On 07/03/15 15:57, Ralph Mowery wrote:
"Spike" wrote

Or, to put it in yet another way...There might only be one 'wave' launched
from the set-up, that propagates in three different 'modes' (for the want
of a better word); so what controls the relative power/energy with which
each 'mode' is propagated?

You have to get it in your head there is not 3 differant waves launched from
the antenna. There is only one wave. As it leaves the antenna, whatever
the wave hits determins if it is ground, sky or whatever. The patern of the
antenna determins how much goes where.

With some antennas the patern is such much of it goes out to the horizon and
not much up in the air. Others radiate much to the vertical and not much
toward the horizon.

Think of it as throwing a rock into the middle a small pond. If there is
noting in the pond, the wave will go out toward the edges equally. If that
same rockis thrown in near the edge of the pond, some of the ripples will n
hit th eedge of the pond near the rock first while it will take some time
for the ripples to hit the other side.
You have the same origional wave, but its propogation is modified as to
where it is at . You do not have seperate waves leaving the rock.

Thanks for the explanation and illustration.

Amateur (and professional) literature abounds with terms like sky wave,
space wave, and surface wave. There are sky wave radars, space wave
radars, and surface wave radars, for example. It isn't unreasonable to
use these as descriptors of what I was trying to find out. This was, to
recap, the relative proportions of the RF power delivered to the aerial
for each of these (whatever one wants to call them), for a typical /M
(mobile) set-up on the MF and low HF bands operating over ground of
average conductivity, a near everyday occurrence in the Amateur
community. The mechanism for the single wave that's transmitted
resulting in (whatever one wants to call them) isn't really of interest,
but the relative proportions that wind up in (whatever one wants to
call them) are.

In terms of your analogy, the rock being thrown into the pool close to
one edge of the pond is the equivalent of the short rod /M aerial
operating close to the ground, mounted on the vehicle. I can imagine
that if the edge of the pond is a gentle sandy slope, the reflected
waves will be different in nature that if the edge of the pond is a
vertical rock. However, this is merely reflecting the different ground
conductivities that might be experienced in the real-life Amateur
situation: some energy will go skywards to a distant receiver, some will
travel through air to a line-of-sight receiver, and some will go to a
receiver in the shadow of a hill that cannot receive either of the other
two (whatever one wants to call them).

--
Spike

"Hard cases, it has frequently been observed, are apt to introduce bad
law". Judge Rolfe