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

The link below leads to a discussion of this subject.

It is a rather long thread, but it might be of interest to members
of this NG.

W8JI's position on this subject was a bit of a surprise to me.

http://www.eham.net/forums/TowerTalk/15930?page=1

RF

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

"Richard Fry" wrote in message
...
The link below leads to a discussion of this subject.

It is a rather long thread, but it might be of interest to members
of this NG.

W8JI's position on this subject was a bit of a surprise to me.

http://www.eham.net/forums/TowerTalk/15930?page=1

RF

I think there's some confusion there about polarisation. VP requires lowest
height to achieve a peak at zero degrees elevation; HP requires a
frequency-specific height and low height usually results in an elevated
beam.

Chris

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

"christofire" wrote:
I think there's some confusion there about polarisation. VP requires
lowest height to achieve a peak at zero degrees elevation; HP requires a
frequency-specific height and low height usually results in an elevated
beam.
____________

But a v-pol monopole up to 5/8-wavelength in electrical height, and mounted
with its base near the earth _always_ launches its maximum relative field at
zero degrees elevation (the horizontal plane) -- regardless of the quality
of the r-f ground it uses, its operating frequency, or earth conductivity at
the antenna site.

Radiation launched at low elevation angles by such a monopole is
progressively less than in the horizontal plane. But its h-plane radiation
(especially), and its low-angle radiation as launched are nowhere nearly as
poor as shown in a NEC-2 analysis for these values over real earth -- which
is what leads to the erroneous conclusions of many people.

The reason for this is that a NEC-2 analysis over a "real" earth is based on
the field surviving at an infinite distance from the monopole, and over over
a flat earth, at that !

But if that was the true radiation envelope of the elevation pattern
actually launched by that monopole, then daytime AM broadcasting would be
impossible (reality check).

The real-world, h-plane field intensity measurements made in 1937 from such
v-pol monopoles at 3/10 of a mile over real earth of poor conductivity by
Brown, Lewis & Epstein of RCA showed peak fields that were within a few
percent of the theoretical maximum possible for monopole heights of about 45
through 90 degrees.

RF http://rfry.org

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

Oh gawd, I hate to get into these mud brawls BUT...
The regs were quoted a couple of messages back and it says - exerpted:
1. 50 watts ERP
2. And defines a dipole as shall be considered 0 dBd for the purposes
of this regulation in defining ERP (as opposed to the usual 6.14 dBi
over average ground)...

Now, typical of anything the feds define, it will be unintelligible...
It is clear to me that the intent was to define the dipole as having a
power gain of 1 (one) for the purposes of defining what constitutes 50
ERP when driven with 50 watts...

So, one might assume that it means that 50 watts into a dipole is
considered 50 ERP - but it does not say that,,, It says for regulatory
purposes that the power gain of a dipole is considered to be ZERO...

Which means - as I my math teacher proved - that 50 X 0 = 0 - per
the regulation...
Given that the regs define the output of a dipole on 60 meters to be 0
ERP you can run 50 watts into any antenna with a power gain of 50 OVER
A DIPOLE to meet the maximum allowed ERP... (which is why lawyers
make a living)

denny - k8do

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

The regs were quoted a couple of messages back and it says - exerpted:
1. 50 watts ERP
2. And defines a dipole as shall be considered 0 dBd for the purposes
of this regulation in defining ERP (as opposed to the usual 6.14 dBi
over average ground)...

Now, typical of anything the feds define, it will be unintelligible...
It is clear to me that the intent was to define the dipole as having a
power gain of 1 (one) for the purposes of defining what constitutes 50
ERP when driven with 50 watts...

So, one might assume that it means that 50 watts into a dipole is
considered 50 ERP - but it does not say that,,, It says for regulatory
purposes that the power gain of a dipole is considered to be ZERO...
Which means - as I my math teacher proved - that 50 X 0 = 0 - per
the regulation...

No it does not!!!

It says that the gain is zero *dB*, to convert from dB to a linear quantity,
which you can multiply, you must divide by 10 and then take the antilog.

So 0/10 = 0,
and antilog 0 = 1

So your sum is actually 50 X 1 = 50, not 50 X 0 = 0

It is much easier if you work in dB where you just have to add or subtract.
50W = 17dBW
so 17dBW plus a gain of 0dB = 17dBW

73
Jeff

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

Gee, Richard, it's only been seven months this time since you last
posted essentially the same comments and questions. You were going a
year or so between.

Here are a couple of the previous ones, with my responses. Anyone
interested in more information can do a google groups search of my
postings on this newsgroup containing "surface wave".

4-20-2008:

Richard Fry wrote:
"Roy Lewallen"
However, you can't compensate for this factor when the ground is
poor by improving the ground system. The reason is that the reflection
takes place much farther from the antenna than nearly any ground system
extends. And low angle radiation, where the improvement is most needed,
reflects the greatest distance away.
___________

Roy, didn't the experiments of Brown, Lewis & Epstein of RCA in ~1937
show that the h-plane field measured 3/10 mile from a vertical monopole
of about 60 to 88 degrees in height, over a set of 113 buried radials
each 0.41 WL, was within several percent of the theoretical maximum for
the applied power as radiated by a perfect monopole over a perfect
ground plane? And conductivity at the NJ test site was poor -- 4 mS/m
or less.

That tends to show that the fields radiated at very low elevation
angles also will be close to their theoretical values when measured at
this radial distance, even though ground conductivity at the antenna
site is poor. The relative field (E/Emax) for radiators of these
heights and propagation paths approximately equals the cosine of the
elevation angle.

I believe we've discussed this before, so I'll be brief.

Their calculation of the field at the receiving site when the radial
system is perfect was adjusted for the effect of ground wave attenuation
caused by the imperfect ground conductivity. If the ground between the
antenna and receiving site were perfect, the field strength would have
been greater.

Also, I'm speaking of sky wave. Ground reflection isn't a factor in
determining surface wave, which is what they measured and which isn't of
interest to most amateurs.

The greatest radiated fields always will be directed in or near the
horizontal plane when measured/calculated for such conditions. This
also will be true for any monopole from infinitesimal to 5/8 wavelength
in height, although the elevation pattern of monopoles from /4- to
5/8-WL no longer are described by the cosine function (see
http://i62.photobucket.com/albums/h8...omparison.jpg).

Elevation patterns show maximum relative field centered at various
elevation angles above the horizon, when those fields are measured at
progressively longer radial distances from the monopole, due to the
propagation loss for the surface wave over other than a perfect, flat,
infinite ground for those ranges. Earth curvature and terrain
diffraction add to those losses for longer surface wave paths over real
earth, and for very great distances the h-plane relative fields falls to
~zero.

As I thought you were aware, the surface wave propagates considerably
differently than the sky wave.

But that pattern shape is not the pattern shape originally radiated
by the monopole, it also includes the effects of the propagation
environment at the range where it was measured (or calculated).

If this were not true then MW broadcast stations would have
essentially zero coverage area for their groundwave signals.

It would be a mistake to design HF antenna systems based on optimizing
surface wave propagation as AM broadcasters do, unless you desire
communication for distances not exceeding a few miles.

