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Re: VLF power transmission



"Gigantic VLF transmitters because antenna efficiency (on both ends of
the
link) is low, not because path loss is high. Actually the path loss is
pretty low for such systems (compared to shortwave at 10 MHz).  At 15
kHz,
the wavelength is 20 km, so it's not like you can string up a half wave
dipole in the trees. And, because the antenna is close to the ground (in
terms of wavelengths) the ground losses in the antenna are significant.
In
fact, there isn't any advantage in having the antenna above the ground
when
your max height is a small fraction of a wavelength, so you might as
well
bury it, which they do."

1. The efficiency of typical VLF antennas (power radiated divided by
power supplied to the loading coil) can run as high as 50% in a
well-designed system with adequate ground plane.

2. Last statement is incorrect.  The only part of the antenna that DOES
radiate is the vertical lead (or leads).  The top wires just provide
capacitive loading to get more current into the vertical part.  These
systems use very elaborate "counterpoises" (conductors resting on top of
the ground or buried just deeply enough to be out of the way) to
minimize ground losses.  As for burying antennas in the ground, that is
for an entirely different (and VERY inefficient) type of ELF antenna."

SUGGESTED READING

	"VLF RADIO ENGINEERING" by Watt.

Ed



<<<< This thread on VLF antennas is getting off the subject of Tesla coils.
- Terry >>>>