Below is a link to the description of a topband inverted L antenna with
dimensions and installation assumptions that could be useful to the
owner of an average-sized city lot.
https://s20.postimg.org/xz7eiwgwd/Self-_Resonant_Inv_L_for_160_mtrs.gif
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Topband Reflector Archives
Previously -
>... I ran across this, which was originally posted
> on the Broadcasting list ...
__
Below is a link from a followup post there with a
NEC4.2 analysis of the performance of a 1/4-wave
monopole driven against a set of 4 x 1/4-wave,
elevated, horizontal radials.
A NEC4.2 model of a tee using a 60-ft tall vertical conductor shows 29 -j
0.04 ohms at 1.9 MHz when connected at the top to the center of a horizontal
conductor 89 feet in length.
The tee was base-driven against 16 x 33-foot radials buried 4 inches in 5
mS/m, d.c. 13 earth. Conductor ODs are
Recent clips from one Topband post:
... EZNEC Pro4 can segment ground along a line into two arbitrary ground
properties, ... The brief summary of modeling results is there is
significant benefit at elevation angles 20 degrees towards the salt water
IF the antenna is less than 0.7 wavelengths
When I first re-read my opening post on the Topband site I thought I had
transposed some numbers in it, and posted that I would correct them.
On further review I had not, so no corrections are necessary.
RF
_
Topband Reflector Archives - http://www.contesting.com/_topband
NEC modeling to determine the effects on the fields radiated by a vertical
monopole when siting it near a salt-water coastline can be highly misleading
if the surface wave field is not considered.
For example, the plots linked below show that for average earth conductivity
the E-field at 5
Below is a link to the groundwave field of a 1 kW non-directional AM
broadcast station located about 1 mile from the Atlantic, in Florida.
The groundwave field shown is based on the FCC M3 conductivity map, and
their GW propagation charts for this frequency and power.
The space wave fields
Have a look at 1KW 1130 AM on Hilton Head Island, SC (WHHW-AM). At 12 noon
on any day, I can easily ride that signal down the Space
Coast of FL and about 10 miles inland. That's the entire coast of GA,
part of SC and half of FL.
That's pretty much as shown for them (link below). Nice signal
Some may wonder why I posted the groundwave coverage contour of an AM
broadcast station as being relevant to this thread. Hams are mostly
interested in the space wave radiated by an antenna system.
The NEC4.2 plots linked below show how the space wave and ground wave fields
launched by a
With reference to the quote below from the interesting paper titled The
Brown Paper and Conclusions with a Ham Focus - N6MW March 25, 2015, linked
in the OP of this thread title:
\\ The field strengths are always compared with that expected for the same
antenna height but over a perfectly
Conclusions from graphics of the Brown, Lewis Epstein ground systems
experiments (linked below)...
- When relatively few buried radials are used, there is little improvement
in the GW E-field radiated by monopoles with a physical height of 77 degrees
or longer when those radials exceed about
For discussion...
http://s20.postimg.org/kq2k6pox9/Current_Distr_on_Buried_Radials.jpg
R. Fry
_
Topband Reflector Archives - http://www.contesting.com/_topband
Is it conventional to compare the surface wave fields at a distance so near
the Radial length and the wave length?
I chose a horizontal plane distance that would be just a bit into the far
field radiation of that system, so as to minimize groundwave propagation
loss.
Greater distances would
Reply to W8JI post of Sat, 28 Feb 2015 19:14:07 -0500:
The source of the r-f current flowing on buried radials is the r-f current
flowing in the earth as a result of radiation from the vertical monopole.
(etc)
It seems to me that answer ignores other effects.
1.) If we remove the earth,
The feedpoint connection, in all cases of vertical antennas, whether the
system is shunt fed or series fed, or even if it is an end-fed half wave,
ties one feed terminal to the ground or counterpoise system. It has to be
that way, and the current out into that counterpoise (whatever the
Comments to two earlier posts by separate posters (clips below):
But if indeed a less lossy ground means that fewer radials are needed to
be placed in the field, then the coupling to the less lossy ground is
greater which I would expect to mean more loss in the radial field which
would then
... As I understand, the primary loss mechanism for ground mounted vertical
systems is EM field penetrating the lossy material below. To lower this
loss, one needs to prevent this ground penetration. ...
