On Sun, 01 Oct 2006 20:36:23 -0700, Roy Lewallen
wrote:

To get the numbers I came up with, all you need is the equation for the
radiation resistance of a small loop and the resistance of copper wire.
It shouldn't be hard to find the equation for the small loop, and it's
very simple. At those frequencies, the resistance of the wire should be
nearly the same as the DC resistance, so all you need is a copper wire
table(*). Both should be readily available on the web.

Small magnetic loops with gains in -30 ..-60 dB range can be usable
for receiving due to the extreme noise levels on LF and VLF, but for
transmitting, they are far to lossy.

To get any significant communication distance, you would need a
vertical polarised signal. The popular antenna among 135 kHz
experimenters as well as in LF aeronautical beacons is a vertical
tower with as much top capacitance as you can put up.

Look at the antenna systems of old ships using the LF band, these have
multiple parallel wires erected between the masts in the bow and
stern. These wires form the top capacitance and a vertical wire going
directly from it isolator on the radio room to the top wires, which is
the actual vertical radiator. The top loading will increase the
current in the vertical conductor and hence vertical radiation.

Paul