Roy Lewallen, W7EL

4-22-2006:

Richard Fry wrote:
"Roy Lewallen" wrote:
The maximum far field (sky wave) gain of a ground mounted
quarter wave vertical over average ground, with a completely
lossless ground system, is on the order of 0 dBi, and this occurs at
roughly 25 degrees above the horizon (both depending on
frequency as well as ground characteristics).
_____________

The above is an understandable conclusion using NEC analysis, however
it is not supported empirically. If it was, AM broadcast stations would
perform very much differently than they do.

NEC analysis has been supported many times by measurement and observation.

The measured data in Brown, Lewis & Epstein's 1937 benchmark paper
"Ground Systems as a Factor in Antenna Efficiency" proved that the
*radiated* groundwave field from a vertical monopole working against 113
buried radials each 0.41 lambda in length was within a few percent of
its calculated peak value for a radiation pattern with maximum gain in
the horizontal plane. The path length for the measurement was 0.3 miles,
which was in the far field of the vertical monopole configurations measured.

Yes. The question is what is the calculated value. B, L, and E
normalized their measurements to the unattenuated field strength at one
mile for 1000 watts radiated power. I couldn't find anywhere in their
paper where they explained how they determined the ground attenuation
between the antenna and their observation point.

BL&E's measurements, and the results of thousands of measurements
made of the groundwave fields of MW broadcast stations using such radial
ground systems ever since demonstrate that their peak gain always lies
in the horizontal plane.

No, the field strength is strongest at low elevation angles only close
to the antenna, as you further explain below.

It is true that, as a groundwave propagation path becomes longer, the
field measured at increasing elevations above the earth at distant
ranges might be higher than measured at ground level at those ranges.
But that is not because more field was launched by the original radiator
toward those higher elevations -- it is because the the groundwave path
has higher losses, which accumulate as that path lengthens. Therefore a
NEC plot showing the conditions reported in the quote above do not
accurately depict the elevation pattern as it is launched from the
radiator, and the groundwave field it will generate.

Of course the standard far field analysis doesn't accurately depict the
field close to the antenna -- it's a plot of the field at points very
distant from the antenna, as clearly explained in the manual. NEC allows
you to include the surface wave if you want, and it accurately shows the
total field including the surface wave at a distance of your choice.
(Accurate, that is, up to a hundred km or so, beyond which the deviation
of the flat ground model from the curved Earth begins affecting results.)

Don't feel bad -- Reg has a lot of trouble understanding this, too.

There are software programs designed for calculating MW groundwave
field strength given the FCC "efficiency" of the radiator and the
conductivity of the path. The radiator efficiency is the groundwave
field developed by the radiator with a given applied power at a given
distance (1 kW @ 1 km). These values must meet a certain minimum level
for the class of station. I think in all cases, they must be within
~0.5 dB of the theoretical value for a radiation pattern with its peak
gain in the horizontal plane. In the case of directional MW antennas,
this performance must be proven by field measurements.

Finally, standard equations show a peak field of ~137.6 mV/m at 1
mile from a 1/2-wave dipole radiating 1 kW in free space. The
calculated groundwave field at 1 mile radiated by 1 kW from a 1/4-wave
vertical MW monopole over a perfect ground plane is ~195 mV/m. This is
the same field as generated by the free space 1/2-wave dipole, when all
radiation is confined to one hemisphere (137.6 x 1.414).

The groundwave fields measured from thousands of installed MW
broadcast antenna systems confirm that their intrinsic radiation
patterns are within a fraction of a decibel of that perfect radiator
over a perfect ground plane, no matter what is the conductivity at the
antenna site (N.B. Reg).

No, the measured fields from quarter wave broadcast antennas are
considerably less than 195 mV/m for 1 kW at one mile, unless perhaps
there's only salt water between the antenna and measurement point. As
you explained above, the surface wave is attenuated with distance. What
you seem to be missing is that the attenuation is strongly dependent on
ground conductivity (between antenna and measurement point, not just at
the antenna site) and frequency, so the actual field strength at one
mile for 1 kW radiated will always be considerably less than the perfect
ground case. The 195 mV/m and associated values for various antenna
heights is the "unattenuated" or "inverse" field, which doesn't include
the surface wave attenuation beyond simple inverse distance field
strength reduction. It's the field strength you'd get if the ground
between antenna and measurement point were perfect, not what you get
over real ground. I'm not very conversant with FCC antenna measurement
methodology, but somewhere the measured field strength is normalized to
the unattenuated field strength by fitting to a ground attenuation
curve, which in turn depends on frequency and ground conductivity. (I've
been told that this is the way broadcasters determine ground
conductivity -- by seeing how far the measured field strength deviates
from the unattenuated value.) I believe that the surface wave
attenuation curves used by the FCC are from the 1937 I.R.E. paper by
K.A. Norton. That paper is also the basis for NEC's surface wave
calculations.

Roy Lewallen, W7EL

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

"Roy Lewallen" wrote
Of course the standard far field analysis doesn't accurately depict the
field close to the antenna -- it's a plot of the field at points very
distant from the antenna, as clearly explained in the manual. NEC allows
you to include the surface wave if you want, and it accurately shows the
total field including the surface wave at a distance of your choice.
_________

Not the versions of NEC used by most amateurs.

Those versions show zero or very low gain in/near the horizontal plane
for a
vertical monopole over real earth. This leads to the common (mis)
belief
that those are the gains of the radiation pattern _originally
generated_
by the monopole.

But that belief is untrue.

RF

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

On Wed, 26 Nov 2008 03:39:41 -0800 (PST), Richard Fry
wrote:

"Roy Lewallen" wrote
Of course the standard far field analysis doesn't accurately depict the
field close to the antenna -- it's a plot of the field at points very
distant from the antenna, as clearly explained in the manual. NEC allows
you to include the surface wave if you want, and it accurately shows the
total field including the surface wave at a distance of your choice.
_________

Not the versions of NEC used by most amateurs.

Those versions show zero or very low gain in/near the horizontal plane
for a
vertical monopole over real earth. This leads to the common (mis)
belief
that those are the gains of the radiation pattern _originally
generated_
by the monopole.

But that belief is untrue.

RF

Roy and others have answered this one in the past too. You employ the
near field table to observe the ground wave. It works approximately
well, even out to the edge of the implicit flat universe. If you
object to flat universes, you are no longer in the realm of ground
wave. If anything, modelers give MORE response in comparison to the
BL&T data.

73's
Richard Clark, KB7QHC

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

Richard Fry wrote:
"Roy Lewallen" wrote
Of course the standard far field analysis doesn't accurately depict the
field close to the antenna -- it's a plot of the field at points very
distant from the antenna, as clearly explained in the manual. NEC allows
you to include the surface wave if you want, and it accurately shows the
total field including the surface wave at a distance of your choice.
_________

Not the versions of NEC used by most amateurs.

Those versions show zero or very low gain in/near the horizontal plane
for a
vertical monopole over real earth. This leads to the common (mis)
belief
that those are the gains of the radiation pattern _originally
generated_
by the monopole.

But that belief is untrue.

