I share the frustration over the very minimal amount of data out there.
However...
Erection of a 260 foot vertical in a testing environment fairly well
requires the facilities of a large antenna range to do the comparisons
below. Thus we are also talking about money, and we are talking about a
subject where all the pressing *commercial *questions have been answered for
nearly a century. We are also talking about research that was done 1920 to
1940, well outside the time of electronic media and as far as I can tell
never converted, again an expensive task with no commercial or government
money to pay for grad students digging it up and putting it on the internet.
How would one justify the grant money?
Besides that, who do you know putting up a 260 foot vertical? Why are we
even talking about that? W8JI has done that. He would :>) Who else?
Does Warren Buffet have a ham license? How does a 260 foot vertical stack
up against HOA restrictions. That's FAA tower listing territory in
metropolitan areas, or near any airport. Lighting requirements. Six acres
for the tower and guys. Back to the realm of the possible for common
folk....
There is an EZNEC issue in *modeling* (vs measuring) ground effects:
Measured ground induction losses in situations *not *using radials, or* less
than dense* or *miscellaneous* radials, on the whole can be significantly*worse
*than modeling would anticipate. Roy Lewallen W7EL, author of EZNEC, will
confirm this, and will also state that the ground *estimation *method in use
cannot cope with dirt with layered characteristics. The ground method
presumes a monolithic, uniform substance, with no changes in moisture, no
changes in anything, proceeding to depth where current is no longer
significant.
The lower frequency penetrates deeper. Deep enough that you find old Bell
Labs stuff about *underground *antennas that apparently worked at LF,
presumably only used for RX, but I don't know that. In typical ham property
this brings items into play such as buried electric cables, buried iron or
steel gas or water pipes, water tables, septic fields, actual layering in
different soil materials from ancient events and weathering over stream
beds. In the vicinity of my QTH this brings into play a layer of heavily
carbonized clay from what was probably a forest fire before human history.
It also includes such things as fill dirt with concrete or road debris used
to level out property before building and then covered with a nice layer of
"good" dirt suitable for plants, trees, grass, etc. And if that's not
enough, then there is variation in moisture content, where soil is at 100%
humidity down three, four, five feet where the temperature of dirt goes to
the standard ground temperature for an area (the temperature in caves,
etc.), even in a drought. Typical dirt underfoot is anything *except *
monolithic.
In EZNEC one can enter the conductivity (S/m) and dielectric constant
directly, assuming you have the stuff to measure that, and the time to
verify that is constant all over your property, *or *you can pick from the
following choices, beginning with awful squared and progressing to the very
best.
Extremely Poor: cities, high bldgs.
Very Poor: cities industrial.
Sandy, dry
Poor: rocky, mountainous
Average: pastoral, heavy clay
Pastoral, med hills and forestation
Flat, marshy, densely wooded
Pastoral, rich soil, US Midwest
Very Good pastoral, rich central US
Fresh water **
Salt water
(** Fresh water is a special case that does not fit on the spectrum from
least conductive to most conductive. If it were arranged by conductivity
only, it would go with "extremely poor". The dielectric constant is the
same as salt water.)
Why list these? Around Raleigh we had an experiment with 151' insulated
dipoles laying directly on the dirt, finding their resonant frequencies, and
feed resistance at resonance, and change from resonance at +/- 50 kHz from
resonance. It was first an experiment to determine typical velocity factors
for creating BOG RX antennas (beverage on ground). The other ramifications
were realized later. The results were unbelievably variable, with measured
velocity factor from 45% to 80%. In some cases varying wildly by position
or orientation on the same property. THIS is what we're trying to estimate
with a monolithic method in EZNEC.
With just a few exceptions, when put in EZNEC and the ground characteristics
adjusted to get the model to produce the measured results, it took poor and
very poor ground settings to get it to match to any decent degree.
This means that induced current in the dirt is indirectly *measured* far
more lossy on average than we expect based on our looking at the EZNEC
ground choices and descriptions.
Dense radials shield us (significantly but not completely) from those
effects where the E fields are the strongest, without them we underestimate
the losses. Also from the dinner plate example, the cost of of seeing the
floor from the light source is more extreme than we first think. To more
closely conform to reality, use a dinner plate that is opaque white in the
center and gradually progresses to transparency at the edge, gradually
seeing more of the dark floor underneath.
