On Fri, 20 Apr 2007 05:40:13 GMT, Owen Duffy wrote:

Richard Clark wrote in
:
...
Why would you think that superposition fails for this?

Richard, I don't... but the failure was to think that such an experiment
indicated that the two interfering waves could be isolated at a point.

Hi Owen,

I presume all of this flows from your statement:
A practical example of this is that an omni directional receiving antenna
may be located at a point where a direct wave and a reflected wave result
in very low received power at the antenna, whereas a directional antenna
that favours one or other of the waves will result in higher received
power. This indicates that both waves are independent and available to
the receiving antenna, the waves do not cancel in space, but rather the
superposition occurs in the antenna.

As Roy did not quote any of your material, I must presume this. Am I
correct?

73's
Richard Clark, KB7QHC

Richard Clark wrote in
news
On Fri, 20 Apr 2007 05:40:13 GMT, Owen Duffy wrote:

Richard Clark wrote in
m:
...
Why would you think that superposition fails for this?

Richard, I don't... but the failure was to think that such an
experiment indicated that the two interfering waves could be isolated
at a point.

Hi Owen,

I presume all of this flows from your statement:
A practical example of this is that an omni directional receiving
antenna may be located at a point where a direct wave and a
reflected wave result in very low received power at the antenna,
whereas a directional antenna that favours one or other of the waves
will result in higher received power. This indicates that both waves
are independent and available to the receiving antenna, the waves do
not cancel in space, but rather the superposition occurs in the
antenna.

As Roy did not quote any of your material, I must presume this. Am I
correct?

Yes

On Fri, 20 Apr 2007 06:49:46 GMT, Owen Duffy wrote:

Richard Clark wrote in
A practical example of this is that an omni directional receiving
antenna may be located at a point where a direct wave and a
reflected wave result in very low received power at the antenna,
whereas a directional antenna that favours one or other of the waves
will result in higher received power. This indicates that both waves
are independent and available to the receiving antenna, the waves do
not cancel in space, but rather the superposition occurs in the
antenna.

As Roy did not quote any of your material, I must presume this. Am I
correct?

Yes

Hi Owen,

And you have already allowed that superposition does not fail. Thus
there must be some other failure to be found in the choice of antenna.
From other correspondence, it is asserted that a gain antenna, by
virtue of its size, cannot be placed in null space (that point wherein
all contributions of energy sum to zero) which is planar and
equidistant between sources (there being two of them for the purpose
of discussion).

Have I described this accurately?

73's
Richard Clark, KB7QHC

Richard Clark wrote:

Hi Owen,

And you have already allowed that superposition does not fail. Thus
there must be some other failure to be found in the choice of antenna.
From other correspondence, it is asserted that a gain antenna, by
virtue of its size, cannot be placed in null space (that point wherein
all contributions of energy sum to zero) which is planar and
equidistant between sources (there being two of them for the purpose
of discussion).

Have I described this accurately?

I think it might be more fundamental and perhaps subtle than just a
limitation of size. If the null space is a whole plane, as with the two
radiating elements of my example, you have an infinite area on which to
construct your antenna, although it would have to have zero thickness.
But even allowing infinitely thin elements, I don't see any way you can
construct it entirely on the plane so it will be more sensitive to
signals coming from one side of the plane than the other. That is, use
any number of elements you want, oriented and phased any way you want,
and as long as all elements lie entirely on the plane, I don't think you
can make it favor the signal from one of the radiators over the other. I
believe you'll find this same problem with any region of total wave
cancellation. I don't have any rigorous proof of this, just intuition
from observing the symmetry, and would be glad to see an example which
would prove me wrong. (It might reveal a whole new class of directional
antennas! Maybe one of Art's Gaussian marvels would do it?) But if I'm
right, then there's no way to do as Owen originally proposed, namely to
determine entirely from a null space that the null is the sum of
multiple fields, let alone the nature of those fields -- at least with a
directional antenna. It has to extend out where it can a sniff of the
uncanceled fields to do that.

Roy Lewallen, W7EL

On Fri, 20 Apr 2007 00:46:07 -0700, Roy Lewallen
wrote:

Richard Clark wrote:

Hi Owen,

And you have already allowed that superposition does not fail. Thus
there must be some other failure to be found in the choice of antenna.
From other correspondence, it is asserted that a gain antenna, by
virtue of its size, cannot be placed in null space (that point wherein
all contributions of energy sum to zero) which is planar and
equidistant between sources (there being two of them for the purpose
of discussion).

Have I described this accurately?

I think it might be more fundamental and perhaps subtle than just a
limitation of size. If the null space is a whole plane, as with the two
radiating elements of my example, you have an infinite area on which to
construct your antenna, although it would have to have zero thickness.
But even allowing infinitely thin elements, I don't see any way you can
construct it entirely on the plane so it will be more sensitive to
signals coming from one side of the plane than the other.

