colinear representation in NEC
 

Cecil Moore wrote:
Jim Kelley wrote:
I agree that electromagnetic traveling waves are the kinds of waves
that propagate on and cause radiation to emanate from an antenna. But
your claims about 'standing waves not changing phase along the antenna'
...

Jim, I thought you have EZNEC.
Here are the currents at all of
the segments along a 20m dipole with 21 segments from end to end.
Please note that in a dipole that is 180 degrees long, the phase
of the (mostly standing-wave) current varies by less than 3 degrees.
How can the current in a 180 degree antenna vary by less than 3 degrees?

It seems to me that computers are completely stupid about certain
things. Could it be a case of garbage in, garbage out?

Quoting my web page: "Standing wave current cannot be used to directly
measure either a valid amplitude change or a valid phase shift through
a loading coil. All of the reported conclusions based on loading coil
measurements using standing-wave current on standing-wave antennas are
conceptually flawed."

And what more authoritative reference could someone cite than their own
web page? :-)

I've never actually known what it was that made you believe Roy had
measured standing wave current - whatever that means. Or, how his
measurements compare with your own measurements of the phenomenon.

Owen had an epiphany of a sort when he realized
that fact of physics.

It may not even be as elusive a fact as one is given to believe around here.

73, ac6xg



20m dipole 3/18/2009 5:28:50 PM

--------------- CURRENT DATA ---------------

Frequency = 14.2 MHz

Wire No. 1:
Segment Conn Magnitude (A.) Phase (Deg.)
1 Open .0836 -2.75
2 .23595 -2.57
3 .37707 -2.38
4 .50791 -2.17
5 .62692 -1.95
6 .73226 -1.71
7 .82218 -1.44
8 .89511 -1.13
9 .94979 -0.78
10 .98539 -0.37
11 1 0.00
12 .98539 -0.37
13 .94979 -0.78
14 .89511 -1.13
15 .82218 -1.44
16 .73226 -1.71
17 .62691 -1.95
18 .50791 -2.17
19 .37707 -2.38
20 .23595 -2.57
21 Open .0836 -2.75

colinear representation in NEC
 

Jim Kelley wrote:
I've never actually known what it was that made you believe Roy had
measured standing wave current - whatever that means.

Good Grief! Could it be that a monopole is a "STANDING WAVE ANTENNA"?
--
73, Cecil http://www.w5dxp.com
"Government 'help' to business is just as disastrous as
government persecution..." Ayn Rand

colinear representation in NEC
 

Cecil Moore wrote:
Could it be that a monopole is a "STANDING WAVE ANTENNA"?

Here's an EZNEC simulation of a 1/4WL monopole. It is
a 1/4WL stub with the wire resistivity adjusted to
simulate monopole radiation. The standing wave current
distribution (lack of phase) and feedpoint resistance
are similar to a monopole.

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

Add a short at the top and a load of 600 ohms in the
shorted segment and observe the traveling wave.

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

Turn on the current phase display and observe the
traveling wave phase shift.
--
73, Cecil http://www.w5dxp.com
"Government 'help' to business is just as disastrous as
government persecution..." Ayn Rand

colinear representation in NEC
 

Cecil Moore wrote:

Could it be that a monopole is a "STANDING WAVE ANTENNA"?

The supposition is true, so the intended implication must be that only
standing wave current can be measured on monopole antennas. And Roy
therefore would have to have measured standing wave current (whatever
that is).

I must decline to agree. :-)

73, ac6xg

colinear representation in NEC
 

On Fri, 20 Mar 2009 17:35:02 -0800, Jim Kelley
wrote:

I must decline to agree. :-)

Couldn't you incline to disagree?

73's
Richard Clark, KB7QHC

colinear representation in NEC
 

Jim Kelley wrote:
Cecil Moore wrote:

Could it be that a monopole is a "STANDING WAVE ANTENNA"?

The supposition is true, so the intended implication must be that only
standing wave current can be measured on monopole antennas. And Roy
therefore would have to have measured standing wave current (whatever
that is).

