Elevation Patterns of Ground Mounted Vertical Monopoles
 

Earlier in another thread I posted the text below, and thought it
would be useful to show some documentation for it, and also
give it more visibility.

QUOTE The point I'm pressing is that ground-mounted verticals
up to 5/8-wave high used by ham operators have the same
elevation pattern shapes as those used by broadcast stations.
The peak radiation launched from all of them occurs in the horizontal
plane, and reduces slowly and smoothly for low elevation angles
above the horizontal plane. It could well be that the DX you do work
results from radiation at a much lower elevation angle than believed
possible when looking at the usual NEC calculations and plots for
that vertical antenna. END

The link below leads to a scan of a graphic from Section 10 of
Terman's Radio Engineers' Handbook (1943). It shows the "takeoff
angles" needed to serve various distances from a ground-mounted,
vertical monopole radiator via skywave, and the resulting skywave
fields there for the conditions stated. The reflection coefficients
apply to the E-layer.

Terman's work shows that the elevation pattern of such a radiator
over lossy earth does not approach zero field near the horizontal
plane -- as is a common interpretation when looking at their NEC
evaluations.

Terman's text (p. 743) also states that the reduction in skywave field
after a peak at ~160 miles results from the ERP at elevation angles
serving those ranges not compensating for the greater losses of those
longer paths.

But the skywave fields at 1000+ miles and takeoff angles of 1 degree
and less are far from approaching zero (no matter what we think NEC
is telling us).

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

Discussion invited...

RF

Elevation Patterns of Ground Mounted Vertical Monopoles
 

When Terman did his work what were considered to be "the broadcast
frequencies"? Even on 80 meters we are well above that range from that
era... There is a major change in polarization response as we go from
160 to 80 meters, and again to 40 meters, etc.

As an active antenna experimenter on 80 meters who keeps records of
which antenna made which contacts, and with the ability to switch
between relatively high horizontal antennas, and vertical antennas of
both a quarter wave and a half wave in height (80 meters), I can tell
you with certainty that less than 5% of my 80 meter DX contest contacts
in 04 and 05 were made on the vertical antennas ... It is the rare DX
station that is clearly better on the verticals compared to the high
dipoles - and when they are stronger on the low angle verticals it is
usually right as the band opens or closes... Based upon my antenna
testing in previous years, for this year's CQWW I am replacing all the
vertical arrays with horizontal arrays... At that point the only
vertical arrays I will have left is on 160...

My gut feeling, based on real results over multiple years, is that the
incoming HF signals rarely peak below 10 degrees - probably less than
5% of the time...

Another issue in Termans work is his decision to characterize the the F
layer as a reflecting mirror... We now know that the ionosphere
refracts and ducts signals as often as it reflects them... I can
suggest that too low of a launch angle of the main wave is deleterious
for HF DX in that such a shallow angle of incidence against the lower
boundary of the F layer allows only reflection and does not allow the
wave front to enter the ducting region higher up, which limits you to
less than 1000 miles first hop.. Whereas a steeper launch angle results
in the wave front penetrating the bottom of the F layer, being
refracted to a shallower angle once inside the ducting region, being
ducted long distances with far less absorption than it would for
multiple hops, and then again refracting and exiting the duct at a
steeper angle than one would expect for such a distance... This to my
mind is a common mechanism for those amazingly strong DX openings we
see...

denny / k8do

Elevation Patterns of Ground Mounted Vertical Monopoles
 

"Denny" wrote
When Terman did his work what were considered to be
"the broadcast frequencies"?

540 kHz to 1,600 kHz.

Another issue in Termans work is his decision to characterize
the F layer as a reflecting mirror...

Sorry, that's a misunderstanding. He states using the E layer in his Fig 55
and in his text.

... I can suggest that too low of a launch angle of the main wave
is deleterious for HF DX in that such a shallow angle of incidence
against the lower boundary of the F layer allows only reflection and
does not allow the wave front to enter the ducting region higher up,
which limits you to less than 1000 miles first hop.

On page 749 of this chapter, Terman writes, "If it assumed that 3-1/2
degrees is the minimum practical angle above the horizon at which rays can
depart from the transmitting antenna, the maximum skip distance
theoretically possible is about 1,700 km for E-layer transmission and 3,000
to 3,500 km for F2-layer transmission. When communication is to be carried
on over longer distances the transmission path must include two or more
hops..."

But if the vertical monopole has an unobstructed path for rays between the
optical horizon and +3-1/2 degrees elevation, then those ranges for a single
hop would increase.

And the reason that 3-1/2 degrees might be a practical limit is not related
to the belief that a ground-mounted vertical monopole has no radiation in
that sector. In fact its relative field in that sector for all practical
purposes is the same as it is in the horizontal plane, where it equals 100%.

