Topband: insulated vs:bare radial wires

[Guy Olinger K2AV]

I partly agree. There is an aspect of "good enough" on an anecdotal
basis.  But for circuit components we have completely reliable ohms
law and formulas, etc, and for antennas not seriously deprecated by
dirt we have models that give quite reliable results. When we get to
radials and vertical antennas over dirt and 160 meters we have issues.

Not that there aren't concerns about sky wave with broadcasters, and
issues with interference caused by sky wave going where they don't
want it, it's just that the patterns are measured at the ground for
certification.  Bread and butter for broadcasters is at the ground,
and the exceptions aren't spreading money around trying to justify
minimalist elevated radial systems at an academic/IEEE level of
accuracy.  They are trying to make money for owners and stock holders,
like every other business.  A federally accepted 120 radial ground
system (that we consider mild overkill) is a minor part of the expense
of a station.

The real problem for us trying to minimize radials is that the method
of "shielding" for buried (bare and insulated - two kinds) and
elevated is not now quantified in a simply measurable, *repeatable*
way, that anyone could test and duplicate. Nor does what some have
been calling "return current" collect all ground current back to the
antenna. The earth can act as a giant lossy capacitor which needs no
return, witness lightning and all the charge propagation effects
associated. It may simply appear as power lost to propagation (energy
goes out, does not come back).

The problems with A/B testing on incoming signals are numerous,
including the fact that looking into an antenna terminated with a non
50 ohm (usually reactive) RX from the sky is not the same as
transmitting out of one. Any feedline length and manufacturing
differences need to be measured precisely and tuned out so that
precisely matched Z's are presented to both and the exact losses
known. Any miscellaneous conductors need to be accounted for,
including the ubiquitous and annoying feedlines.  Any interaction
between the verticals themselves must be removed, which means
switching at the base of the vertical as part of the A/B switch if
they are with a couple of wavelengths. Then there is the problem of
certifying dirt, discussed below.

There is an indirect way to reliably establish the basis of radial
performance and the means for doing it inexpensively have only
appeared in the last 4 or 5 years. Basis meaning just exactly how they
work or not.  We still are at 1937.  We want Hubble grade pictures,
but we don't have Hubble grade digital data to make them from.

The answer is in (boring and tedious, not entertaining) targeted basic
research which measures to tenths of dB's what horizontal wires do to
radiation from vertical radiators above it. Your helicopter analogy is
correct, except you don't get to pick an angle, you have to do them
all.  You have to vary orientation, length and separation of wires,
and do each angle at those variations.  Then you have to repeat the
entire exercise for elevated, buried, buried insulated over variations
in dirt.

Your measuring method must be constant across all those measurements,
and must have means to enforce that.  You must have the mathematical
programs to maps those results to whatever equations match, not just
the easy ones or the ones we would like.

My planning math says that it might take hundreds of testing setups
and tens of thousands of measurements to get enough stuff, and it
probably can't be done at one site in the US because of the need to
run it over a range of soils. In short it is a ghastly research
project which is it's own reason why it hasn't been done. Nobody is
going to do that with a helicopter.

We have already shown that ground is highly anomalous and changes the
velocity factor of wire in it, on it, and above it. An MF dipole on
ground can be carried around, placed down and velocity factors from
45% to 80% measured along with feed impedances from 80 to 140 ohms.
And this only in the Raleigh area. Heaven knows what elsewhere.

A good deal of this variation can be actually measured on one single
piece of property.  In order to certify your A/B results beyond
termination issues, you would need to somehow certify the ground
underneath the two antenna systems as equal.

As to what Joe average ham should need to know to have a good vertical
system, more radials is better to a point.  And if what you can get
away with is 4 elevated radials, then do it and enjoy it.

But as soon as someone says (publishes) that 4 elevated radials over
dirt is as good as 60 buried, let them understand there still is no
research to back that up, just hoping. And until we know a lot more,
it may actually be true in some places and abysmally not true in
others.

73, Guy.

On Sun, Dec 6, 2009 at 5:41 PM, Richard (Rick) Karlquist
<richard at karlquist.com> wrote:
> There is a study on skywave signals on verticals that is on my web
> site.  I listened to actual received signals off the air and A/B'ed
> two antennas.  In one sense, this is not as precise as you couldn't
> detect a 1 dB advantage.  OTOH, these are the real signals you want
> to receive, at the actual angle and of the actual polarization.
> You could do a "scientific" study with a helicopter, but then you
> still have make a judgment as to what arrival angle you want to
> assume, not to mention random polarization.
>
> Broadcasters worry a lot about skywave in a negative sense, so
> there may be studies of skywave vs ground wave.  Skywave is bad
> for them because it causes fading of the ground wave.  Successful skywave
> that causes propagation to great distances has no monetary value
> for advertising purposes.  I have never seen any evidence that the loudest
> vertical for ground wave purposes is not also the loudest vertical for sky
> wave purposes.  If there were a way to selectively favor ground wave, the
> broadcasters would have found it by now.
>
>
> Rick N6RK
>
> Guy Olinger K2AV wrote:
>>>
>>> N6LF established that a few elevated radials, which do not shield the
>>> ground, can be as effective as the traditional on-ground radial field.
>>>  He
>>> also warns that the implementation is far more critical.
>>>
>>> Rick N6RK
>>
>> As far as I can tell with this and other such reports, including the
>> benchmark 1937 work, all the measurements were made at ground level,
>> and would therefore not measure skywave. The ground level measurements
>> do NOT extrapolate to skywave unless one makes certain ASSUMPTIONS.
>> These assumptions have not been challenged, since they have no
>> essential bearing (read worthy of spending money) on commercial MF
>> broadcasting, which requires signal strength readings at the ground
>> for certification.
>>
>> Since amateur communications consists almost entirely of SKY WAVE
>> considerations we will have to provide our own SKY WAVE research.
>>
>> 73, Guy.
>>
>>
>