Bill, W4ZV wrote:
"Earl, I used a Delta from my first NC location for 1 year and then from
my current NC location for 1.5 years. The "best" configuration is a
slightly "squashed" format, with the base longer. The antenna should be
fed at 1/4 wave down from the apex with a 1/4 wave matching stub of 75
ohm coax. This "squashed" format only requires about a 120 ft support
and actually gives improved gain over an equilateral delta. "
======================
EZNEC agrees with that, Bill. Here's the comparison of an equal-sided
delta loop and a "squashed" delta loop. Both are resonant at 1.830 mHz
and are supported by non-metallic masts with their bottom wires 8' above
"good" ground:
Equilateral triangle delta loop:
Each side = 181.6 feet
Total #12 gauge wire length = 544.8 feet
Required support height = 165' 6"
Feedpoint = 45.4' up from either corner (vertical polarization)
Feedpoint resistance = 208 ohms
Gain = 1.80 dBI @ 21.0 degrees
"Squashed" delta loop:
Bottom wire = 230 feet
Side wires = 160.5 feet each
Total #12 gauge wire length = 551 feet
Required support height = 120'
Feedpoint = 40.125' up from either corner (vertical polarization)
Feedpoint resistance = 106 ohms
Gain = 1.9 dBi @ 22.8 degrees
=======================
Bill also said:
You can also install this ("squashed") loop on a 90 foot tower by pulling
the base away from the tower. In fact, this further improves the gain in
the direction the base is moved. I believe this is what W3BGN is using
which works very well. By opening the apex AND pulling the base 30 ft
away to the NE from my 180 ft tower, I theoretically should have had
around 2.5 dB gain over a vertical.
========================
I'll model these other configurations when I find time and post the
results, if you wish.
73, de Earl, K6SE
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