Cecil Moore wrote:
Tom Donaly wrote:
What's the Z0 of a loading coil, Cecil?

Z0 and VF depend upon the geometry of the coil
*and the frequency*. A 75m Texas Bugcatcher coil
has a Z0 of ~3800 ohms and a VF of ~0.02. The
coil that w8ji used for his 3 nS "measurements"
has a Z0 of ~5300 ohms and a VF of ~0.033. I've
generated an EXCEL file that does the calculations:

http://www.w5dxp.com/CoilZ0VF.xls

I've also got a web page that explains why the
current phase in a standing-wave antenna cannot
be used to measure delay.

http://www.w5dxp.com/current2.htm

I have done the suggested bench experiments myself
and the results are nowhere near w8ji's results.
When traveling wave current is used instead of
standing wave current, the delay is obvious on a
dual-trace O'scope.

This is nothing new. It is based on the information
in the IEEE paper which someone presented years ago:

http://www.ttr.com/TELSIKS2001-MASTER-1.pdf

Still using the Tesla coil fella's ideas, are you? A frequency
dependent Z0 is a good trick. What happens when you double the
length of the coil? Does the Z0 stay the same? What if the coil is
infinite? Can you make a quarter wave shorted stub with it? If you
make it a half wavelength long - keeping in mind the velocity factor -
will the impedance looking into the coil equal the impedance of
the load? How do you attach a load to it?
73,
Tom Donaly, KA6RUH

Roy Lewallen wrote in
treetonline:

Owen Duffy wrote:
....
Is NEC capable of modelling the configuration shown at
http://www.vk1od.net/lost/King-22.3b.png (which is the same type of
problem as my figure b)?

A point made by King is that if the three half waves are in phase,
radiation resistance will be quite high (one third current required for
same distant field strength), around 316 ohms against 105 ohms for three
half waves not-in-phase. Presumably these figures are for free space.

This effect is certainly observable in models using my Fig a) (though
half the respective resistances due to the vertical over perfect ground).

The feedpoint impedance looks like it might provide a hint as to whether
currents are actually in-phase.

Exploring that thought, an example (to some extent) of King's Fig 22.3b
is the W5GI Mystery Antenna (see
http://www.w5gi.com/images/w5gimster...aschematic.gif ) which claims
to be three half waves in phase at 14.2MHz. It is very similar to the
diagram above in King though I note that the phasing sections are 105° in
electrical length.

The W5GI is fed with a half wave (at 14.2MHz) of 300 ohm line, then 34'
of RG8X. W5GI reports impedance looking into the RG8X as 42+/-j18. That
suggests the load on the RG8X is 31+j2 or 70-j18. The feedpoint impedance
should be about the same value due to the half wave of 300 ohm low loss
line. Neither impedance is within a bull's roar of 316+j0, and are so low
as to question whether the three half waves are indeed in-phase. (The
highest impedance that would yeild 42+/-j18 on a short length of RG8X
would be around 80+j0, closer to the not-in-phase configuration than the
in-phase configuration).

W5GI's reported feed impedance seem inconsistent with three half waves in
phase, and questions whether the phasing arrangement works as suggested.

Thoughts?

Owen

Tom Donaly wrote:
Still using the Tesla coil fella's ideas, are you?

The title of the article is "RF Coils, ..." The block
diagram of a Tesla coil with a top hat is identical
to a 160m mobile antenna with top hat.

A frequency dependent Z0 is a good trick.

It's no trick - just based on empirical measurements
as explained in the IEEE paper. Measurements proved
that the Z0 of a coil varies with wavelength so
wavelength is included in the empirical formula.
I observed that phenomenon during my own experiments.

What happens when you double the length of the coil?

Same thing as doubling the length of a stub. At a fixed
frequency, the delay through the coil is (roughly) doubled.

Does the Z0 stay the same? What if the coil is infinite?

Length of the coil does not appear in the empirical
formula for Z0 of a coil. Coil diameter, TPI, and
wavelength are the variables. Wire diameter would
obviously have some effect but is not included in
the empirical formula.