A monopole will not radiate without a return path for the r-f current
flowing into/on
Regarding the quotes below:
2.) We see any radial or counterpoise system, close to the radial or
counterpoise, has to have external fields. Those fields must extend out of
the counterpoise, and always cause loss when a counterpoise is near a lossy
media.
3.) We see we only mitigate the loss
... Simply put, the Newburgh area is at least a difficult area and at
worst an entirely inappropriate area to test this thesis. ...
Some may not be aware of the methodology used to determine the FCC
efficiency of an AM broadcast radiator (see
Radials do have standing waves, and so the minimum impedance at the base
will appear when the radial is somewhat less than 1/4 wave long.
Of interest here is that the benchmark Brown, Lewis and Epstein I.R.E paper
on ground systems does not show such standing waves along buried radials
(clip
Their Fig. 7 shows results of simplified (manual) calculations, not
measurement results.
Quoting from page 771 of the BLE paper on ground systems:
The current in the buried wires was measured in each case. This
was accomplished by placing a coil next to the ground wire at a point
where the
Additional from the BLE paper on the subject of standing waves on buried
radial wires...
Figure 11 linked below is based on the r-f currents measured along the
radial lengths shown in Figure 7.
http://s20.postimg.org/k05j5r3al/BL_E_Fig_11.jpg
R. Fry
_
Topband Reflector
Previously, from two different posters...
... it defies logic that radials would NOT exhibit the same current and
voltage distribution of any other conductor carrying RF current.
The ground sucks up the current at such a rate that there is not enough
current left to increase.
Quote from
For most of the past century the intractability of the equations was the
excuse for just laying down textbook overkill radial systems. If you
can't solve the real world problem, then just change the real world to
match the problem you can solve!!!
NEC4 produces accurate answers for monopole
In reality, NEC4 can produce quite accurate results when modeling buried
radial wires and groundwave propagation losses along a real earth path -- as
long as earth conductivity is known for that path and operating frequency.
The link below shows the value of the groundwave E-field at a range
CORRECTION: See FCC §73.190 at the link below, not FCC §73.189 (sorry).
FCC methodology and formulae used to determine the skywave signals
of AM broadcast stations:
http://www.gpo.gov/fdsys/pkg/CFR-2012-title47-vol4/pdf/CFR-2012-title47-vol4-sec73-190.pdf
_
Topband Reflector
... So I would expect the skywave plot to be elongated to the east through
south at the 0.25 mV/m contour line. It appears that the data was generated
using a signal strength prediction program as 50% of the time was used in
the qualifying remarks (50% implies a median value - which likely
Lower angle skip, such as WFAN being received in Europe, Africa, Caribbean,
etc. would definitely be affected. In the extreme, the shape of the
antenna pattern would look more like the one for groundwave.
Below is a link showing the complete 0.15 mV/m groundwave contour of WFAN,
to
The link below shows the transmit site used by WFAN (which is diplexed with
WCBS into the same vertical monopole). The site is located on a small
island in Long Island Sound.
The horizontal distance along the surface of this island on the ENE radials
reaching the sea water of Long Island
From my reading of posts on many ham boards, the prevailing thoughts are
that the nighttime skywave field intensity received from a vertical monopole
is dependent on earth conductivity -- as well as on frequency, radiated
power, path length, and atmospheric conditions.
The plot linked below
Recalling Jim Brown's posting yesterday of Rudy Severn's excellent
recent work, the current maximum in a radial occurs at 0.25 wavelength
from it's open end loss will be minimized when that current maximum
is at the feedpoint.
_
For consideration: The first link below is from
RE: Brian Mattson's post of Friday, 19 Dec 2014 12:23:52 -0500
The velocity of propagation in the MF and HF bands along radial conductors
that lie on, or are buried several inches in the earth is inconsequential.
What DOES matter is the free space wavelength, and the number of those
radial
We can have 67% reflected power and still have nearly 100% of transmitter
power getting into the antenna and being radiated.
