Jim,
Here is a little hard data which may be of some use. The antenna still
exists in somewhat distorted form due to an ice storm last winter.
Conductor height: 23 Meters
Horizontal length: 51 Meters
Perimeter approx. 147 Meters
Conductor: Single 5.7 mm dia. stranded copper, plus plastic insulation.
Lower conductor clearance above ground: 3 Meters, average.
The ground here is made up of glacial droppings -- lots of rocks and
boulders, with gravel and sand. Typical conductivity would be 1 mS/M.
RF bridge measured impedances at 137 kHz showed a fairly constant +j213
Ohms reactance over a wide temperature range. Resistance varied from 1.7
Ohms in winter to 2.05 Ohms in summer, representing a temperature range
from -4C to 23C.
The impedances at 508 kHz were considerably higher, with about +j1100
Ohms reactance year-round, and a winter to summer resistance range of 52
to 62 Ohms. The perimeter of the loop is close to a quarter wave at this
frequency, and the feed point is near the center of the baseline, if
that's of any help.
At 137 kHz, a number of far-field (>5 km) measurements in the pattern
maxima showed about 1 watt ERP (not EIRP) for 400 watts into the
antenna. No measurements were taken at 500 kHz, and the unfortunate
events of last winter would prevent any direct comparison.
Hope this might be of some help in the discussion.
John, W1TAG
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