Hi All,
> Use care in interpreting modeling results relative to the real world. It
> is easy (too easy?) in a model to make a perfectly balanced n-wire radial
> system and quite another to make one in the field. A small imbalance
> (<5% length difference) in one wire of the modeled radial system with 4
> wires makes a considerable difference in the pattern shape. This is
> something that Dick Weber and others have been working on with finding a
> higher Z point for starting the radials, etc.
Read my reply in Comm Quarterly to this theory.
Everyone seems to dismiss simple physics. The ONLY way balancing current
exactly will prevent radiation is if:
1.) The radials are in the far field of the point of interest. In other
words, if the radial is so far above earth it "looks like" radiation comes
from one point with equal and opposite currents and potentials, that point
on the ground will see no radiation or induction fields.
That won't be the case if the radial is less than a height much greater
than it's length, or 1/2 wl or more above earth. At heights less than that,
the radial system will couple to lossy earth no matter what is done in the
radial system. Making the radials system dense by adding wires will reduce
unwanted coupling.
2.) If the radial is installed in a non-homogenous environment, or over
soil with varying electrical characteristics, balancing current will INSURE
the radial system radiates in the far field.
Since most of us have a lot of crap around the radials, and the dirt is
never the same conductivity and moisture content under each radial, it is a
certainty that the radial system will radiate in the far field even with
perfectly balanced currents in the wires because unwanted and unequal
current in their surroundings will upset cancellation.
> So even if more radials than 4-8 were to reduce gain by the NEC-4
> indicated amount of well under 0.1 dB, they may have other functions of
> equal or greater importance. With elevated radials, one may not need the
> full 120 recommended for underground use, but more than 4 can relieve
some
> imbalance problems if one does not have the engineering wherewithal to
> make a perfectly symmetrical system or cannot adopt one of the
alternative
> strategies in recent literature.
I disagree that the "strategies" would ever work. I did a test in an open
pasture, with nothing but dirt below the radials. Radials were ten feet
high on 80 meters.
Four loaded radials .125 wl long produced LESS FS in every direction and
much less bandwidth than four elevated radials. 16 ground mounted radials
were about 1 dB up from four elevated radials and had much broader
bandwidth. 60 ground mounted radials were several dB better than four
loaded radials, and about 3 dB better than 16 radials on the ground.
This is the second time I measured this in a test setup, and it was also
measured at BC stations when radials were changed. To date, the isn't a
single comparison of the systems WITH ONLY A RADIAL CHANGE that supports
any of these theories. In comparison, there are several systems where
measurements have shown the opposite. (I think N7CL will also support this)
I measured this stuff here on my farm before installing verticals, because
I like to do the least work possible for a good signal. I now have 60
radials on every vertical, that includes a 160 meter four square with 1/4
wl verticals and a 200 ft omni - vertical. You can bet if I didn't
absolutely have to do that work, I wouldn't have done it.
The free lunch program hasn't reached antennas just yet, unfortunately! New
theories are nice, but they need verification before publication.
73 Tom
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