Richard,

Is that you, or did your evil twin steal your role on RRAA?

Try reading my comment again. If you still disagree, then perhaps you
should crack open any elementary physics or optics textbook.

I did not mention antennas or lobes. I was commenting on your assertion
that the horizontal polarization is "shorted out" at a conducting
surface. Utter nonsense.

73,
Gene
W4SZ



Richard Clark wrote:
On Wed, 05 May 2004 22:38:06 GMT, Gene Fuller
wrote:


Richard,

Are you sure you meant the statements quoted below?

Horizontal polarization bounces just fine from "horizontally conducting
surfaces". Indeed, when a mixed polarization wave hits a conducting
surface the horizontal polarization in the reflected wave is enhanced,
not "short-circuited". This is the same phenomenon that is the related
to Brewster's angle.

Perhaps you really meant to say that a special guided wave mode, namely
the ground wave, does not support horizontal polarization.

73,
Gene
W4SZ

Richard Clark wrote:

[Lots of more or less correct stuff snipped]


A horizontally polarized antenna seeing a horizontally conducting
surface is a scenario that describes a self-short-circuit.
Horizontally polarized waves meeting the earth (a conductive one)
immediately snuff themselves (how long would your car battery last
with a screwdriver held across its poles?).



Hi Gene,

Vertical polarization is the only mode that the Brewster Angle works
for (that's why polarized sunglasses work so well, they are
contra-polarized for what DOES reflect).

To test your hypothesis, use EZNEC over a perfect ground and note the
distinct difference at low angles (less than 5 degrees). The
horizontal radiation lobe is an example of Lambertian (another Optics
term) distribution where the maximal gain is observed directly
overhead, and only when phases positively combine (due to the high
surface conduction presenting a second source). Other phases give
rise to this Lambertian distribution which is much like the lobe
characteristics of a headlight glowing in the fog.

73's
Richard Clark, KB7QHC

Gene, W4SZ wrote:
"---I was commenting on your assertion that the horizontal polarization
is "shorted out" at a conductive surfacce."

Richard Clark`s description may be indelicate but as I recall, Terman
says rouighly the same in several instances. Wish I had a copy at hand.
Terman says that a horizontally polarized low-angle wave suffers a phase
reversal upon reflection and as the difference in path length is
negligible between incident and reflected waves at low angles, the waves
being of opposite phase add to zero.

Best regards, Richard Harrison, KB5WZI

On Wed, 5 May 2004 21:49:41 -0500, (Richard
Harrison) wrote:

Gene, W4SZ wrote:
"---I was commenting on your assertion that the horizontal polarization
is "shorted out" at a conductive surfacce."

Richard Clark`s description may be indelicate but as I recall, Terman
says rouighly the same in several instances. Wish I had a copy at hand.
Terman says that a horizontally polarized low-angle wave suffers a phase
reversal upon reflection and as the difference in path length is
negligible between incident and reflected waves at low angles, the waves
being of opposite phase add to zero.

Indelicate or blunt, the results are the same. The Lambertian
distribution of a characteristic that is painfully 30 dB down due to
the presence of a perfect conductor plainly evidences severe loss. It
can't be the ohmic loss of conduction as this would negate the premise
of a perfect conductor, it can't be the dissipation factor of an
insulator for the same reason.

The electric dipole moment is clearly bridged by a conductor, by
definition. As such, at the interface, it must collapse completely
into a current which gives rise to counter emf, the two waves cancel
as a function of phase - the proof again is found in the Lambertian
distribution that vanishes completely with the removal of ground (why
horizontal antennas are held up in the air). The more remote the
ground, the greater the variation of phase and the distribution, and
yet the low angles never fully recover (the death embrace of ground is
always there).

The ONLY deficit the vertical sees is in the characteristic Z of the
interface presenting a Brewster Angle that allows unfettered passage
of power through the interface and traps it. Again, it is the ratio
of the characteristic Zs that account for this. If you could contrive
to find an earth characteristic of 4000 Ohms instead of Salt Water's
40, then you would observe the EXACT SAME characteristics of
propagation. The poorest earth almost looks like the Z of the æther.
This means that the power impinging upon it is trapped (because ray
tracing would reveal it trying to penetrate the earth to re-emerge in
the antipodes). Hence the conduction explanation is a contrivance
that fits only through the imposition of a limited experience.

