Cecil Moore wrote:

Jim Kelley wrote:

i.e. what Roy said. But I think there's still more to it. I tried to
give the other Richard a hint about it but it didn't resonate.


Then obviously your XC didn't equal your XL.

Probably just a difference in wavelength.

ac6xg

On Fri, 04 Nov 2005 11:42:43 -0800, Jim Kelley
wrote:
This would be a
given seeing that the parasitic elements would be virtually invisible,
rendering the "driven" element un-differentiable from the simple
dipole.

i.e. what Roy said.

On Wed, 02 Nov 2005 00:11:09 -0800, Roy Lewallen among many things wrote:

I have to admit, I was looking at this a[s] more of a problem of equal
signals arriving from all directions

Hi Jim,

I also approached the problem the same way, this is in glaring
contrast to what I've written in the past two posts which are vastly
divergent from this sense of "equal signals."

As I originally presented data from the model of "equal signals
arriving from all directions" it presented that a dipole's response
was separable from that of a yagi, and showed more response which
contradicts some correspondents, and aligns with others.

Such an outcome stands to reason, the yagi cannot see all sources, the
dipole can. If I illuminated the yagi from each source in turn (all
others off) and correlated the response to the source's angle, the
composite would simply reveal the characteristic yagi response lobe
and the sum of those powers MUST fall below the total power available
to the dipole.

The one over-riding difference between all these scenarios and the
expectations of the yagi is that the yagi is not illuminated with a
plane field, but with a radial field. The composite front of many
sources presents a complex antenna (the yagi) with the appearance of a
wave of extremely high curvature impinging upon it. The mechanics of
gain/directivity are not going to function in the same manner to that
yagi for both fashions of applying the power. Hence the yagi fails to
exhibit a higher response than the simple dipole.

73's
Richard Clark, KB7QHC

Richard Clark wrote:

On Fri, 04 Nov 2005 11:42:43 -0800, Jim Kelley
wrote:

This would be a
given seeing that the parasitic elements would be virtually invisible,
rendering the "driven" element un-differentiable from the simple
dipole.

i.e. what Roy said.


On Wed, 02 Nov 2005 00:11:09 -0800, Roy Lewallen among many things wrote:


I have to admit, I was looking at this a[s] more of a problem of equal
signals arriving from all directions


Hi Jim,

I also approached the problem the same way, this is in glaring
contrast to what I've written in the past two posts which are vastly
divergent from this sense of "equal signals."

As I originally presented data from the model of "equal signals
arriving from all directions" it presented that a dipole's response
was separable from that of a yagi, and showed more response which
contradicts some correspondents, and aligns with others.

Such an outcome stands to reason, the yagi cannot see all sources, the
dipole can. If I illuminated the yagi from each source in turn (all
others off) and correlated the response to the source's angle, the
composite would simply reveal the characteristic yagi response lobe
and the sum of those powers MUST fall below the total power available
to the dipole.

The one over-riding difference between all these scenarios and the
expectations of the yagi is that the yagi is not illuminated with a
plane field, but with a radial field. The composite front of many
sources presents a complex antenna (the yagi) with the appearance of a
wave of extremely high curvature impinging upon it. The mechanics of
gain/directivity are not going to function in the same manner to that
yagi for both fashions of applying the power. Hence the yagi fails to
exhibit a higher response than the simple dipole.

73's
Richard Clark, KB7QHC

Let me thank you again for the work you've put in on this. The thing
is, the idea of squeezing a dipole field pattern into the shape of a
Yagi pattern for example, pretty much dictates that with the proper
field geometry, we should be able to realize equal amounts of energy in
both antennas. I think that's the correct answer. I'm just trying to
see a way to get to it. Another approach might be to integrate the
results from a large number of point sources.

73, AC6XG

Richard Clark wrote:
. . .
Such an outcome stands to reason, the yagi cannot see all sources, the
dipole can. If I illuminated the yagi from each source in turn (all
others off) and correlated the response to the source's angle, the
composite would simply reveal the characteristic yagi response lobe
and the sum of those powers MUST fall below the total power available
to the dipole.


Yet if you provide the same power to the dipole and the Yagi and
integrate the total field from each, the total field powers from both
are the same.

So is reciprocity invalid?

Roy Lewallen, W7EL

On Fri, 04 Nov 2005 15:45:39 -0800, Roy Lewallen
wrote:

Richard Clark wrote:
. . .
Such an outcome stands to reason, the yagi cannot see all sources, the
dipole can. If I illuminated the yagi from each source in turn (all
others off) and correlated the response to the source's angle, the
composite would simply reveal the characteristic yagi response lobe
and the sum of those powers MUST fall below the total power available
to the dipole.


Yet if you provide the same power to the dipole and the Yagi and
integrate the total field from each, the total field powers from both
are the same.

