An awful lot of our advice depends on unnoticed assumptions based in the
commercial BC paradigm.
Go to any place where there is a commercial AM BC tower. Figure out a one
wavelength radius circle around the tower(s) . Tell me how many trees you
see in the circle(s). Tell me whether it is mostly level. Tell me how many
above-ground conductors bisect the area. Tell me if it is cluttered by
anything other than mandatory buildings, and how large they are. Tell me if
the field surface is uniform grass or has a lot of roots that would take
the actual "ground" characteristics completely off a straight line scale of
"pure" ground characteristics.
In testing velocity factor for in/on ground RX antennas in the NC counties
around Raleigh/Durham, we discovered that in the same back yard a 90 degree
reorientation of the test DOG (dipole on ground) could make enormous
difference of VF, clearly indicating that trying to actually put down VF
compensated 1/4 wave radials could not be done with a single test DOG
figure. Also the VF varied wildly with varying height above actual ground.
One had to notch through the grass down to the actual surface of the dirt,
for the entire length, to get repeatable figures. On top of the grass, and
notched down to or just barely into the dirt gave very different answers.
Just barely into the dirt was the most consistent, but still varied with
moisture content. One needed to AVOID measuring in a dry season, unless
that was normal for most of the year.
The problem with the typical "as many as you can" of whatever advice is
that the unbalanced from miscellaneous length, environment and density as
you go around the compass *induces additional loss*. The commercial BC
paradigm is full size, dense and uniform all around. They do not discuss
the effects of the miscellany we hams introduce into radial implementation.
It is not allowed. The uniformity is real estate bought, cleared,
bulldozed, and specifically constructed. "60 plus radials of 1/4 wave"
advice to a ham is an unexplained advice to create the BC grade uniformity.
For many locations, the full size, dense and uniform all around
installation of 16 to 32 raised radials will outperform on/in ground
radials. This is because the RF fields can be uniform all around in the
elevated, and the particulars of the location (as in buried radials in the
woods, or back yards with buried iron pipe and electrical feeds) will
defeat uniformity in on/in ground radials and add losses due to the actual
entire content of the stuff underfoot. Raised anything in the woods does
add a significant unavoidable maintenance chore. But remember that all the
factual praise of on/in ground radials depends on the *assumed* context of
commercial BC uniformity of installation and location.
There is a certain level of on/in ground radial miscellany, or even
elevated radial miscellany, that will be clearly beaten using an FCP or
even as few as four 1/8 wave elevated tuned radials for counterpoise. With
these arrangements the current maximum can be moved up the vertical wire,
which helps elevate radiation above local clutter for low angles, be it
buildings or trees.
Radials really need that commercial BC grade uniformity in all its aspects.
Or we become lossily counterpoise-limited.
73, Guy K2AV
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