Bob and all,
We can go on and on about this, sound like professionals,
and even read or write long detailed articles. The fact of
the matter is no one can answer any detailed questions
unless someone is in an ideal controlled situation.
It's solidly established that 50-60 radials about 1/4 wl
long gets our systems over 90 percent of every last bit of
radiated power when we have a reasonably tall vertical, say
1/8th wave or more. That's it, there is no more power to
wring out of the system.
When the system deviates from a typical smooth flat area of
pasture or meadow, if the radials are elevated, if they are
limited in direction or length, or any of a half dozen other
common problems all we really have is a guess. We can
certainly describe how to get the last 3% efficiency in a
perfect system....but factually the variation in soils and
surroundings probably adds 30% variation in what would
actually work best. This is especially true when the radial
system is truncated in some directions or when the soil is
non-homogeneous (as most locations probably have).
W7EL and myself went through a thing here a few months ago
trying to measure my soil conductivity. We followed a few
well-written articles about soil conductivity
measurements...and the results were all over the place. With
a laboratory grade impedance test set my soil is either
30mS/meter or much less than 1mS/meter...depending on what
particular measurement method we used.
I know it doesn't sound professional to say this but having
spent many hundreds of hours measuring systems using actual
FS measurements when **only the radials** were changed, the
sad fact is the only accurate universal answer is to use as
many radials as you can and make them as long and as
straight as you can make them. You either have to tie
everything possible into the ground system, or you could
have an elevated resonant system that has NO ground
connection. No ground connection includes an RF ground path
back through the coax shield when you are using a few
elevated radials, because the simple act of connecting the
common point of the radials to a lossy earth connection
(like through the coax shield) can cost you something up to
1dB.
At my last two locations 10-15 radials on or in the ground
were about equal to four elevated radials in a ground
isolated system. The FS also quit increasing at about 50
radials (buried or elevated, it made no difference) and any
connection to a ground rod from the elevated system
noticeably reduced the measured field strength.
Just install as many radials as long, straight, and spread
out as you can manage, and that's it. No need to go over 50
radials. You never pay a price in signal strength from
having too many radials, but you can from having too few or
too short.
73 Tom
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