Re: [OT] Power over radio is it a true thing or just a myth ?
2009/8/24 Shachar Shemesh shac...@shemesh.biz Michael Vasiliev wrote: The power of the signal is inversely proportional to the square of distance. That is not precisely accurate. An undirected point source of EM radiation (or any other type of energy) transmits energy that expands on a sphere from the point of transmittal. The surface area of the sphere expands proportionally to R^2. Therefor, the law of conservation of energy dictates that the energy received over a constant area receiver (say, a 1 cm^2 energy receiver) will decline proportionally to the square of the distance from the transmitter. As a side note - does that prove that our universe only has three dimensions? It only means that your problem has a symmetry of 3 dimensions. Consider an ideal omnidirectional antenna on the plane - sends an identical signal to the same height, and nothing above and below. Then the energy loss would indeed be 1/R. This only means that the omnidirectional antenna is a problem with 2D symmetry, not that the world has less dimensions. Flatland phylosophy is always clearer. http://en.wikipedia.org/wiki/Flatland However, if our transmitter is directional, and you keep the transmitter beam focused, so that it does not expand, there is no reason for the energy to almost not discard at all. Of course, the medium through which you transmit the energy may absorb some of it (assuming it is not a vacuum), and it may disperse some more of it, but there is no reason to get 1/R^2, or even 1/R. In order not to lose energy at all, you will need an ideal wave guide ( http://en.wikipedia.org/wiki/Waveguide). If we stick to the air as our media, then you will need a unidirectional antenna. This is also an idealization, as an antenna which points to one direction, projects energy to the opposite direction as well, and there is also significant power loss to the sides. Orna. Shachar ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
Re: [OT] Power over radio is it a true thing or just a myth ?
On Aug 30, 2009, at 3:00 PM, Orna Agmon Ben-Yehuda wrote: If we stick to the air as our media, then you will need a unidirectional antenna. This is also an idealization, as an antenna which points to one direction, projects energy to the opposite direction as well, and there is also significant power loss to the sides. Often it can be only omnidrectional in 2 dimensions and only if you want to power a circular area. If you want to power all the devices in your apartment for example, you can place an omnidirectional antenna in the center, or a narrower beam antenna in a corner. The advantages of a center one is obvious, you get more power in more all of the apartment. A corner antenna placed in the corner where the demand is greater, e.g. kitchen, laundry, etc and farthest from where the demand is the least, e.g. in a bedroom where you want lights, a clock and maybe a TV or radio has a distinct advantage in power levels output and the radiation the residents are exposed to. This has a practical application in the world of computers as you want to place a WifI transmitter close to your computers if they are clustered and as far away as possible from anyone else's. So I place mine where they leak out of the building about 5 meters into a common entrance yard, but don't reach the street, instead of at the other end of the apartment where they would. Either way, I have no desire to radiate WiFi, or if I could electrical power, down into the ground or up into my neighbor's or the street. Geoff. -- geoffrey mendelson N3OWJ/4X1GM Jerusalem Israel geoffreymendel...@gmail.com ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
Re: [OT] Power over radio is it a true thing or just a myth ?
Very off topic. On Aug 28, 2009, at 12:28 PM, Michael Tewner wrote: 88 Miles per hour? http://en.wikipedia.org/wiki/Oldsmobile_88 Geoff. -- geoffrey mendelson N3OWJ/4X1GM Jerusalem Israel geoffreymendel...@gmail.com ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
Re: [OT] Power over radio is it a true thing or just a myth ?
On Tue, Aug 25, 2009 at 11:25 AM, Oleg Goldshmidt p...@goldshmidt.orgwrote: On Tue, Aug 25, 2009 at 10:40 AM, Gilad Ben-Yossefgi...@codefidence.com wrote: Oleg Goldshmidt wrote: Once you have satisfied yourself that N=3, you can derive R^-2 easily from flux considerations. Until, of course, the invention of the flux capacitor... http://en.wikipedia.org/wiki/DeLorean_time_machine Oh, anything is possible if you travel through space-time in a DeLorean... In particular, when you travel close to the speed of light you emit mostly in the forward direction, not isotropically... ;-) when you travel close to the speed of light 88 Miles per hour? -- Oleg Goldshmidt | o...@goldshmidt.org ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
Re: [OT] Power over radio is it a true thing or just a myth ?
