I have a question similar to but different from the one posted a few lines
below. How do you determine the quality of an antenna ground at HF on an
absolute basis? Not how well have I maximized what Mother Nature gave me at
my QTH by adding radials, but how good is my ground compared to other
stations' grounds at other locations? I have read about the advantages of
seawater, ground conductivity etc as guidelines, but how is overall ground
quality (not just soil resistivity) determined objectively if indeed that is
possible at all?

George K6GW

On Thu, 02 Sep 2004 03:53:46 GMT, "GW"
wrote:

I have a question similar to but different from the one posted a few lines
below. How do you determine the quality of an antenna ground at HF on an
absolute basis? Not how well have I maximized what Mother Nature gave me at
my QTH by adding radials, but how good is my ground compared to other
stations' grounds at other locations? I have read about the advantages of
seawater, ground conductivity etc as guidelines, but how is overall ground
quality (not just soil resistivity) determined objectively if indeed that is
possible at all?

Hi George,

You compare a measured value with the theoretical, the difference is
loss. Less loss = better (objective goal expressed subjectively).

To state the objective goal objectively, you describe the difference
in dB. However, this quickly devolves to a subjective test, because
only your contact can appreciate the difference, and too often the
difference is less than many other factors of variability (like
fading).

So, let's put this in objective terms. With a dozen radials down, you
could double or quadruple that to achieve 2dB more power out. 2dB on
the conventional S-Meter may barely register more than a needle's
width change while your signal is otherwise dropping and rising 10dB
through a QSO. Go the limit (theoretical of course) of 120 radials
and you perhaps achieve 3 to 4 dB or two needle's widths.

Another objective test is to measure the resistance and compare it to
theoretical. However, take care to observe that theory covers a lot
of ground (no pun) principally depending upon the thickness of the
radiator. To take a useful and common indicator, that value would be
36 Ohms. If you measured 50 Ohms, the excess 14 Ohms could be thought
to be residing in poor connections and the loss of ground. You would
then tighten connections and add radials to shield against ground
loss. Hence by these actions, resistance would lower, and oddly (that
is, in contradiction to misguided expectations) SWR would rise. It is
unlikely you will add enough radials to achieve theoretical, but close
enough counts in RF, hand grenades, and H-Bombs.

It is called the law of diminishing returns (a business concept) where
the more you put into the ground is not matched in continued, improved
performance. It is the first few that count the most.

73's
Richard Clark, KB7QHC

GW asked (clip):
How do you determine the quality of an antenna ground at HF
on an absolute basis? Not how well have I maximized what
Mother Nature gave me at my QTH by adding radials, but
how good is my ground compared to other stations' grounds
at other locations?
______________

A low-resistance ground connection for a transmit antenna is important to
the received signal level only when the antenna design requires it as a
reference for its driven element, such as with the vertical radiators used
in MW broadcasting.

Most HF/VHF/UHF transmit antennas do not need, or use an earth ground for
efficient radiation. As practical proof of this, recall that airborne
antennas have no connection at all to earth ground, but still work just
fine. And the transmit antennas used in commercial FM & TV broadcast are
installed at the top of a tall tower, many wavelengths (and ohms) above
earth potential. The tower is grounded for safety reasons, but the
radiation patterns and received signal levels from those antennas would be
the same even if that tower was not grounded.

RF

Visit http://rfry.org for FM broadcast RF system papers.

"GW" wrote
I have a question similar to but different from the one posted a few lines
below. How do you determine the quality of an antenna ground at HF on an
absolute basis? Not how well have I maximized what Mother Nature gave me
at
my QTH by adding radials, but how good is my ground compared to other
stations' grounds at other locations? I have read about the advantages of
seawater, ground conductivity etc as guidelines, but how is overall ground
quality (not just soil resistivity) determined objectively if indeed that
is
possible at all?

================================

The performance of a ground electrode system cannot be separated from that
of an associated antenna. But at least the antenna can be standardised by
assuming it to be a simple vertical of given height. And we won't go far
wrong by assuming the antenna efficiency to be 100 percent.

