Roy Lewallen wrote:
Here's an experiment to try.
Take Cecil's model of the vertical with the loading coil. Add a single
horizontal wire, 10 feet long, connected at the top of the loading coil.
That is, make the new wire go from 0, 0, 26 to 10, 0, 26. Notice how
much current there is in the horizontal wire. Notice how much different
the current is in the vertical below the wire compared to above the
wire. Look familiar?

And please note that horizontal wire generates lots of horizontally
polarized radiation where there is none for the horizontal stub alone.
--
73, Cecil http://www.qsl.net/w5dxp



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Huh?

The stub produces just as much horizontally polarized radiation as the wire.

Run your stub vertical model with an elevation plot, and azimuth angle
of 90 degrees. Click FF Tab. Note the magnitude of the horizontal
component -- roughly -30 dBi. Then repeat with the experimental model
with the single horizontal wire.

As I mentioned in my lengthy posting, the radiation from the stub isn't
a large part of the overall field, and this certainly shows it. But it's
certainly enough to disturb the vertical's current. Exactly the same
thing holds for the straight wire. Common mode current is common mode
current. No magic, no mysterious phenomena "not accounted for" by EZNEC.

Roy Lewallen, W7EL

Cecil Moore wrote:

And please note that horizontal wire generates lots of horizontally
polarized radiation where there is none for the horizontal stub alone.

Roy Lewallen wrote:

The stub produces just as much horizontally polarized radiation as the
wire.

Not true. The wire produces 2 dB more radiation than the stub. Given
that the stub is located in a high current region compared to the wire,
it is significant how much the stub doesn't radiate. If you replace
the stub with an equal length of single wire, it radiates 4 dB more
than the stub.

Run your stub vertical model with an elevation plot, and azimuth angle
of 90 degrees. Click FF Tab. Note the magnitude of the horizontal
component -- roughly -30 dBi. Then repeat with the experimental model
with the single horizontal wire.

Thanks, Roy, that's an angle I had not looked at. Results are above.

As I mentioned in my lengthy posting, the radiation from the stub isn't
a large part of the overall field, and this certainly shows it. But it's
certainly enough to disturb the vertical's current. Exactly the same
thing holds for the straight wire. Common mode current is common mode
current. No magic, no mysterious phenomena "not accounted for" by EZNEC.

What EZNEC doesn't account for is the phase delay through a bugcatcher
coil which is an appreciable percentage of a wavelength. EZNEC is incapable
of modeling a bugcatcher coil. The only coil that EZNEC is capable of modeling
is one that does not and cannot exist in reality.

Therefo One cannot use EZNEC to try to prove the current is the
same at both ends of a bugcatcher coil which is what kicked off
this entire discussion.
--
73, Cecil http://www.qsl.net/w5dxp



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Cecil, W5DXP wrote:
"What EZNEC doesn`t account for is the phase delay through the
bugcatcher coil which is an appreciable percentage of a wavelength."

It needs to have enough delay to replace that missing from the resonant
length of the antenna as ON4UN shows in his Fig 9-22.

Inductors are retardation coils.. They delay current change much as a
flywhell inhibits change in rotation. When voltage is applied to an RL
circuit, current is a function of time. If reactance in a circuit is
low, instantaneous current is almost in-phase with instantaneous applied
voltage. There is little if any delay of current in response to applied
voltage. If inductance in a circuit is high, delay of current is high.
Terman gives an example of inductive delay on page 643 of his 1955
edition:

"Another type of artificial line, suitable for low power operation,
consists of a coaxial cable in which the inner conductor is a continuous
coil of small wire wound on an insulating cylindrical core. This greatly
increases inductance per unit length of line with corresponding
reduction in velocity and increase in time delay per unit length. It is
possible with such a line to obtain a round-trip transit time of as much
as 1 microsecond in a length of two feet.

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:

Cecil, W5DXP wrote:
"What EZNEC doesn`t account for is the phase delay through the
bugcatcher coil which is an appreciable percentage of a wavelength."

It needs to have enough delay to replace that missing from the resonant
length of the antenna as ON4UN shows in his Fig 9-22.

This is true in order to get the feedpoint voltage and current in phase,
i.e. in order to resonate the antenna.