Then could someone please explain why the manufacturers of ham, broadcast
AM/FM/TV, and other transmitters specify the maximum SWR (e.g., minimum
return loss) for the
Hello Paul,
RE:
Typically a transmitter will fold-back delivered power when its output Z
is fixed (e.g., 50 or 70-ohm) and SWR exceeds some predetermined amount
set by the manufacturer. This is typical of broadbanded solid-state
amplifiers with a fixed output Z that use no output matching
Dan AC6LA wrote:
...To help resolve the issue I modeled a ?/4 vertical with and without the
ground wave at multiple slant (radial) distances and plotted the results.
etc
Dan's AutoEZ charts remove all doubt about the issue of whether or not the
ground wave contributes to monopole radiation
Guy Olinger wrote:
NEC is the process that indicates the unproven/undisproven notch.
Based on the AutoEZ charts linked here by AC6LA, the existence of this
notch is true only if NEC is misused and/or misunderstood.
_
Topband Reflector Archives -
The link in the opening post of this thread shows an interesting, animated
analysis of the elevation gains of a monopole, based on a NEC far-field
analysis not including the surface wave.
I then posted this comment, Reality is that radiation leaving the monopole
at elevation angles of at
Guy Olinger wrote:
Just to mention that the prior opinion is controversial and not
universally agreed upon. Nor to date has anyone surfaced with actual
measurements made at the distances (25 to 50 km) and with span of altitudes
(0 to 10 km) to either prove or disprove either side.
Not
Just to note that the low-angle radiation produced by monopoles is not
accurately shown by a NEC model/study that does not include the surface
wave, regardless of whether one or two ground-plane media are specified in
the model.
Below is a link to a NEC study of the low-angle fields of a
Here is a clip of a post I made on another website in answer to a question
there, which might be of interest here also...
Below is a link to a graphic from a NEC4.2 study showing how unequal-length
buried radials affect the groundwave fields of a 1/4-wave monopole, for
approximately the
K3VAT: Just to clarify: 60 radials are 1/4 wave
and 60 radials [appear to be] 1/8 wave, is that correct?
Yes, that's correct.
_
Topband Reflector Archives - http://www.contesting.com/_topband
The r-f loss at the operating frequency in a set of buried radials varies
with the conductivity and permittivity of the earth in which they are
buried.
The NEC4.2 study below shows that for poor earth conditions (within about
1/2WL from the base of the monopole), the number and length of
Elevated radial wires perform much differently than buried radial wires.
Elevated, horizontal radial wires having self-resonant 1/4 wavelength used
as all, or part of an elevated counterpoise for a monopole, tee, or inverted
L should NOT have a low-Z (direct) path to the earth at the operating
A response to David Raymond's questions on elevated monopole systems
was posted to the listserver on Jan 22, 2014 (link below).
http://lists.contesting.com/archives//html/Topband/2014-01/msg00189.html
_
Topband Reflector Archives - http://www.contesting.com/_topband
Guy Olinger wrote:
...the presentation shows the max of the four elevated at *minus* 1.17,
while the buried radials are minus 0.71. That means the 4 elevated are
about a half dB inferior to dense buried.
The text of my post first including the URL for my NEC study (link below)
stated that
Guy Olinger postulated for a while, then wrote:
... Run the four elevated over the radial field. ...
You posted that you have NEC4, Mr Olinger. Why not do that yourself then,
rather than ask someone else to do it for you? Post your results and the
bases for them, as I have done for my
Guy Olinger wrote:
Careful here ... The presence of 0.4 wavelength buried radials turns the
ground underneath from the typically inferior Carolina medium into a
superior composite medium. Use of four elevated radials **over that
composite medium** is far superior to four elevated over 2-3-4
Guy Olinger posted:
NEC 4.x ground calculation is *tuned* for the *money* paradigm, the
commercial MF BC paradigm. It underestimates ground loss where radials
would not be accepted as kosher by the FCC. ... Just don't equate NEC
to natural law.
Some may believe/promote the concept that
C. Cunningham wrote:
If you get up to 4 symmetrical elevated radials there's not much to be
gained by adding more. There's been a lot of work done in the broadcast
industry using elevated radials to replace deteriorated buried radial
fields that shows that pretty clearly. It was published in
Dave W0FLS wrote:
With the radials being 4.9 meters above ground, do the radials literally
come up to the tower and then travel down the leg to connect to the ground
side of the insulator or do they travel in close to the tower and angle
downward?
From the text of that paper, it appears that
Guy Olinger wrote (responding to a quote from me that he included):
Such characteristics would apply to the use of elevated radial systems by
ham radio operators as well as they do for AM broadcast stations.