Michael Tewner wrote: Until, of course, the invention of the flux capacitor... http://en.wikipedia.org/wiki/DeLorean_time_machine Oh, anything is possible if you travel through space-time in a DeLorean... In particular, when you travel close to the speed of light you emit mostly in the forward direction, not isotropically... ;-) when you travel close to the speed of light 88 Miles per hour? Despite popular belief, the speed of light is only fixed in vacuum and scientists long acknowledged the fact that light may travels in different and lesser speeds when going through different materials, such as air, or water. 88 miles per hour, it would seem, is the speed of light as it travels through Hollywood movies. I specifically state Hollywood here, because, recent evidence show that speed traveling via a French movie for example, will be closer to 25kph, whereas in Bollywood movie it would be infinitesimally close to 88 miles per day. Interesting enough, Light travels through Israeli movies in speed close to American ones (88 mph) but, complain much more then the American counterpart when it doing so. Strangely, a love affair between an homosexual Palestinian Sumu wrestler who is in fact a Mossad agent living in Lod is also involved. And don't even get me started on the speed of Lite. Gilad :-) -- Gilad Ben-Yossef Chief Coffee Drinker CTO Codefidence Ltd. Web: http://codefidence.com Cell: +972-52-8260388 Tel: +972-8-9316883 ext. 201 Fax: +972-8-9316884 Email: gi...@codefidence.com Check out our Open Source technology and training blog - http://tuxology.net Now the world has gone to bed Darkness won't engulf my head I can see by infra-red How I hate the night. ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
Re: [OT] Power over radio is it a true thing or just a myth ?
Please excuse me for answering a humorous post seriously. Gilad Ben-Yossef wrote: Despite popular belief, the speed of light is only fixed in vacuum and scientists long acknowledged the fact that light may travels in different and lesser speeds when going through different materials, such as air, or water. Again, not precisely accurate. While light will, indeed, travel slower through any material denser than vacuum, this is not what the term speed of light refers to. To the best of my knowledge, speed of light refers to a basic property of the universe (how fast will any change of any field propagate), and that is the property that goes into the time warping formulas (the famous c in Lorentz transformation). Just because light travels through glass at 30% less speed does not mean you have to aim 30% lower if you want to freeze time (unless, and this is something I'm not 100% clear about, YOU are traveling through glass as well). 88 miles per hour, it would seem, is the speed of light as it travels through Hollywood movies. At least that one seems pretty accurate. This also explains why pretty much anything looks different when viewed through the filters of a Holywood movie. The huge refraction coefficient acts like lens, only much more powerful. Shachar -- Shachar Shemesh Lingnu Open Source Consulting Ltd. http://www.lingnu.com ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
Re: [OT] Power over radio is it a true thing or just a myth ?
What the fuck are you doing? I did not see that movie yet... Please write spoiler and leave a few empty the next time. On יום שישי 28 אוגוסט 2009 13:17:06 Gilad Ben-Yossef wrote: Interesting enough, Light travels through Israeli movies in speed close to American ones (88 mph) but, complain much more then the American counterpart when it doing so. Strangely, a love affair between an homosexual Palestinian Sumu wrestler who is in fact a Mossad agent living in Lod is also involved. ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
RE: [OT] Power over radio is it a true thing or just a myth ?
