wrote in message
...
On Sat, 20 Jun 2009 21:13:51 GMT, "Dave" wrote:


what you are missing is the 'real world'. eznec is probably modeling over
a
perfectly flat infinite surface. In the far field in a perfect world the
signal along the surface is a combination of ground wave and sky wave, the
ground wave decays rapidly with distance leaving the sky wave which will
always be very small along the surface. now remember, the frame of
reference is at ground level, not the antenna height, so zero degrees is
along the infinite flat surface. And there is nothing in there that
models
where the other antenna is... it just creates a picture of how the
strength
of the fields are at a given elevation/azimuth angle from the reference
point.

Dave,
Your paragraph above helped. For VHF and above, in the real world, am
I better off using EZNEC's "free space" setting instead of real
ground? I know at HF frequencies, where antennas are often close to
the ground, it makes a big difference, but could free space be a
better approximation of VHF antenna many wavelengths off the ground?

Pat

yes, it will probably be a better approximation, especially if the two
antennas are in sight of each other. the ground effect is mostly
appropriate for hf and at very long distance. vhf has many other effects
that cause reflections and ducting that kind of over ride the ground image
model that most modeling programs use.