The voltage needs 180 degrees round trip delay from the feedpoint to
the end of the antenna and back.

The current needs 360 degrees round trip delay from the feedpoint to
the end of the antenna and back. 180 degrees of that comes from the
reversal of direction at the open end.

Can someone please measure the delay through a 75m bugcatcher coil?
I simply do not believe it is zero, i.e. faster than light.
--
73, Cecil http://www.qsl.net/w5dxp



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I hope the readers will forgive me if I considered the radiation of the
two cases to be equal, not worrying about a couple of dB difference in
the range of -30 dBi. Actually, I know of no way to ascertain the total
radiation from the stub or wire alone, since it occurs at all azimuths
and elevations, producing both horizontal and vertical components, and
adds to and modify's the vertical's pattern. What I meant to say was
that the radiation characteristics are certainly very similar, and both
have the same general effect on the vertical's current distribution.
And, both for exactly the same reason. Cecil's earlier statement that
the wire radiates while the stub does not is certainly and demonstrably
not true, and the 2 dB difference in field strength isn't at all
evidence that one radiates more total energy than the other.

As for the statement that "EZNEC doesn't account for is the phase delay
through a bugcatcher coil", that's entirely true. As I've said several
times now, an EZNEC coil "load" is a lumped element model, which has
equal currents at its two terminals. A coil with significant physical
length doesn't behave like a lumped inductor, and therefore not like the
EZNEC model. I believe, but have no proof, that approximating a lengthy
coil with a combination of wire and load models will produce reasonable
results, but that's the best you can do with NEC based programs like
EZNEC. (Or with MININEC-based programs for that matter.)

Anyone who attempts to model a lengthy coil as a lumped "load" component
won't get results that closely model reality, for the same reason that
anyone who attempts to model a long wire as a short wire will be
disappointed. Neither should be a surprise.

Roy Lewallen, W7EL

Cecil Moore wrote:
Roy Lewallen wrote:

The stub produces just as much horizontally polarized radiation as the
wire.


Not true. The wire produces 2 dB more radiation than the stub. Given
that the stub is located in a high current region compared to the wire,
it is significant how much the stub doesn't radiate. If you replace
the stub with an equal length of single wire, it radiates 4 dB more
than the stub.

Run your stub vertical model with an elevation plot, and azimuth angle
of 90 degrees. Click FF Tab. Note the magnitude of the horizontal
component -- roughly -30 dBi. Then repeat with the experimental model
with the single horizontal wire.


Thanks, Roy, that's an angle I had not looked at. Results are above.

As I mentioned in my lengthy posting, the radiation from the stub
isn't a large part of the overall field, and this certainly shows it.
But it's certainly enough to disturb the vertical's current. Exactly
the same thing holds for the straight wire. Common mode current is
common mode current. No magic, no mysterious phenomena "not accounted
for" by EZNEC.


What EZNEC doesn't account for is the phase delay through a bugcatcher
coil which is an appreciable percentage of a wavelength. EZNEC is incapable
of modeling a bugcatcher coil. The only coil that EZNEC is capable of
modeling
is one that does not and cannot exist in reality.

Therefo One cannot use EZNEC to try to prove the current is the
same at both ends of a bugcatcher coil which is what kicked off
this entire discussion.

Roy Lewallen wrote:
I hope the readers will forgive me if I considered the radiation of the
two cases to be equal, not worrying about a couple of dB difference in
the range of -30 dBi.

Actually, a more fair comparison is to replace the stub with a wire and
move the rest of the antenna over ten feet so it goes up 25 feet, zigs
to the side by ten feet, and then goes up another 25 feet from there.
That makes the current in the stub and the current in the horizontal
section approximately equal. With that configuration, the radiation
from the horizontal section is 12 dB greater than from the stub, i.e.
24 times as great. Seems the stub works pretty well after all.

Anyone who attempts to model a lengthy coil as a lumped "load" component
won't get results that closely model reality, for the same reason that
anyone who attempts to model a long wire as a short wire will be
disappointed. Neither should be a surprise.

What kicked off this discussion in the first place is that someone claimed
to know the current below and above a bugcatcher type coil based on modeling
loads in EZNEC. Presumably, he was indeed in for a surprise.
--
73, Cecil http://www.qsl.net/w5dxp



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