I'll have to counter that the two radial figures in your quoted RCA
study are not about defining what goes wrong with minimalist and
miscellaneous downward extrapolation of dense and uniform radial
systems. It's about setting a context for the main purpose of the
study which is the superior efficiency of 120 times 0.4 wavelength
radials. The study was not done to do a pathology on crap radial
systems, but underline the superior worth of dense and uniform.
1) The first assumption is that 3 MHz is the same as 1.8 with
essentially no radials around. It's turning out that if you're
talking about non dense and non uniform, it's not the same. It's
changing as you go down to a lower MF that exhibits some strange
behaviors I've never seen on eighty meters. Tests for a given
frequency need to be done on that frequency. BUT if you have a dense
and uniform radial system you don't see the weirdness. This is an
important distinction. The ASSUMPTION is that the stuff goes bad the
same, but that wasn't the point of the 1937 testing. The GOOD end of
the results were the point. At root of all these studies (and properly
so) is their goal to pin down the point where you get MAXIMUM
BENEFITS, not to carefully quantify exactly how bad you can get if you
DON'T go for the best. You can see where the FCC 120 0.4 wavelength
radial figure came from. Once they got that pinned down, the research
party for how to do BC stations right was over. No-brainer to buy the
land and put down copper in lieu of everlasting power bill penalties.
2) Sky wave behavior is ASSUMED to be the same as at the ground. This
is risky because of the loss mode presumptions used with the ground
based field strength. If there is growing ground transparency at the
lower frequencies, and the field strength at ground is IMPROVED
(absent dense radials) because of whatever unknown mechanism, then the
performance of fewer radials will score TOO HIGH at the ground for
extrapolation to sky wave. This is heavily suspected (not proved) on
my part because it would explain so much. The proof will require
burying current sensors that are self contained, battery operated and
contain recording devices, running tests, and then digging them up to
unload the data. Or connecting them with air-breathing testers above
ground with fiber optics. These kind of ground current things could
not be done in the past because the wires connecting sensors would
skew the measurements, and they knew that. What is really going on in
the ground is still the undiscovered country. Remember that the famed
Mr. Beverage had a BURIED 500 kHz TRANSMITTING antenna at one point
that worked. Dense and uniform radials do their magic by taking the
ground underneath OUT of the equation, so we DON'T have to know about
it. Unless we can't do dense and uniform, of course.
3) There are just too many grotesque differences as measured on RBN,
even after all the various (and rightly pointed out) caveats are dealt
with. And that is not a rub on this RCA study. All these studies have
this blind spot, as if measurement at the ground is in it's own world
and seemingly unrelated to skywave. There are often order of
magnitude discrepancies with projections of the old studies and RBN
readings. The 1/4 wave radial drawing shows a difference between the
2 and 60 radials as 116/176 mv or 3.6 dB. Something else in the real
world can produce 20 dB differences in sky wave at far points, other
factors held equal. It is a fact that putting down lots of radials
cleans that up. More radials is better is no urban myth. Dense and
uniform really does work the best. But two askew radials often seems
to do orders of magnitude worse than such material as the RCA study
would suggest. One 100w station in Minnesota went from barely working
and being heard in North Carolina, to working Europe, just by picking
up his two 1/4 wave radials off the ground, and folding them back
elevated to the feed. The old stuff is simply not accounting for true
anecdotes like that. The feedpoint had to be retuned, of course.
4) I don't know how I would find out the exact methodology of how they
laid the radials in the RCA Labs case. Were they cut shorter and
shorter? Did they PICK UP the radials in lowering the count, or just
disconnect them at the center. K7LXC et al in their multiband
vertical comparison found differences based on the ground drying out.
Did the '37 study drench the field to start? How did they deal with
that? How did they deal with the changing impedance at the feed point
as radials were varied? A) constant current in the radiator for a set
height as radial count changed, with constant power in the radiator to
set the current for various heights? Or B) just constant power to the
feed? The former is a classic researcher's technique, done that way
to isolate the effect of the radials from other current changing
issues. The latter is what happens to hams. And it means that you
can't use the Labs Case 3.6 dB difference to say that 2 radials is
only 3.6 dB down from 120 radials if what you're talking about is how
much amplifier to add in lieu of adding radials to your radial field
to work Europe from the US. You have to know what the effective
series R of the radial system is, what the feed R for the vertical is,
figure the loss for the two in series and at least ADD 3.6 dB to that
loss. And if there is some ground modality enhancement skewing the
3.6 dB you would have to add that difference as well. Just one more
reason the RBN tells a truth seemingly untouched by the old studies.
Note that if you're dense and uniform, none of this nastiness applies.
Shameless plugs for real radial systems will continue.
5) And at this point, buried in anecdotal material, I am willing to
surmise that the single helicopter measurement suite I have heard
about in conjunction with some radial tests was made to confirm that
the skywave was as predicted over the DENSE, LONG, gold standard
version they were proving in. Not done over the crap setup. We are
interested in how the crap setup works, because that is what is so
often getting done out there. We need to know how crap setup actually
works so we can devise alternatives to do maximum improvements where
dense and uniform is not possible.
I've been the meter guy in a helicopter making commercial field
strength measurements at heights (and with a GPS to nail the
measurement points). You don't have to go very far back in time for
helicopter measurements, without the aid of GPS, to have necessary
"approximate" aspects to the data. The helicopter guy had JUST
INSTALLED the GPS, and it was his favorite new toy.