ubergeek-mode Actually, the speed of light *in a vacuum* is the universal constant, invariant regardless of the observer's frame of reference. 'C' is so defined - the speed of light in vacuum. This is now understood to be such a basic constant that in 1983, the meter was defined in terms of the speed of light: The definition states that the meter is the length of the path traveled by light in vacuum during a time interval of 1/299,792,458 of a second. http://www.mel.nist.gov/div821/museum/timeline.htm Note that when a particle exceed the speed of light *in a given medium*, it gives off cerenkov radiation, analogous to a sonic boom. This is the blue glow you see in the water surrounding nuclear reactors - pretty cool. http://en.wikipedia.org/wiki/Cherenkov_radiation /ubergeek-mode Rony _ From: linux-il-boun...@cs.huji.ac.il [mailto:linux-il-boun...@cs.huji.ac.il] On Behalf Of Shachar Shemesh Sent: Friday, August 28, 2009 1:30 PM To: Gilad Ben-Yossef Cc: Linux-il@cs.huji.ac.il Subject: Re: [OT] Power over radio is it a true thing or just a myth ? Please excuse me for answering a humorous post seriously. Gilad Ben-Yossef wrote: Despite popular belief, the speed of light is only fixed in vacuum and scientists long acknowledged the fact that light may travels in different and lesser speeds when going through different materials, such as air, or water. Again, not precisely accurate. While light will, indeed, travel slower through any material denser than vacuum, this is not what the term speed of light refers to. To the best of my knowledge, speed of light refers to a basic property of the universe (how fast will any change of any field propagate), and that is the property that goes into the time warping formulas (the famous c in Lorentz transformation). Just because light travels through glass at 30% less speed does not mean you have to aim 30% lower if you want to freeze time (unless, and this is something I'm not 100% clear about, YOU are traveling through glass as well). 88 miles per hour, it would seem, is the speed of light as it travels through Hollywood movies. At least that one seems pretty accurate. This also explains why pretty much anything looks different when viewed through the filters of a Holywood movie. The huge refraction coefficient acts like lens, only much more powerful. Shachar -- Shachar Shemesh Lingnu Open Source Consulting Ltd. http://www.lingnu.com ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
Re: [OT] Power over radio is it a true thing or just a myth ?
Oleg Goldshmidt wrote: Once you have satisfied yourself that N=3, you can derive R^-2 easily from flux considerations. Until, of course, the invention of the flux capacitor... http://en.wikipedia.org/wiki/DeLorean_time_machine Gilad :-) -- Gilad Ben-Yossef Chief Coffee Drinker CTO Codefidence Ltd. Web: http://codefidence.com Cell: +972-52-8260388 Tel: +972-8-9316883 ext. 201 Fax: +972-8-9316884 Email: gi...@codefidence.com Check out our Open Source technology and training blog - http://tuxology.net Now the world has gone to bed Darkness won't engulf my head I can see by infra-red How I hate the night. ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
Re: [OT] Power over radio is it a true thing or just a myth ?
On Tue, Aug 25, 2009 at 10:40 AM, Gilad Ben-Yossefgi...@codefidence.com wrote: Oleg Goldshmidt wrote: Once you have satisfied yourself that N=3, you can derive R^-2 easily from flux considerations. Until, of course, the invention of the flux capacitor... http://en.wikipedia.org/wiki/DeLorean_time_machine Oh, anything is possible if you travel through space-time in a DeLorean... In particular, when you travel close to the speed of light you emit mostly in the forward direction, not isotropically... ;-) -- Oleg Goldshmidt | o...@goldshmidt.org ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
Re: [OT] Power over radio is it a true thing or just a myth ?
Oleg Goldshmidt wrote: In particular, when you travel close to the speed of light you emit mostly in the forward direction, not isotropically... I didn't know physics dealt with gastro functions. Shachar -- Shachar Shemesh Lingnu Open Source Consulting Ltd. http://www.lingnu.com ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
Re: [OT] Power over radio is it a true thing or just a myth ?
