Owen Duffy wrote:
I suspect that it is a technique to try to maximise the current moment to
get the highest radiation resistance. They then build out the radation
resistance with loss to achieve a specification maximum VSWR for direct
feeding at the base with 50 ohm line.

It could also be a technique to move part of the
loading up to the top of the antenna. I once won
a CA shootout with a top-loaded junk box antenna
that, in EZNEC, looks something like this:

http://www.w5dxp.com/SHOOTOUT.EZ
--
73, Cecil http://www.w5dxp.com

On Dec 4, 1:26 pm, Cecil Moore wrote:
Owen Duffy wrote:
I suspect that it is a technique to try to maximise the current moment to
get the highest radiation resistance. They then build out the radation
resistance with loss to achieve a specification maximum VSWR for direct
feeding at the base with 50 ohm line.

It could also be a technique to move part of the
loading up to the top of the antenna. I once won
a CA shootout with a top-loaded junk box antenna
that, in EZNEC, looks something like this:

I think the main reason they do that is to improve current
distribution.
The tighter windings near the top make it act more like a
lumped coil which is raised from the base.
This should provide a more constant current level up the whip.
It's done for the same reason people raise the usual coils used
on a bugcatcher , or whatever. To improve current distribution.
And most don't add any extra loss on purpose.
Most add a extra small winding at the base to act as a
matching coil.
If you take one of those helical whips, IE: hamstick, etc,
and add a longer stinger whip, you will have a pretty decent
antenna.
I used a 20m hamstick on 40m, by adding a 4-5 ft stinger
and it worked very well. Almost as well as the typical
bugcatcher.
But I later rebuilt that antenna by stripping the helical windings,
adding a bigger "lumped" coil, and it was pretty much electrically
the same as a bugcatcher. It works all bands 80-10 now.
MK

Cecil Moore wrote:

Jim Kelley wrote:

Honestly, Cecil, it's pretty hard to know what you mean considering
the reckless way you throw around the term 'phase'. I'll grant that
you might know what you mean, but I don't see how you can expect
anyone else to.


Jim, if you have trouble understanding the word "phase",
look it up in a technical dictionary. I don't have time
to waste my time teaching everyone the principles of AC
waves in EE201.

Thanks. Sorry for the unfinished thought. I meant that because of the
reckless way you use the term, I don't know how you expect others to
know what you intend by it when you use it.

FYI: For a signal proportional to cos(x)*cos(wt), the
phase doesn't change with 'x'. That's why standing wave
current cannot be used to measure delay.

Perfect example. The phase of a cosine wave at it's absolute maximum
amplitude is either 0 or 180 degrees. Each point along a sinusoidal
plot represents a different phase angle. Phase varies with time at a
fixed position, or varies with position at a fixed time. For it to
have meaning there must be a reference. You have a habit of switching
references without noticing or making note of it. This makes some of
your comments a bit confused sounding, if not blatantly inaccurate.

With regard to your comment above, if the maximum amplitude and period
of a sinusoidal wave are both known, then given any instantaneous
amplitude and, knowing whether the slope is positive or negative, the
instantaneous phase can be readily determined. FYI: Phase angle (wt)
is found on the x axis of a sinusoidal plot. When period or
wavelength and length are equated, as is the case with a resonant
antenna then phase and position are functionally related.

73, ac6xg

wrote:
If you take one of those helical whips, IE: hamstick, etc,
and add a longer stinger whip, you will have a pretty decent
antenna.

Even better is to extend the base section by a
few feet.
--
73, Cecil http://www.w5dxp.com

On Dec 4, 3:12 pm, Cecil Moore wrote:
wrote:
If you take one of those helical whips, IE: hamstick, etc,
and add a longer stinger whip, you will have a pretty decent
antenna.

Even better is to extend the base section by a
few feet.
--
73, Cecil http://www.w5dxp.com

I do that too... I have a solid hustler mast
I use for that.
MK

Jim Kelley wrote:
You have a habit of switching
references without noticing or making note of it. This makes some of
your comments a bit confused sounding, if not blatantly inaccurate.

Jim, it's all your fault for not being telepathic. :-)
I admit that my thought processes are somewhat chaotic
but remember, order often comes out of chaos. I've
experienced an epiphany or two in my time.

