Standing morphing to travelling waves, and other stupid notions
 

Cecil Moore wrote:

Jim Kelley wrote:

I think he might have said it because he's not particularly good with
words. If anything, he probably should have said that standing waves
should just be called interference patterns.


I'll buy that, Jim. I believe that Hecht left out the adjective,
"EM". If he meant standing waves don't deserve to be called EM waves,
I agree 100%. However, standing waves seem to meet the broad definition
of "wave".

I could be wrong, but don't E-fields and H-fields from traveling waves
superpose to form net E-fields and H-fields? Wouldn't the net fields
have vectors whose direction and magnitude are determined by the
vectors which correspond to the traveling wave fields?


Of course. Now try to convince Gene of that fact of physics. In
spite of his earlier assertions about the differences between
traveling waves and standing waves that agreed with my side of
the argument, he seems to have switched sides. (For political
reasons)?

In the case of a radiator, the emanating energy is a result of the
superposition of fields radiated by the currents traveling on the
antenna. I could be mistaken, but it seems to me that superposition
should yield the same result by either approach. If so, then for a
single element radiator, the field pattern would appear as though a
standing wave on the antenna had created the field.

ac6xg

Standing morphing to travelling waves, and other stupid notions
 

Roger Sparks wrote:
Having the assumption that energy does
not pass the zero voltage point strikes at the heart of
the traveling wave concept. I can not see what would
reflect the waves to prevent energy passage at the zero
voltage point, nor can I see a way to get the results we
see between reflection points, if we disallow energy passage
at zero voltage points.

The medium at the zero voltage point is homogeneous.
Nobody has produced a reference for or example of
reflections occurring in a homogeneous medium. Until
such evidence is introduced, it is probably safe to
assume that reflections in a homogeneous medium in
the real world are impossible (except in a human
mind where anything is possible).
--
73, Cecil http://www.w5dxp.com

Standing morphing to travelling waves, and other stupid notions
 

Richard Clark wrote:
Roger Sparks wrote:
All this embedded markup makes it exceedingly difficult to read in a
plain text reader for a plain text forum.

Just instruct Agent to display in plain text.
--
73, Cecil http://www.w5dxp.com

Standing morphing to travelling waves, and other stupid notions
 

Jim Kelley wrote:

In the case of a radiator, the emanating energy is a result of the
superposition of fields radiated by the currents traveling on the
antenna. I could be mistaken, but it seems to me that superposition
should yield the same result by either approach. If so, then for a
single element radiator, the field pattern would appear as though a
standing wave on the antenna had created the field.

ac6xg

The field created by any conductor is proportional to the current
flowing on the conductor. You can divide this current into "forward" and
"reverse" waves, or any combination of currents you want, just as long
as they all add up to the total current. Assuming the conductor is
immersed in a linear medium (e.g., air), you'll get exactly the same
result by finding the fields from each of the individual currents you've
chosen and adding them together, as you will by adding the currents
first to get the total current and finding the field it creates. That's
an example of the application of superposition.

Roy Lewallen, W7EL

Standing morphing to travelling waves, and other stupid notions
 

Jim Kelley wrote:
In the case of a radiator, the emanating energy is a result of the
superposition of fields radiated by the currents traveling on the
antenna. I could be mistaken, but it seems to me that superposition
should yield the same result by either approach. If so, then for a
single element radiator, the field pattern would appear as though a
standing wave on the antenna had created the field.

On a 1/2WL dipole, for instance, of the total amount of
average energy existing on the antenna, approximately
80% of that energy is in the standing wave. The other
20% is radiated as real power presumably from the traveling
waves because standing waves contain no real power. Like
impedance transformation on a transmission line with
reflections, the standing wave on the dipole is used
to transform the relatively high Z0 of the antenna wire
down to the relatively low feedpoint impedance of the
antenna. The source re-supplies the radiated power to
keep the average standing wave energy constant.

Since the standing wave energy is being used to transform
impedances, it cannot also be used for radiation purposes -
like the energy in a standing wave on a transmission line
cannot be used both to transform impedances and to heat
up a load.
--
73, Cecil http://www.w5dxp.com

Standing morphing to travelling waves, and other stupid notions
 

Cecil Moore wrote:


Since the standing wave energy is being used to transform
impedances, it cannot also be used for radiation purposes -
like the energy in a standing wave on a transmission line
cannot be used both to transform impedances and to heat
up a load.

Would you care to elaborate on the idea that "energy is being used to
transform impedances"?

ac6xg

Energy and Work
 

On Wed, 16 Jan 2008 18:53:44 -0500, "AI4QJ" wrote:

the wording in your statement above may need
some modification such as:

I think not. What this leads to is Cecilaboration that informs none
of the discussion.

This thread alone could turn into further amendments of what Feynman
authored (and all scrambling to lay intellectual claim for his Oscar).

Simple case in point, it may need some modification such as:
1. accounting for the force of viscosity;
2. accounting for the force of magnetism (ferro, para, and the rest);
3. accounting for the force of gravity;
4. accounting for the force of angular momentum;
5. accounting for the force of local tide;
6. accounting for the force of wind shear;
7. accounting for the force of advertising......

The arguments already filling the tea cup can't even raise the
temperature for a decent brew.

73's
Richard Clark, KB7QHC

Standing morphing to travelling waves, and other stupid notions
 

Jim Kelley wrote:

Cecil Moore wrote:
Since the standing wave energy is being used to transform
impedances, it cannot also be used for radiation purposes -
like the energy in a standing wave on a transmission line
cannot be used both to transform impedances and to heat
up a load.

Would you care to elaborate on the idea that "energy is being used to
transform impedances"?

If reflections are nonexistent, no transformation takes
place, i.e. there is no SWR circle, just a point at the
center of the Smith Chart and the system is flat.

If reflections exist, then the superposition of the
forward wave and reflected wave transforms the
load impedance to some other impedance on the SWR
circle.

A 1/4WL transformer, for instance, will not transform
unless there are reflections present.
--
73, Cecil http://www.w5dxp.com

Standing morphing to travelling waves, and other stupid notions
 

Keith Dysart wrote:
So you seem to be claiming that the following two statements can be
simultaneously true:

1. Power [recall p(t)=v(t)*i(t)] is the rate at
which energy is transferred.
2. Energy can be transferred when the power is zero.

To my simple intellect, one of these statements must be false.


The second statement is an oversimplification - it switches between two
inconsistent sets of boundaries. Energy is being transferred within the
system as a whole, even though the power p(t) at some individual points
within the system is zero. If you look consistently at the system as a
whole, there are no contradictions.


--

73 from Ian GM3SEK

Standing morphing to travelling waves, and other stupid notions
 

On Jan 17, 2:07*am, Ian White GM3SEK wrote:
Keith Dysart wrote:
So you seem to be claiming that the following two statements can be
simultaneously true:

1. Power [recall p(t)=v(t)*i(t)] is the rate at
* which energy is transferred.
2. Energy can be transferred when the power is zero.

To my simple intellect, one of these statements must be false.

The second statement is an oversimplification - it switches between two
inconsistent sets of boundaries. Energy is being transferred within the
system as a whole, even though the power p(t) at some individual points
within the system is zero. If you look consistently at the system as a
whole, there are no contradictions.

Expanding on statement 1) from above....
p(t) = v(t) * i(t)
computes the power moving between two networks
separated by the point at which v and i are
measured.

Expanding on statement 2...
Cecil's claim is that the "energy in" the
forward and reflected waves travel from end
to end on the transmission line.

Applying statement 1) to any point on an open
circuited transmission line where the current
or voltage is always 0 will yield a power that
is always 0.

Applying statement 2) to this same point yields
that energy is crossing this point.

This seems to me to be a definite contradiction
between 1) and 2) for the specific situation under
consideration.

...Keith