RF

I'm not aware of such a widely held misconception, but it is indeed untrue.

You must have conducted some sort of survey to find out what "version"
of NEC-2 is used by most amateurs, you know more than I do about it.
Although there are a few minor variations of NEC-2, there's not enough
difference to justify characterizing them as different "versions". And
every one I've seen has the capability of producing data which include
the surface wave. It's done with a simple entry on the RP "card".

A number of different compilations of NEC-2, every one of which as far
as I know which includes ground wave analysis, can be had at
http://www.si-list.net/swindex.html. You can also get the manual there,
where you can learn about how to get the ground wave data from it.
You're obviously much more interested in ground wave field strengths
than most amateurs, so I suggest that you download one of the free NEC-2
compilations, and the manual, and them for your investigations.
Remember, it's done with the RP "card".

Roy Lewallen, W7EL

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

Richard Clark wrote:

Roy and others have answered this one in the past too. You employ the
near field table to observe the ground wave. It works approximately
well, even out to the edge of the implicit flat universe. If you
object to flat universes, you are no longer in the realm of ground
wave. If anything, modelers give MORE response in comparison to the
BL&T data.

With EZNEC, you have to use the near field analysis to include the
ground wave; direct ground wave analysis isn't included in EZNEC because
it's of very limited use to most amateurs. In fact, it's really of
interest only to AM broadcasters and a very few other very small and
specialized users, who just about universally use EZNEC Pro which does
include direct ground wave analysis.

But anybody who's interested in direct ground wave analysis can also use
one of the other modeling programs which includes it, or use NEC-2
itself, available free from http://www.si-list.net/swindex.html. The
manual is available there also. NEC-2 produces field strength data
including the ground wave if requested with the proper entry on the RP
"card".

Roy Lewallen, W7EL

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

"Roy Lewallen" wrote
With EZNEC, you have to use the near field analysis to include
the ground wave; direct ground wave analysis isn't included in
EZNEC because (etc).
_________

After the comments of Richard Clark and you, Roy, I attempted to use
EZNEC to determine the ground wave (see link below).

The near-field analysis of EZNEC for radiation in the horizontal plane
at a point 1 km from a 1/4-wave monopole having two ohms in series
with a Mininec r-f ground, while radiating 1 kW over an earth
conductivity of 8 mS/m is shown as 72 mV/m.

The same setup when analyzed using the FCC's radiation efficiency for
this monopole height, and their propagation charts for these
conditions shows about 295 mV/m as the result, which value is
supported by the measured performance of real-world AM broadcast
stations, and is also a value in a range that could be expected from
the BL&E data.

Hopefully you or Richard Clark can tell me the reason(s) for this
difference, which could easily be my own setup of the NEC model.

Roy, would you mind posting the ground wave value EZNEC Pro reports
for these conditions?

http://i62.photobucket.com/albums/h8...FldExample.gif

RF

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

On Wed, 26 Nov 2008 11:41:04 -0800 (PST), Richard Fry
wrote:

Hopefully you or Richard Clark can tell me the reason(s) for this
difference, which could easily be my own setup of the NEC model.

I modeled their structures as they built them explicitly (they had
many variations), at the frequency they used, took readings at the
distance they reported. For your 1 kilometer distance (not one they
used), I get 303 mV/m at 3 MHz for their 70 foot radiator over a field
of 113 x 135 foot radials with an average ground conductivity. When I
use their distance of a mile, I get 188 mV/m, all else identical.
Their paper reports by formula that I should see 194.5 mV/m.

It would appear that with the average of the two distances, my model
accords quite closely to BL&E. That average would suggest results are
within an unreasonable accuracy given my experience with making RF
power determinations at the bench. However, my model is repeatable,
the paper is chiseled into the granite of history and your original
complaint seems to be moot.

73's
Richard Clark, KB7QHC

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

Earlier posts in this thread:

From: "Richard
Date: Wednesday, November 26, 2008 12:00 PM

Roy and others have answered this one in the past too. You employ the
near field table to observe the ground wave. It works approximately
well, even out to the edge of the implicit flat universe. If you
object to flat universes, you are no longer in the realm of ground
wave. If anything, modelers give MORE response in comparison to the
BL&T data.

Then I posted my result of using the near-field analysis of EZNEC
showing a value much LESS than the "modeler" value for those
conditions when using the BL&E data and the FCC curves.

Following that is posted:

From: "Richard Clark"
Date: Wednesday, November 26, 2008 3:32 PM

I modeled their structures as they built them explicitly (they had
many variations), at the frequency they used, took readings at the
distance they reported. For your 1 kilometer distance (not one they
used), I get 303 mV/m at 3 MHz for their 70 foot radiator over a field
of 113 x 135 foot radials with an average ground conductivity. When I
use their distance of a mile, I get 188 mV/m, all else identical.
Their paper reports by formula that I should see 194.5 mV/m. ...

No, the BL&E paper (accurately) stated that 194.5 mV/m is the
theoretical maximum field possible at 1 mile for 1 kW radiated by a
perfect 1/4-wave monopole over a perfect ground plane. The peak
values they measured came very close, but never quite achieved that
value.

It would appear that with the average of the two distances, my model
accords quite closely to BL&E.

Mr. Clark - kindly note that in your first quote above you say that,
if anything, "modelers" show MORE response than BL&E Then when
pressed a bit you say that your model "accords quite closely" with
BL&E.

Yet the results of my EZNEC near-field model showed considerably LESS
ground wave field at 1 km than either the FCC approach or the BL&E
data.

Clarifications, please?

RF

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

Richard Fry wrote:
. . .
No, the BL&E paper (accurately) stated that 194.5 mV/m is the
theoretical maximum field possible at 1 mile for 1 kW radiated by a
perfect 1/4-wave monopole over a perfect ground plane. The peak
values they measured came very close, but never quite achieved that
value.

Can you explain why they very nearly accomplished this perfect ground
value even though the ground wave signal had to propagate one mile over
ground of finite conductivity? What do you think would have happened to
the signal strength if the mile of intervening ground had been replaced
by a perfect ground?

It would appear that with the average of the two distances, my model
accords quite closely to BL&E.

Mr. Clark - kindly note that in your first quote above you say that,
if anything, "modelers" show MORE response than BL&E Then when
pressed a bit you say that your model "accords quite closely" with
BL&E.

Yet the results of my EZNEC near-field model showed considerably LESS
ground wave field at 1 km than either the FCC approach or the BL&E
data.

If you can answer the questions I asked above, you should understand why
EZNEC doesn't predict the same value as the obviously (to me) normalized
BL&E values. I'll look into the correspondence between EZNEC and FCC
predictions.

Roy Lewallen, W7EL

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

On Wed, 26 Nov 2008 14:49:06 -0800 (PST), Richard Fry
wrote:

When I
use their distance of a mile, I get 188 mV/m, all else identical.
Their paper reports by formula that I should see 194.5 mV/m. ...

No, the BL&E paper (accurately) stated that 194.5 mV/m is the
theoretical maximum field possible at 1 mile for 1 kW radiated by a
perfect 1/4-wave monopole over a perfect ground plane. The peak
values they measured came very close, but never quite achieved that
value.