Such a statement requires qualification if the basis of the BC experience
includes
Most, as in nearly all of the licensed AM broadcast stations in the U.S. use
all three of the devices listed below (together) to reduce the probability
of lightning damage to their transmit systems when using base-insulated
towers.
1. A static drain choke leading from the base of the tower
The radiation toward an elevation angle of 5 degrees shown in the surface
wave plot continues in essentially a straight line, to reach the
ionosphere.
I'm still puzzled by these statements.
Its clear that a NEC far-field analysis over a real earth path omits a
significant amount of low
???
__
Note that for 1 kW of applied power, the maximum inverse distance field 1
mile from a 5/8-wave vertical is 275 mV/m compared to 195 mV/m from a
1/4-wave vertical.
The difference is 20log(275/195) = 2.99 dB, which supports the point of my
post.
RF
_
We were shocked to find that the existing 1/4 wl performed better than the
much taller Vertical.
The link below compares the elevation patterns of monopoles ranging from a
1/4-wave to 5/8-wave in height. These are the patterns launched by these
monopoles as they exist a few wavelengths from
BC stations tried 5/8 wavelength antennas to maximize their groundwave
coverage. Unfortunately, the high angle lobe produced a skywave that caused
severe interference fading at night out in their desired coverage area.
Most 50 kW, 24/7, omnidirectional MW broadcast stations such as WJR, KMOX
Jack WS3N wrote:
Then it would seem that what you call the surface wave must be the
remaining part of the complete solution, and so it must decay exponentially
in the vertical direction. ... a decaying solution can't be projected in a
straight line and assumed to reach the ionosphere.
The
Paul Christensen, W9AC wrote:
The surface wave tool most be used in conjunction with the normal modeling
application to get a complete and accurate vertical profile from 0 through
90 degrees.
Agreed.
That a vertical monopole 5/8 wavelength and less in height, using a less
than perfect
Rudy Severns wrote:
Tom's correct, the issue is not resonance but rather what, if anything,
happens when you have a so-so conductor/insulator (a tree) in the
near-field and/or further out. Do the losses matter?
Here are several data points on this subject.
Recording the
A certain Topband poster apparently originated and supports driving a 160m
vertical monopole against an elevated, folded counterpoise (FCP) in
situations where dense and uniform buried radials are deemed
impractical/undesirable/unnecessary.
Recently this same proponent posted this exchange in
RE: Capability of NEC for Accurate Modeling of Groundwave Fields Close to a
Monopole using Elevated Radials
As an example...
The FCC groundwave propagation chart for 1490 kHz (Graph 18-A) shows that
the field at 1 km over 1 mS/m earth is 51% of the inverse distance field.
The inverse
Guy Olinger posted:
...The very same NEC 4.2 with raised quarter wave radials over routine real
life ground made of dirt will show field intensities in the ground. (etc
etc)
___
Sorry, but this is a misunderstanding/misuse of NEC for this situation.
The r-f currents flowing in
(C) How many elevated radials are just enough...?
Depends on how many dB you want to throw away. If you can, do 12 to
16. 32 is the kill-the-loss, never-look-back number.
The link below leads to a detailed post on this topic by William Culpepper,
a broadcast consulting
As for the affect of trees on EM waves, below are the results of some simple
measurements I posted earlier on another board.
___
Recording the relative readings on the dBµ and S/N displays of a Tecsun
PL-310 tuned to a directional station about 52 miles east of me on 790 kHz,
Don k4kyv wrote:
I would be interested in looking at any actual experimental data compiled
to quantify ground losses, using physical antennas fed with physical rf
watts with data collected using a variety of physical ground planes.
In 1937, Brown, Lewis and Epstein of RCA Labs published a
Carl wrote:
My point all along is that ground losses change the shape of the main lobe
curve at low elevations and reduce signal levels there.
Just to note that NEC4 analyses of the fields of the elevation plane pattern
from a monopole using a set of buried radial ground wires show
Rick N6RK:
On 12/16/2012 8:31 AM, Tom W8JI wrote:
You likely had an antenna with 1/2 wave of wire spooled up on a short
fiberglass rod, which would never behave like a half-wave.
You are exactly right. Unfortunately, this myth dies hard.
