There seems to be mass confusion even among the gurus on
this newsgroup as to the difference between standing-wave
current, as exists on a 1/2WL dipole, vs traveling-wave
current, as exists on a terminated antenna like a rhombic.

I have prepared two EZNEC files that should run on the
free demo version of EZNEC as well as on the commercial
edition. These two files clearly show the difference in
the two types of currents.

The standing-wave example is designed to illustrate
standing-wave current. All of the forward energy is
reflected at the open end of the wire. The total
current displayed by EZNEC is the sum of the forward
and reflected currents which are close to equal.

The traveling-wave example is designed to illustrate
traveling-wave current. Most of the forward energy
is dissipated in the load resistor rather than being
reflected. The total current displayed by EZNEC is
the sum of the forward and reflected currents with
the reflected current minimized to a negligible value.

Each EZNEC file consists of a 1/4WL wire run horizontal
one foot above ground at 4 MHz. In the standing-wave file,
the wire is open and unterminated. In the traveling-wave
file, the wire is terminated to ground by its characteristic
impedance. To view EZNEC's tabulated current at each of the
18 segments along the 1/4WL, simply click on "Load Dat".

The standing-wave file is:

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

The traveling-wave file is:

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

In the following results (directly from EZNEC) please
note the almost constant phase reported for the
standing-wave current vs the continuously changing
phase reported for the traveling-wave current.

Here are the values of current at each segment for the
standing-wave example as reported by EZNEC:

EZNEC+ ver. 4.0

standing wave 12/18/2007 9:11:33 AM
--------------- LOAD DATA ---------------
Frequency = 4 MHz

Load 1 Current = 0.9974 A. at -0.01 deg.
Load 2 Current = 0.9874 A. at -0.02 deg.
Load 3 Current = 0.9703 A. at -0.03 deg.
Load 4 Current = 0.9461 A. at -0.04 deg.
Load 5 Current = 0.915 A. at -0.05 deg.
Load 6 Current = 0.8773 A. at -0.06 deg.
Load 7 Current = 0.8332 A. at -0.07 deg.
Load 8 Current = 0.783 A. at -0.08 deg.
Load 9 Current = 0.7271 A. at -0.08 deg.
Load 10 Current = 0.6659 A. at -0.09 deg.
Load 11 Current = 0.5999 A. at -0.09 deg.
Load 12 Current = 0.5295 A. at -0.10 deg.
Load 13 Current = 0.4553 A. at -0.10 deg.
Load 14 Current = 0.3777 A. at -0.10 deg.
Load 15 Current = 0.2974 A. at -0.10 deg.
Load 16 Current = 0.2148 A. at -0.11 deg.
Load 17 Current = 0.1307 A. at -0.11 deg.
Load 18 Current = 0.0447 A. at -0.11 deg.

Here are the values of current at each segment for the
traveling-wave example as reported by EZNEC:

EZNEC+ ver. 4.0

traveling wave 12/18/2007 9:18:19 AM
--------------- LOAD DATA ---------------
Frequency = 4 MHz

Load 1 Current = 0.9992 A. at -3.12 deg.
Load 2 Current = 0.9983 A. at -8.11 deg.
Load 3 Current = 0.9977 A. at -13.08 deg.
Load 4 Current = 0.9972 A. at -18.05 deg.
Load 5 Current = 0.9970 A. at -23.02 deg.
Load 6 Current = 0.9970 A. at -27.99 deg.
Load 7 Current = 0.9973 A. at -32.96 deg.
Load 8 Current = 0.9978 A. at -37.92 deg.
Load 9 Current = 0.9985 A. at -42.87 deg.
Load 10 Current = 0.9993 A. at -47.82 deg.
Load 11 Current = 1.0000 A. at -52.75 deg.
Load 12 Current = 1.0010 A. at -57.67 deg.
Load 13 Current = 1.0030 A. at -62.58 deg.
Load 14 Current = 1.0040 A. at -67.48 deg.
Load 15 Current = 1.0050 A. at -72.36 deg.
Load 16 Current = 1.0060 A. at -77.23 deg.
Load 17 Current = 1.0070 A. at -82.09 deg.
Load 18 Current = 1.0080 A. at -86.97 deg.
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:
There seems to be mass confusion even among the gurus on
this newsgroup as to the difference between standing-wave
current, as exists on a 1/2WL dipole, vs traveling-wave
current, as exists on a terminated antenna like a rhombic.

I have prepared two EZNEC files that should run on the
free demo version of EZNEC as well as on the commercial
edition. These two files clearly show the difference in
the two types of currents.

Heavily clip.......

The standing-wave file is:

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

The traveling-wave file is:

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

clip.....

Hi Cecil,

I tried the files and they work well. Congratulations on a clever use
of zero resistance loads. I have not seen that technique used before
but it certainly allows for a good EZNEC demonstration.

EZNEC is a great program.

73, Roger, W7WKB

Roger wrote:
I tried the files and they work well. Congratulations on a clever use
of zero resistance loads. I have not seen that technique used before
but it certainly allows for a good EZNEC demonstration.

