I haven't been following this particular discussion of "standing wave
antennas" vs "traveling wave antennas" because it looks to me like just
another diversion to avoid confronting the sticky problems with
alternative theories, and one that's been used and discussed many times
before. But I see that EZNEC's report of SWR has been mentioned, so I'd
like to make sure that readers understand what it means.

EZNEC reports an "SWR" for each source, and will also plot this as a
function of frequency. This is *not* the SWR on an antenna (assuming
that you can even rigorously define it), nor is it necessarily the SWR
on a transmission line to which the source is connected, if it is
connected to a line. It's only an alternate way of describing the
impedance seen by the source, just like your transmitter's SWR meter.
The reported SWR is the the SWR which would exist on a 50 ohm
transmission line if that transmission line were connected between the
source and its load, whether one is or not. It shows the same value as
your transmitter SWR meter would if you replaced the source with your
transmitter. An alternate SWR Z0 value can be specified so you can also
see what the SWR would be on a transmission line of some other
impedance. It's not necessary, or even likely, that there will be a
transmission line or even wire (again, if you can even define SWR for a
single conductor) which actually has an SWR equal to the value reported
by EZNEC.

If you were to connect your transmitter to a 50 ohm load through a half
wavelength 300 ohm transmission line, the SWR on the transmission line
would be 6:1, but your rig's SWR meter would read 1:1. If you modeled
this with EZNEC, it would show the 50 ohm SWR as 1:1 (like your
transmitter SWR meter). If you set the alternate SWR Z0 to 300 ohms, it
would correctly show the 300 ohm SWR to be 6:1. If you connected your
transmitter directly to a 150 ohm resistor, your rig's SWR meter (and
EZNEC's 50 ohm SWR) would read 3:1, even though there is no transmission
line of any impedance and therefore no standing waves anywhere.

Roy Lewallen, W7EL


Richard Clark wrote:
On Fri, 04 Jan 2008 10:55:37 -0600, Cecil Moore
wrote:

Richard Clark wrote:
A traveling-wave antenna needs an SWR close to ~1:1 to be
a good example. Whether by accident or on purpose, yours
is a very poor example.
I used your Traveling Wave antenna. :-
http://www.w5dxp.com/TravWave.EZ

Good grief, Richard! You cannot use the 8.4:1 50 ohm SWR
reading for the SWR on a wire with a characteristic
impedance of 411 ohms. I see what you did now and it
is was more than stupid.

The load resistor is 411 ohms.

So it was, so it is, and so shall it always be to demonstrate a
dramatic variation of CURRENT. All rather standard stuff. The SWR
report from EZNEC is source based, and that source was 100km distant
from the RECEIVE antenna - wholly remote from my care and
consideration. I didn't make your mistake, you made it alone for
yourself. Mount it like a trophy on your mantle with the rest.

With great misfortune, TravWave.EZ is, as you say, an atrocious
antenna, and nothing like what Beverage designed which my second
example more clearly reveals. I simply used your poor antenna so as
to increase the likelihood of its impeachment by its designer. This,
of course, triggered the script where that author condemned his own
creation; and all the choreographed marks were hit precisely as
anticipated.

Dear readers,

With such limp struggles as offered by Cecil, this has long passed the
point of being a challenge. It rarely takes much effort to crack his
arguments open, but having done it several times here alone, it can
only be described as a Sado-Masochistic spectacle. My arm is getting
tired with swinging the whip and Cecil's groans have long since lost
their siren call. Perhaps some future outrage from Cecil will
invigorate the song of the lash.

When dawn breaks, it will no doubt reveal TravWave.EZ disowned and
cast out of the home as a fraud. I will undoubtedly be described as
its immoral progenitor because TravWave.EZ is so obviously the spawn
of a demented troglodyte slipped into Cecil's nest like a cuckoo's
egg.

73's
Richard Clark, KB7QHC