Below is a link to a page on this topic
There is no magic about 120 radials, and long before 120 radials are
reached the increase in field strength pretty much stops.
According to the 1937 BLE experiments and IRE paper, this depends on their
length.
If they are short (~0.15WL), then there is little improvement in radiated
field
Tim N3QE wrote:
And I think clear channel stations do not cut back power at night... do
clear channel stations actually still exist?
There are about 116 AM broadcast stations in the U.S. using 50 kW
transmitter power during the day. Some of them reduce power at night,
however KFMB (760 kHz)
In my first post of this date I wrote, Another important observation to be
made from that NEC data is that space-wave radiation from elevation angles
below ~2 degrees equals the radiation in the groundwave at 1,300 meters
downrange.
That distance is incorrect. The correct distance is 3,000
Mike W0BTU wrote:
... how about 1/2 wave monopoles, or monopoles between 90 and 180 degrees?
Could they be useful at any distance on 160?
All monopoles of all electrical heights of 5/8WL and less _radiate_
(launch) maximum relative field (E/Emax) in the horizontal plane --
regardless of
Bruce-K1FZ wrote:
AM broadcast band antennas 5/8 1/2 wave tall are rarely used any more.
I noticed a reduction of the tall AM towers starting about the 1960's.
Guy Olinger replied:
Wouldn't that have corresponded to the FCC's reduction in clear-channel
strategies, and more local market
Lloyd Berg N9LB wrote:
There were numerous technical write ups about stations who wanted the
maximum theoretical ground wave signal and spent big bucks to put up 5/8
wave verticals. They were always disappointed in the unexpectedly reduced
coverage area that resulted. Most of the reasoning
Ward N0AX wrote:
... The electron gyrofrequency (I just *love* saying gyrofrequency, don't
you?) in the lower layers ... is much closer to 1.8 MHz and causes the wave
coupling to change dramatically in ways that are not well understood. This
changes with latitude and time of day (or night).
Dave WX7G wrote:
For DX we are interested in elevation angles from 3-15 degrees. How much
error is there in a NEC model of a monopole at these elevations?
The link below shows the NEC4.2 fields for a seawater path on 1850 kHz. The
calculated field at 1 km in the horizontal plane for 1 kW of
Tom W8JI wrote:
My point is that does not tell us what happens at the ionosphere.
If I just take a simple program like EZNEC, and use a small sense antenna
out in the distance, the results follow the trend you posted from the
helicopter. ... AFAIK, we do not have measurements of arrival
Guy Olinger wrote:
I have not personally seen work to validate signal strength and prove the
mechanics of arrival at various altitudes at 50 km. ... NEC4 says that
it doesn't continue. But NEC4 also nicely predicts the 2.8 km helicopter
measurements.
This depends totally on the accuracy
The tall vertical tower was definitely worse compared to shorter verticals,
and had almost no short skip signal around Georgia. I had isolation chokes
for lights and a base insulator, but that 300+ foot tower was so poor I
never used it as a vertical.
Not sure what frequency this comment
Mike wrote:
We know the radius of the earth and have a good idea of the takeoff angle
from a given monopole height. (etc)
What is your (or anybody's) definition/understanding of the term takeoff
angle?
R. Fry
___
Topband reflector -
Cristi YO3FFF wrote:
That means, the radiation pattern will be affected too because the
electromagnetic wave will be much curved to the ground, so the
groundwave intensity will be direct proportional with the conductivity
Is it right?
Other things equal, the field values in the vertical plane
Some earlier posts have implied that monopoles installed at sites with poor
earth conductivity don't produce much low angle radiation. Probably this is
based on an observation of the NEC far-field pattern over poor earth, and
looking at an assumed take-off angle from the monopole.
However
Guy Olinger wrote:
We will run NEC4 near field calculations on a 1/4 wave radiator with 120
buried 0.4 wavelength radials at 1.825 MHz, soil char of (5, .13). Even at
30 (thirty) km the depth of the notch near ground is still increasing. ...