I also have a bad habit of declaring something invalid
when it is only irrelevant. It is the conclusions drawn
from irrelevant measurements that are invalid, not the
measurements themselves.

The convention that I try to use is the EZNEC convention.
Everything is referenced to the source signal. When I say
the phase of a standing wave is unchanging, I mean that it
has the same phase as the source signal at the feedpoint
and is the same phase as reported by EZNEC. I apologize for
not being clear about that.

With regard to your comment above, if the maximum amplitude and period
of a sinusoidal wave are both known, then given any instantaneous
amplitude and, knowing whether the slope is positive or negative, the
instantaneous phase can be readily determined.

Take I = K1*cos(x)*cos(wt), a standing-wave equation.
Let t be any fixed value. cos(x) is an amplitude value
and does NOT vary with time. Therefore, the phase of the
standing-wave signal is constant at any particular time
and does NOT depend upon position along the wire or coil.

Now take I = K2*cos(x+wt), a traveling-wave equation.
Let t be any fixed value. The length dimension 'x'
has an effect on phase, i.e. the phase of of the
signal indeed does depend upon BOTH position AND time.

Anyone who understands the math would not dare show
his ignorance by asserting that the delay through a
100T coil is 3 ns on 4 MHz or that the measured phase
shift through a loading coil is somehow proportional
to the delay through the coil in a standing-wave antenna.
--
73, Cecil http://www.w5dxp.com

Jim Kelley wrote:


Cecil Moore wrote:

Jim Kelley wrote:

Honestly, Cecil, it's pretty hard to know what you mean considering
the reckless way you throw around the term 'phase'. I'll grant that
you might know what you mean, but I don't see how you can expect
anyone else to.


Jim, if you have trouble understanding the word "phase",
look it up in a technical dictionary. I don't have time
to waste my time teaching everyone the principles of AC
waves in EE201.

Thanks. Sorry for the unfinished thought. I meant that because of the
reckless way you use the term, I don't know how you expect others to
know what you intend by it when you use it.

FYI: For a signal proportional to cos(x)*cos(wt), the
phase doesn't change with 'x'. That's why standing wave
current cannot be used to measure delay.

Perfect example. The phase of a cosine wave at it's absolute maximum
amplitude is either 0 or 180 degrees. Each point along a sinusoidal
plot represents a different phase angle. Phase varies with time at a
fixed position, or varies with position at a fixed time. For it to have
meaning there must be a reference. You have a habit of switching
references without noticing or making note of it. This makes some of
your comments a bit confused sounding, if not blatantly inaccurate.

With regard to your comment above, if the maximum amplitude and period
of a sinusoidal wave are both known, then given any instantaneous
amplitude and, knowing whether the slope is positive or negative, the
instantaneous phase can be readily determined. FYI: Phase angle (wt) is
found on the x axis of a sinusoidal plot. When period or wavelength and
length are equated, as is the case with a resonant antenna then phase
and position are functionally related.

73, ac6xg

It's hardly surprising that Cecil thinks there's no phase information in
a standing wave, since he leaves it out on purpose. "Cos(x)*Cos(wt)" is
just flat wrong. It's supposed to be "Cos(x + d/2)*e^(i(wt + d/2))." "d"
is the phase difference between a wave traveling in the forward
direction and an equal amplitude wave traveling in the opposite
direction. This is pretty poor shooting for a guy who claims a
degree in symbol slinging.
73,
Tom Donaly, KA6RUH

Tom Donaly wrote:
It's hardly surprising that Cecil thinks there's no phase information in
a standing wave, since he leaves it out on purpose. "Cos(x)*Cos(wt)" is
just flat wrong. It's supposed to be "Cos(x + d/2)*e^(i(wt + d/2))." "d"
is the phase difference between a wave traveling in the forward
direction and an equal amplitude wave traveling in the opposite
direction. This is pretty poor shooting for a guy who claims a
degree in symbol slinging.

I copied the equations from "Optics", by Hecht, page
289 in the 4th edition.

Unfortunately, it is apparent that you will sacrifice
your technical ethics to try to discredit me. Everything
I have written is referenced to a source at zero degrees.
Your extra terms do absolutely nothing except obfuscate
the concepts. One can only assume that obfuscation is your
ulterior motive.