No? No what? Is your rejection rhetorical? a dramatic conceit? Is
there some cognitive gap between "by formula" and "theoretical" you
are trying to mine? To what purpose?

Are you demanding an exact accounting between measured vs. modeled? If
so, my model comes within 2mV/m of their graphed data (which, in its
own right, does not mean they actually measured that particular
cardinal point but as it encompasses their explicitly stated variables
is tantalizingly close enough). Expectations of accuracy performed in
the field for a continuum of points (verging on 1%) for a fabricated
argument of more/less is seeking advantage where there is no salvation
to be found.

It would appear that with the average of the two distances, my model
accords quite closely to BL&E.

Mr. Clark - kindly note that in your first quote above you say that,
if anything, "modelers" show MORE response than BL&E Then when
pressed a bit you say that your model "accords quite closely" with
BL&E.

There is more than one model involved as described by BL&E. I
explicitly selected from one of several available - all of which I
have modeled. The model I describe conforms to far more of their
variables available than those expressed by you. It also exhibited
more response than your 1kM touchstone. Is this touchstone derived
from BL&E or some other source unknown to all here, but you? It seems
when I followed your offering, you want to challenge its authority.

Those two data points I offer exhibit variations of barely a quarter
dB about the touchstones you supply (one available from BL&E), and
which you fall considerably short of in your own effort. Their
average around these touchstones average is an amazingly small
difference. The difference between the model I selected, and the one
they report (one in the same) is on order of 0.1dB. If this does not
constitute an accord, then I would suggest you have more water to
carry than myself to turn modeling results into congruency. I am not
particularly motivated to improve things when my experience suggests
that it is a fool's mission given it implies accuracies that were
beyond what was achievable in that cold winter field, 70 odd years
ago.

Yet the results of my EZNEC near-field model showed considerably LESS
ground wave field at 1 km than either the FCC approach or the BL&E
data.

Clarifications, please?

You don't provide enough detail of your model to be able to point to
anything in error, but by the multitude of your statements, it doesn't
sound like you have spent enough time in the practice of modeling. The
rest of my discussion below hardly reveals anything beyond the obvious
- for one versed in the craft.

My models were arrived at through the simple, but tedious craft of
close reading and conforming to expressed facts in the literature.
Some art was involved in the selection from a choice of grounds, for
which such choice drives a wide variation of results. Does this sound
familiar? Even there, calling it art denies the information supplied
by photographs revealing a very commonplace description: Pastoral. My
choice of ground characteristics, if anything, hardly exhibits a
radical departure. In fact I choose no other ground than average for
the vast majority of my modeling. Within the confines of the
abilities of the model to support buried wire, that was performed by
suggestions offered in the help manual (clarity is achieved in reading
that too and is generally obtained in the course of considerable
exposure to the toolset). Here, the radials hovered less than half an
inch above ground instead of buried six inches beneath. Perhaps this
explains the remaining 0.1dB variation, but I doubt it. To infer such
tight coupling between model and measure is a fantasy only Art would
embrace to prove we can't trust established theory.

73's
Richard Clark, KB7QHC

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

"Roy Lewallen" wrote
Richard Fry wrote:
. . .
No, the BL&E paper (accurately) stated that 194.5 mV/m is the
theoretical maximum field possible at 1 mile for 1 kW radiated by a
perfect 1/4-wave monopole over a perfect ground plane. The peak
values they measured came very close, but never quite achieved that
value.

Can you explain why they very nearly accomplished this perfect ground
value even though the ground wave signal had to propagate one mile over
ground of finite conductivity?
___________________

BL&E made their surface-wave measurements 3/10 of a mile from their 3
MHz monopole transmit site.

MW ground loss for the surface wave across a path that short is low,
regardless of ground conductivity. This may be seen in the scan
linked below, which was taken from Terman's Radio Engineers Handbook,
1st Edition, page 681.

The scan doesn't show distances less than 1 mile, and the curves are
based on higher ground conductivity than BL&E had to work with -- but
an extrapolation of those curves to the BL&E conditions should
convince most reasonable readers of the conclusion in my paragraph
above.

The BL&E paper published in the Proceedings of the IRE states (page
771) "For each antenna height, 0.2 watt of power was fed into this
antenna, and the field intensity was measured at 0.3 of a mile. This
figure was then converted to a basis of a power of 1000 watts and a
distance of one mile."

So BL&E did not normalize their readings to account for ground loss
either at 3/10ths of a mile or one mile, but apparently they did
assume that the effect of the ground loss was the same at those two
distances. That error would not be large, however.

What do you think would have happened to the signal strength
if the mile of intervening ground had been replaced by a perfect
ground?

They would have measured 194.5 mV/m, referenced to 1 kW of radiated
power. As it was, they reported about 191 mV/m (max).

I'll look into the correspondence between EZNEC and FCC
predictions.

Thanks. That will be interesting.

http://i62.photobucket.com/albums/h8...sFrequency.jpg

RF

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

RC: Their paper reports by formula that I should see 194.5 mV/m. ...

RC: No? No what?

RF: No, the BL&E paper (accurately) stated that 194.5 mV/m is the
theoretical maximum field possible at 1 mile for 1 kW radiated by a
perfect 1/4-wave monopole over a perfect ground plane. The peak
values they measured came very close, but never quite achieved
that value.

RC: Are you demanding an exact accounting between measured vs.
modeled? If so, my model comes within 2mV/m of their graphed
data (which, in its own right, does not mean they actually measured
that particular cardinal point but as it encompasses their explicitly
stated variables is tantalizingly close enough).

If you are happy with the results of your modeling, then well and good
for you.

But the near-field value calculated by EZNEC and as shown in my URL is
far short of the result of the BL&E study, and also of the FCC's
propagation curve value for those conditions.

So far neither you nor Roy has suggested that the near-field analysis
I posted was based on an incorrect model, and there was enough
information about it in my clip to determine that.

BTW, a distance of 1 km from a 1 MHz, 1/4-wave monopole is no longer
in its near field, the boundary of which in this case is less than 150
feet from the monopole.

RF

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

On Thu, 27 Nov 2008 05:34:56 -0800 (PST), Richard Fry
wrote:

So far neither you nor Roy has suggested that the near-field analysis
I posted was based on an incorrect model, and there was enough
information about it in my clip to determine that.

Ah, we are working from a script. I am suggesting that your model is
incorrect. You asked what to do, I would suggest fixing it. You have
been provided with the necessary references. Let us know when you
succeed, but skip reports of failure. As you say, you have already
provided enough information.

73's
Richard Clark, KB7QHC

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

Richard Clark wrote:
I am suggesting that your model is incorrect.
__________

And I am suggesting that your model is incorrect.

Please show your work to the same extent that I showed mine (or more,
if you believe that to be necessary).

Otherwise all we have from you about this is undocumented.

RF

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

On Thu, 27 Nov 2008 11:39:07 -0800 (PST), Richard Fry
wrote:

And I am suggesting that your model is incorrect.

You have the cogent characteristics of my model, now demonstrate your
suggestion by showing its incorrect feature(s). It may even reveal
how you failed to obtain better results for your own model.