Hi Roy,

I presume by your response that it affirms my description. Moving on
to your comments, it stands to reason that the reduction of the
argument proves you cannot build an antenna with directivity within a
very specific constraint - the null space. As there is zero dimension
on the axis that connects the two sources, then no directivity can be
had from a zero length boom as one example. Other examples would
demand some dimension other than zero along this axis is where I see
the counter-argument developing.

... But if I'm
right, then there's no way to do as Owen originally proposed, namely to
determine entirely from a null space that the null is the sum of
multiple fields, let alone the nature of those fields -- at least with a
directional antenna. It has to extend out where it can a sniff of the
uncanceled fields to do that.

This then suggests that there is something special about null space
that is observed no where else. That is specifically true, but not
generally. What is implied by null is zero, and in a perfect world we
can say they are equivalent. Even a dipole inhabiting that null space
would bear it out, whereas an antenna with greater directivity along
that axis would not.

However, if we open up the meaning of null to mean a point, or region,
within which we find a minimum due to the combination of all wave
contributions, then I would say a directive antenna is back in the
game, and that it exhibits Owens proposition (if I understand it - but
I still need to see Owen's elaboration).

73's
Richard Clark, KB7QHC

Richard,

As often happens, I don't think we're fully communicating.

Richard Clark wrote:

I presume by your response that it affirms my description. Moving on
to your comments, it stands to reason that the reduction of the
argument proves you cannot build an antenna with directivity within a
very specific constraint - the null space. As there is zero dimension
on the axis that connects the two sources, then no directivity can be
had from a zero length boom as one example. Other examples would
demand some dimension other than zero along this axis is where I see
the counter-argument developing.

In the two antenna example, the null space is a plane. Since the plane
is infinite in extent, you can create in that plane an antenna with a
boom of any length, and therefore with arbitrarily high directivity.
However, if you restrict that antenna to lie entirely in the null plane,
that directivity won't be in a direction such that the antenna will
favor one radiator over the other. Therefore it can't tell if the null
plane is simply an area in space with no field, or whether it's the
result of two superposing fields. And I believe this is true for any
antenna, of any size, orientation, or design that you can construct
which lies completely in that plane.

This then suggests that there is something special about null space
that is observed no where else. That is specifically true, but not
generally. What is implied by null is zero, and in a perfect world we
can say they are equivalent. Even a dipole inhabiting that null space
would bear it out, whereas an antenna with greater directivity along
that axis would not.

But I'm claiming you can't get directivity such that you can favor one
radiator over the other, by any antenna lying entirely in the null
space. In other words, any antenna you build in that null space will
detect zero field. The special thing about null space is simply that
it's a limit, and it makes a good vehicle for illustration because we
can more easily distinguish between nothing and something than between
two different levels.

However, if we open up the meaning of null to mean a point, or region,
within which we find a minimum due to the combination of all wave
contributions, then I would say a directive antenna is back in the
game, and that it exhibits Owens proposition (if I understand it - but
I still need to see Owen's elaboration).

I'll extend my hypothesis to include all such regions. Create a null
space or region of any size or shape by superposing any number of waves.
I claim that any antenna, regardless of size or design, lying entirely
in that space or region will detect zero signal. In fact, no detector of
any type which you can devise, lying entirely within that null space or
region, will be able to detect anything or otherwise tell the difference
between the superposition and a simple region of zero field. It will
take only a single contrary example to prove me wrong.

Roy Lewallen, W7EL

On Fri, 20 Apr 2007 12:46:50 -0700, Roy Lewallen
wrote:

But I'm claiming you can't get directivity such that you can favor one
radiator over the other, by any antenna lying entirely in the null
space. In other words, any antenna you build in that null space will
detect zero field.

Hi Roy,

No dispute there either.

The special thing about null space is simply that
it's a limit, and it makes a good vehicle for illustration because we
can more easily distinguish between nothing and something than between
two different levels.

That is distinctive as being binary, certainly; but I am sure there is
something between two different levels that are distinguishable to the
same degree. The difference between 0 and 1 is no greater than
between 1 and 2.

However, if we open up the meaning of null to mean a point, or region,
within which we find a minimum due to the combination of all wave
contributions, then I would say a directive antenna is back in the
game, and that it exhibits Owens proposition (if I understand it - but
I still need to see Owen's elaboration).

I'll extend my hypothesis to include all such regions. Create a null
space or region of any size or shape by superposing any number of waves.

But this says nothing of the quality of "null" as I extended it above
which could be supported by a directional antenna. As I am still
unsure of the nature of Owen's proposition, I will leave the quality
of "null" for Owen to discuss or discard.

73's
Richard Clark, KB7QHC