The link below leads to another of Terman's graphs, this time showing the
measured fields vs distance out to about 2600 miles with MW freqs between
640 kHz and 1190 kHz . About these curves Terman writes," At great
distances from the transmitter the skywave intensity drops off more rapidly
than inversely with distance (see Fig 56) presumably because the reflection
coefficient becomes less when the angle of incidence of the skywave
approaches glancing, and also because at at considerable distances the
skywave may have made two or three round trips between the ionosphere and
the earth before reaching the receiving point."

http://i62.photobucket.com/albums/h8...ermanFig56.jpg

RF




Whereas a steeper launch angle results
in the wave front penetrating the bottom of the F layer, being
refracted to a shallower angle once inside the ducting region, being
ducted long distances with far less absorption than it would for
multiple hops, and then again refracting and exiting the duct at a
steeper angle than one would expect for such a distance... This to my
mind is a common mechanism for those amazingly strong DX openings we
see...

denny / k8do

Elevation Patterns of Ground Mounted Vertical Monopoles
 

Yup, I made a typo when I said "F" layer in relation to Terman's
discussion of the E layer, - probably because I intended to discuss the
F layer...

But, I bring us back to the topic, no where do I see HF mentioned in
the quotes from Terman... Ground wave transmission becomes markedly
poorer beginning somewhere around a thousand KC - which is why hams
were relegated to the waste land of 200 meters and down....

BTW, here is an interesting discussion of the D and E layers for VLF
propgation...
http://www.aavso.org/observing/progr.../vlfprop.shtml

But to bring us back to the major complaint which seems to be that the
Nec engine doesn't model the last few degrees over ground very well, so
that the zero angle is discarded by the software... Richard seems on a
mission to prove the NEC engine wrong - well, I agree, the NEC engine
does have limitations for low angle signals which is why the authors
have installed an angle cut off... Per Richard's citations, Terman's
data proves that for MW signals - but not for HF ( a different kettle
of fish)...

If we look at the ham antenna literature over the 50 years predating
the advent of the NEC engine, we do not see much championing of the 5/8
wave vertical for lower HF... Since these folks did not have the NEC
engine poisoning their thinking one has to ask why the lack of
interest... The explanation for that, in my mind, is because it does
not have significant propagation advantage at HF offsetting it's
greater mechanical and financial burden to install... And because the
high angle lobes that are beginning to bulge are disadvantageous with
an antenna that is intended for low angle receiving/transmitting...

In my case I have a 4/8 wave vertical for 80 meter sitting on an
elevated base... Extending it to 5/8 wave would be a trivial task -
but I see no advantage to doing so...

denny / k8do

Elevation Patterns of Ground Mounted Vertical Monopoles
 

On 26 Sep 2006 11:56:36 -0700, "Denny" wrote:

the NEC engine
does have limitations for low angle signals which is why the authors
have installed an angle cut off... Per Richard's citations

Hi Denny,

Having done a bajillion designs in EZNEC, I take exception to this
comment for two reasons:

1. The low angle signals portrayed (or modeled) are easily
demonstrable and are certainly experienced by the any Ham;

2. EZNEC (notwithstanding other packages) easily offers 0 degree
field data that is within 1 dB of the classic Brown, Lewis, Epstein
findings.

If there is any anachronism in the NEC packages; then it is the
presumption of an Earth with infinite radius (no curvature). Here,
the far field curves diverge from the near field projections (and yet
you can still recover from that divergence if you wish, it is merely
tedious).

73's
Richard Clark, KB7QHC

Elevation Patterns of Ground Mounted Vertical Monopoles
 

Oh, and here is a citation from the KN4LF web site that I have long
forgotten about conciously but my subconcious must have been nibbling
at because I suddenly had a compulsion to check his web site...
quote
************************************************** **********************************************8
Another note! When it comes to 160 meter vertical antenna's you can get
a lower take off angle (TOA) from a full 1/4 wave vertical or
electrical 1/4 wave tee vertical of 10-20 deg., versus ~30 deg. with
the inverted L. However it's a moot point as the night time E layer MUF
blocks 160 meter low angle transmitted radio signals from ever reaching
the F layer to be propagated. So unlike with HF propagation, MF
propagation success does not require the lowest of take off angles.
Also higher take off angles of 30-40 deg. via the inverted L are better
able to take advantage of the low signal loss E valley-F layer
propagation duct mechanism, a form of Chordal hop propagation.
************************************************** ********************************************
unquote

OK, so we are mixing theory with empirical results here, but, if having
the lowest possible angle of antenna response at 160 and 80 meters was
the best, by now a majority of the flagship contest stations would be
equipped with 5/8 wave vertical arrays, and they are not... I only know
of one major contest station that uses a 5/8 wave vertical on either of
the bottom HF bands...
My own experience is that the 1/4 wave vertical is superior on 160 but
not on 80... Nor is the half wave vertical on 80 superior to a high
dipole... The 80/160 vertical sits over a hundred half wave radials...
The high dipole hangs over forest with below average sandy soil......

denny / k8do

Elevation Patterns of Ground Mounted Vertical Monopoles
 

"Denny" wrote
But, I bring us back to the topic, no where do I see HF mentioned
in the quotes from Terman... Ground wave transmission becomes
markedly poorer beginning somewhere around a thousand KC -
which is why hams were relegated to the waste land of 200 meters
and down....
_________

Just to point out that, although groundwave _propagation loss_ is greater
when progressing from lower to higher radio frequencies, the radiation
patterns and peak gains in the horizontal plane from ground-mounted vertical
radiators remain the same for corresponding radiator heights in wavelengths
and equal r-f ground resistances, no matter what the frequency.