Can you make a quarter wave shorted stub with it?

Yes, but you need a ground plane close by. Mininec ground will do.
Here's a 75m Texas Bugcatcher coil loaded with its Z0 impedance
modeled over Mininec ground.

http://www.w5dxp.com/coil505u.EZ

The current phase shift through the coil is clearly visible
by displaying "Load Dat". The delay through the coil (EZNEC)
is roughly proportional to the phase shift, i.e. about 38
degrees. The coil is 0.5 feet long with a calculated VF
of 0.02 so the calculated phase shift (without EZNEC) is
about 36 degrees. That's pretty close agreement.
If you make it a half wavelength long - keeping in mind the velocity
factor -
will the impedance looking into the coil equal the impedance of the load?
How do you attach a load to it?

Here's the Texas Bugcatcher coil modeled at the first (1/4WL)
self-resonant frequency of 7.96 MHz:

http://www.w5dxp.com/coil505s.EZ

I have not experimented with 1/2WL self-resonance. The above
file seems to be 1/2WL self-resonant at about 19.2 MHz but
the 75m Texas Bugcatcher coil, at 19.2 MHz, does not meet
the guidelines for validity given in the IEEE article.

Reference:
http://www.w5dxp.com/current2.htm
http://www.w5dxp.com/current.htm
http://www.w5dxp.com/CoilZ0VF.xls
http://www.ttr.com/TELSIKS2001-MASTER-1.pdf
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com
"Government 'help' to business is just as disastrous as government
persecution..." Ayn Rand

Owen Duffy wrote:
The feedpoint impedance looks like it might provide a hint as to whether
currents are actually in-phase.

At a 1/4WL monopole's resonant frequency, the forward antenna
current and reflected antenna current are in phase. The two
component voltages are 180 degrees out of phase. The feedpoint
resistance is [|Vfor|-|Vref|]/[|Ifor|+|Iref|] where these are
antenna voltages and currents on a standing-wave antenna.

If the feedpoint impedance is purely resistive it appears
that the two component waves must be in phase or 180 degrees
out of phase.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com
"Government 'help' to business is just as disastrous as government
persecution..." Ayn Rand

Cecil Moore wrote:

Roy reported that the phase shift across a loading coil wasn't
measurable which is a true statement because the standing wave
current indeed doesn't change phase across a coil or through a
wire.

He wasn't measuring "standing wave current", whatever that is. You
should probably examine his test setup more carefully.

But he then used that same evidence to support w8ji's
ridiculous 3 nS delay through a 75m mobile loading coil when
there is no relationship between standing wave current phase
and the delay through a loading coil. Traveling wave current
must be used to measure the delay through a loading coil,
something I have been saying for years.

And after all those years you still haven't provided any measurements
that support what you've been saying. And as far as I know, neither has
anyone else. But I'm happy to stand corrected.

73, ac6xg

Jim Kelley wrote:
He wasn't measuring "standing wave current", whatever that is.

Sorry Jim, of course he was, since standing wave current
is the primary current that exists on standing wave
antennas like the antenna Roy used to measure his currents.

You keep saying "whatever that is" when it is well
defined in most any antenna book. That you don't
understand standing wave current on standing wave
antennas is just a statement of ignorance - no
offense intended - apparently Roy is just as ignorant.

Perhaps you should study and understand the
difference between a standing wave antenna like
a dipole and a traveling wave antenna like a
terminated Rhombic. Balanis has a good discussion
of such. Here's a quote: "Standing wave antennas,
such as the dipole, can be analyzed as traveling
wave antennas with waves propagating in opposite
directions (forward and backward) and represented
by traveling wave currents..."