73's
Richard Clark, KB7QHC

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

Richard Clark wrote:
You have the cogent characteristics of my model, now demonstrate your
suggestion by showing its incorrect feature(s).

You gave no characteristics of the NEC construction and settings for
your model (cogent or otherwise), as I did for mine. You only stated
the results you say you got.

Even Roy Lewallen wrote that he will look into the correspondence of
my EZNEC solution with the FCC value for those conditions -- which Roy
probably wouldn't choose to do if there was good agreement between
them, or my "near field" model was obviously incorrect to him.

RF

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

On Thu, 27 Nov 2008 13:39:46 -0800 (PST), Richard Fry
wrote:

You gave no characteristics of the NEC construction and settings for
your model (cogent or otherwise), as I did for mine.

On Wed, 26 Nov 2008 11:41:04 -0800 (PST), Richard Fry wrote:

The near-field analysis of EZNEC for radiation in the horizontal plane
at a point 1 km from a 1/4-wave monopole having two ohms in series
with a Mininec r-f ground, while radiating 1 kW over an earth
conductivity of 8 mS/m is shown as 72 mV/m.

When I observe the operational characteristics of EZNEC (you report
you use it above) AND I observe that it does not offer a Near Field
analysis for Mininec r-f ground (as you report you use above) THEN I
have to wonder how you arrive at a figure of 72 mV/m (as you report
you obtained above). Other than version differences or updates in the
program that supercede mine, I rely on the advice found in the Help
manual provided:
Near field analysis is disabled when MININEC-type ground is selected.
...Use some other ground type for near field analysis.

Your failure to heed this advice seems consistent with your repeated
ignorance of EZNEC's capacity to perform Near Field Analysis. Also
consistent is the complete absence of radials in your model - the
hallmark (cogent) research of BL&E's "Ground Systems as a Factor in
Antenna Efficiency." This consistency propagates into your near field
report - where did you get
is shown as 72 mV/m.
from?

Did you achieve this valuation through a novel upgrade feature found
in EZNEC 5? If so, I bet the help entry still suggests that mininec
type ground is not preferred (and that you ignored that commentary
too). The differences in models to replicate BL&E results well
illustrates this for any version issue you may reveal.

73's
Richard Clark, KB7QHC

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

On Nov 27, 10:46*pm, Richard Clark wrote:

When I observe the operational characteristics of EZNEC (you report
you use it above) AND I observe that it does not offer a Near Field
analysis for Mininec r-f ground (as you report you use above) THEN I
have to wonder how you arrive at a figure of 72 mV/m (as you report
you obtained above). Other than version differences or updates in the
program that supercede mine, I rely on the advice found in the Help
manual provided:

Near field analysis is disabled when MININEC-type ground is selected.
...Use some other ground type for near field analysis.

Obviously, near-field analysis was not disabled by/in EZNEC for my
model definition. The surface-wave value of 72 mV/m at 1 km for 1 kW
of radiated power is shown in the screen clip I linked to in my first
post about this.

Also consistent is the complete absence of radials in your model - the
hallmark (cogent) research of BL&E's "Ground Systems as a Factor in
Antenna Efficiency."

The r-f loss of the radial system is accounted for in my model by the
two ohms of resistance inserted between the base of the monopole and
ground, as shown in my screen clip. This two ohms is approximately
the r-f loss of a set of 120 buried radials, each 1/4-wave in physical
length.

The peak gain of the elevation pattern in my model (see my screen
clip) is consistent with such a ground loss and the selected ground
conductivity, so this approach appears to be valid.

Hopefully Roy Lewallen will weigh in, as he has time, to comment on
the methods and results of our two analyses -- although probably Roy
will need more details about your model construction than you have so
far been willing to provide.

I will be content to let the chips fall where they may.

RF

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

On Fri, 28 Nov 2008 03:53:00 -0800 (PST), Richard Fry
wrote:

Near field analysis is disabled when MININEC-type ground is selected.
...Use some other ground type for near field analysis.

Obviously, near-field analysis was not disabled by/in EZNEC for my
model definition.

How very odd, when this comes as a distinct contradiction with your
explicit:
The near-field analysis of EZNEC for radiation in the horizontal plane
at a point 1 km from a 1/4-wave monopole having two ohms in series
with a Mininec r-f ground, while radiating 1 kW over an earth
conductivity of 8 mS/m is shown as 72 mV/m.
where the question remains at:
where did you get
is shown as 72 mV/m.
from?
It is evident your field quote is NOT from this specific Mininec r-f
ground model of yours above.

As you admit you had near-field analysis available above (you still do
not explain how in the context of a mini-nec ground per your stated
model's characteristics), and you do not describe any radial treatment
(cogent elements of the BL&E paper "Ground Systems as a Factor in
Antenna Efficiency"), and you do describe a 1/4 radiator (not found in
BL&E experimental data), then your call for suggestions on how to fix
your model's failure in the context of BL&E becomes an obscure moving
target. My "suggestion" alters slightly with do it right or discard
it as trash. There aren't really many other alternatives.

Hopefully Roy Lewallen will weigh in, as he has time, to comment on
the methods and results of our two analyses -- although probably Roy
will need more details about your model construction than you have so
far been willing to provide.

More interesting would be his enquiry or explanation into how you
defeated the lock-out for a feature that is a poor method for near
field analysis. I find it more intriguing in how you embrace it in
spite of stated cautions to employ other methods. Yes, this novel
adaptation of Mininec r-f ground to near field solutions bears more
explanation from some source. I cannot imagine that explanation will
improve your model's performance to equal mine however. That is
already well evident.

As for more details, the BL&E paper "Ground Systems as a Factor in
Antenna Efficiency" is the totality of my sources. Those practiced in
the craft of modeling and proficient with its tools will find it
sufficiently informing if they hadn't already proceeded to a
successful implementation from my descriptions in this thread.

73's
Richard Clark, KB7QHC

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

On Nov 28, 12:51*pm, Richard Clark

where the question remains at: where did you get
...72 mV/m from?

It is evident your field quote is NOT from this specific Mininec r-f
ground model of yours above.

Can you not view the screen clip at the link I posted showing this?
Why do you keep asking?

All of the windows shown in my screen clip resulted from the NEC model
data appearing in the upper left window of that clip, and all windows
in the clip appeared on the screen at same time and were driven by
that data. Note the selection of a Real/MININEC ground in the EZNEC
window in the upper left corner, and the further selection of a
"medium ground" on the line below. One of the other windows there
shows the "near-field" value of 72 mV/m at 1 km for 1 kW of radiated
power for this model. Are you comprehending all that is shown in that
clip?

More interesting would be his enquiry or explanation into how you
defeated the lock-out for a feature that is a poor method for near
field analysis.

No defeat of such was necessary. EZNEC produced the data results for
my model exactly as shown in my screen clip, with no complaints or
subterfuge on my part.

RF

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

On Fri, 28 Nov 2008 12:07:05 -0800 (PST), Richard Fry
wrote:

On Nov 28, 12:51*pm, Richard Clark

where the question remains at: where did you get
...72 mV/m from?

