On Jan 1, 11:21*am, wrote:
I haven't really given this much thought, but seems to me the
low angle radiation that does reach the ionosphere and would
be useful for very long ranges would be considered the lower angles
of the space wave, and would be separate from the ground or surface
wave...

I totally agree. That is the point I have been trying to make:
radiation from low elevation angles is not attenuated virtually to
zero before it reaches the ionosphere.

RF

Richard Fry wrote:
On Jan 1, 11:21 am, wrote:
I haven't really given this much thought, but seems to me the
low angle radiation that does reach the ionosphere and would
be useful for very long ranges would be considered the lower angles
of the space wave, and would be separate from the ground or surface
wave...

I totally agree. That is the point I have been trying to make:
radiation from low elevation angles is not attenuated virtually to
zero before it reaches the ionosphere.

RF

I'm completely confused about the point you were trying to make. You
called NEC results "misleading" when showing only "far field" (sky wave,
without surface wave) results, and implied that the surface wave must be
considered when determining skip performance. Are you now agreeing that
it correctly shows the amount of radiation at low angles which is
capable of reaching the ionosphere? If so, what's misleading about it?
Or are you saying that the field strength capable of reaching the
ionosphere at low angles is greater than NEC "far field" (sky wave)
analysis reports? And if so, how much greater and why?

Roy Lewallen, W7EL

wrote:
On Jan 1, 9:28 am, Richard Fry wrote:

Again, I do not, and never have considered the surface wave to be
important in skywave communications. The reason I referred to it was
to show that if it exists with substantial relative field close to the
radiator, then so does substantial radiation exist there at low
elevation angles, and which can serve the most distance ranges using a
single reflection from the ionosphere.

RF

I haven't really given this much thought, but seems to me the
low angle radiation that does reach the ionosphere and would
be useful for very long ranges would be considered the lower angles
of the space wave, and would be separate from the ground or surface
wave, whichever you would want to call it.. I tend to use "ground
wave",
but I've always considered it separate from the "space wave" as
I call it..
As a difference between the two, the ground wave would follow the
curvature of the earth, but the lowest angles of the space wave would
not. They would continue at the original angle, which naturally would
lead them to the ionosphere eventually. At low angles too if
measured from the transmitter location.
Anyway, seems to me almost all radiation that strikes the
ionosphere at low angles would be from the space wave, not the
ground wave.
I dunno if this makes any sense or is totally correct.. MPG will
vary..

Yes, that's correct. And NEC (and EZNEC) correctly show this low angle
sky wave radiation in their "far field" (sky wave only) analysis. The
surface wave isn't of much interest to anyone except AM broadcasters,
except perhaps some amateurs interested in local (a few tens of miles)
ground wave communication on 160 meters.

Roy Lewallen, W7EL

On Jan 1, 3:46*pm, Roy Lewallen wrote:

I'm completely confused about the point you were trying to make.
You called NEC results "misleading" when showing only "far field"
(sky wave, without surface wave) results, and implied that the
surface wave must be considered when determining skip per-
formance.

No, I did not write that the surface wave must be considered when
determining skywave performance. Your understanding of what I posted
is incorrect. Please re-read what I posted previously, and quote us
any of my text that you believe supports your present conclusion about
this.

Do you reject the data in the Terman and Laport plots I linked to
showing that the most distant, single-hop skywave coverage over a
real, curved earth originates from space wave radiation at very low
elevation angles (less than 5 degrees above the horizontal plane at
the transmit antenna site)?

Are you now agreeing that it (far-field NEC) correctly shows the
amount of radiation at low angles which is capable of reaching
the ionosphere?

Absolutely not, and I am rather surprised that, apparently,
you believe and support this concept.

RF

On Dec 31 2008, 4:10*pm, Roy Lewallen wrote:
dBi is more than just dB. It's field strength (in dB) relative to a
known standard.

Roy, certainly you must recognize that the term dBi is not a direct
unit, or measure of field intensity (field strength). The direct,
primary unit of measure of field intensity in accurate, common use is
volts/meter (V/m).

The term dBi is only a measure of the relative gain of a particular
radiator in particular directions stated in decibels with respect to
an isotropic radiator.

Other things equal, the field intensity at a given location is
determined by the gain of a transmit antenna system along paths
serving that location ALONG WITH the matched, r-f power applied to the
feedpoint of that antenna.

The gain of a transmit antenna system in dBi includes nothing about
the absolute amount of power it radiates in various directions.
Therefore by itself, antenna gain(s) in dBi cannot define the absolute
field intensity in standard units/sub-units of V/m that such an
antenna can produce at a given location.

Ergo "dBi" is not a measure of absolute field intensity (field
strength).

RF