Low-angle Elevation Gain of a 1/4-wave Vertical Monopole
 

On Nov 30, 6:27*pm, Richard Clark wrote:
However, resourcing the top engineers of the AM field for their
observations of sky-wave and ground-wave field strengths (a typical
service application) where they combine destructively (the "fading
wall"); at a distance of 70 miles, for 50% of the time, both signals
are equal (with propagation variations of phase accounting for
fading).
__________

With more research you'll find that the fading zone is not located a
fixed 70 miles away from every AM station.

The fading zone occurs wherever the skywave and groundwave are
approximately equal, and that varies with frequency, the elevation
pattern of the monopole, the conductivity of the groundwave path, and
the altitude of the ionosphere.

Most Class A (50 kW, non-directional day & night) AM broadcast
stations use a monopole of about 195 degrees in height, as this
extends the groundwave coverage radius over that of a 90 degree
monopole without generating a substantial high-angle lobe to interfere
with the groundwave where it otherwise would have a useful value.

Where substantial skywave signals are present from a ~195 degree
radiator, the groundwave already has been attenuated by propagation
loss to a low and nearly unusable value. This increases the distance
to the fading zone, and reduces its width.

This, too, is from the research of RCA's George Brown of BL&E fame, as
a result of his investigation and correction in 1935 of a serious
amount of nighttime fading from a ~225 degree monopole used by 50 kW
WCAU in Philadelphia.

RF

Low-angle Elevation Gain of a 1/4-wave Vertical Monopole
 

Earlier I wrote:
I'm not considering that the ground wave signal _provides_ any of that
low-angle DX coverage. It is the direct radiation existing in the
radiation pattern of the monopole at low elevation angles that can do
so.

.... and as a postscript --

Even though in most cases amateurs don't care about the ground wave
from a vertical monopole, a lesson can be taken from the broadcast
community in that maximizing the radiation from a monopole at angles
less than ten degrees will maximize the distance to the single-hop
coverage radius (other things equal).

This can be done by using a vertical monopole greater than 1/4-wave in
electrical height. A 5/8-wave vertical provides the highest gain in
that elevation sector.

RF

Low-angle Elevation Gain of a 1/4-wave Vertical Monopole
 

On Mon, 1 Dec 2008 03:28:23 -0800 (PST), Richard Fry
wrote:

Radiation from the monopole from zero to 10 degree elevation is not
"poorer by 12 dB" than that launched at 40 degrees. It is greater.

This is the suggestion of your own supplied graphic. I thought it
rather obtuse as a topic of introduction too.

The _reception_ of such radiation is a different matter, as the total,
skywave path length, and therefore the propagation losses are
different for those elevation sectors.

And yet you discount that as an NEC analysis, strange. All far-fields
are taken from the perspective of distance.

73's
Richard Clark, KB7QHC

Low-angle Elevation Gain of a 1/4-wave Vertical Monopole
 

On Mon, 1 Dec 2008 04:09:34 -0800 (PST), Richard Fry
wrote:

On Nov 30, 6:27*pm, Richard Clark wrote:
However, resourcing the top engineers of the AM field for their
observations of sky-wave and ground-wave field strengths (a typical
service application) where they combine destructively (the "fading
wall"); at a distance of 70 miles, for 50% of the time, both signals
are equal (with propagation variations of phase accounting for
fading).
__________

With more research you'll find that the fading zone is not located a
fixed 70 miles away from every AM station.

Laport is authority enough for an instance for me. His data drawn
from field experience supports my model employing your reference which
responds to your complaint:
NEC far-field analysis this would seem impossible,
due to the greatly reduced fields in this sector
a statement that lacks quantifiables, and against which Laport's
example and my model only vary by 0.7 dB.

As I have asked in the past, what are your expectations for the
accuracy you expect? If it is tighter than 1dB (something exceedingly
difficult to accurately measure in the field for an absolute), then
that has been demonstrated. If it is tighter than that, your
expectations exceed the capacity of the equipment of that era that
established the FCC groundwave charts.