An inverted-V dipole can be converted from a
standing wave antenna to a traveling wave antenna
by terminating the ends with a load connected to
mininec ground. Here is an inv_V and a terminated
inv_V modeled in EZNEC. Please look at the "Currents"
display until you understand the meaning of the
phase angles.

http://www.w5dxp.com/inv_v.EZ (standing wave antenna)

Phase angle of the current varies by 2.72 degrees
along each 90 degrees of antenna. This is the current
that Roy used.

http://www.w5dxp.com/inv_vT.EZ (traveling wave antenna)

Phase angle of the current varies by 90 degrees
along each 90 degrees of antenna. This is the current
that Roy should have used.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com
"Government 'help' to business is just as disastrous as government
persecution..." Ayn Rand

Cecil Moore wrote:
Jim Kelley wrote:
He wasn't measuring "standing wave current", whatever that is.

Sorry Jim, of course he was, since standing wave current
is the primary current that exists on standing wave
antennas like the antenna Roy used to measure his currents.

The only current flowing on an antenna is the current traveling from one
end to the other.

You keep saying "whatever that is" when it is well
defined in most any antenna book.

I have the ARRL Antenna Book. Where might I find 'Standing Wave
Current' defined, or at least a description of how to measure it?
Perhaps it's in a section about 'Standing Wave Power'?

That you don't
understand standing wave current on standing wave
antennas is just a statement of ignorance - no
offense intended - apparently Roy is just as ignorant.

Sounds authoratative. I wonder if anyone is buying it?

73, ac6xg

Jim Kelley wrote:
The only current flowing on an antenna is the current traveling from one
end to the other.

Since standing waves cannot exist without the underlying
component traveling waves, to avoid conceptual blunders,
one needs to deal directly with the component traveling
waves. Your statement is based on a purely mathematical
shortcut which exists only in the human brain, not in
reality, and obscures the actual speed-of-light physics
necessary for an EM wave to even exist.

The current can be artificially parsed the way you
are doing it but that parsing leads to the very
misconception under which you are laboring. The same
thing happened with w8ji's and w7el's "measurements"
involving delays through loading coils. The actual
component physics, as explained in any reasonably
technical antenna book is:

Total current = forward current + reflected current

Itot = Ifor + Iref (phasor addition)

Reference: "Antenna Theory", Balanis, 2nd edition

Balanis, page 488:
"The sinusoidal current distribution of long open-ended
linear antennas is a standing wave constructed by two
waves of equal amplitude and 180 degrees phase difference
at the open end traveling in opposite directions along
its length. ... The current and voltage distributions
on open-ended wire antennas are similar to the standing
wave patterns on open-ended transmission lines."

Balanis, page 489:
"Standing wave antennas, such as the dipole, can be
analyzed as traveling wave antennas with waves
propagating in opposite direstions (forward and
backwards) and and represented by traveling wave
currents, If and Ib in Figure 10.1a."

In a standing wave antenna, e.g. a 1/2WL dipole, there
exists a forward wave that gives up about 10% of its
energy content to radiation. The remaining 90% of the
wave encounters the open end of the antenna and is
reflected. So, just as in the case of an open-circuit
stub, we have a forward current component flowing in
one direction and a reflected current component flowing
in the other direction. Many of the mistakes and mis-
conceptions about antennas are based on your false
assertion above.

I have the ARRL Antenna Book.

:-) The ARRL Antenna Book doesn't even have "traveling
wave antennas" in its index. It does state: "Unterminated
long-wire antennas are often referred to as 'standing
wave antennas'". Please reference a reasonably technical
antenna book like "Antennas", by Kraus. "A sinusoidal
current distribution (on a standing wave antenna) may be
regarded as the standing wave produced by two uniform
(unattenuated) traveling waves of equal amplitude moving
in opposite directions along the antenna."

I wonder if anyone is buying it?

It doesn't matter if anyone is buying it. What matters
is technical validity. Your first statement above is
technical invalid. Given the free space description of
standing waves of light given by Hecht in "Optics", your
assertion above would lead one to believe that the photons
comprising the standing wave of light must be at rest even
though that's an impossibility (except in the human mind).

Here's what a couple of references say about standing waves.
"Electrical Communication", by Albert:

"Such a plot of voltage is usually referred to as a
*voltage standing wave* or as a *stationary wave*.
Neither of these terms is particularly descriptive
of the phenomenon. A plot of effective values of
voltage, appearing as in Fig. 6(e), *is not a wave*
in the usual sense. However, the term "standing wave"
is in widespread use."

