Roy Lewallen wrote:
I've always regarded a "standing wave" as being a description of the
envelope caused by the interference between forward and reverse
traveling waves.

If you have "Fields and Waves ..." by Ramo and Whinnery,
take a look at the equation for standing wave voltage
and current on page 285 of the 2nd edition.

Ex = E*e^j(wt-Bz) + E'*e^j(wt+Bz)

Roy, that is NOT the equation for an envelope.
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:
Roy Lewallen wrote:
I've always regarded a "standing wave" as being a description of the
envelope caused by the interference between forward and reverse
traveling waves.

If you have "Fields and Waves ..." by Ramo and Whinnery,
take a look at the equation for standing wave voltage
and current on page 285 of the 2nd edition.

Ex = E*e^j(wt-Bz) + E'*e^j(wt+Bz)

Roy, that is NOT the equation for an envelope.

It's too bad you don't have the foggiest notion as to just
what it is the equation of. Much of the thousands of posts
could have been avoided if that were the case.
73,
Tom Donaly, KA6RUH

Owen Duffy wrote:
Walter Maxwell wrote:
It appears to me that even with all the successive posts on the
subject of power in the standing wave, you all seem to be missing the
ingredient that proves why there is no useable power in the standing
wave. It is because the current and voltage in the standing wave are
90° out of phase. Multiplying E x I under this condition results in
zero power.

I am trying to make sense of this and the first issue is what you mean by
the term "standing wave".

Walt is right.
Let's look at an arbitrary example of forward and reflected
voltage and current instantaneous phasors at one point on a
particular line.

Vfor = 100v at 45 degrees, Ifor = 2 amps at 45 degrees

The forward voltage and forward current are in phase.

Vref = 100v at -45 degrees, Iref = 2 amps at 135 degrees

The reflected voltage and reflected current are 180 degrees
out of phase.

Now calculate the total voltage and total current.

Total voltage = 2*100cos(45) = 141.4v at 0 deg

Total current = 2*2sin(45) = 2.83a at 90 deg

For a pure standing wave, the instantaneous voltage is
*always* 90 degrees out of phase with the instantaneous
current. There are no V*I*cos(A) watts in a pure standing
wave. There are only V*I*sin(A) VARS.

However, the VARS in the standing wave require energy
which can be converted to watts by I^2*R losses.
--
73, Cecil http://www.w5dxp.com

Tom Donaly wrote:
Cecil Moore wrote:
Roy Lewallen wrote:
I've always regarded a "standing wave" as being a description of the
envelope caused by the interference between forward and reverse
traveling waves.

If you have "Fields and Waves ..." by Ramo and Whinnery,
take a look at the equation for standing wave voltage
and current on page 285 of the 2nd edition.

Ex = E*e^j(wt-Bz) + E'*e^j(wt+Bz)

Roy, that is NOT the equation for an envelope.

It's too bad you don't have the foggiest notion as to just
what it is the equation of. Much of the thousands of posts
could have been avoided if that were the case.

The technical content of your posting is noted. Here is what
it is the equation of:

http://www.chemmybear.com/standing.html
--
73, Cecil http://www.w5dxp.com

I'm surprised that standing waves seem so hard for people to understand.
They're simply a spatial pattern formed by the interference between
forward and reflected waves or, if you prefer, from the solution to a
general transmission line problem with boundary values applied. I'd hope
that even a brief look at a text would make it clear what standing waves
are, and what they are not.

Roy Lewallen, W7EL

Cecil Moore wrote:

...
I guess the authors of the textbooks never thought anyone
would be so ignorant as to believe that EM waves can stand
still. :-)

EM waves are photonic in nature must travel at the speed of
light in the medium. A standing wave stands still and oscillates
in place. Therefore, A standing wave is not an EM wave - It is
something else, by definition.

Guess if you told me we were all communicating on "entangled antennas"
(and, yes, a 1:1 relationship to entangled particles)--I'd have to, at
least, give it a thought! ROFLOL!

Merry Xmas OM,
and warm regards,
JS ;-)

Dave Heil wrote:

...
Inside the microwave oven, the microwaves bounce off the metal internal
walls and set up complex 'standing wave' patterns. As with any wave,
microwaves have peaks and troughs and the intensity of the microwaves is
greatest in the peaks and troughs and lowest at points in between.
...

Actually, a bit more than that, even ...

Water molecules are slightly magnetic, they are spinning like hell on
those "humps of the standing wave"--friction cooking, you will excuse my
"artistic authors' license" ... or not, in ALL of this ... ;-)

However, the standing wave is much more appreciated, by me--at this
point, thanks to Cecil. And, my attention is always drawn towards
"little oddities" which can serve as diversion. And, the standing wave
IS cooking the turkey--in my humble opinion ... you could say, "I
believe in standing waves."

But then, tomorrow night, I'll be up very late with cookies and milk.
Yanno, I've never seen 'em--yet? ;-)

Regards,
JS

John Smith wrote:
Dave Heil wrote:
[...]

forgot ...

Merry Xmas Heil,
JS

Roy Lewallen, W7EL wrote:
"As any text can tell you, the value of Z (ratio of V to I) varies along
a line which has a reflected waves (i.e., has a standing wave)."

Not exactly, maybe the apparent Z. Uniform line is assumed and it has a
Zo determined only by line structure. Zo is identical for a signal
traveling in either direction. However, a directional coupler must be
used to measure voltage and current traveling in one direction while
ignoring voltage and current traveling in the opposite direction. A Bird
wattmeter uses a directional coupler.

Voltage to current ratio on a line with reflections and standing waves
is of little practical value except for determinimg whether the capacity
of the line is exceeded or nearly so.

I would argue that a microwave oven uses the real power delivered to its
contents and not the standing wave as an article attached to another
poster`s comments stated.

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:

...
I would argue that a microwave oven uses the real power delivered to its
contents and not the standing wave as an article attached to another
poster`s comments stated.

Best regards, Richard Harrison, KB5WZI


Nice thing about microwave ovens? They can be filled with a material
and the standing waves seen visually, no math needed ... rather handy,
really!

Regards,
Merry Xmas,
and to all a goodnight,
JS