All ground-mounted, vertical monopoles through 5/8-wavelength in height
develop maximum radiated relative field in the horizontal plane. If the
vertical radiator is 1/4-wave tall, then the _radiated_ elevation pattern is
approximately a function of the cosine of the elevation angle, no matter
what the ground conditions are, at and near the radiator site.

These are the distinctions I am trying to make, because the common belief
seems to be that the relative field of the elevation pattern launched by a
ground-mounted vertical is dependent on ground conditions, and always zero
in the horizontal plane to peak at some greater elevation angle.

The field strengths measured by Brown, Lewis & Epstein in the benchmark 1937
study defining an effective r-f ground were taken at 3 MHz. And for the
best-case radial ground system the groundwave fields at 3/10 of a mile were
within a few percent of the theoretical maximum possible for that radiated
power over a perfectly conducting earth -- even though the tests were done
in NJ over a path of rather poor conductivity -- maybe 4 mS/m. It's clear
from this that even in the low HF spectrum, the field radiated from their
test antenna over a poor earth path was not zero in the horizontal plane!

RF

Elevation Patterns of Ground Mounted Vertical Monopoles
 

On Tue, 26 Sep 2006 16:22:15 -0500, "Richard Fry"
wrote:


All ground-mounted, vertical monopoles through 5/8-wavelength in height
develop maximum radiated relative field in the horizontal plane. If the

Richard,is this true in general, or is it restricted to perfect ground
(infinite size, perfect conductor, perfectly flat).

NEC models would suggest that the major lobe of a monopole up to 5/8
wave over "real" ground is dependent on the ground characteristics,
and can be quite high relative to the 0deg to 3deg region that people
are focussing upon.

Owen
--

Elevation Patterns of Ground Mounted Vertical Monopoles
 

"Owen Duffy" wrote
On Tue, 26 Sep 2006 16:22:15 -0500, "Richard Fry"
wrote:
All ground-mounted, vertical monopoles through 5/8-wavelength in height
develop maximum radiated relative field in the horizontal plane. If the

Richard,is this true in general, or is it restricted to perfect ground
(infinite size, perfect conductor, perfectly flat).

NEC models would suggest that the major lobe of a monopole up to 5/8
wave over "real" ground is dependent on the ground characteristics,
and can be quite high relative to the 0deg to 3deg region that people
are focussing upon.
__________________

For the shape of the relative field elevation pattern, it is true in
general. A poor r-f ground for the monopole (i.e., a ground of high r-f
resistance) will change the peak gain of that radiated elevation pattern,
but not its shape.

NEC evaluations typically don't show 100% relative field in the horizontal
plane in the elevation pattern radiated by a vertical monopole except over a
perfectly conducting ground plane, which is the root of all this confusion.

Once the radiation is launched, then it becomes subject to the propagation
losses for the path and frequency. But for verticals up to 5/8-wave tall,
peak relative field always lies in the horizontal plane, regardless of the
ground conditions on and near the radiator site. This is the basis used by
the FCC in determining the coverage capabilities of AM broadcast stations,
and has been proven to be a rather accurate approach going back some 60
years.

RF

Elevation Patterns of Ground Mounted Vertical Monopoles
 

"Denny" wrote
If we look at the ham antenna literature over the 50 years predating
the advent of the NEC engine, we do not see much championing of the 5/8
wave vertical for lower HF... Since these folks did not have the NEC
engine poisoning their thinking one has to ask why the lack of
interest... The explanation for that, in my mind, is because it does
not have significant propagation advantage at HF offsetting it's
greater mechanical and financial burden to install... And because the
high angle lobes that are beginning to bulge are disadvantageous with
an antenna that is intended for low angle receiving/transmitting...
__________________

A 5/8-wave vertical is more expensive than a 1/4-wave vertical for sure.
But the high-angle lobe that develops when the radiator height exceeds
1/2-wavelength maybe isn't as serious as thought. At HF, probably the
groundwave is gone before that high-angle radiation returns to the earth via
skip, so it won't cause self-interference even if you are trying to use the
groundwave.

Below is a link to a clip from the FCC website, showing the elevation
patterns for vertical radiators of several heights in wavelengths. For a
given applied tx power, the sidelobe of the 5/8-wave vertical is
significantly greater in radiated field than that of a 1/4-wave from about
60 to 80 degrees. But the 5/8-wave has higher radiated field than the
1/4-wave at elevation angles below ~18 degrees -- which would benefit HF
DX.

AM broadcast stations operating full time with 50 kW transmitters tend to
use radiators of about 195 degrees in height. This gives them much of the
gain advantage over a 1/4-wave in and near the horizontal plane, which helps
their groundwave and DX coverage. But radiators of that height have an
insignificant high-angle lobe to worsen their self-interference at the edge
of their groundwave coverage area. Of course because of the frequency,
their groundwave can cover an area having a large radius.

http://i62.photobucket.com/albums/h85/rfry-100/73.jpg

RF