"College Physics", by Bueche and Hecht:

"These ... patterns are called *standing waves*, as
compared to the propagating waves considered above.
*They might better not be called waves at all*, since
they do not transport energy and momentum."
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com
"Government 'help' to business is just as disastrous as government
persecution..." Ayn Rand

Jim Kelley wrote:
The only current flowing on an antenna is the current traveling from one
end to the other.

Let's assume you are correct. Here are a few questions:

1. Given a 90 degree monopole fed against an infinite
ground plane, what would be the phase at the top of the
antenna compared to the phase at the feedpoint for any
instant in time?

2. Why would the feedpoint impedance of a 1/4WL monopole
be more than a magnitude less than the feedpoint impedance
of an infinite monopole?

3. Where does the above current go when it hits the open-
circuit at the top of the monopole?

4. Why is the total energy in the E-field at the top of the
monopole so high?
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com
"Government 'help' to business is just as disastrous as government
persecution..." Ayn Rand

Owen Duffy wrote:
Roy Lewallen wrote in
treetonline:

Owen Duffy wrote:
...
Is NEC capable of modelling the configuration shown at
http://www.vk1od.net/lost/King-22.3b.png (which is the same type of
problem as my figure b)?

A point made by King is that if the three half waves are in phase,
radiation resistance will be quite high (one third current required for
same distant field strength), around 316 ohms against 105 ohms for three
half waves not-in-phase. Presumably these figures are for free space.
. . .

I looked up the section in King, Mimno, and Wing and was pretty
disappointed. It's one of my favorite references, and I usually find the
explanations clear. But the description of that antenna is pretty vague,
with considerable hand waving ("[Operation of coaxial stubs] is much
less satisfactory than that with the open-wire stubs. . ." without
explaining why). And in the explanation of the open-wire stubs, the
authors seem to state that the wires must carry purely differential
currents. And their models (Fig. 22-4) do show purely differential
coupling from the antenna to the stubs.

I speculate that they really didn't understand how these antennas
worked, had discovered that the coaxial sleeve versions didn't work or
at least didn't work as well -- and didn't show the proper impedance --,
but didn't fully understand why. King, in particular, was and is one of
the giants of antenna theory, and leaves us a lifetime of brilliant
insight and rigorous mathematical analysis. But at least at the time
that book was published, they lacked the modeling tools we have today.

This effect is certainly observable in models using my Fig a) (though
half the respective resistances due to the vertical over perfect ground).

The feedpoint impedance looks like it might provide a hint as to whether
currents are actually in-phase.

It surely does. Given the currents on and locations of the end wires,
the modification to the center wire can be calculated from mutual
coupling considerations. And I think this is a clue that led King,
Mimno, and Wing to conclude that something was amiss with the coaxial
version.

Exploring that thought, an example (to some extent) of King's Fig 22.3b
is the W5GI Mystery Antenna (see
http://www.w5gi.com/images/w5gimster...aschematic.gif ) which claims
to be three half waves in phase at 14.2MHz. It is very similar to the
diagram above in King though I note that the phasing sections are 105° in
electrical length.

The W5GI is fed with a half wave (at 14.2MHz) of 300 ohm line, then 34'
of RG8X. W5GI reports impedance looking into the RG8X as 42+/-j18. That
suggests the load on the RG8X is 31+j2 or 70-j18. The feedpoint impedance
should be about the same value due to the half wave of 300 ohm low loss
line. Neither impedance is within a bull's roar of 316+j0, and are so low
as to question whether the three half waves are indeed in-phase. (The
highest impedance that would yeild 42+/-j18 on a short length of RG8X
would be around 80+j0, closer to the not-in-phase configuration than the
in-phase configuration).

W5GI's reported feed impedance seem inconsistent with three half waves in
phase, and questions whether the phasing arrangement works as suggested.

Thoughts?

I doubt that it does.

Roy Lewallen, W7EL