So is reciprocity invalid?

Hi Roy,

No, the presumption:
that this specific problem supports that reciprocity
is invalid.

Feel free to exhibit that the sum of powers, from identical remote
sources, located in a locus of points equidistant from a given point,
applied to
1. a dipole;
2. a yagi
demonstrate identically recovered power.

This is not the same as applying the same power to both and
integrating at a locus of points equidistant from a given point.

I could, of course, be wrong. I will investigate further if you have
any constructive suggestions such as Jim offered. I think it would be
instructive to be able to confirm it through available tools.

73's
Richard Clark, KB7QHC

On Wed, 02 Nov 2005 22:27:45 -0800, Richard Clark
wrote:

On Fri, 28 Oct 2005 20:37:07 GMT, Ron wrote:

Assume an incoming rf signal has exactly the same strength in all 3
dimensions i.e., completely omnidirectional. Question: would an
antenna having gain capture any more signal power than a completely
omnidirectional antenna with no gain?

Hi All,

Well, it is time to discard the speculation and let modeling approach
this for an answer that at least offers more than swag.

First we strip away the sphere and solve this in two dimensions. To
do that we simply construct a ring of sources surrounding the
prospective antennas and let the winning design emerge.

EZNEC+ ver. 4.0

Dipole in Ring of Sources 11/2/2005 10:00:48 PM

--------------- LOAD DATA ---------------

Frequency = 70 MHz

Load 1 Voltage = 4.783 V. at 23.52 deg.
Current = 0.06643 A. at 23.52 deg.
Impedance = 72 + J 0 ohms
Power = 0.3177 watts

Total applied power = 2000 watts

Total load power = 0.3177 watts

Taking the determination above as the "standard" I then have
progressed to place an NBS yagi in three space about the center to
obtain its best result.

All such expressions (x,y,z) of the placement of the NBS yagi are with
respect to its "driven" element.

0,0,0 Power = 0.2091 watts
..5,0,0 Power = 0.2198 watts
1,0,0 Power = 0.1429 watts
1.5,0,0 Power = 0.1026 watts
2,0,0 Power = 0.1601 watts
2.5,0,0 Power = 0.2113 watts
3,0,0 Power = 0.1571 watts
3.5,0,0 Power = 0.06028 watts
4,0,0 Power = 0.04128 watts

So, within one quadrant, and over the space of roughly a wavelength,
and at intervals of roughly one eighth wavelength, nothing emerges as
being equal to the "standard" above. Except perhaps a hidden peak
between 0,0,0 and .5,0,0. To investigate this:
..25,0,0 Power = 0.2286 watts
examining further:
..125,0,0 Power = 0.2219 watts
nope, examining further:
..375,0,0 Power = 0.2278 watts
nope, examining further:
..30,0,0 Power = 0.2291 watts
nope, examining further:
..35,0,0 Power = 0.2285 watts
nope, looks like the one before at .30,0,0 is the new sweet spot.

Now, to proceed to investigate the other quadrants to see if there is
symmetry:
-3.5,0,0 Power = 0.03997 watts
0,3.5,0 Power = 0.005925 watts
0,-3.5,0 Power = 0.005859 watts

This last offers that on the Y axis there is a strong symmetry, and
along the X axis there is a moderate symmetry. Now, in regard to both
the X and the Y axis, there is a moderate symmetry. If we were to
look at the fine data attempting to find the peak, we should notice
that the "center" of the antenna lies between the "driven" element and
its reflector. My having chosen the "driven" element as the nominal
center was in error and my guess is that if I re-visited the same
quadrant test above, with that new center at the sweet spot, then we
would find very strong symmetry in all four quadrants. I will add
that the Y axis data supports this due to its strong symmetry that is
relatively immune from the choice of antenna center - at least at this
scale.

Putting that aside, it is enough to suggest that barring an
exquisitely positioned peak of rather a sharp rise, then the yagi
exhibits a poorer response compared to a dipole of approx. 1.4dB.

Others are encouraged to investigate further to reclaim that missing
dB or to put the horns to my error.

73's
Richard Clark, KB7QHC

On Fri, 04 Nov 2005 15:39:18 -0800, Jim Kelley
wrote:

Another approach might be to integrate the
results from a large number of point sources.

Hi Jim,

I just did that - literally.

73's
Richard Clark, KB7QHC

Dear friends:

Reciprocity principle it is not violated in this situation but... which
are the antennas?,

Let us feed a directional antenna that emits a hypothetical conical
beam = 1 sr, pointed toward north pole of the inner surface of the
sphere, for example. The radiant intensity or radiometric flow for
unit of solid angle in the area illuminated by the antenna, will be 1
W/sr, ok?.

