On Thu, 8 Dec 2005 21:44:07 +0000 (UTC), "Reg Edwards"
wrote:

I have been informed my GRNDWAV3 program is in error - it calculates
the power input to a matched receiver to be 6dB greater than it ought
to be, or exactly 4 times the correct power input.

Most of my programs calculate results based on what I consider to be
fundamental reasoning. But GRNDWAV3 is one of the few where I have
adapted formulae from the text books or 'bibles'.

My informant is an Icelandic amateur who appears to know what he is
talking about and is mathematically very convincing. For various
resons, for the time being I propose to leave him out of this
discussion. That is, of course, if a discussion should evolve.

The problem fundamentally revolves around the gain of short vertical
antennas, both transmitting and receiving, above a perfect ground,
relative to isotropic. But for present purposes what an isotrope
actually is can be forgotten about. It exists only in one's
imagination.

Numbers cannot be avoided. So let's keep them as simple as possible by
starting with the MF standard of 1 Kilowatt, radiated from a short
vertical antenna above a perfect ground. Actual antenna height and
frequency don't matter.

According to the text books, the field strength from 1 Kw at 1
kilometre = 300 millivolts, which (according to the text books) is
correctly calculated by my program.

To calculate matched reciever input power from field strength it is
necessary to state vertical antenna height, frequency and radiation
resistance. Again choosing simple values -

An alternative is to calculate the power collected by a lossless,
matched receiver as Pr=S*A.

In this case, S=0.3**2/(120*pi)

Kraus derives A (the effective apperture) for a short dipole to be
3/8/pi*wavelength**2.

This gives the power collected by the receiver as 6.4mW. If the
antenna and receiver were disected by the ground plane, wouldn't there
be 3.2mW developed in each half of the receiver load?

Owen
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