It is evident your field quote is NOT from this specific Mininec r-f
ground model of yours above.

Can you not view the screen clip at the link I posted showing this?
Why do you keep asking?

Because in a commercial release, suitable to professional and
scholarly reporting, it is obviously locked out as an available option
- by design and documented as so. A screen shot does not describe
your actions. You need only explicitly state that when you selected
the mini-nec ground model, that you had the NF button available and
you selected it. If such is the case, it is a bug in Roy's demo -
caveat emptor. I don't do research with demo applications.

The long and short of it is that what your poor model reveals is a
departure from the data found in the BL&E paper "Ground Systems as a
Factor in Antenna Efficiency." You
1. do not have a construction of radials of any type;
2. do not have a radiator sized to their specification;
3. employ an engine (mini-nec) which is poorly suited to the task;
4. excite the model at a frequency not supported in data in BL&E;
5. fail to note the documented advisories about near field operation
below 3MHz when such analysis is available.

There is no point in asking for how to "fix it" when your model is
irreconcilably crippled. Using a demo version of EZNEC is not suited
to the task. You couldn't even use my model as it is constructed with
fine granularity that exceeds the capacity of EZNEC, and supported
only with EZNEC+. There are alternatives that are free, and unlimited
in their segment counts available which is necessary for a proper
analysis. Caveat emptor still prevails, and you get the quality of
support you pay for.

I would "suggest" given all the cautions, contrarian advisories
offered, and warnings direct from the tool's author, that their
cumulative effect would seem to doom you to disappointment if you
demand something better than several percent concurrence to the data
supplied in the BL&E paper "Ground Systems as a Factor in Antenna
Efficiency" when abstracted to other applications.

73's
Richard Clark, KB7QHC

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

On Nov 28, 3:24*pm, Richard Clark posted:

Can you not view the screen clip at the link I posted showing this?
Why do you keep asking?

Because in a commercial release, suitable to professional and
scholarly reporting, it is obviously locked out as an available option
- by design and documented as so.

A screen shot does not describe your actions. *You need only
explicitly state that when you selected the mini-nec ground model,
that you had the NF button available and you selected it. *

To humor you, then... I explicitly state that when I selected the Real/
MININEC ground model, I had the NF button available and that I
selected it. The result of that analysis is included in the screen
clip at the link I posted, and which you seem unable to comprehend.

Also please note that I have already described and documented my EZNEC
model and actions in far more detail than you have done for yours, so
far.

Note further that the Demo versions of EZNEC operate exactly the same
as the paid versions, except for the number of segments permitted in
the model -- which was not a factor in the model I constructed. I'm
sure that Roy or someone else will correct me if that statement is
provably wrong.

The long and short of it is that what your poor model reveals is a
departure from the data found in *the BL&E paper *"Ground Systems as a
Factor in Antenna Efficiency." *You

1. *do not have a construction of radials of any type;

Their effect was included as I described in an earlier post. I will
understand if this concept evades you.

2. *do not have a radiator sized to their specification;

A 1/4-wave monopole is a 1/4-wave monopole, regardless of the
operating frequency. The intrinsic radiation envelope for a given
radiated power actually launched by such a monopole (e.g., apart from
the effects of the propagation environment) is the same at all those
frequencies.

If not, the FCC would/could not have adopted the results of the BL&E
experiments at 3 MHz as applicable to the entire MW AM broadcast band
(which they did).

3. *employ an engine (mini-nec) which is poorly suited to the task;

A MININEC ground itself is not an engine. It is a only a condition
used by the NEC engine.

4. *excite the model at a frequency not supported in data in BL&E;

See my response to your 2 above. In reality, surface-wave ground
losses in the MW BC band are less than at the 3 MHz freq used in the
BL&E studies, so the applicability of their findings is even more
relevant to BC operations.

5. *fail to note the documented advisories about near field operation
below 3MHz when such analysis is available.

No such advisory was presented by/in EZNEC during the process of
generating and analyzing my model.

I suggest you cool it for a while, and wait to see what Roy Lewallen
might post about all of this.

RF

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

It's possible to run a near field analysis using MININEC type ground
with some v. 4.0 and all v. 3.0 and earlier versions of EZNEC. However,
the results will be wrong. The problem with using near field analysis
and MININEC type ground was discovered while v. 4.0.27 was current, and
the restriction preventing that combination was introduced at v. 4.0.28
in August 2006. So only v. 4.0.28 and later programs have this
restriction. Please see the last paragraph of this posting for remedies.

In EZNEC v. 4.0.28 and later, the NF Tab button is greyed out whenever a
MININEC-type ground is specified. If it's clicked, you'll see a message
that near field analysis is disabled when MININEC-type ground is
specified. If you click Help in the message window, it'll open the
manual topic which discusses real ground types. There, you'll find:

---------------

Near field analysis is disabled when MININEC-type ground is selected.

Tests have shown that, because of the fundamental way NEC does
calculations, near field analysis with MININEC-type ground can produce
significantly erroneous results, particularly in the vicinity of a wire
which is connected to ground. This is really a contrived situation
anyway, because the only way to achieve a ground connection for a real
antenna comparable to the MININEC-type ground model is to install a
radial system. This will alter the ground conductivity and local fields,
so the MININEC-type ground model isn't really representative of
conditions near a grounded wire in any case. Use some other ground type
for near field analysis.

---------------

If the conclusion that EZNEC near field results differ from the FCC
ground wave predictions is based on a near field analysis with
MININEC-type ground, I'm not surprised at the disagreement. The analysis
should be redone with a large number of radials just above the ground,
and High Accuracy ground used instead of MININEC-type ground.

Two reminders:

1. As explained in the EZNEC manual, "near field" analysis isn't
restricted to the near field. It's actually "total field" -- including
ground wave -- and is accurate at any reasonable distance. The "near
field" nomenclature is carried over from NEC.
2. The EZNEC ground model is flat and infinite in extent. So the
predicted direct line field begins deviating from actual field values
where the curvature of the Earth becomes a significant factor.

Anyone using EZNEC v. 3.0 and earlier should avoid using the combination
of near field analysis and MININEC-type ground. Anyone using v. 4.0
should update his program to the last revision of that version, 4.0.39.
You can find instructions on updating in the manual, Support/Updates
(Maintenance Releases). To determine which revision you have, click Help
in the main program window, then About EZNEC. I strongly recommend that
v. 5.0 users periodically check for updates.

Roy Lewallen, W7EL

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

On Fri, 28 Nov 2008 15:39:35 -0800 (PST), Richard Fry
wrote:

wait to see what Roy Lewallen might post about all of this.

Are you going to ask for a refund?

73's
Richard Clark, KB7QHC

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

Richard Fry wrote:
. . .
Note further that the Demo versions of EZNEC operate exactly the same
as the paid versions, except for the number of segments permitted in
the model -- which was not a factor in the model I constructed. I'm
sure that Roy or someone else will correct me if that statement is
provably wrong.
. . .

You are correct. The demo is exactly the same as the standard EZNEC
program except for the segment limitation. But I recommend using the
current demo program rather than an older version or revision. Demo
programs can be updated at any time by downloading and installing the
current demo from http://eznec.com/demoinfo.htm. The old program can be
uninstalled first if desired; otherwise the new one will overwrite the
old one. This process won't harm any saved description files.