Further, when you go up flying for something like that, it is PLANNED.
Points, altitudes, climbing times, descending times, and horizontal
travel times and make measurements hovering and gradually descending
are laid out in a book that is being read as the process goes on. The
pilot's time is spent entirely operating the aircraft, avoiding other
traffic and moving to points read by the meter guy. JUST A SINGLE SET
of data run on only one set of conditions on the ground uses up the
fuel and flight time and chases the copter back to the airport for
fuel. You would be making an airport cycle for each set of data if
you were running multiples. And, personally, you would not get me to
do two of those in a day. FAR too busy and nerve-wracking. You make
those count. No extra cycles thrown in to make some hams happy on an
issue not related to THE money issue paying for the helicopter ride.
The money issue that had me up there was phase cancellation distortion
in a quadrant of the FM coverage area. We had to know if the field
from the antenna was smoothly varying or not with changes in height
and bearing, and how it played out over the coverage area. MFR said
antenna would side mount on the big tower, but apparently did not
account for interaction with the tower cross members. The field
strength in the air at various distances and bearings proved it out.
Get UP, measure THAT, and get DOWN. Period. Bossy station manager
has a budget. Helicopter pilot cut off some of my tests anyway, fuel
got down to the go home level. Station Manager peeved about time to
actually get tests. Fussy about the cost, but the results made our
case.
Readings were used to make a case with the MFR and things went forward
from there and got rectified. Did NOT go back up to see if things
changed. Bossy station manager has a budget.
Again back to the point that RBN (carefully used) is the first real
sky wave measuring gizmo not filled with tons of assumptions, that us
plain folk have easy access to. The data needed to really deal with
and confront issues for sky wave and the un-dense and un-uniform is
being gathered now. Really for the first time in history. We just
need to get past invalid assumptions about what happens when one
extrapolates a proven dense and uniform downward into the murky waters
of minimal and miscellaneous "radial" counterpoises.
73, Guy.
On Sun, Nov 6, 2011 at 5:41 AM, Richard Fry <rfry@adams.net> wrote:
> Guy Olinger wrote:
>>Hams have suffered in the confined circumstances by attempting various
>>minimalist extrapolations of commercial radial methodology. The rub is
>>that commercial grade research was never done on non-dense,
>>non-uniform solutions.
>
> That isn't exactly correct, Guy.
>
> The 1937 real-world experiments of Brown, Lewis & Epstein of RCA Labs
> includes measured data for sets of of radials varying in number from 2 to
> 113, and in length from 0.137 to 0.412 lambda. The paper at
> http://i62.photobucket.com/albums/h85/rfry-100/BLandERadials.gif shows the
> results for the longer two sets.
>
>>Bell Labs and all the radio pioneer giants have already been there,
>>but not for the non-dense non-uniform radial-disadvantaged crowd,
>>and not much for skywave.
>
> The results of the BL&E experiments show that for monopole heights ranging
> from about 45º to > 90º using 113 or more symmetrical, buried radials each
> at least 0.412 lambda physical length in free space, the groundwave field
> measured 3/10 mile from the monopole will be within several percent of its
> theoretical maximum value for the same applied power to a perfect monopole
> driven against a perfect ground plane.
>
> In essence this means that the real conductivity of the earth in which that
> number/length of radials is buried has a very little affect on the radiation
> "launched" by that monopole antenna system.
>
> These tests were done at 3 MHz at a site in NJ where earth conductivity was
> not better than 4 mS/m, so they certainly are applicable for 160-m monopole
> systems used by hams.
>
> A good means to test the performance of a monopole antenna system is to
> measure the groundwave field it produces within 1/2 mile or so, and compare
> it to the theroretical value it would have if that power was radiated by
> that system with zero loss in its connection to r-f ground (as per BL&E).
> Doing this accurately takes an expensive, calibrated F.I. meter which few
> hams have, but maybe they could borrow/rent one for a few hours from a local
> AM broadcast station. The results of the test would show whether they could
> benefit from adding more/longer wires to a given set of less than 120 x
> 1/4-wave buried radials.
>
> Rather than be overly concerned about the conductivity of the earth within
> 1/2-lambda of a monopole, one could install a "broadcast" type system of 120
> x 1/4-wave buried radials, and be done with it. Such systems using monopoles
> having physical heights of 45º to > 90º will radiate about 95% of the
> applied power, regardless of soil conductivity within the area of the
> radials.
>
> Once radiation is launched from a vertical monopole* it is subject to
> whatever real earth conductivity exists beyond the radius of the buried
> radial system. That will affect both the groundwave and the skywave.
>
> But there isn't much that be done about this, except to move the monopole
> system to a geographical region having better conductivity.
>
> * The shape of the elevation pattern from a given monopole is the same no
> matter what the application. All unloaded monopole heights up to 5/8 lambda
> radiate (launch) maximum field in the horizontal plane. Hams may be more
> interested in skywave propagation paths than some Class C AM broadcast
> stations, but that does not mean that a monopole has zero field in the
> horizontal plane and at small elevation angles above it, as sometimes is
> concluded by looking at "far-field" plots produced by NEC software, and
> found in antenna textbooks.
>
> RF
>
> _______________________________________________
> UR RST IS ... ... ..9 QSB QSB - hw? BK
>
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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