Replace the perfect conductor of an imaginary world with that of a
realistic earth and the Horizontal's low angle response still sucks to
the tune of 30dB down (for the terminally anal, perhaps closer to
-26dB). This says Horizontals suffer for the same reason irrespective
of earth conductivity (unless perhaps you are on a mile high mountain
of glass ). In some sense, this suggests that at least you don't have
to worry about it too much because there is nothing you can do about
it (although I have disproved this too).

On the other hand, for verticals, the variation of earth
characteristics gives rise to a wide variation in low angle response.
And for some earth characteristics, the vertical is clearly the winner
by an order of magnitude (dare I say in excess of one S-Unit?).

Is this boon conduction borne? If Salt water with a pathetic
conductivity orders of magnitude beneath nichrome wire is superb, then
by the facile logic of conductivity, we should see remarkable
performance boosts for a plain of silver. No, the conductivity
argument is simply the tales we tell frightened children who awake
from DX nightmares. ;-)

73's
Richard Clark, KB7QHC

"Richard Clark" wrote

The electric dipole moment is clearly bridged by a conductor, by
definition. As such, at the interface, it must collapse completely
into a current which gives rise to counter emf, the two waves cancel
as a function of phase - the proof again is found in the Lambertian
distribution that vanishes completely with the removal of ground (why
horizontal antennas are held up in the air). The more remote the
ground, the greater the variation of phase and the distribution, and
yet the low angles never fully recover (the death embrace of ground is
always there).

Richard, would the dipole's performance thus be improved by bedding the
ground with sand, and hurt by adding ground radials? Same true if the dipole
was at some compromise between 1/4 wave and the desired 1/2 wave above
ground?

Regards,

Jack Painter
Virginia Beach, Va (where mostly sand exists anyway)

"Richard Clark" wrote

The electric dipole moment is clearly bridged by a conductor, by
definition. As such, at the interface, it must collapse completely
into a current which gives rise to counter emf, the two waves cancel
as a function of phase - the proof again is found in the Lambertian
distribution that vanishes completely with the removal of ground (why
horizontal antennas are held up in the air). The more remote the
ground, the greater the variation of phase and the distribution, and
yet the low angles never fully recover (the death embrace of ground is
always there).

Richard, would the dipole's performance thus be improved by bedding the
ground with sand, and hurt by adding ground radials? Same true if the dipole
was at some compromise between 1/4 wave and the desired 1/2 wave above
ground?

Regards,

Jack Painter
Virginia Beach, Va (where mostly sand exists anyway)

On Thu, 6 May 2004 12:47:58 -0400, "Jack Painter"
wrote:

"Richard Clark" wrote

The electric dipole moment is clearly bridged by a conductor, by
definition. As such, at the interface, it must collapse completely
into a current which gives rise to counter emf, the two waves cancel
as a function of phase - the proof again is found in the Lambertian
distribution that vanishes completely with the removal of ground (why
horizontal antennas are held up in the air). The more remote the
ground, the greater the variation of phase and the distribution, and
yet the low angles never fully recover (the death embrace of ground is
always there).

Richard, would the dipole's performance thus be improved by bedding the
ground with sand, and hurt by adding ground radials? Same true if the dipole
was at some compromise between 1/4 wave and the desired 1/2 wave above
ground?

Hi Jack,

A good question, and one that brings out the one of my elliptical
statements about having disproven you don't have to worry, because
there is nothing you can do.

In fact you can do something, however, it separates the discussion of
ground insofar as near field and far field issues.

IF you add a ground screen below a horizonal antenna, you CAN improve
your communications efficiency (your contact, with sufficient
resolution, could see an improved, stronger signal).

This, of course, has no strength in its argument in the far field, the
same problem exists of the complete collapse of the electric field
through its polarization giving rise to a canceling current. The near
field application (where the media does NOT exhibit a 377 Ohm
characteristic) is one of shielding the source from loss (which is
largely a dielectric loss, not a conductive, Ohmic loss).

Richard Harrison, KB5WZI, has already recalled Terman's treatment, but
having no reference handy, he hadn't really pulled it together.

The point of the matter is that for a conductive ground, the electric
fields are laid across a short. The obvious occurs and that electric
field collapses into a magnetic field (through the short circuit
current that necessarily follows) at the interface. This simple
statement is enough to evidence the reversal of fortune (magnetic
replacing electric in the face of its initiating source spells short
circuit city).