If that same portion of the imaginary sphere receive from outer space,
an energy convergent flow on the same previously illuminated area for
the beam with a density = 1 W/sr, naturally the directional antenna
would be able to pick up it entirely, the principle of reciprocity is
respected (not violated?)

Now we make the same thing with a isotropic radiator (same power = 1
W).
The energy density that crosses the sphere's surface going out, now is
1 W / (4*pi) sr, ok?.

If for that surface, comes from the outer side, energy with that same
density and we pick up it with the same isotropic antenna we obtain one
watt, truth again? (and the principle of reciprocity would be ok )

Now let us suppose that same energy density 1/(4*Pi) W, received from
the whole surface of the sphere.

Let us reinstall the directional antenna instead of the isotropìc one.


How much energy it will be able to pick up 1 watt? or 1 / 4*Pi watt?

(could 1 W be picked up if the directive antenna only "see" an sphere's
area corresponding to 1 sr?)

Perhaps, the problem would not be on the reciprocity principle but in
the way of applying it to this example.


If instead of outlining the problem with antennas and radio signals,
the friend had outlined it with another energy form, luminous, for
example, and instead of antennas it had proposed light reflectors,
would the answers be the same ones?

I believe that it is legítimate (rightfull?) to associate this problem
with related phenomenon of radiant energy flow in general.

I also believe that the analogy between directional antennas and a
luminous reflectors it is applicable, otherwise we would be to a step
of violating the conservation of the energy principle... :)

Puf...!, I hope I`ll be able to translate this...

73's of Miguel Ghezzi (LU 6ETJ)
------------------------------------------------------------------------

El principio de reciprocidad se cumple en esta situación pero...
¿cuales son las antenas?,

Alimentemos una antena direccional que emita un haz conico hipotetico
de 1 sr, apuntada hacia el polo norte de la superficie interior de la
esfera, por ejemplo. La intensidad radiante o flujo radiometrico por
unidad de ángulo solido en la zona iluminada por la antena, sera 1
W/sr, ok?.

Si esa misma porcion de la esfera imaginaria recibiera desde exterior
un flujo de energia convergente sobre la misma area anteriormente
iluminada por el haz con una densidad = 1 W/sr, naturalmente la antena
direccional seria capaz de recogerla integramente, el principio de
reciprocidad se cumple...

Ahora hacemos lo mismo con un radiador isotropico (la misma potencia, 1
W).
La densidad de energia que atraviesa la superficie interior de la
esfera ahora es 1 W/(4*pi) sr, ok?. Si por esa superficie pasara,
procedente del exterior, energía con esa misma densidad y la
recogieramos con la misma antena isotropica volveriamos a obtener un
watt ¿verdad? (y el principio de reciprocidad continuaria
cumpliendose...)

Supongamos ahora esa misma densidad de energía 1/(4*Pi) W, recibida
desde fuera por toda la superficie de la esfera.

Reinstalemos la antena direccional en lugar de la isotrópica,

Cuanta es la energía podra ella recoger 1 watt? or 1/ 4*Pi watt?

(¿acaso podria recoger 1 W si solo "puede ver" una zona de la esfera
de 1 sr?)

Tal vez, el problema no estaria en el principio de reciprocidad sino en
la manera de aplicarlo a este ejemplo.

Si en vez de plantear el problema con antenas y señales de radio, el
amigo lo hubiera planteado con otra forma de energia,
luminosa, por ejemplo, y en vez de antenas hubiera propuesto
reflectores de luz, las respuestas serian las mismas?

Yo creo que es legitimo asociar este problema con los fénómenos
relacionados con el flujo de energía radiante en general.

Tambien creo que la analogia entre una antena direccional y un
reflector es aplicable, de lo contrario estariamos a un paso de violar
el principio de conservación de la energía... :)

Puf...! espero poder traducir esto bien...

73's de Miguel Ghezzi (LU 6ETJ)

Richard Clark wrote:
Others are encouraged to investigate further to reclaim that missing
dB or to put the horns to my error.

Of course, you have deviated considerably from the original
infinite number of coherent sources.
--
73, Cecil http://www.qsl.net/w5dxp

"Cecil Moore" wrote
Of course, you have deviated considerably from the original
infinite number of coherent sources.

================================

You guys sure know how to enjoy yourselves trying to analyse
hypothetical situations.

Without any loss in precision, just imagine an isotropic receiver
surrounded by 6 equal intensity beams focussed upon it. Forget all
about an infinite number of radiators.

Or, better still, forget all about the original exceedingly
ill-defined question by a leg-puller. You have been trolled. You
should be ashamed of yourselves for being taken in by such a question.

By the way, the subject of "antenna gains" is amongst the most
confusing of all old-wives' tales. It's worse than so-called VSWR
measurements on non-existent transmission lines. Or from which ends,
or the middle bit, of a dipole does the radiation occur.
----
Reg.