It's a way to "measure" the current without disturbing
the current. Do you see how the EZNEC current has a
reference phase and thus is a "snapshot" in time? Do
you see how traveling-wave current travels and standing-
wave current just appears to stand there? Since EM waves
cannot just stand there and must necessarily move at the
speed of light, a standing-wave is just an artifact of
superposition (a magical illusion for some). It has no
stand-alone existence aside from its forward and reverse
component EM waves that indeed do travel at the speed of
light (adjusted for velocity factor).

EZNEC is a great program.

Yes indeed, like the Smith Chart, it is a great antenna
tool. I've been a satisfied customer for 20 years,
since I first purchased ELNEC. ELNEC and EZNEC
have been great tutors for me. If someone doesn't
want to buy it, the free demo version of EZNEC
available from http://www.eznec.com is quite a free
lunch and although limited to 20 segments, is very
useful on wire dipoles and monopoles and learning
how they work.
--
73, Cecil http://www.w5dxp.com

Roger wrote:

Congratulations on a clever use of zero resistance loads.

I am probably missing something, but why not just show the currents
and phase in the 'View Antenna' window ?

4nec2 wrote:
Roger wrote:

Congratulations on a clever use of zero resistance loads.

I am probably missing something, but why not just show the currents
and phase in the 'View Antenna' window ?
Maybe I am missing something. I can not get a numeric record of the
phase and current in the "View Antenna" window. I am using version 4.0.

Roger wrote:
Maybe I am missing something. I can not get a numeric record of the
phase and current in the "View Antenna" window. I am using version 4.0.

You do get a *graphic* record of the current amplitude in
the "View Antenna" window. It is unclear exactly what
is displayed when the current phase box is selected.

You do NOT get a numeric record in the View Antenna
window. For a numeric record, you must use the "Loads"
and "Load Dat" feature.
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:
Roger wrote:
Maybe I am missing something. I can not get a numeric record of the
phase and current in the "View Antenna" window. I am using version 4.0.

You do get a *graphic* record of the current amplitude in
the "View Antenna" window. It is unclear exactly what
is displayed when the current phase box is selected.

Although one can get a current amplitude plot vs length
from EZNEC, it seems impossible to get a current phase
plot vs length. That's probably why so many people are
confused. Click on "Currents" and transfer that data
to EXCEL to make things a lot clearer.
--
73, Cecil http://www.w5dxp.com

Roger wrote:
4nec2 wrote:
Roger wrote:

Congratulations on a clever use of zero resistance loads.

I am probably missing something, but why not just show the currents
and phase in the 'View Antenna' window ?
Maybe I am missing something. I can not get a numeric record of the
phase and current in the "View Antenna" window. I am using version 4.0.

In all versions, the View Antenna display shows the currents only
graphically and not numerically. There are three ways to find the
numerical value of current at a particular segment:

1. Click the Currents button at the left of the main window. This gives
the currents at all segments.
2. Insert a zero ohm load at the segment of interest and click Load Dat
to see its current.
3. Insert a zero volt voltage (not current) source at the segment of
interest and click Src Dat to see its current.

Roy Lewallen, W7EL

Roy Lewallen wrote:
1. Click the Currents button at the left of the main window. This gives
the currents at all segments.
2. Insert a zero ohm load at the segment of interest and click Load Dat
to see its current.

Why doesn't EZNEC accurately plot those currents on the
antenna display?
--
73, Cecil http://www.w5dxp.com

4nec2 wrote:
Roger wrote:

Congratulations on a clever use of zero resistance loads.

I am probably missing something, but why not just show the currents
and phase in the 'View Antenna' window ?

For current phase, EZNEC does not display the same
absolute phase as the "Load Dat" function reports.
That would appear to be a bug in the EZNEC GUI
software.

I'm glad you asked that question. Perhaps W7EL can tell
us why EZNEC does not display the same current phase as
it reports in the "Load Dat" function. EZNEC seems to
display the current amplitude correctly but it is unclear
exactly what EZNEC is displaying when the current phase
box is selected. That's why I used the "Load Dat" feature.

Here is a graphic using the "View Antenna" window for
the EZNEC files TravWave.EZ and StndWave.EZ.

http://www.w5dxp.com/eznec.jpg

Looking at TravWave.EZ with the current phase turned
off, the current displayed is indeed the amplitude of
the current up and down the wire which is essentially
a constant RMS magnitude.

But with the current phase turned on, the display does
not display the same phase reported by "Load Dat". It
displays a cosine function when the actual phase function
is a straight sloping line varying from 0 degrees at the
feedpoint to -90 degrees at the load resistor. What
EZNEC is actually displaying associated with phase
is unclear, confusing, and misleading.

StndWave.EZ has the same unclear display for phase.
The current amplitude is the correct cosine function
but the current phase is misleading. The "Loads Dat"
function says the phase varies from 0 degrees at the
feedpoint to -0.11 deg at the open end of the wire,
i.e. virtually no change at all in phase up and down
the wire. Yet EZNEC displays a cosine function for the
current phase the meaning of which is unclear.

To answer your question, EZNEC does not display phase
when the current phase box is selected. It is unclear
to me exactly what EZNEC is displaying when the current
phase box is selected.
--
73, Cecil http://www.w5dxp.com