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

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)