To Tom and those on the reflector that are following the elevated radial
discussion.
On Fri, 06 Mar 1998 14:48:18 +0000 Tom Rauch
<10eesfams2mi@mass1-pop.pmm.mci.net> writes:
>Hi Carl,
>
>> Tom...Rauch that is...I'm getting confused...again.
>> Are you saying that a vertical with X number of elevated radials is
>6dB
>> below the same radiator with X number of on ground radials?
>
>With four carefully pruned resonant radials elevated six feet
>(measured on 80 meters), the field strength was about 4 or so dB down
>from 64 radials, either elevated or on the ground. That was MEASURED
>at one site with one antenna and one meter, not modeled by NEC. The
>only change was in the radials themselves, and it was read on a
>meter.... not a computer.
>
>> Or lets try it this way....a ground mounted radial system of say 64
>> radials would need how many elevated radials at 20' elevation to
>have the
>> same efficiency?
>
>According to my measurements, if the height was 12 feet on 160, it
>would take about 20 or 30 elevated radials to equal 64 on the
>ground. That's a good savings, but not quite the magic of being able
>In spite of this, I have no idea if I am one dB down from ideal
>or ten dB. I certainly have no idea how my antenna efficiency
>compares to my antenna system in Conyers three months ago,
>or how it compares to my signal when I lived in Ohio ten years ago.
>Any claim I would make would be a gut feeling, not a fact.
Nor do I have any idea as to efficiency. My gut feeling is that this site
is not as good as my old QTH 4 miles away, 400' lower in elevation and
surrounded by swamps.
But it does good enough most of the time and I have no intention of going
to a on ground radial system.
SNIPS
>
>On the other hand I measured a system (four elevated were down about
>5 dB from ideal on 80 meters), I know as a fact what was measured at
>WVNJ AM (six elevated up ~30 ft on each tower were about 7 dB from
>ideal on a four tower array), and I suspect what N7CL says the
>military measured (about six dB) is true, and that other people who
>have tried both systems on ONE antenna say they notice an
>improvement.
>
>Myself, I'll go with a few actual direct comparisons over computer
>model "measurements" or loosely applied "FCC proof estimates"
>any day.
Here is a comment from someone that would disagree with your assumption
the the FCC uses loosely applied estimates.
Carl
FYI, here is a quote from a technical paper delivered by Clarence
Beverage (nephew of THE Beverage) at the 49th NAB Broadcast
Engineering Conference (a few years ago) entitled: "New AM Broadcast
Antenna Designs Having Field Validated Performance", concerning
antenna tests done in Newburgh, N.Y. under special FCC authority.
"The antenna system consisted of a tower 120 feet in height with a base
insulator at the 15 foot elevation and 6 elevated radials a quarter
wavelength in length spaced evenly around the tower and elevated 15
feet above the ground. The system operated on 1580 kHz at a power of
750 watts. The efficiency of the antenna was determined by radial field
intensity measurements [in 12 directions] extending out to distances up
to
85 kilometers. The measured RMS efficiency was 287 mV/m
[normalized] to 1 kW at 1 kilometer, which is the same measured value as
would be expected for the tower above 120 buried radials."
I would be so bold as to suggest Tom that tests run out to 50 miles or so
cannot be called minor.
Here is a followup note:
Hi Carl,
Yes, some AM stations have been authorized to operate with elevated
radial systems. Some (or possibly all) of those stations were required
to
conduct field tests to confirm that the elevated radial systems were
producing field strengths equivalent to those which would have been
generated from the same towers with buried radial systems conforming
to FCC rules. All that info is in DC and I don't have access to it here
in
Gettysburg.
Based on my reading of all of the Christman articles on computer
modeling of elevated radial systems and on my reading of several field
test evaluations of elevated radial systems, it is my PERSONAL belief
that a properly constructed elevated radial system is fully equivalent to
a
buried radial system of 120 radials. I have seen NO documentation to the
contrary. If such documentation in the form of field test results
gathered
by a competent AM consulting engineer exists, I would like to see it. I
will
gladly pay reproduction and mailing costs for such materials.
I have no axe to grind in this matter, Carl, as you know. I am simply
interested in separating fact from fiction. I have spoken at great
length
with Al Christman on this subject and, in my personal opinion, his
conclusions concerning equivalency are, as yet, unchallenged by any
facts (not opinions!) or measurements to the contrary. "
>From the above, and from a person I highly respect, I would add my own
personal opinion that the FCC tests AND the BCB industry are a bit more
competent than you give them credit for.
Add further that many universities now have access to NEC-4 which can
accurately model ground effects.
73 Carl KM1H
>
>I'm hoping to do some tests on 160 this spring, as I add a second
>tower in an empty pasture far from the present antennas. I'll let you
>know when and if I do that test.
>73, Tom W8JI
>w8ji.tom@MCIONE.com
>
>--
>FAQ on WWW: http://www.contesting.com/topband.html
>Submissions: topband@contesting.com
>Administrative requests: topband-REQUEST@contesting.com
>Problems: owner-topband@contesting.com
>
_____________________________________________________________________
You don't need to buy Internet access to use free Internet e-mail.
Get completely free e-mail from Juno at http://www.juno.com
Or call Juno at (800) 654-JUNO [654-5866]
--
FAQ on WWW: http://www.contesting.com/topband.html
Submissions: topband@contesting.com
Administrative requests: topband-REQUEST@contesting.com
Problems: owner-topband@contesting.com
|