Hi Steve,
Your description of the TLDL intrigued me and I couldn't keep from
modeling it, hi.
I modeled it as an equal-sided triangle 132' on each side. To keep the
bottom wire 10' high, the apex is at 114.3'.
For top loading, it required two horizontal 82.175' wires attached at the
apex and run perpendicular to the plane of the loop.
I did all modeling at 1.830 mHz with the feedpoint in the center of
either side of the loop (which looks like it's very close to the best
place for minimun horizontal polarization). The feedpoint Z of this
antenna is about 187 ohms (zero reactance at 1.830 mHz).
I then ran the top-loading wires so that they were in the same plane as
the loop. To maintain resonance at 1.830 mHz, the wires had to be
slightly longer (84' each). The feedpoint Z was about the same as the
first model. Both antennas have an almost circular radiation pattern,
with a front-to-side ratio of about 1 dB.
I then sloped the top-loading wires downward (so they maintained a
30-degree angle with the 114.3' vertical support) and perpendicular to
the plane of the loop. To maintain resonance at 1.830 mHz, the wires
each had to be 93.3' long. (At the 30-degree angle, the bottoms of the
wires are 33.5' high and spaced 46.65' from the support.)
This antenna looked every bit as good as the models with the horizontal
top-loading. The pattern was slightly more oval, with a front-to-side
ratio of about 2 dB. The big surprise was that the feedpoint Z dropped
to about 66 ohms, which would allow it to be easily fed with 50- or
75-ohm coax.
Because it doesn't need a ground radial system makes this an appealing
low-angle vertically polarized antenna (max radiation is at about 23
degrees over "good" soil), but it requires a pretty tall support.
All of my modeling was done using a non-metallic support mast, by the
way. A metallic tower used as a support will, no doubt, have an effect
on the antenna dimensions and radiation pattern.
73, de Earl, K6SE
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