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[TenTec] 30 meter loop antenna

To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Subject: [TenTec] 30 meter loop antenna
From: "Carl Moreschi" <n4py@arrl.net>
Reply-to: Carl Moreschi <n4py@arrl.net>,Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Sat, 2 Feb 2008 21:27:01 -0500
List-post: <mailto:tentec@contesting.com>
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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