On 3/7/2015 6:13 AM, Spike wrote:
On 07/03/15 09:34, Jeff wrote:

Since a vertical aerial that I described initially emits all three of
these waves, I was interested in the relative amounts of the RF power
supplied to the antenna that goes into each. For example, does the sky
wave component take 90% of the power, leaving 10% for the space and
surface waves? What phenomena control this?

You are missing the point Spike, the antenna has no knowledge of how the
power that it radiates will propagate. It all depends on how much power
leaves the antenna at what angle, and what angle the antenna is
positioned relative to ground.

All the antenna has is a polar response of how much power is radiated at
what angle. It is that angle and the way the atmosphere reacts at any
particular time that controls the propagation of waves. This can vary
with time of day etc.

What controls the polar diagram is the physical dimensions of the
antenna, the height above ground, the conductivity of the ground, the
proximity of other objects, and other factors.

Thanks for the comments, Jeff. Perhaps I'm not being clear enough.

Look at the issue this way.... While it's clear that the totality of the
e/m emissions from from the antenna depend on factors such as length,
height, and ground, (and I originally assumed a particular set-up in the
OP) there are three distinct methods by which such a transmission can be
received: the sky wave path to a distant receiver, a space wave to a
line-of-sight receiver (that could easily be outside the surface wave
range) and the surface wave to a receiver tucked into the far side of a
hill with no sky wave or space wave path. It can be expected that
increasing the transmit power will increase the received signal at all
three locations, but the question I'd like to see answered is: what
proportion of the power supplied to the antenna goes to each of these
three phenomena, which all arise every time the transmitter is keyed.
They might all be connected by the conditions you mention, I'm not
suggesting they aren't, but for the set-up I originally described, what
are the proportions of the power supplied to the antenna that contribute
to each?

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?

The case I'm particularly interested in is the short-rod vertical not
connected to ground, in the MF/low-HF bands, as might be found in a /M
set-up.

What you are not grasping is that these "modes" of transmission have
*nothing* to do with the antenna really. As others have said, the
antenna only transmits different signal strengths in different
directions. How much power sent in a given direction is only loosely
connected to how much power ends up in these different reception modes
if at all.

The real issue is what do you expect to do with these numbers if you
have them? I expect that any equations you find for received signal
strength will already factor in these relative values giving a received
signal strength as a function of *total* power radiated from the antenna.

Are you trying to compare the effectiveness of different antenna for
different receiving modes?

--

Rick