side (33 feet) at 50 feet above the
ground and stretched between 2 trees. At the bottom point, which is 22
feet
above ground, I connected some very low loss 75 ohm cable I had. I made
a
tight coil of 18 feet of this cable ( 6 inch diameter) at the feed point
to
act as a current balun to stop radiation from the feedline. Now full wave
loops are 100 ohm antennas at this feedpoint. The normal way to match
them
is to run a quarter wave of 75 coax and then switch to 50 ohm cable. The
quarter wave of coax will convert a 100 ohm impenace to 50 ohms. But I
had
a huge amount of this low loss 75 ohm cable so I decided I could run the
entire length I needed (150 feet) in all 75 ohm cable. As long as the
total
length of cable is an odd multiple of quarter waves, it will still match
50
ohms. So I used 150 feet to get to my antenna switch box and then I added
an additional half wavelength of cable (40 feet). I then used an MFJ
antenna analyzer and began shortening the cable length 1 foot at a time
until I found the 50 ohm point. I ended up cutting back 18 feet of cable
to
get to this point. So now I have my 30 meter loop with a 1.0 SWR and no
splice points at all along the entire cable. I am finding this loop is
performing very well. I have been comparing it with my 130 foot inverted
L.
My inverted L favors north-south and my new loop favors east-west, so the
2
antennas give me excellent all around coverage.
Carl Moreschi N4PY
121 Little Bell Drive
Bell Mountain
Hays, NC 28635
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