To: <topband@contesting.com>
> Date: Fri, 13 Mar 1998 19:44:05 +0100
Hi Uli,
> If I had the space I would place two (to begin with) resonant elevated
> radials
> in exactly opposite directions and switch the braid of the coax feedline of
> my
> inverted-L (17m vertical + abt 35 m horizontal) between my grounded radials
> and
> the elevated ones (keeping the feedline isolated from ground by a sufficient
> number of ferrite beads). FS measurements outside the near field and/or
> S-meter
> reports of some reliable hams in the immediate neighbourhood should show the
> difference in performance with an accuracy of better than one db.
The "S" meter is a good idea, since you could easily use a precision
attenuator pad to calibrate the meter. That would actually be MUCH
more accurate than a field strength meter that depends on measuring
mV/m over a varying path, if you could guarantee nothing changed at
the receive site during the test.
The flaw with that method is the ground mounted radials, even when
not connected, still reduce earth losses. Imagine the coupling
between two long parallel wires on 160, spaced only a few feet
apart. With the radials, it would be the same.
> I wouldn't expect that anybody with an elaborate radial system (how many of
> us
> can really manage?) can actually gain anything before getting the elevated
> radials a quarter wavelength above ground, but it might be interesting to
> find
> out how poor your ground system must be before it is worthwile replace it by
> an
> elevated system relatively close to ground.
I tested an elevated system in Conyers. I installed a 1/4 vertical
over four elevated resonant radials and measured the FS at one mile
across an open path. I then lowered the radials and measured FS again.
I repeated this experiment, changing only the radials, until I had 64
radials installed.
With less than 16 radials, the elevated system showed a few dB
advantage, less advantage as the number of radials was increased. At
64 radials it made no difference at all if the radials were elevated
or in contact with the bare soil. The net difference between the
4 elevated radial system and 64 radials was about five dB. Hardly
earth shaking, but well worth the work.
By the way, contrary to what was posted earlier about WVNJ, they did
find a conventional ground system of 120 1/4 wl radials improved FS
over the elevated system of six radials per tower. WVNJ's total
improvement in FS was about seven dB in the best directions and 5 dB
in the poorest.
The test quoted was for 120 .11 wl radials, a test that the
engineering firm later admitted was a flawed test. That's the problem
with relying on someone's written "conclusions" without understanding
the test and what it really measured.
The reason I know all this is I was a paid consultant for WVNJ, and
gave advice to the engineering firm they hired. Because of that, I
have all the original reports and original data. I dislike seeing
data misquoted or taken out of full context just to "cook" the
results.
> Being unable to try it myself I'd very much like to volunteer in collecting
> the
> data and summarizing the results.
This summer I intend to repeat the tests here, since I now live over
greatly different soil (and now have hundreds of acres of open
pasture land), and include 160 meters.
Some people seem to think this is "ego driven" or I have some sort of
grudge. The only reason I want to do it is because, despite searching
for years, I've NEVER been able to find confirming data. All I find
are speculations based on multistep methods that likely aren't
accurate within several dB, such as the FS measurements in
mountainous or cluttered terrain.
A simple A-B test of one antenna eliminates all theses inaccuracies,
but to my knowledge that was only done at my house and at WVNJ. I
believe N7CL was party to some A-B tests for the military, that
ALSO agreed with the results at WVNJ and my own personal tests.
Believe me, if the systems work and are within a dB of a full size
system, I'll be the FIRST to quit buying radial wire in 35,000 foot
lots. And I'll share that info with others just as freely as I share
the info I have to this point, despite the name calling that goes on.
The biggest thrill 160 offers for me is learning how things work,
and meeting other people who do. I strongly dislike being accused of
self motivation or falsehoods after spending hundreds of hours
pouring over data and giving the results away for free.
73, Tom W8JI
w8ji.tom@MCIONE.com
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