Engineering Quality is a numerical measure of how well something serves its
intended purpose.

Since the purpose of a ground + antenna system is to radiate em waves the
only possible numerical measure of Quality is radiating power efficiency
measured as a percentage.

With beautiful and fortunate simplicity, the radiating efficiency of such a
system is given by -

Eff = Rrad / ( Rrad + Rloss ) times 100%.

where Rrad is the antenna's radiation resistance looking into the base of
the antenna, and Rloss is the resistance looking into the focal point of the
ground electrode system, immediately under the antenna, such as a set of
radial wires. Or it may be a single rod.

It is impossible to separately measure Rrad and Rloss. But Rrad can be
calculated from the antenna's height and diameter and the two can be
measured together. From the combined single measurement the efficiency can
easily be calculated.

And that's where we part company with simplicity.

To calculate your "Quality on an absolute basis" of just the single ground
rod involves a list of numerical variables as long as your arm. To calculate
Quality of a system of radials imposes an impossible, intractible problem in
statistics.

To compare one system with another would involve everybody with several
lifetimes of fundamental research, measurement and guesswork which would get
nobody anywhere.

However, because radio is by far the most inexact of all the engineering
sciences, it doesn't matter a toss. All measurements are subject to error.
In most of which even the standard deviations can only be guessed at. When
will the next flare occur on our unstable Sun?

Radio engineers are quite accustomed to allowing safety margins of plus or
minus 15 or 20 dB along propagation paths. Even then distortion and error
rates are quoted. Brute force and ignorance and a lot of luck prevail.

So it doesn't matter whether or not Rloss lies between 1 and 10 ohms when
used with your top-band inverted-L and you havn't the foggiest idea what the
soil resistivity is in YOUR back yard.

Incidentally, ground loss is not only smaller in sea water, it is also
smaller with soil resistivities of several thousand ohms and greater.
There's a maximum somewhere in between.

To crudely estimate ground loss, download program RADIALS2 from website
below. It's all crammed into only 70 kilo-bytes. Nobody has yet complained
it gives the wrong answers.
--
.................................................. ..........
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
.................................................. ..........

On Thu, 2 Sep 2004 14:27:37 +0000 (UTC), "Reg Edwards"
wrote:

Incidentally, ground loss is not only smaller in sea water, it is also
smaller with soil resistivities of several thousand ohms and greater.
There's a maximum somewhere in between.

Hi George,

The statement above falls into the category of "Old Wives' Tales."
Given the choice for conductors, Sea Water ranks 6 or 7 orders of
magnitude in worse conductivity than any metal (or even carbon) you
would care to pick. By this logic, you should do everything in your
power to operate in an open pit coal mine. ;-)

We won't go into the egregious error of soil resistivity for the same
reasons of senior matriarchal fabrications.

The "legendary" characteristic of Sea Water is found in its far field
reflective characteristic which is remarkable, due largely to its huge
SWR to fields (the same SWR that would occur with the supposed several
thousand ohms of soil). That small boats use a patch on the bottom of
the keel to offer a counterpoise to RF simply exhibits how little
ground development is necessary when the huge asset of reflectivity
dominates this large loss of a poor ground connection (you should also
note the ironic application of "ground" in this regard).

To crudely estimate ground loss, download program RADIALS2 from website
below. It's all crammed into only 70 kilo-bytes. Nobody has yet complained
it gives the wrong answers.

For that matter, no one has even offered it works! Principally
because it places the onus on you proving one of two things:
1. it does work;
2. it does not work.
How can you tell? ;-)

You would stand a better chance with such forecasts using the old
Magic 8-Ball which would at least offer the occasional honest answer
like "Can't answer right now, try again."

Punchinello,

So, old man, tell us when you are going to offer any substantive
method that gives numbers to these illusions of ground you offer? The
soil of your back garden, much less Britain hardly are representative
of a much greater continental expanses beyond that little island you
occupy. The examples of your erroneous generalizations against
reality would be instructive if you simply expanded (embarrassingly
perhaps) on your kitchen calculations of mud calibration. After all,
its been simply YEARS since you offered such suggestions to no obvious
Kelvinian payoff.