I must decline to agree. :-)

About 90% of the total current on an open-ended 1/4WL
monopole is standing wave current with close to unchanging
phase. That's why a 1/4WL monopole is called a "standing
wave antenna".

That is the current that Roy and Tom used so the component
traveling wave, accounting for about 10% of the total current
where the phase shift actually occurs, was mostly ignored and
swamped by the huge component standing wave.

This is such a simple concept - I don't see the problem
in understanding that a wave with the following equation
doesn't change phase with position (x). The phase is the
same over 90 degrees of length no matter what fixed x and
fixed t are chosen. EZNEC supports that fact of physics.
Here's the standing wave equation from "Optics", by Hecht:

E(x,t) = 2E01*sin(kx)*cos(wt) quoting "Optics", by Hecht:

"[Standing wave phase] "doesn't rotate at all, and the resultant
wave it represents doesn't progress through space - its a standing
wave."

Another interesting thing about the standing wave equation
is that the sign of (wt) can be reversed, i.e. standing waves
don't move in either direction - they just stand there. EM
waves cannot stand still so "EM standing wave" is an oxymoron.

Quoting one of my college textbooks, "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."

From "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."

One can use EZNEC's VERT1.EZ to view the essentially
unchanging phase on a standing wave monopole. Just look
at the difference in phase between the feedpoint and a
point 45 degrees up the antenna. In 45 degrees of antenna,
the current phase changes by 3.65 degrees. That is the
current Roy used to measure phase shift through a coil
in order to support w8ji's 3 nS delay "measurements".
--
73, Cecil http://www.w5dxp.com
"Government 'help' to business is just as disastrous as
government persecution..." Ayn Rand

colinear representation in NEC
 

Owen Duffy wrote:
"Tom Donaly" wrote in
:

...
Why would NEC reduce a TL two-port to a lumped load? Two-port
parameters can handle transmission line problems quite well without
the simplifying assumption that all components are of zero length.

Hi Tom,

I expect that NEC does model the propagation delay from end to end on a
transmission line. My comment was that NEC reduces a s/c TL stub to a
lumped load for the stub input end which is inserted in the vertical.


No it doesn't do prop delay. It does a steady state model. The TL is
just another two port that gets dumped into a giant matrix which is
solved as a system of linear equations. Think of TL as a special case of NT.

colinear representation in NEC
 

Jim Lux wrote:
No it doesn't do prop delay.

The prop delay is easily calculated by loading the TL
with Rload=Z0 and observing the resulting traveling wave
phase shift while taking VF into account. In the same
manner, the prop delay through a loading coil can be
calculated.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com
"Government 'help' to business is just as disastrous as government
persecution..." Ayn Rand

colinear representation in NEC
 

Cecil Moore wrote:
Jim Lux wrote:
No it doesn't do prop delay.

The prop delay is easily calculated by loading the TL
with Rload=Z0 and observing the resulting traveling wave
phase shift while taking VF into account. In the same
manner, the prop delay through a loading coil can be
calculated.

What's the Z0 of a loading coil, Cecil?
73,
Tom Donaly, KA6RUH

colinear representation in NEC
 

Jim Lux wrote:
Owen Duffy wrote:
"Tom Donaly" wrote in
:
...
Why would NEC reduce a TL two-port to a lumped load? Two-port
parameters can handle transmission line problems quite well without
the simplifying assumption that all components are of zero length.

Hi Tom,

I expect that NEC does model the propagation delay from end to end on
a transmission line. My comment was that NEC reduces a s/c TL stub to
a lumped load for the stub input end which is inserted in the vertical.


No it doesn't do prop delay. It does a steady state model. The TL is
just another two port that gets dumped into a giant matrix which is
solved as a system of linear equations. Think of TL as a special case of
NT.

What kind of two port does NEC use, Jim? What is "just another two port?"
73,
Tom Donaly, KA6RUH