I did exactly what you are describing several years ago. I thought I had
documented the design but, darned if I can find it right now. The antenna
was a full wave 80m delta loop cut for the low end of the band. I was
chasing 5BDXCC and CW was where I did most of my operating.
The loop was pretty much equilateral with the apex at the top of my HDX-572
tower. I make it fit, I tilted the loop out probably 10 to 15 degrees. I
used an Almond tree on one end and a 15' pole on the other end for support.
The base of the triangle was probably 12-15' above the ground. I fed the
loop 1.4 wave down from the Apex on the left side looking at the loop from
| / \ Not to scale but should
give you the picture. where X is the feed point;
| / \ The loop was actually
pretty much equilateral...diagram isn't.
| / \
FEED POINT ----- X| \
I used a length of 75 Ohm RG11 I think it was to match the loop and at
3.505 it shows about 50 ohms and 1.1:1 VSWR.
I used this antenna on both cW and phone with a tuner for 75m. it was not at
all optimum on 75, but it would radiate pretty well. On CW this antenna was
an absolute killer and with my Henry 2K-3 I didn't wait in line too long in
pile ups. This feed point will give you vertical polorization so it isn't
the best receiving antenna in noisy conditions and I often used my 2 el 40m
Yagi to listen to weak signals with pretty good success.
Getting one of these loops up and tuned takes some effort, I think I had to
whittle on the length 3 or 4 times but once you have it up and singing, you
will not regret the effort. Mine, unfortunatly came down in a wind storm
just a couple of years ago and I have never put it back up. It helped me
get that 5BDXCC which was the mission. The full wave loop is a real killer
if you can keep it up.
I'm sure with a litle research you can find the formula for the RG-11
matching stub. From memory it was in the neighborhood of 20 something feet
and I think the design was from one of the ON4UN articles. Good luck, you
will love the loop on 80m!
"Politicians are like diapers...they both need changing often and for the
same reason" Mark Twain.
Date: Wed, 3 Feb 2010 14:28:06 -0600
From: Stuart Browne <firstname.lastname@example.org>
Subject: [TowerTalk] Feeding a Delta Loop
Content-Type: text/plain; charset=ISO-8859-1
I'm looking at installing a Delta Loop for 80 m. on my 75' tower. The low
end of the triangle will be about 20' off the ground ( the tower is on my
rooftop (flat). I know that the conventional wisdom is a feed point in the
center of the lower side of the equilateral triangle which is around 50
ohms. ON4UN describes feeding a DL at 1/4 wl from the Apex of the triangle
to achieve a 23 deg take off angle (which is what I'm after).
I'm looking for any "real world" feedback as to the pros/cons of feeding a
DL at the apex, lower center, corner or 1/4wl from the apex.
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