At 50 km out the minimum at 100m height is -28.69
Guy Olinger wrote:
I find it curious that some of those that so insist on
standing-man-with-meter in affairs regarding performance of antennas are
willing to accept a considerable logical reach on upward launching of
ground wave without the appropriate metric **at altitude**. ... But I got
no
Guy Olinger wrote:
** What was the station and location? This allows us to view the location
ourselves with Goggle Earth and other tools. etc etc etc
The data I posted was sent to me as a courtesy by the consulting engineer
who measured and compiled it. He performed these measurements as a
Guy Olinger wrote:
But to prove it we can't use standing-man-with-meter. He may just be
sensing the current in the ground just below his feet that will never be
airborne. We need sitting-man-with-meter-in-helicopter to go up there and
prove that what you get from the ground up to twenty
We need sitting-man-with-meter-in-helicopter to go up there and prove that
what you get from the ground up to twenty thousand feet out (at) 20 miles
is a blend, and not a notch.
Below is a link to the fields calculated by NEC-4.2 for those conditions,
and also for a horizontal distance of 0.1
Mike W4EFI wrote:
I get that at any point in the far field there is RF current in the ground
due to the space wave from the transmitter reflecting obliquely off
ground.
If the earth had perfect conductivity then an EM wave radiated into space
from a vertical monopole would have no tilt
Guy Olinger wrote (about measuring earth conductivity):
Figure out how to do that for a small lot backyard in an old European
village with 900 year old homes.
Here is one method:
http://www.technik.dhbw-ravensburg.de/~lau/groundconductivity.html
Cristi YO3FFF wrote:
From Terman (as Richard Fry mentioned):
http://i62.photobucket.com/albums/h85/rfry-100/TermanFig55.jpg
First hop distance on E layer reflection for given angles is:
20 degrees = 300miles, 30 degrees = 200miles
__
But note that Terman shows much longer 1st
The elevation patterns of vertical monopoles over real earth has been
discussed in recent threads here
(http://lists.contesting.com/archives//html/Topband/2012-10/msg00140.html).
The common belief based on NEC far-field elevation patterns for those
conditions shows little relative field at low
I have not been able to locate these FCC curves (and it appears that they
may have been withdrawn).
Here is the link...
http://www.fcc.gov/encyclopedia/m3-map-effective-ground-conductivity-united-states-wall-sized-map-am-broadcast-stations
___
I have not been able to locate these FCC curves (and it appears that they
may have been withdrawn).
The FCC groundwave MW propagation curves are available here...
http://www.fcc.gov/encyclopedia/am-broadcast-groundwave-field-strength-graphs-sections-73183-and-73184
Conclusion: The less ground conductivity the higher is the antenna
elevation radiation angle. This is a negative impact for DX!
Cris, Tom, Paul et al
This belief is common when looking at the far-field elevation pattern of a
vertical monopole in MoM results, or in antenna textbooks. That
On your referenced fields graph you caption Measured vs. Calculated
intensity, but the traces are not differentiated. Which traces on the graph
are measured and which are calculated?
The chart at the top of the page contains only data calculated by NEC.
The chart titled
The measured data linked below shows how the number of buried radials
affects the performance of monopoles of various height to 90 degrees, for an
applied power of 1 kW. Earth conductivity at the test site was about 4
mS/m.
http://i62.photobucket.com/albums/h85/rfry-100/BLandERadials.gif
Guy Olinger wrote:
Can you pass along your source of information that BLE was done over 4
mS/m soil, ... Or are you using the FCC map for typical soil conductivities
and presuming a common New Jersey value and no variation at the site?
It is my presumption that for their cost and logistics,
Just to note that Edmund Laport (once the Chief Engineer of RCA
International) did not support the use of ground screens in his textbook
RADIO ANTENNA ENGINEERING (page 121), citing eddy current losses around the
closed-loop circuits of such ground screens.
More common for AM broadcast
A common belief seen on the web is that if buried radials are not installed
over some azimuth sector around a monopole, then the azimuth radiation
pattern of that monopole will become distinctly directional.
But as an extreme illustration of this situation, below is a link to a NEC-4
model of
W8JI wrote:
At my present QTH on 40 meters, somewhere around 15 evenly spaced radials
flattened off the measured field strength improvement. Even 60 radials
would have been a waste of wire.
The number and length of equally-spaced buried radials needed for a monopole
depends rather heavily on
What I am saying is that ground loss must increase the higher we go in
frequency, attenuating the surface wave more and more the higher and higher
we go.
But Rich is also talking about the radiation at zero degrees bouncing off
the ionosphere and returning to the earth at some distant point.
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