Hi, Tom,
You wrote:
"TOA is affected by ground a long distance out from a vertically
polarized radiator. That has little to do with ground systems near and
under the antenna."
I didn't say otherwise, and I totally agree. It's the ground near/under
the Ewe which influences optimum termination and size of the Ewe, which
in turn influence the TOA (as well as far field ground).
========
"A EWE is really two vertical radiators, with a single wire phasing line
that feeds them. The current is 180 degrees out of phase in the
verticals, plus delayed by "S" (the space of the elements or length of
the wire)."
I agree with the 180-spacing statement, but I'm unsure how the vertical
sections are 180 out of phase. Is this because one vertical element is
upside-down compared to the other?
========
"In order to have good directivity, the current in the system has to be
uniform. That requires the top wire to NOT radiate or NOT be over (and
coupled to) lossy soil. It also requires a good non-radiating
termination at each end."
The current decreases gradually along the wire from its feedpoint to the
terminated end. The current at the termination end is about 78% of the
current at the feedpoint in a 50' long Ewe with 10' ends and terminated
by 775 ohms. And, of course, the current phase changes gradually along
the wire - about 57 degrees along the course of a 50' horizontal section
on 1830 kHz (which agrees with the 180-S "law" for unidirectivity in a
50' long Ewe).
The horizontal section radiates broadside to the wire, but to a much
lesser degree than the vertical sections.
========
"K9AY loops are the same way. Stick them on a crummy ground, and they
very likely won't work as well as they can."
In modeling, I can't get the K9AY antenna to perform anywhere near as
good as the plots in his article in QST, no matter what the ground . My
modeling shows the Ewe to be superior to the K9AY loop.
=========
"Since the 70's, I've used two and more element phased arrays for
receiving. I tried an EWE, mainly to eliminate the feedlines and
broadband matching devices my systems normally require. I had very poor
results until I installed a ground screen under the EWE. The ground
screen was so much work, I abandoned the idea (the goal was to save
effort, not make life more difficult)."
Designing phasing/matching sections for an Ewe (or any) array can be
quite complex. That's one area where modeling software shines.
Modeling shows that a 4-el endfire/broadside has as good or better
pattern than a good Beverage, BTW.
Re the ground screen, "more work than it's worth" is my opinion also.
==========
Re inductively loading:
"I would certainly agree that is true IF the EWE is a real mess to start
with. But a properly terminated EWE has travelling waves, NO standing
waves. Adding a reactance in series with the system will produce a
degradation is signal, unless you simply haven't conjugately matched the
feedpoint to the receive system and the added reactance is forming part
of an impedance transformation system."
Travelling waves? I thought that applied to Beverages, not Ewes. Please
elaborate.
I agree with your statement about matching. The inductive loading method
is a simple way for the conjugately uninitiated.
============
"The last thing in the world you want is an inductively loaded EWE,
loaded at only one end. Any non-symmetry at one end of the system would
destroy the symmetry of the two vertical sections. Those vertical
sections MUST have equal currents with a phase shift of 180-S for a
unidirectional pattern, and EQUAL currents in the case of equal size
vertical sections for a complete backfire null."
How can the currents in the two vertical sections of an Ewe possibly be
equal? Modeling shows up to over 70dB F/B. It also shows no change in
results (other than feedpoint lack of reactance) in an inductively loaded
Ewe vs. no loading..
============
"Even the author of EZNEC cautions against putting too much faith in
accuracy of models with low horizontal wires near ground, or antennas
connected to ground. The error between a low dipole and the real world
thing using full blown NEC-2 is about 5 dB, according to published data.
If it can't accurately model a dipole close to earth, it probably can't
accurately model an EWE."
Perhaps because W7EL knew that is why he added NEC Sommerfeld corrections
to his NEC-2 based software. EZNEC has been shown to be in close
agreement with NEC-4 results. Using this as the ground for low
horizontal wires can't be all that bad.
Ewe modeling results must be close to the real world, otherwise there
wouldn't be so many happy users of Ewes.
73, de Earl, K6SE
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