73's
Richard Clark, KB7QHC

Low-angle Elevation Gain of a 1/4-wave Vertical Monopole
 

On Dec 1, 10:11*am, Richard Clark wrote:
On Mon, 1 Dec 2008 03:28:23 -0800 (PST), Richard Fry
The _reception_ of such radiation is a different matter, as the total,
skywave path length, and therefore the propagation losses are
different for those elevation sectors.

And yet you discount that as an NEC analysis, strange. *All far-fields
are taken from the perspective of distance.
____________

Far-field NEC analysis does not consider propagation loss for a
skywave and its reflection from the ionosphere.

Terman's Fig 55 does that, as well as to include earth curvature in
such loss figures.

//

Low-angle Elevation Gain of a 1/4-wave Vertical Monopole
 

On Dec 1, 10:21*am, Richard Clark wrote:
As I have asked in the past, what are your expectations for the
accuracy you expect? *If it is tighter than 1dB (something exceedingly
difficult to accurately measure in the field for an absolute), then
that has been demonstrated.
_________

If you can truly get within 1 dB of the FCC curves with your NEC model
in the AM broadcast band then that's good enough for me. Probably not
good enough for the FCC, though.

RF

Low-angle Elevation Gain of a 1/4-wave Vertical Monopole
 

On Dec 1, 10:21*am, Richard Clark wrote:
On Mon, 1 Dec 2008 04:09:34 -0800 (PST), Richard Fry
With more research you'll find that the fading zone is not located a
fixed 70 miles away from every AM station.

Laport is authority enough for an instance for me. *His data drawn
from field experience supports my model...
_______

And supporting my statement about the location of the fade zone not
being a fixed 70 miles from a monopole, note this quote starting at
the bottom of page 103 of that text applying to Laport's Fig 2.7 (your
cited authority):

"For a 190 degree radiator, the fields are not shown because it is
known immediately from the chart thus far computed that the signal
will be severely noise-limited before arriving at the distance where
fading is objectionable."

As Laport wrote his book Radio Antenna Engineering in 1952, he would
have been working from the advantage of the research and discoveries
of George Brown about this subject some 23 years earlier.

RF

Low-angle Elevation Gain of a 1/4-wave Vertical Monopole
 

On Mon, 1 Dec 2008 08:52:58 -0800 (PST), Richard Fry
wrote:

Far-field NEC analysis does not consider propagation loss for a
skywave and its reflection from the ionosphere.

Terman's Fig 55 does that, as well as to include earth curvature in
such loss figures.

And this is relative to what?

73's
Richard Clark, KB7QHC

Low-angle Elevation Gain of a 1/4-wave Vertical Monopole
 

On Mon, 1 Dec 2008 09:45:28 -0800 (PST), Richard Fry
wrote:

And supporting my statement about the location of the fade zone not
being a fixed 70 miles from a monopole, note this quote starting at
the bottom of page 103 of that text applying to Laport's Fig 2.7 (your
cited authority):

Laport says much more than that about the fading wall. It took only
his one instance to correlate his chart to your chart and to my model
to give me pause to wonder what you are griping about when you
complain:
...NEC far-field analysis this would seem impossible,
due to the greatly reduced fields in this sector ....
a statement that lacks quantifiables. "Impossible" is
yellow-journalism fluff and the less than 1dB variations is within the
accumulation of field errors of the "possible" that went into
engineering reports. "Impossible" and "possible" are, to all intents
and purposes, describing the same thing.

What is it that is impossible? Or is this about seeming?

73's
Richard Clark, KB7QHC

Low-angle Elevation Gain of a 1/4-wave Vertical Monopole
 

On Dec 1, 12:25*pm, Richard Clark wrote:

And this is relative to what?

To my post saying:

On Mon, 1 Dec 2008 04:09:34 -0800 (PST), Richard Fry
With more research you'll find that the fading zone is not located a
fixed 70 miles away from every AM station.

followed by your post saying:

And yet you discount that as an NEC analysis, strange. All far-fields
are taken from the perspective of distance.

You're not following.

RF