2009/8/24 Shachar Shemesh shac...@shemesh.biz Michael Vasiliev wrote: The power of the signal is inversely proportional to the square of distance. That is not precisely accurate. An undirected point source of EM radiation (or any other type of energy) transmits energy that expands on a sphere from the point of transmittal. The surface area of the sphere expands proportionally to R^2. Therefor, the law of conservation of energy dictates that the energy received over a constant area receiver (say, a 1 cm^2 energy receiver) will decline proportionally to the square of the distance from the transmitter. As a side note - does that prove that our universe only has three dimensions? it would if : 1. the origin of the signal is a point in all dimensions (which is usualy not true as you transmit continusly in the time dimension(but may transmit a pulse), dunno about other possible dimensions) 2. it is omnidirectional in all dimensions (which is not true either in the time dimension, dunno about other dimensions as well) AFAIK, according to general relativity, the world is 4D. according to string theory, there are more dimensions ... erez. However, if our transmitter is directional, and you keep the transmitter beam focused, so that it does not expand, there is no reason for the energy to almost not discard at all. Of course, the medium through which you transmit the energy may absorb some of it (assuming it is not a vacuum), and it may disperse some more of it, but there is no reason to get 1/R^2, or even 1/R. Shachar -- Shachar Shemesh Lingnu Open Source Consulting Ltd.http://www.lingnu.com ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
Re: [OT] Power over radio is it a true thing or just a myth ?
Erez D wrote: AFAIK, according to general relativity, the world is 4D. according to string theory, there are more dimensions ... I think we have enough flame wars over FOSS matters. Let's not go into strings, as that would not only be a flame war, but an off topic one at that. Shachar -- Shachar Shemesh Lingnu Open Source Consulting Ltd. http://www.lingnu.com ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
Re: [OT] Power over radio is it a true thing or just a myth ?
On Tue, Aug 25, 2009 at 11:56 AM, Shachar Shemesh shac...@shemesh.bizwrote: Erez D wrote: AFAIK, according to general relativity, the world is 4D. according to string theory, there are more dimensions ... I think we have enough flame wars over FOSS matters. Let's not go into strings, as that would not only be a flame war, but an off topic one at that. i agree this is OT (the whole thread is), but i do not think this is a flame war. the string theory includes both quanum and relativity theories. as is, relativity is a subset of string, as the linux kernel is a subset of ubuntu. so its like talking about a flame war between ubuntu and the kernel. (i added this reply just to put some oil in the flame war engine, yala makot ;-) erez. Shachar -- Shachar Shemesh Lingnu Open Source Consulting Ltd.http://www.lingnu.com ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
Re: [OT] Power over radio is it a true thing or just a myth ?
Erez D wrote: On Tue, Aug 25, 2009 at 11:56 AM, Shachar Shemesh shac...@shemesh.biz mailto:shac...@shemesh.biz wrote: Erez D wrote: AFAIK, according to general relativity, the world is 4D. according to string theory, there are more dimensions ... I think we have enough flame wars over FOSS matters. Let's not go into strings, as that would not only be a flame war, but an off topic one at that. i agree this is OT (the whole thread is), but i do not think this is a flame war. the string theory includes both quanum and relativity theories. as is, relativity is a subset of string, as the linux kernel is a subset of ubuntu. so its like talking about a flame war between ubuntu and the kernel. (i added this reply just to put some oil in the flame war engine, yala makot ;-) And I'm refusing to go there. Shachar -- Shachar Shemesh Lingnu Open Source Consulting Ltd. http://www.lingnu.com ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
Re: [OT] Power over radio is it a true thing or just a myth ?
The power of the signal is inversely proportional to the square of distance. Why do you think such a feat would be possible? Boris shtrasman wrote: Sorry for the OT , But i guess using systems in other ways then they had been designed is a bug that not only i posses. I heard a lot about wireless power transition , while I heard about products that provide close distant power transmitting (1) what about using public wifi in my area ? I met many people that heard about some one that know some one that has access to device that uses radio signal to transfer low amount of power in short ranges. As i googled about it i guess it can be done using rectennas but only in close range to _High_ power radio transmitters (2) My question is it possible to be done with small radio signal equipment as Wi-Max and Wi-Fi ,Perhaps even with the new terrestrial transitions. Do any one have links to this kind of devices ? (1) http://www.economist.com/sciencetechnology/tq/displayStory.cfm?story_id=13174387 (2) http://www.telegraph.co.uk/technology/3336114/Over-to-you-Mythical-electricity.html 10x in advance. -- Sincerely yours, Michael Vasiliev ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
Re: [OT] Power over radio is it a true thing or just a myth ?
