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#11
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Antenna gain question
I think Cecil was being facetious :-)
Ron wrote: No, I'm just trying to understand antenna gain. Ron Cecil Moore wrote: Ron wrote: Maybe I should restate my question. Assume a receiving antenna is in the center of a sphere and the received signal is coming in equal amounts from all points on the surface of the sphere. Are you trying to receive the background radiation left over from the big bang? That's the only source outside of the sphere that I know of that can accomplish your boundary condition. |
#12
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Antenna gain question
Ron, W4TQT wrote:
"Question: would an antenna having gain capture any more signal than a completely omnidirectional antenna with no gain?" Directive gain depends entirely on the distribution of radiated power. See 1955 Terman page 870. The antenna gain figure is identical for transmitting or receiving. To take full advantage of gain in a line of sight path, the electric vector must be parallel with that received. Cross polarization can cause up to almost 30 dB signal loss. There are directional antennas that receive vertical and horizontal polarizations equally well. Yes. An antenna with gain captures more signal than an antenna with no gain when both are in their best positions and equally distant fron the same signal source. Best regards, Richard Harrison, KB5WZI |
#13
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Antenna gain question
Richard Harrison wrote:
Yes. An antenna with gain captures more signal than an antenna with no gain when both are in their best positions and equally distant fron the same signal source. This thread has got me wondering. Which antenna would capture more Big Bang Background Radiation? -- 73, Cecil http://www.qsl.net/w5dxp |
#14
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Antenna gain question
Here's a related question that may help you answer yours:
Do all (assume lossless) antennas with the SAME directionality caputre the same signal power? If the answer to that one is "no," then I think you must first further qualify your question, or it will be like comparing canteloupes and grapes. Cheers, Tom |
#15
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Antenna gain question
On 29 Oct 2005 14:18:02 -0700, "K7ITM" wrote:
Do all (assume lossless) antennas with the SAME directionality caputre the same signal power? Is "directionality" equivalent to the well known term Directivity? Owen -- |
#16
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Antenna gain question
Roy Lewallen, W7EL wrote:
They'll intercept equal amounts, assuming both are lossless. The directional antenna will intercept a larger fraction than the isotropic antenna in the directions it favors, and less in others. The total will be be the same. In reverse, this is equivalent to calculating the average gain of the antennas, which is the same for all lossless antennas. Roy Lewallen, W7EL Hello to all, my name is Miguel, LU 6ETJ. It is a pleasure to read this group. This topic is really an interesting question... Modestly I would want to point out the following thing: Imagine an inner radiant spherical surface with a finite and uniform density radiant energy. Aim a directional antenna with a directivity of, for example, one stereoradian on any direction. How is it able to such an antenna to receive equal quantity of energy of a smaller portion of the sphere than an antenna that is able to receive the energy taken place by the entirety sphere? 73´s of Miguel Ghezzi (LU 6ETJ) Untranslated text for reference (my written english is a little poor ;( ): Hola a todos, mi nombre es Miguel LU 6ETJ. Es un gusto leer este grupo. Este tópico es realmente una interesante pregunta... Modestamente desearía señalar lo siguiente: Imagine la parte interior de una esfera radiante, con una densidad de energia radiante finita y uniforme. Apunte un antena direccional con una directividad de, por ejemplo, un estéreo radian en cualquier dirección. ¿Cómo puede tal antena recibir igual cantidad de energía de una porción menor de la superficie radiante, que una antena que es capaz de recibir la energía producida por la totalidad de la esfera? 73´s de Miguel Ghezzi (LU 6ETJ) |
#17
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Antenna gain question
On 30 Oct 2005 10:41:53 -0800, "lu6etj" wrote:
Imagine an inner radiant spherical surface with a finite and uniform density radiant energy. Aim a directional antenna with a directivity of, for example, one stereoradian on any direction. How is it able to such an antenna to receive equal quantity of energy of a smaller portion of the sphere than an antenna that is able to receive the energy taken place by the entirety sphere? Hi Miguel, You are quite right. Only an isotropic antenna can take all the energy as only an isotropic could have transmitted it. The uniform distribution and the spherical geometry force this solution even though it is a practical impossibility. The real question is, how did that energy get turned around to come back? 73's Richard Clark, KB7QHC |
#18
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Antenna gain question
Richard Clark wrote:
The real question is, how did that energy get turned around to come back? A conductive Dyson's sphere? -- 73, Cecil http://www.qsl.net/w5dxp |
#19
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Antenna gain question
Would it be possible that the question went by the following thing?
When we study directional or isotropic receiving antennas, we assume for example: Punctual sources generating spherical wave fronts (convex) or infinitely far away punctual sources creating plane wave fronts for all the practical effects. Under these conditions the receiving antennas are "outer" of the radiant sphere; this way, the effective area of a directional antenna represents a bigger external surface and it intercepts more energy than the corresponding to an isotropic antenna, then everything agrees with what we have learned on the directivity of the antennas, but in this example the conditions are inverted, now we don't have plane or convex fronts, we have concave fronts. The solution under the new conditions is different from the habitual one... I think that the environment of the problem is similar that of the Kirchhoff law of thermal radiation: "a small sphere inside a radiant sphere". I also think that the conditions of this problem could be similar (and therefore taken place artificially) to those of light`s receiver inside a luminous sphere. In this case we proceed as when we study the entropía of an isolated system, in such a system the entropía can diminish, although that is not possible for the whole universe (I suppose this allows me to escape elegantly of Richard's question... ; D 73´s for all, and thank you very much for your very interesting and instructive habitual postings. Miguel Ghezzi (LU 6ETJ) Spanish text for reference (withouts my translation errors). ¿Sería posible que la cuestion pasara por lo siguiente?: Cuando estudiamos antenas receptoras direccionales o isotropicas asumimos por ejemplo: Fuentes puntuales generando frentes de onda esféricos (convexos) o fuentes puntuales infinitamente alejadas que producen frentes de onda planos para todos los efectos practicos. En estas condiciones las antenas receptoras están "fuera" de la esfera radiante; así, el área efectiva de una antena direccional representa una superficie exterior mayor e intercepta más energía que la correspondiente a una antena isotrópica, entonces todo concuerda con lo que hemos aprendido sobre la directividad de las antenas, pero en este ejemplo las condiciones se invierten, ahora no tenemos frentes planos o convexos, sino de frentes cóncavos. La solución en las nuevas condiciones es diferente de la habitual... Pienso que el entorno del problema es parecido al de la ley de Kirchhoff de la radiación térmica: "una pequeña esfera dentro de una esfera radiante". También pienso que las condiciones de este problema pudieran ser similares (y por lo tanto producidas artificialmente), a las de un receptor de luz dentro de una esfera luminosa. En este caso procedemos como cuando estudiamos la entropía de un sistema aislado, en tal sistema la entropía puede disminuir, aunque eso no sea posible para el universo entero (supongo que eso me permite huir elegantemnnte de la pregunta de Richard ;D 73's para todos y muchas gracias por sus interesantes e instructivos escritos habituales. Miguel Ghezzi (LU 6ETJ) |
#20
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Antenna gain question
On 30 Oct 2005 15:50:50 -0800, "lu6etj" wrote:
although that is not possible for the whole universe (I suppose this allows me to escape elegantly of Richard's question... ; D 73=B4s for all, and thank you very much for your very interesting and instructive habitual postings. Hi Miguel, Can there be an escape? Ron's question was posed with an impossible proposition. A collapsing sphere of electromagnetic energy? This has so many so many fantastic presumptions built in. I hope this translates well for you (it does not make sense in any language). 73's Richard Clark, KB7QHC |
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