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

"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

"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

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

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

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

"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

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

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