Michael Vasiliev wrote: The power of the signal is inversely proportional to the square of distance. Why do you think such a feat would be possible? Since i don't know physics i lake the basics for this question. As i understood from googling it is possible to get some power from high power radio signals (1). Since i believe that radio broadcasting (AM) allow power transfer i ask about other types of transmittance. I guess this will be true only for analog transition since i believe that with digital some one will lower the amount of power for the signal, is my guess correct ? After reading part of a book in a close area i start to understand that it is a myth to use Wi-Fi as a power generation , the question about Terrestrial and Wi-Max still exists. Boris shtrasman wrote: Sorry for the OT , But i guess using systems in other ways then they had been designed is a bug that not only i posses. I heard a lot about wireless power transition , while I heard about products that provide close distant power transmitting (1) what about using public wifi in my area ? I met many people that heard about some one that know some one that has access to device that uses radio signal to transfer low amount of power in short ranges. As i googled about it i guess it can be done using rectennas but only in close range to _High_ power radio transmitters (2) My question is it possible to be done with small radio signal equipment as Wi-Max and Wi-Fi ,Perhaps even with the new terrestrial transitions. Do any one have links to this kind of devices ? (1) http://www.economist.com/sciencetechnology/tq/displayStory.cfm?story_id=13174387 (2) http://www.telegraph.co.uk/technology/3336114/Over-to-you-Mythical-electricity.html 10x in advance. -- Boris Shtrasman - | IM : bori...@jabber.org| | URL : myrtfm.blogspot.com | --- ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
Re: [OT] Power over radio is it a true thing or just a myth ?
Michael Vasiliev wrote: The power of the signal is inversely proportional to the square of distance. That is not precisely accurate. An undirected point source of EM radiation (or any other type of energy) transmits energy that expands on a sphere from the point of transmittal. The surface area of the sphere expands proportionally to R^2. Therefor, the law of conservation of energy dictates that the energy received over a constant area receiver (say, a 1 cm^2 energy receiver) will decline proportionally to the square of the distance from the transmitter. As a side note - does that prove that our universe only has three dimensions? However, if our transmitter is directional, and you keep the transmitter beam focused, so that it does not expand, there is no reason for the energy to almost not discard at all. Of course, the medium through which you transmit the energy may absorb some of it (assuming it is not a vacuum), and it may disperse some more of it, but there is no reason to get 1/R^2, or even 1/R. Shachar -- Shachar Shemesh Lingnu Open Source Consulting Ltd. http://www.lingnu.com ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
Re: [OT] Power over radio is it a true thing or just a myth ?
I'll bite - it's OT, but too much fun to skip... ;-) 2009/8/24 Shachar Shemesh shac...@shemesh.biz: As a side note - does that prove that our universe only has three dimensions? Technically, no, though many philosophers (as opposed to physicists or mathematicians) will say it does. The number of dimensions does not follow from R^-2, but if you live in a 3D world then R^-2 follows... ;-) I have not checked every statement on http://en.wikipedia.org/wiki/Spacetime#Privileged_character_of_3.2B1_spacetime, but it does have useful pointers that I'd myself recommend. [disclosure: I *am* a physicist]. The R^-2 character of gravity is arguably even more important than radiation, but the mathematical reason is the same. If you are interested in proving that our world is 3D then probably the most important set of physical/anthropic arguments that derive N=3 from the observable universe was proposed by Ehrenfest (and Weyl: Ehrenfest concentrated on gravity and Weyl on electromagnetism) in the early 20ies - a reference is in the Wikipedia article above. For those interested in an in-depth discussion of why the Universe is what it is I recommend The Anthropic Cosmological Principle by Barrow Tipler (see the reference in the Wikipedia link) - it's big, but real fun to read, IMHO. Unfortunately, I don't have a copy and I can't recall from memory how much background it assumes. -- Oleg Goldshmidt | o...@goldshmidt.org ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
Re: [OT] Power over radio is it a true thing or just a myth ?