Roy Lewallen, W7EL

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

Richard Fry wrote:
"Roy Lewallen" wrote
With EZNEC, you have to use the near field analysis to include
the ground wave; direct ground wave analysis isn't included in
EZNEC because (etc).
_________

After the comments of Richard Clark and you, Roy, I attempted to use
EZNEC to determine the ground wave (see link below).

The near-field analysis of EZNEC for radiation in the horizontal plane
at a point 1 km from a 1/4-wave monopole having two ohms in series
with a Mininec r-f ground, while radiating 1 kW over an earth
conductivity of 8 mS/m is shown as 72 mV/m.

The same setup when analyzed using the FCC's radiation efficiency for
this monopole height, and their propagation charts for these
conditions shows about 295 mV/m as the result, which value is
supported by the measured performance of real-world AM broadcast
stations, and is also a value in a range that could be expected from
the BL&E data.

Hopefully you or Richard Clark can tell me the reason(s) for this
difference, which could easily be my own setup of the NEC model.

Roy, would you mind posting the ground wave value EZNEC Pro reports
for these conditions?

http://i62.photobucket.com/albums/h8...FldExample.gif

RF

My model has 120 0.5 wavelength radials buried 1.2 feet deep (the
unusual depth due to rescaling another model). Ground conductivity 8
mS/m, dielectric constant 13. The antenna is 0.25 wavelength high. The
whole structure is made from #12 wire to eliminate any problems due to
dissimilar diameters. Field strength is Ez at 1000 meters with 1000
watts applied.

Using the NEC-4D calculating engine, EZNEC Pro/4 shows (NF = near field
analysis, GW = far field analysis with ground wave):

Z = 40.08 + j27.91
GW = 297.7 mV/m
NF = 297.7 mV/m

Same, but with 0.25 wavelength radials:

Z = 39.56 + j26.55
GW = 292.7 mV/m
NF = 292.7 mV/m

Note that the feedpoint R and field strength don't exactly correlate if
you make the assumption that the resistance difference is due to loss.
This would be due to a slightly different current distribution on the
radiator due to interaction with the different ground fields. Other
experiments have shown that the impedance will also vary some with
radial burial depth.

Following are the results using the NEC-2D engine with a 0.25 wavelength
vertical and 120 0.5 wavelength radials one foot above the ground, all
other conditions otherwise the same. This analysis can be run with
EZNEC+, but only the NF results will be available:

Z = 66.83 + j1.894
GW = 230.0
NF = 229.7

As above, but 0.25 wavelength radials:

Z = 32.42 + j18.87
GW = 311.4
NF = 311.4

Elevated radials, even when elevated only this amount, show distinct
resonance effects, and making them longer than about 0.25 wavelength
often results in reduced efficiency which I think is due to movement of
the radial current maxima away from the center. The above results
illustrate these phenomena. While slightly elevated radials can be used
to approximate buried ones, as you can see the substitution isn't perfect.

The same 0.25 wavelength vertical over perfectly conducting (or MININEC)
ground showed a Z of 37.95 + j21.49 ohms. However, the resistances of
the various examples above aren't just this resistance plus loss
resistance, since the current distribution isn't quite the same when
radials are present.

The results you got weren't valid due to use of MININEC ground with near
field analysis, as I explained in another posting. As you can see, you
can get reasonably good results using EZNEC+ and near field analysis,
although the vast majority of people this intensely interested in the
mechanisms of AM broadcasting aren't hobbyists but rather professional
engineers who are using EZNEC Pro/4.

Roy Lewallen, W7EL

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

On Nov 29, 1:10*pm, Roy Lewallen wrote:

As you can see, you can get reasonably good results using
EZNEC+ and near field analysis, although the vast majority
of people this intensely interested in the mechanisms of AM
broadcasting aren't hobbyists but rather professional
engineers who are using EZNEC Pro/4.
________

Thanks very much for your numbers and comments, Roy.

I would never have thought to try to use EZNEC near-field analysis to
compute the groundwave if I hadn't read the suggestion to do so in
this thread. That was my first, and will be my last attempt at that.

When I need to calculate the MW ground wave for a particular distance,
monopole height, frequency and ground conductivity I use the FCC
method of first determining the inverse distance field of the radiator
at 1 km for 1 kW of radiated power, and then using that value in a
program I have with the FCC's MW propagation curves in digitized form.

My point when starting this thread was to show that the elevation
pattern radiation actually launched by vertical monopoles on any
frequency does not have a zero/very low relative amplitude at/near the
horizontal plane, which from what I read on these NGs seems to be a
popular belief.

RF

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

Richard Fry wrote:
On Nov 29, 1:10 pm, Roy Lewallen wrote:

As you can see, you can get reasonably good results using
EZNEC+ and near field analysis, although the vast majority
of people this intensely interested in the mechanisms of AM
broadcasting aren't hobbyists but rather professional
engineers who are using EZNEC Pro/4.
________

Thanks very much for your numbers and comments, Roy.

I would never have thought to try to use EZNEC near-field analysis to
compute the groundwave if I hadn't read the suggestion to do so in
this thread. That was my first, and will be my last attempt at that.

I've suggested it to you on at least one of the several occasions you've
brought this subject up, in the thread "Rhombics" on Oct. 1, 2006.
I've also mentioned it at least 10 other times on this newsgroup going
back as far as 1998. Reg used to entertain himself by periodically
complaining about EZNEC's lack of ground wave analysis, and most of
those postings mentioning the near field technique were in response to
his postings. I see you've taken on that aspect of Reg's former source
of entertainment. You and Reg were just about the only hobbyists who
have this intense interest in EZNEC and ground wave analysis, and now
that Reg is gone it's pretty much down to you. Of course you could
directly get the results you want from NEC-2, which is free and readily
available. I assume the reason you don't simply do that is that it
wouldn't be as amusing.

When I need to calculate the MW ground wave for a particular distance,
monopole height, frequency and ground conductivity I use the FCC
method of first determining the inverse distance field of the radiator
at 1 km for 1 kW of radiated power, and then using that value in a
program I have with the FCC's MW propagation curves in digitized form.

Since you can use this method to get results you believe to be correct,
why do you need EZNEC? If you want another program to give you the same
answers, why not use NEC-2? NEC uses the same method as the one used to
generate the FCC's curves. But I believe the FCC curves account for
Earth curvature while NEC doesn't, so I'm told they begin deviating at
somewhere around a couple of hundred miles.

My point when starting this thread was to show that the elevation
pattern radiation actually launched by vertical monopoles on any
frequency does not have a zero/very low relative amplitude at/near the
horizontal plane, which from what I read on these NGs seems to be a
popular belief.

I don't believe I've ever read that. But if anyone does believe it, a
much larger number believe just about the opposite -- that the signal
strength from a vertical is maximum at zero elevation angle at great
distances from the antenna. This of course comes from the ubiquitous
plots of the pattern of a vertical over perfect ground.

