The gain at low elevation angles is low only if you're distant from the
antenna, and ground reflection is taking place -- EZNEC's far field
analysis assumptions don't apply to a typical antenna measurement setup.
Low far field gain at low angles is due to interference between the
direct radiation and radiation reflected from the ground. This can and
does occur when measuring antennas which are relatively close, but not
to the extent you see in idealized far field modeling results, where the
antennas are effectively an infinite distance apart. I don't have a
great deal of real experience in measuring antennas, but believe that
the common practice is to try to put the antennas high and relatively
close together. It shouldn't be difficult to get a pretty good idea of
the amount of signal cancellation you'd get for a given height and
spacing, by setting up and solving a pretty simple geometry/trigonometry
problem. Or you could model the two antennas over ground at their
proposed positions, with a source in the transmitting antenna and a
matched load in the receiving antenna, and look at the power delivered
to a load as the height and spacing are changed.

Fortunately, dipoles and moderate size Yagis have similar elevation
patterns for at least moderate angles relative to straight-on. That
means that the percentage of signal directed toward the ground and
therefore arriving at the receive antenna as a reflection will be about
the same for a reference dipole as for a test Yagi. So whatever
attenuation occurs, it should be about the same for the two antennas.
This wouldn't hold, though, for a very long Yagi or for high-angle
reflections from antennas which are high and close together. It's one of
the factors that make really good antenna measurements tricky.

Roy Lewallen, W7EL


Tarmo Tammaru wrote:
"Roy Lewallen" wrote in message
...

There are a lot of factors that can potentially ...............


Roy,

Does one have to worry about elevation? Generally the gain at 0 degrees
elevation is very low. Does this apply when the two antennas are facing each
other in plain line of sight? should he raise the transmit antenna to say,
15 degrees above the receiving antennas?

Tam/WB2TT