On 8/23/2009 3:03 PM, Boris shtrasman wrote: Sorry for the OT , But i guess using systems in other ways then they had been designed is a bug that not only i posses. I heard a lot about wireless power transition , while I heard about products that provide close distant power transmitting (1) what about using public wifi in my area ? I met many people that heard about some one that know some one that has access to device that uses radio signal to transfer low amount of power in short ranges. As i googled about it i guess it can be done using rectennas but only in close range to _High_ power radio transmitters (2) My question is it possible to be done with small radio signal equipment as Wi-Max and Wi-Fi ,Perhaps even with the new terrestrial transitions. Do any one have links to this kind of devices ? I don't have a link now but I saw a thread somewhere about the myth of stealing power from powerlines with a large coil, and the calculation came to the point if I remember the numebers correctly that you may be able to run a 1.5v light bulb using several tons of copper if your are several feet from the power line. I doubt wifi is any better in this respect. (1) http://www.economist.com/sciencetechnology/tq/displayStory.cfm?story_id=13174387 (2) http://www.telegraph.co.uk/technology/3336114/Over-to-you-Mythical-electricity.html 10x in advance. ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
Re: [OT] Power over radio is it a true thing or just a myth ?
On Mon, Aug 24, 2009 at 4:33 PM, Michami...@post.tau.ac.il wrote:
I don't have a link now but I saw a thread somewhere about the myth of
stealing power from powerlines with a large coil, and the calculation came
to the point if I remember the numebers correctly that you may be able to
run a 1.5v light bulb using several tons of copper if your are several feet
from the power line.
I doubt wifi is any better in this respect.
The *basic* calculation is not very difficult. I believe the most
powerful long- or medium-wave broadcasting transmitters have a nominal
power of 2.5MW. Assume you have a 2MW transmitter 1km from your house.
Assume it actually radiates 2MW of power - I wouldn't be surprised if
efficiency was around 20% or so, but let's assume 2MW is actually
emitted isotropically. Neglect losses (that are, in reality, very
considerable), and put a round antenna with radius of 1m on your roof.
Assume that your antenna collects 100% of the radiation. The result is
2MW*pi*1m^2
= 0.5W,
4*pi*1km^2
which might be enough to light a 1.5V light bulb with a resistance of
4Ohm (assuming no losses again).
Given that your losses are likely to reduce usable power by a couple
of orders of magnitude compared to the above, you will *not* be able
to light a small light bulb by any stretch of imagination.
Looking up the effective radiated power of your WiFi router (divide
the nominal power by 5 if not quoted directly) and plugging the
parameters in the formula above (what's your receiving antenna size?)
is left as an exercise to anyone who keeps the router's documentation
in the bottom drawer.
--
Oleg Goldshmidt | o...@goldshmidt.org
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Re: [OT] Power over radio is it a true thing or just a myth ?
Good, now put back the context you've omitted, take your antenna specs and prove it with numbers. Solutions that will make the fly-by birds go poof or yourself arrested and your equipment seized do not count. Shachar Shemesh wrote: Michael Vasiliev wrote: The power of the signal is inversely proportional to the square of distance. That is not precisely accurate. An undirected point source of EM radiation (or any other type of energy) transmits energy that expands on a sphere from the point of transmittal. The surface area of the sphere expands proportionally to R^2. Therefor, the law of conservation of energy dictates that the energy received over a constant area receiver (say, a 1 cm^2 energy receiver) will decline proportionally to the square of the distance from the transmitter. As a side note - does that prove that our universe only has three dimensions? However, if our transmitter is directional, and you keep the transmitter beam focused, so that it does not expand, there is no reason for the energy to almost not discard at all. Of course, the medium through which you transmit the energy may absorb some of it (assuming it is not a vacuum), and it may disperse some more of it, but there is no reason to get 1/R^2, or even 1/R. Shachar -- Shachar Shemesh Lingnu Open Source Consulting Ltd. http://www.lingnu.com -- Sincerely yours, Michael Vasiliev ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
Re: [OT] Power over radio is it a true thing or just a myth ?