Here's what Gene Fuller had to say about this subject:

Regarding the cos(kz)*cos(wt) term in a standing wave:

Gene Fuller, W4SZ wrote:
In a standing wave antenna problem, such as the one you describe,
there is no remaining phase information. Any specific phase
characteristics of the traveling waves died out when the startup
transients died out.

Phase is gone. Kaput. Vanished. Cannot be recovered. Never to be
seen again.

Why don't you two get back to us after you thrash out the
details upon which you disagree?
--
73, Cecil http://www.w5dxp.com

On Tue, 04 Dec 2007 10:36:29 -0800, Roy Lewallen
wrote:

Richard Clark wrote:

Hi Roy,

EZNEC refuses to operate with Tom's coil (wire overlaps and geometry
issues if I recall from the last failure).

Please contact me by email if you think there's EZNEC isn't doing
something as you think it should. I'll either explain why it's doing
what it does or, if there's a bug, will fix it.

Roy Lewallen, W7EL

Hi Roy,

The complaint is:
Wire 3 segment length too short. L = .01914 m; recommended min. =
..07495 m.
and so on for 800+ lines.

Attempting to find the Src Data results in:
Wires 3 and 10 contact improperly or are too close.
Wires 3 and 11 parallel and contacting.
Wire 3 end 2 contacts improperly or is too close to wire 12.
and so on...

However, on close examination
Pilot Error
The wire is too thick (I noticed this in modeling Tom's coil at the
Corum calculator and hadn't done the correction yet in EZNEC). The
geometry still complains, but it doesn't inhibit processing.

Thanx anyway.

73's
Richard Clark, KB7QHC

Cecil Moore wrote:
Ian White GM3SEK wrote:
Cecil Moore wrote:
I'm not reclassifying anything. The differences between traveling-wave
antennas and standing-wave antennas have been known for many decades.
Oh good! Exactly where do *you* draw the line between them; and why?
Please justify this by giving examples of two antennas that are very
close to your chosen line, but on opposite sides.

Glad to oblige. The two classical examples are a 1/2WL dipole
vs a terminated rhombic. The differences are obvious. The ends
of the standing-wave 1/2WL dipole are open-circuited so forward
waves undergo a total reflection. Ideally, the traveling-wave
rhombic is terminated in its characteristic impedance so
reflections are eliminated.

The equation for the current in a 1/2WL dipole is roughly
proportional to cos(x)*cos(wt). The equation for the current in
an ideal rhombic is proportional to cos(x+wt) where w=2*Pi*F.
For anyone with a math background, those differences are more
than obvious and I pointed that out years ago.


Thank you; it's useful to clarify from time to time what you do mean,
because many of these disputes are because people are using the same
terms with different meanings.

Then please justify the difference between your two different
classifications of current.

I don't have to justify that, Ian. Mathematics automatically
justifies it for me. If you would simply take the time to understand
the difference between cos(x)*cos(wt) and cos(x+wt), you would
understand it also.

The current in an ideal rhombic is 100% forward current proportional
to cos(x+wt). The current in a 1/2WL dipole is the sum of two
currents. The forward current is roughly proportional to cos(x+wt)
just as it is in the rhombic. The reflected current is roughly
proportional to cos(x-wt) and when those two traveling-wave currents
are added the resultant standing-wave current is proportional to
cos(x)*cos(wt), a completely different kind of current as is obvious
from their different equations.

The mathematics is clear enough, but it provides no justification
whatever for your conceptual leap to "a completely different KIND of
current" (my emphasis). You are only doing that to justify the different
kind of behavior that your model demands for a loading inductance - in
other words, you are trying to patch one error by adding a second error.

I suspect (although it's difficult to separate from the other known
errors) that you are also hopping between two different definitions of
"phase", one for each case, without noticing that you are doing do.

If instead you were to accept that current is simply the net movement of
electrons, and inductance always responds to that in a consistent way,
you would find the whole topic much simpler than you make it out to be.

The Boyer paper that I referenced yesterday shows exactly how the model
of an antenna as a reflective unterminated transmission-line handles
inductive loading.


--

73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek