Roy Lewallen wrote in
:

Correction:

Roy Lewallen wrote:

Superposition means the following: If f(x) is the result of
excitation x and f(y) is the result of excitation y, then the result
of excitation (x + y) is f(x + y). . .

That should read:

Superposition means the following: If f(x) is the result of excitation
x
and f(y) is the result of excitation y, then the result of
excitation
(x + y) is f(x) + f(y). . .
^^^^^^^^^^^
I apologize for the error. Thanks very much to David Ryeburn for
spotting it.


Fine Roy, the maths is easy, but you don't discuss the eligible
quantities.

As I learned the superposition theoram applying to circuit analysis, it
was voltages or currents that could be superposed.

Presumably, for EM fields in space, the electric field strength and
magnetic field strength from multiple source can be superposed to obtain
resultant fields, as well as voltages or currents in any circuit elements
excited by those waves.

For avoidance of doubt, power is not a quantity to be superposed, though
presumably if it can be deconstructed to voltage or current or electric
field strength or magnetic field strength (though that may require
additional information), then those components may be superposed.

The resultant fields at a point though seem to not necessarily contain
sufficient information to infer the existence of a wave, just one wave,
or any specific number of waves, so the superposed resultant at a single
point is by itself of somewhat limited use. This one way process where
the resultant doesn't characterise the sources other than at the point
seems to support the existence of the source waves independently of each
other, and that there is no merging of the waves.

Is anything above contentious or just plain wrong?

Owen

"Owen Duffy" wrote in message
...
Roy Lewallen wrote in
:

Correction:

Roy Lewallen wrote:

Superposition means the following: If f(x) is the result of
excitation x and f(y) is the result of excitation y, then the result
of excitation (x + y) is f(x + y). . .

That should read:

Superposition means the following: If f(x) is the result of excitation
x
and f(y) is the result of excitation y, then the result of
excitation
(x + y) is f(x) + f(y). . .
^^^^^^^^^^^
I apologize for the error. Thanks very much to David Ryeburn for
spotting it.


Fine Roy, the maths is easy, but you don't discuss the eligible
quantities.

As I learned the superposition theoram applying to circuit analysis, it
was voltages or currents that could be superposed.

Presumably, for EM fields in space, the electric field strength and
magnetic field strength from multiple source can be superposed to obtain
resultant fields, as well as voltages or currents in any circuit elements
excited by those waves.

For avoidance of doubt, power is not a quantity to be superposed, though
presumably if it can be deconstructed to voltage or current or electric
field strength or magnetic field strength (though that may require
additional information), then those components may be superposed.

The resultant fields at a point though seem to not necessarily contain
sufficient information to infer the existence of a wave, just one wave,
or any specific number of waves, so the superposed resultant at a single
point is by itself of somewhat limited use. This one way process where
the resultant doesn't characterise the sources other than at the point
seems to support the existence of the source waves independently of each
other, and that there is no merging of the waves.

Is anything above contentious or just plain wrong?

Owen

yes, superposition is meant to work directly on voltage, current, electric
fields, and magnetic fields. it can be extended by adding appropriate extra
phase terms to power or intensity as cecil prefers to use.

you are at least partially correct. a measurement at a single point at a
single time can only give the sum of the fields at the instant of
measurement. make a series of measurements at a point over time and you can
infer the existance of different frequency waves passing the point, but not
anything about their direction or possibly multiple components. add
measurements at enought other points and you can resolve directional
components, polarization, etc. assuming your points are properly
distributed... this means that a small probe (like a scope probe) can only
make a record of voltages/currents or fields at a single point and can't
tell anything about direction. add a second probe and you could detect the
direction of travel of waves on a wire.

Dave wrote:
yes, superposition is meant to work directly on voltage, current, electric
fields, and magnetic fields. it can be extended by adding appropriate extra
phase terms to power or intensity as cecil prefers to use.

That seems to be common knowledge except for some
(narrow-minded?) posters here. Powers do not superpose
but there is a method of adding power (densities)
that has been acceptable to physicists for at least
a century and may date back to Young, Fresnel, and
Huygens.
--
73, Cecil http://www.w5dxp.com

"Dave" wrote in news:ZPmWh.759$dM1.190@trndny07:


"Owen Duffy" wrote in message
...
Roy Lewallen wrote in
:

Correction:

Roy Lewallen wrote:

Superposition means the following: If f(x) is the result of
excitation x and f(y) is the result of excitation y, then the
result of excitation (x + y) is f(x + y). . .

That should read:

Superposition means the following: If f(x) is the result of
excitation x
and f(y) is the result of excitation y, then the result of
excitation
(x + y) is f(x) + f(y). . .
^^^^^^^^^^^
I apologize for the error. Thanks very much to David Ryeburn for
spotting it.


Fine Roy, the maths is easy, but you don't discuss the eligible
quantities.

As I learned the superposition theoram applying to circuit analysis,
it was voltages or currents that could be superposed.

Presumably, for EM fields in space, the electric field strength and
magnetic field strength from multiple source can be superposed to
obtain resultant fields, as well as voltages or currents in any
circuit elements excited by those waves.

For avoidance of doubt, power is not a quantity to be superposed,
though presumably if it can be deconstructed to voltage or current or
electric field strength or magnetic field strength (though that may
require additional information), then those components may be
superposed.

The resultant fields at a point though seem to not necessarily
contain sufficient information to infer the existence of a wave, just
one wave, or any specific number of waves, so the superposed
resultant at a single point is by itself of somewhat limited use.
This one way process where the resultant doesn't characterise the
sources other than at the point seems to support the existence of the
source waves independently of each other, and that there is no
merging of the waves.

Is anything above contentious or just plain wrong?

Owen

yes, superposition is meant to work directly on voltage, current,
electric fields, and magnetic fields. it can be extended by adding
appropriate extra phase terms to power or intensity as cecil prefers
to use.

you are at least partially correct. a measurement at a single point
at a single time can only give the sum of the fields at the instant of
measurement. make a series of measurements at a point over time and

Dave, I was continuing in the assumed context of coherent sources.

you can infer the existance of different frequency waves passing the
point, but not anything about their direction or possibly multiple
components. add measurements at enought other points and you can
resolve directional components, polarization, etc. assuming your
points are properly distributed... this means that a small probe
(like a scope probe) can only make a record of voltages/currents or
fields at a single point and can't tell anything about direction. add
a second probe and you could detect the direction of travel of waves
on a wire.

Yes, I understand.... Thanks.

Owen Duffy wrote:
For avoidance of doubt, power is not a quantity to be superposed, though
presumably if it can be deconstructed to voltage or current or electric
field strength or magnetic field strength (though that may require
additional information), then those components may be superposed.

The single bit of additional information required is the phase
angle between the voltages (or currents or fields). Optical
physicists deduce the relative phase angle by the ratio of
intensity (power density) in the bright rings vs the dark rings.
We hams can deduce the relative phase angle by the ratio of
forward power (density) to reflected power (density). Our task
as hams looking at a one-dimensional transmission line is much
easier than the task of optical physicists looking at visible
light in three-dimensional space. Our transmitted CW signals are
coherent and collinear in a transmission line, something that
optical physicists can only dream of.

The resultant fields at a point though seem to not necessarily contain
sufficient information to infer the existence of a wave, just one wave,
or any specific number of waves, so the superposed resultant at a single
point is by itself of somewhat limited use. This one way process where
the resultant doesn't characterise the sources other than at the point
seems to support the existence of the source waves independently of each
other, and that there is no merging of the waves.

That is the case in a majority of examples. But in the case
of two coherent collinear waves superposed in a one-dimensional
transmission line where the resultant is the same at every point,
we can safely assert that those two waves have ceased to have an
existence independent of each other. The idea of two waves
canceling all up and down the transmission line yet continuing
their separate existences until their combined zero energy level
is dissipated (or not) is a pipe dream. If ExB = 0, the energy
in those canceled waves went the other direction a long time ago
and those waves have ceased to exist in their original direction
of travel, i.e. they have interacted and canceled.

When two waves combine to a zero energy level, the pre-existing
energy in those two waves is "redistributed in the direction
of constructive interference". In a one-dimensional transmission
line, there are only two possible directions. If waves superpose
to zero energy in one direction, their energy components are
"redistributed" in the only other direction possible. If the energy
ceases to flow in the reverse direction, then it must flow in the
forward direction. That's why Pforward = Psource + Preflected.
Anything else would violate the conservation of energy principle.
--
73, Cecil http://www.w5dxp.com

Owen Duffy wrote:

Fine Roy, the maths is easy, but you don't discuss the eligible
quantities.

As I learned the superposition theoram applying to circuit analysis, it
was voltages or currents that could be superposed.

Presumably, for EM fields in space, the electric field strength and
magnetic field strength from multiple source can be superposed to obtain
resultant fields, as well as voltages or currents in any circuit elements
excited by those waves.

For avoidance of doubt, power is not a quantity to be superposed, though
presumably if it can be deconstructed to voltage or current or electric
field strength or magnetic field strength (though that may require
additional information), then those components may be superposed.

The resultant fields at a point though seem to not necessarily contain
sufficient information to infer the existence of a wave, just one wave,
or any specific number of waves, so the superposed resultant at a single
point is by itself of somewhat limited use. This one way process where
the resultant doesn't characterise the sources other than at the point
seems to support the existence of the source waves independently of each
other, and that there is no merging of the waves.

Is anything above contentious or just plain wrong?

No, I agree entirely, except for

This one way process where
the resultant doesn't characterise the sources other than at the point
seems to support the existence of the source waves independently of
each other, and that there is no merging of the waves.

which I don't understand. We lose information when we add or otherwise
operate on two numbers to get one. (Which I think is what you might be
saying.) Given a number which is the sum of two others, we can't tell
from that sum alone what the two original numbers were. The same is
naturally true of superposed or added, if you prefer, waves or fields.
Power has the same problem (among others) -- given even an instantaneous
power, we can't tell without some other information (such as the complex
impedance) what the constituent voltage and current were.

Roy Lewallen, W7EL

Roy Lewallen wrote:
Given a number which is the sum of two others, we can't tell
from that sum alone what the two original numbers were.

Seems as though those two numbers interacted and
then lost their separate identities, huh?
--
73, Cecil http://www.w5dxp.com