Guess that's enough for now. Maybe you can go a little longer before
bringing it up again the next time? In the meantime, I suggest you
either update your v. 4.0 EZNEC demo program or replace it with v. 5.0.
The demo programs are still free.

Roy Lewallen, W7EL

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

On Nov 29, 4:51*pm, Roy Lewallen wrote:

Since you can use this method to get results you believe
to be correct, why do you need EZNEC?

Roy:

Don't _you_ believe that the results I posted using the FCC method I
described to be "correct?"

Regardless, and to answer your question -- I don't really need
EZNEC. But it can be interesting to see how various analytic methods
compare.

Quite a few years ago and after due investigation/consideration, I
paid about $300 for the NEC-2 products of one of EZNEC's competitors,
because I preferred its graphical output choices and print quality,
its higher segment limit compared to EZNEC+, and the customization it
allowed in its printed output legends. This capability included the
synthesis and import into the NEC model of any one of many dozens of 2-
D and 3-D structures, to their specific mechanical specifications
defined by the NEC user.

The main reason I use EZNEC occasionally is to investigate the claims
of others who use EZNEC.

Sorry to be blunt , Roy, but then you asked.

RF wrote:
My point when starting this thread was to show that the elevation
pattern radiation actually launched by vertical monopoles on any
frequency does not have a zero/very low relative amplitude at/near the
horizontal plane, which from what I read on these NGs seems to be a
popular belief.

Roy Lewallen responded:
I don't believe I've ever read that. But if anyone does believe it, a
much larger number believe just about the opposite -- that the signal
strength from a vertical is maximum at zero elevation angle at great
distances from the antenna.

?? My reading of these NGs shows that many/most amateur radio
operators ignore/discount the fact that the peak radiation launched by
a vertical monopole of 5/8 lambda or less in height ALWAYS occurs in
the horizontal plane., regardless of the operating frequency, or the r-
f ground in use.

The radiation/reception characteristics at low elevation angles of
such an antenna can be useful in establishing contacts with the most
distant possible single-hop DX sites, can they not?

RF

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

Richard Fry wrote:
. . .
?? My reading of these NGs shows that many/most amateur radio
operators ignore/discount the fact that the peak radiation launched by
a vertical monopole of 5/8 lambda or less in height ALWAYS occurs in
the horizontal plane., regardless of the operating frequency, or the r-
f ground in use.

I don't think most amateurs care about the locally launched radiation,
except when dealing with local RFI. That low angle radiation decays to
essentially nothing within a few miles at HF and even less at VHF and
above. So it's of no use for communicating beyond a few miles.

The radiation/reception characteristics at low elevation angles of
such an antenna can be useful in establishing contacts with the most
distant possible single-hop DX sites, can they not?

RF

They can not. I see you're still a bit confused about what happens to
that ground wave signal. Beyond a few miles at HF, that low angle
radiation decays to essentially zero. The pattern of the field beyond
that distance resembles the one reported by EZNEC and other programs
giving distant far field data. And they correctly show that unless the
ground has very high conductivity at the reflection point, there will be
very little field remaining at very low angles beyond that ground wave
decay distance.

The performance of an antenna when communicating with a distant station
is precisely what EZNEC is attempting to show you. If you want to know
how it will do at various elevation angles for DX, or even at distances
of a few hundred miles, look at those plots. At HF, ground wave analysis
will only tell you how well the antenna will do when talking with
someone across town. Which is why there's very little interest in ground
wave analysis among amateurs, HF broadcasters, or just about anyone
except AM broadcasters.

Roy Lewallen, W7EL

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

On Nov 29, 9:21*pm, Roy Lewallen wrote:
Richard Fry wrote:
The radiation/reception characteristics at low elevation angles of
such an antenna can be useful in establishing contacts with the most
distant possible single-hop DX sites, can they not?

They can not. I see you're still a bit confused about what happens to
that ground wave signal. Beyond a few miles at HF, that low angle
radiation decays to essentially zero. The pattern of the field beyond
that distance resembles the one reported by EZNEC and other programs
giving distant far field data. And they correctly show that unless the
ground has very high conductivity at the reflection point, there will be
very little field remaining at very low angles beyond that ground wave
decay distance.
_______

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. No ground reflection is necessary to create that field - it is
launched by the monopole itself.

Below is a link to a clip from Terman's Radio Engineers Handbook, 1st
edition, showing that the greatest single-hop range for skywave
signals occurs from the radiation of the monopole at elevation angles
of less than ten degrees. But looking at a NEC far-field analysis
this would seem impossible, due to the greatly reduced fields in this
sector that NEC shows for a vertical monopole over real earth.

This clip was done for MW frequencies, but the concept would apply
equally at HF, would it not?

http://i62.photobucket.com/albums/h8...ermanFig55.jpg

RF

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

On Sun, 30 Nov 2008 04:20:33 -0800 (PST), Richard Fry
wrote:

showing that the greatest single-hop range for skywave
signals occurs from the radiation of the monopole at elevation angles
of less than ten degrees.

Which is uniformly poorer by 12 dB than that launched at 40°.

73's
Richard Clark, KB7QHC

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

On Sun, 30 Nov 2008 04:20:33 -0800 (PST), Richard Fry
wrote:

But looking at a NEC far-field analysis
this would seem impossible, due to the greatly reduced fields in this
sector that NEC shows for a vertical monopole over real earth.

NEC is not a propagation modeler.

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).

The graph you supply suggests that this 70 mile distance is obtained
by a launch angle (for the sky-wave) of 60 degrees. The NEC far-field
analysis for the BL&E antenna of 70 foot tall radiator in a field of
113 135 foot radials over average ground has a response of -2.32dB @
60° and -1.61dB @ 1° which shows a pretty close accord with field
reports from Laport (Fig 2.7).

73's
Richard Clark, KB7QHC

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

Richard Fry 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. No ground reflection is necessary to create that field - it is
launched by the monopole itself.

Below is a link to a clip from Terman's Radio Engineers Handbook, 1st
edition, showing that the greatest single-hop range for skywave
signals occurs from the radiation of the monopole at elevation angles
of less than ten degrees. But looking at a NEC far-field analysis
this would seem impossible, due to the greatly reduced fields in this
sector that NEC shows for a vertical monopole over real earth.

This clip was done for MW frequencies, but the concept would apply
equally at HF, would it not?

http://i62.photobucket.com/albums/h8...ermanFig55.jpg

RF


I for one, think you correct. What is "launched" at the antenna obeys
physics laws at 100 ft., 1000 ft., 10,000 ft., 100,000 ft., 1,000,000
ft. ... the signal does not ever suffer magical, mystical, supernatural
manipulations--EVER!

Regards,
JS

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

On Nov 30, 5:57*pm, Richard Clark wrote:
On Sun, 30 Nov 2008 04:20:33 -0800 (PST), Richard Fry wrote:
showing that the greatest single-hop range for skywave
signals occurs from the radiation of the monopole at elevation angles
of less than ten degrees.

Which is uniformly poorer by 12 dB than that launched at 40°.
_________

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.

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. This accounts for the lower
value of received field at the greater distances, as shown in Terman's
Fig 55.

RF