For those of you with EZNEC, to see the effects of radial reduction or
miscellaneous placement, construct a model with 120 radials. Reduce to 60 if
your version won't permit that many segments. This is very easy in the wires
window using "create" and "radials". Set the ground description to "Very
Poor". Do all computations with 3D plot type.
For those of you without the NEC-4 version, to model buried radials use
radials two wire diameters above the ground. (Lewallen's excellent EZNEC
help material on this subject is a good read).
This will probably give an overly pessimistic distant result with "FF plot",
but just ignore that, it's one of those "other issues". Write down the best
pattern gain and the "Average Gain" figure that appears on the bottom of the
main window after running FF plot on your overkill start model. This is your
reference. Ignore the absolute value of these numbers and concentrate on the
CHANGE as items are tinkered with. This is showing you the most likely
CHANGE in results if you were performing this experiment for real on your
own property. Hitting the absolute value is a fair controversy, and
involves even more convoluted issues than those presented here.
Change the radiator to see what happens to the best pattern gain and angle,
and to average gain. Look at the differences between the overkill quarter
wave and the quarter wave as radials become fewer and/or "miscellaneous".
In many, not all, cases the change in pattern gain can outweigh the loss in
average gain. If that's at an angle you want, it's a winner in spite of the
increasing overall loss.
I would think that some of you out there MUST have that uniform deep
monolithic rich "pastoral" soil and DO get the good results in spite of a
certain degree of sparseness or non-uniformity. I am jealous to a degree
you cannot imagine, but the XYL is NOT moving. But the egregious error is
to extrapolate that very good fortune as if it were the common or the
default state, and having hams spending their hard-earned bux and time on
erecting 160 antenna solutions that *require *that good fortune to function
well, and without that good fortune are doomed to throw away significant dB
and even QSO-blocking dB running 100 watts or QRP.
The ancient forest fire here, and the double water table, and the
transitions from carbonized clay to hard-pan almost rock clay to sand, to
regular clay, to hauled in fill dirt of only God knows what characteristics,
septic fields, etc., mean that use of "average" ground in EZNEC computations
for my property is a total pipe dream. For my property, especially since
there is no room for the ground-shielding commercial solution, the
only-elephant-in-the-room issue for me on 160 performance is how to avoid
ground induction losses. You are listening to my attempt at that on the air
with NO radials at all on my inverted L. Since I have no way to have dense
and uniform radials on my property, why bother with radials at all.
The counterpoise in use is specifically designed to "self cancel" fields
from the counterpoise current as much as possible, and the radiator is
designed to get the current max as high as possible (up 70 to 90 feet on a
3/8 wave L). This also increases the feed Z to the 90 ohm region and further
cuts down on uncancelled current in the counterpoise, correspondingly
FURTHER reducing lossy induced ground current. There are no unintended,
undiagnosed, unaccounted for ground losses from sparse or miscellaneous
radials because there are no radials. Lossy common mode current on the
feedline is eliminated with an isolation transformer at the feed, and I used
various devices to keep the feedline from being a significant conductor in
the near field.
See you on the air.
73, Guy.
On Tue, Sep 20, 2011 at 8:45 AM, Rik van Riel <riel@surriel.com> wrote:
> On 09/17/2011 01:19 PM, Richard (Rick) Karlquist wrote:
>
> > I'm still waiting to see an actual measurement showing that a 1/2
> > wave vertical with minimal radials is worse than a 1/4 wave
> > vertical with radials. My measurements were over high conductivity
> > ground. Maybe they would be different in the desert.
>
> That's hard to imagine.
>
> A 1/2 wave vertical without any radials at all is only
> a few dB (2-6 depending on ground type and exact antenna
> shape) below that of a 1/4 wave vertical over totally
> perfect ground.
>
> I'm sure a 1/4 wave vertical with 8 raised radials,
> all raised maybe 10-20ft above ground, would be better
> still - but only by a few dB and it'd take up a lot
> more real estate...
>
> --
> All rights reversed.
> _______________________________________________
> UR RST IS ... ... ..9 QSB QSB - hw? BK
>
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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