At a distance (along the magic 0° DX launch angle), BOTH the source
and its reflection (or image) in the ground below it, are at an equal
distance to the observer. Thus the distant observers (if they could)
see TWO sources that are 180° out of phase. Thus everywhere along
this meridian, those two signal completely cancel. With tongue in
cheek, let's call this 100dB down. This happens ONLY for horizontal
polarized signals. By shielding ground beneath the horizontal
antenna, you are doing nothing to change this star fixed fate; but you
are improving efficiency with a net positive gain, relatively
speaking. You simply have two stronger signals canceling.

At higher angles, lets call them 5° or higher (sometimes much higher)
the path lengths of the two sources diverge from equality (a phase
shift is introduced) as the signal strength attempts to pull toward
the free space value, some 30dB higher. If you pull your attention
successively higher, you eventual come to the point where the two path
lengths introduce enough phase difference that they combine to a net
signal that is greater than the free space value. This, by the way,
does not constitute DX opportunity and is crowed about as the great
NVIS advantage (in other words, the sufferer has no options and is
content to make lemonade). This exercise describes the Lambertian
distribution, a classic example of Optical sources.

Raising the horizontal is much the same gain story. It removes itself
from the cold embrace of earth's loss, and it introduces a new phase
combination. Thus the lobes may lower from the Zenith, but you will
never see them pulled all the way down to the horizon, such is the
fate of horizontality. ;-)

73's
Richard Clark, KB7QHC

Richard,

I am well aware of the properties of the phase reversal, cancellation of
direct and reflected waves, and so on. I have no substantive
disagreements with Terman.

I suspect Richard Clark was exercising a bit of poetic license by
stating that the horizontal polarization was "shorted" at the conducting
ground plane, perhaps in a vain attempt to simplify his explanation to
the original poster.

However, this statement is simply wrong. If it were true there would be
no NVIS nor any reflections at all from a normal incidence wave on a
conducting surface. Radar would not work. Mirrors would not work.

Wave cancellation is not such a difficult topic (except on RRAA). There
is no need to invoke phony arguments about waves "shorting".

73,
Gene
W4SZ

Richard Harrison wrote:
Gene, W4SZ wrote:
"---I was commenting on your assertion that the horizontal polarization
is "shorted out" at a conductive surfacce."

Richard Clark`s description may be indelicate but as I recall, Terman
says rouighly the same in several instances. Wish I had a copy at hand.
Terman says that a horizontally polarized low-angle wave suffers a phase
reversal upon reflection and as the difference in path length is
negligible between incident and reflected waves at low angles, the waves
being of opposite phase add to zero.

Best regards, Richard Harrison, KB5WZI

Gene, W4SZ wrote:
"There is no need to invoke phony arguments about waves "shorting"."

Shorting waves does not annihilate them. It merely reflects them. A
short is a low-resistance conductor.

A transmission line short is a low-impedance U-turn for for the wave`s
current which forces the voltage between conductors to zero.
Cancellation of the electric field sends its energy for an instant to
the magnetic field. As these two conjoined fields continuously
regenerate each other, the electric field is immediately recreated by
the enhanced magnetic field. The electric field goes from zero at the
short to double the incidet just 1/4-wave back from the short due to
addition of the incident and reflected wave vectors (phasors).

For a complete reflection in a short, you need zero resistance.
Otherwise, resistance consumes some of the available energy.

When a radio wave strikes the ground, it is reflected. Angle of
reflection equals the incidence angle but because the earth is an
imperfect reflector the reflection is ncomplete. Reflection depends on
incidence amgle, wave polarization, frequency, and type of earth. The
reflection occurs as if the R-F wave were an optical wave.

NVIS is simple to do by using a horizontal dipole up 1/4-wave above the
earth. The wave is delayed 90-degrees in travel to the earth. It is
delayed 180-degrees by earth reflection. Then, another 90-degrees of
delay is experienced in the reflected wave`s return to the vicinity of
the dipole. The 360-degree total round-trip delay puts the reflected
wave back in-phase with newly emerging radiation from the dipole in its
travel toward the zenith. If the ionosphere can reflect this high-angle
energy, it can cause reception fairly close to the transmitter.

Best regards, Richard Harrison, KB5WZI