On Aug 24, 2009, at 4:33 PM, Micha wrote: I doubt wifi is any better in this respect. WiFi is limited in Israel to 100mW EIRP (Effictive incident radiated power), so the most that could come out of a Wifi antenna would be 100mW. When I tested my BEZEQ router with a microwave oven leakage detector (they use the same frequencies) at about 3 cm the WiFi signal was . 35mW per CM2. At a meter that would be about 1/1000 of that, (slightly less than 1/900th to be exact), or .0035 Watts. Geoff. -- geoffrey mendelson N3OWJ/4X1GM Jerusalem Israel geoffreymendel...@gmail.com ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
Re: [OT] Power over radio is it a true thing or just a myth ?
Oleg Goldshmidt wrote: I'll bite - it's OT, but too much fun to skip... ;-) 2009/8/24 Shachar Shemesh shac...@shemesh.biz: As a side note - does that prove that our universe only has three dimensions? Technically, no, though many philosophers (as opposed to physicists or mathematicians) will say it does. The number of dimensions does not follow from R^-2, but if you live in a 3D world then R^-2 follows... ;-) I read the link you gave, but have not found why it does not prove it. The closest I got (which was not stated) is that if N3 for our universe, then the laws of physics are much more complex than what we know. It seems very clear that if the laws we know are a close approximation of the real laws of physics, then the only explanation to the experiments we are conducting is that the world only has 3 physical dimensions. Shachar -- Shachar Shemesh Lingnu Open Source Consulting Ltd. http://www.lingnu.com ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
Re: [OT] Power over radio is it a true thing or just a myth ?
On Mon, Aug 24, 2009 at 5:21 PM, Shachar Shemeshshac...@shemesh.biz wrote: I read the link you gave, but have not found why it does not prove it. You will, I hope, agree with me that the fact that you have not found it there does not actually mean that R^-2 = N=3... ;-) All I said was that if you assume N=3 then you get R^-2, but this does not mean that the reverse is also true. The closest I got (which was not stated) is that if N3 for our universe, then the laws of physics are much more complex than what we know. Complexity would not be a truly compelling argument. Correspondence to experimental results, on the other hand, is convincing. Ehrenfest showed that for N3 planetary systems and galaxies could not be stable. Later the same was shown for electron orbits in nuclei. In an N3 world none of these systems could exist (for experimentally observed times). Electrodynamics works (i.e., is consistent with experiment on the basic level, e.g., no pulse distortions in vacuum) only for N=3. All that is stated, admittedly very laconically. The physics/math is highly non-trivial, so you can't expect to get it from a Wikipedia article. Once you have satisfied yourself that N=3, you can derive R^-2 easily from flux considerations. -- Oleg Goldshmidt | o...@goldshmidt.org ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
Re: [OT] Power over radio is it a true thing or just a myth ?
Oleg Goldshmidt wrote: On Mon, Aug 24, 2009 at 5:21 PM, Shachar Shemeshshac...@shemesh.biz wrote: I read the link you gave, but have not found why it does not prove it. You will, I hope, agree with me that the fact that you have not found it there does not actually mean that R^-2 = N=3... ;-) All I said was that if you assume N=3 then you get R^-2, but this does not mean that the reverse is also true. You state that, and then you delve on to prove the opposite. You lost me. The way I know science, we have: - A mathematical model saying that neither galaxies nor atoms are stable if N!=3 - Empirical evidence that both galaxies and atoms are stable The way I know how science works, pending further changes in the whole way laws of physics are understood (but it would have to be a pretty fundamental change, that pretty much scraps everything and starts from scratch), we can say that the Universe is three dimensional. Being as it is that the above is as close to certainty that any physicist might hope to get (make that - any scientist), it is usually phrased it is proven that the Universe is three dimensional. Shachar -- Shachar Shemesh Lingnu Open Source Consulting Ltd. http://www.lingnu.com ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
Re: [OT] Power over radio is it a true thing or just a myth ?
On Mon, Aug 24, 2009 at 7:14 PM, Shachar Shemeshshac...@shemesh.biz wrote: You state that, and then you delve on to prove the opposite. You lost me. The way I know science, we have: - A mathematical model saying that neither galaxies nor atoms are stable if N!=3 - Empirical evidence that both galaxies and atoms are stable Neither of which is R^-2... -- Oleg Goldshmidt | o...@goldshmidt.org ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