73's
Richard Clark, KB7QHC

"Richard Clark" wrote (clip):
The "legendary" characteristic of Sea Water is found in its far field
reflective characteristic which is remarkable, due largely to its huge
SWR to fields (the same SWR that would occur with the supposed several
thousand ohms of soil).
____________

How does the statement above reconcile with the fact that groundwave daytime
signal strength is far better over a sea water path than any ground path?
There is (essentially) no returning skywave signal to reflect during
daylight hours.

Observe the daytime field strength contours shown on the link below for WABC
radio, for example.

http://www.radio-locator.com/cgi-bin...atus=L&hours=D

RF

On Thu, 2 Sep 2004 11:46:00 -0500, "Richard Fry"
wrote:

"Richard Clark" wrote (clip):
The "legendary" characteristic of Sea Water is found in its far field
reflective characteristic which is remarkable, due largely to its huge
SWR to fields (the same SWR that would occur with the supposed several
thousand ohms of soil).
____________

How does the statement above reconcile with the fact that groundwave daytime
signal strength is far better over a sea water path than any ground path?

Hi OM,

Perhaps you should attend the quote above again. For instance, how is
it that statements in agreement require "reconciliation?"

73's
Richard Clark, KB7QHC

"Richard Clark" wrote (clip posted by R. Fry):
The "legendary" characteristic of Sea Water is found in its far field
reflective characteristic which is remarkable, due largely to its huge
SWR to fields (the same SWR that would occur with the supposed several
thousand ohms of soil).
____________

How does the statement above reconcile with the fact that groundwave
daytime
signal strength is far better over a sea water path than any ground path?
R. Fry.

Hi OM,

Perhaps you should attend the quote above again. For instance, how is
it that statements in agreement require "reconciliation?"

73's
Richard Clark, KB7QHC

So you are saying that sea water paths provide far better groundwave
propagation than overland paths because sea water a such a good reflector?

RF

Richard Clark wrote:
"The legendary characteristic of Sea Water is found in its far field
reflective characteristic which is remarkable due largely to its huge
SWR to fields---."

Yes, a wave striking the sea finds a high reflection coefficient and
ground waves do well too.

I am looking at a broadcast allocation book prepared by Cleveland
Institute of Radio Electronics in 1959. Many changes in stations and
coverage since then, but the book contains an estimated ground
conductivity map for the U.S.A. which probably has changed very little
since then.

Coastal Texas is almost as good as it gets when it comes to soil on the
map, 30 millimhos per meter. Seawater is not shown on the map but its
conductivity is given as 5,000 millimhos per meter or 167 times as good
as the best soil. Around New York City, conductivity is shown between
0.5 and 4 millimhos. Surface irregularities caused by structures make
additional attenuation.

The conductivities shown on the map are probably good averages as the
preparers had the propagation data of thousands of broadcast stations
which proved their performance to the FCC to work with.

Terman has a ground constant table on page 808 of his 1955 of his 1955
edition. Sea water is given a conductivity of 45,000 micromhos per cm,
or 45 millimhos per cm.

John Cunningham says in "The Complete Broadcast Antenna Handbook: on
page 309 that:
"The conductivity of the earth ranges from about 2 millimhos per meter
for dry sandy locations to as high as 5 mhos/m for sea water."

I think the figures given above are in reasonable agreement. I haven`t
researched the conductivity of carbon, but it is reasonably high being
used for motor brushes, battery electrodes, and vacuum tube plates.

Best regards, Richard Harrison, KB5WZI

"Richard Harrison" wrote (clip):
I am looking at a broadcast allocation book prepared
by Cleveland Institute of Radio Electronics in 1959.
Many changes in stations and coverage since then,
but the book contains an estimated ground conductivity
map for the U.S.A. which probably has changed very little
since then.
________________

The FCC's version of the US ground conductivity map is available on line at
http://www.fcc.gov/mb/audio/m3/

RF