[Lowfer] Ultimate LOWFER Transmitter? (LONG)

[John Davis]

>> This is not comparable to the conditions as Stewart stated them.  If one
>> were to do as you say, then certainly only the coil losses would be in
>> parallel, not the ground loss.  Furthermore, the two masts would
>effectively
>> be in parallel (as, therfore, would the coils) so resonance would not be
>> achievable without even larger inductors with still more loss each....
>>
>
>Why is it not comparable  ?    Are you saying that if we have two masts
over
>a continuous ground plane and we measured a certain ground loss.    Then we
>break the ground plane in two between the two radiators, the measured
losses
>are divided by two ?

Nope.  We have two separate ground planes for two separate radiators, with
EACH of the said ground planes large enough to capture the great majority of
the current from the radiator associated with it, right from the beginning.
In the typical LowFER case, this requires a ground system with radius
roughly equal to the physical height of the antenna.  This is why two
close-spaced parallel radiators over a single ground plane (whether later
split or remaining continuous) are not comparable to Stewart's conditions.

>> When such antennas are fed in parallel and do NOT share a common ground
>> system, then it is the *multiple ground system losses* that are in
>>parallel,
>> not just the coil losses as in your postulated conditions
>>
>
>They are not, but lets try and convince you why.   Going back to Stewart's
>stated scenario where he stated that running the two identical systems in
>parallel produces the same radiation resistance as the single system (here
>we *all* agree).    Let's say we are going to maintain the same far field
>strength (therefore same near field).    If we have the same near field
>strength, all the objects which contributed to losses (trees, bushes,
>ground, outhouse, etc) are going to suck up the same power irrespective of
>whether that near field is produced by one radiator or two.    How can you
>gain efficiency when the same power is lost for the same far field strength
>?


This is begging the question.  (I use this term, not as our news media do
erroneously when they mean to say something raises new questions, but
instead  in the proper debating sense; namely, attempting to use a
restatement of the proposition being debated, itself, as proof of the
argument.)

There is no reason to simply assume the near field losses total up to be the
same for the same far field strength.  That's what we're trying to
determine.

>How about these other losses (like trees, bushes etc.).  Do they suddenly
>dissipate half the power in the same field strength ???    How does this
>work ?    They still have the same induced currents flowing in them and so
>dissipate the same power. If not, how do the trees know what they are
>supposed to do :-)
>

Most trees are smarter than we think.  Or at least, that's what they tell me
when I ask them.  :-)

But it is not valid to assume the same currents flowing in all these objects
as before, because we have split the power between multiple radiators.

>I re-iterate,   I believe those part of the losses which are coil losses or
>any other wiring losses are reduced by paralleling, but the ground losses
>(which you are trying to cover up by the chicken wire nets) or
environmental
>losses (trees and bushes) are not.


Now it's my turn to ask: how can _that_ be possible?

The resistances involved in ground system loss are just as real in EVERY
sense as the coil losses.  When efficiency of an electrically short antenna
is calculated, the starting point is to compare the (calculable) radiation
resistance to the TOTAL measured resistance at operating frequency at the
antenna terminals.  Within that TOTAL resistance are the losses in the coil
(which can be measured separately, of course), in series with a lumped value
of resistance that represents the total of all other loss factors (whether
you can measure them individually or not).  As far as the RF is concerned,
there is no way mathematically or through verbal rationalization to consider
the coil resistance differently in any way from all other loss components.
Real power is dissipated, so a loss is a loss is a loss...

I wish Bill C. were here to add a more rigorous analysis such as you seek.
I myself am just barely convinced of the legitimacy of the principle, but
I'm not the mathematician that would be needed to prove it.  Still, it has
been demonstrated in practice.  I can suggest another way of looking at the
matter, though.  The field strength in V/m from each radiator can
legitimately be _summed_ according to the superposition theorem since, per
Stewart's stated conditions, the individual radiators are outside each
other's induction zone (for an electrically short antenna, that same radius
we mentioned before, roughly equivalent to each element's physical height).
This is not dependent on the strength of the magnetic or electric fields
impinging on loss factors within the induction zone, only on the RF current
in the individual radiating elements and their effective height.

73,
John











    How
>can two independent radiators suddenly double their efficiency just by
>feeding them in parallel ?  Note that if each radiator was outside the near
>field then connecting them in parallel would result in the halving of
*both*
>the radiation resistance component and the losses as seen at the terminal.
>You say that for close spacings the radiation resistance stays the same,
but
>the ground losses are halved, but not when they are too close, where you
>agree they are not.   Unless you are having an each way bet by making the
>ground losses independent, but the mechanism for generating radiation
>resistance conveniently not.
>
>So, in summary, to put it another way (and test everyones' patience), I
>believe that radiators separated far enough to be truly independant
(outside
>near field) and placed in parallel will have their impedances halved (Rrad
+
>Rloss), but maintain the same ratio.    Radiators in the near field of each
>other and placed in parallel will maintain the same radiation resistance
and
>losses (and the same ratio).    That is, they maintain the same
>efficiencies.    Maybe there would be some second-order effects, but
nowhere
>near a 3dB gain.
>
>You, if I understand it correctly, are saying that somewhere in between
>closely spaced radiators (my 1m spacing where you say Stewart's assertion
>doesn't work) and the larger (greater than near field separation where any
>antenna textbook will say it doesn't work), there is a magic zone where
>efficiency jumps proportionally to the number of radiators (at least for
low
>values of N).   A kind of "mummy bear" zone.   I must say that is outside
my
>knowledge and would be intrigued to learn how this works.
>
>73s Steve Olney VK2ZTO
>
>BTW, Stewart states the radiation resistance stays the same, but you say
>your rough measurements show there IS a transformation of radiation
>resistance.   So even your own experience doesn't agree with his
statements.
>Folded radiators exhibit transformation (i.e., folded dipole),  parallel
>radiators do not.
>
>"Man made mathematics and models, to *convince him/herself that s/he
>comprehends* the reality that God made."
>
>
>
>
>
>
>
>
>
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