OK, sorry about my short answer, but to really explain how modern RF transmission works is more complicated than a short slashdot post.
I think I can guess your resoning in the parent, and I think you make a mistake. If we take your example with the green photons, A(t) is the amplitude of the signal, i.e. the number of incoming photons per second. But if all the photons are exactly the same kind of green, then F(t) is fixed and can not transmit any information. Because if we change F(t), then we will change the colour of the photon. In the case with a single frequency transmitter we can only change the amplitude. (Which in turn will widen the spectrum of the transmitted signal. From Shannon we get that we must occupy a non-zero bandwidth in order to be able to transmit any information at all.)
In RF we can either change the frequency of the signal, or the amplitude. High-capacity modulation schemes changes both at the same time, as in 64-QAM etc.
If this does not solve your problem, please define, in physics terms if you prefer, what A(t) and F(t) is to be interpreted as in your equation.
"Now, a phased array of parabolic dishes is obviously no different from a phased array, except you're specifying the unit antenna technology."
What I suggested was not a phased array of parabolic dishes, but one parabolic dish, on a servo-controlled gimbal. This has the same properties of being able to follow a certain transmitter in spatial space, without using any phased-array technology.
Phased arrays is in engineering language a specific technology where the signals from two or more separate antennas are combined to synthesize another, more directive, antenna. By varying the phase and amplitudes in the combination we can steer the main direction of the phased array electronically. By using more advanced combination mathematics we can sythesize multiple main beams, but then we need more elements in the array. Very nice technology, having many applications, but still not anything fundamentally different from placing a highly directive antenna on a gimbal.
(All this applies in the reverse to transmission also.)
And there is still no difference. Two parabolic dish antennas on the same mast can differentiate between two physically separated sources on the same frequency. No fundamental difference, as I said.
The benefit from the phased arrays are mainly that they are more compact than a set of dish antennas, and that they are electronically steerable, that is, you can choose the direction electronically instead of mechanically rotating an antenna.
Please educate me how phased arrays are fundamentally different from other directional antennas, such as parabolic dishes??? Which have coexisted with the FCC for quite some time...
My short answer: in no way. And the introduction of phased arrays does give benefits, but in no way reduce the need for spectrum planning.
Actually, yes. Like nearly 100 years of development within radio transmission technology. Ordinary QAM modulation is more or less what you describe: to send independent information in the phase and the amplitude regime.
And there are problems with UWB and collisions. And the addition of UWB or CDMA only adds the complexity of assigning codes to transmitters, and does not remove the frequency planning part. If you do not suggest putting a stop to a lot of scientific applications. (and military. and radar. and instrument navigation. etc.)
"I think the key point not being well expressed in the article is that the spectrum above about 3 GHz is not as precious and should be opened to more comercial use."
And how do you make that judgement? Some applications work better at higher frequencies, like point-to-point radio links (f.ex. sattelites) and radar. There is also a lot of future communication systems studied at higher frequencies (17GHz and 60GHz, for example).
I do not see how this part of the spectrum is less valuable, especially as it also supports more bandwidth. (One could argue that the lower frequencies are less valuable as they travel far and thus make spectrum reuse schemes much more less efficient.)
Price of computing power with the same performance as a ten year old PC: almost free... In comparison with the modern PC with the "supercomputer power".
Shows that the simpler solution still is the cheaper one...
Are you seriously saying that the early US rockets did not rely a lot on the design of the German V2 rocket??? From having seen both, I must say that they are very similar! The same trust vectoring scheme, for example.
(And Von Braun was supervising the design of the Redstone rockets, at least according to Wikipedia?)
There is a difference between banning something because it is sure to make the plane crash, and banning something because it might make a plane crash. You assume that mobile phones are banned because of the first, but it might be the latter.
Ask yourself: If it were the case that mobile phone use would crash a plane every 10.000 landing, would you allow it to be used? Or every 100.000 landing? Especially in the US with the system of suing people for negligence?
(AFAIK, one reason for not being allowed to use anything during takeoff and landing is because mobile phones, electronic games and laptops are too good at playing projectiles if the plane has to make an emergency stop...)
I doubt that it is original 48 kHz master DAT tapes - The studios I have been into which do productions for CD has switched the button on the DAT deck to 44.1 kHz a long time ago, and never moved it since...
Which raises the question of resampling...
The travelling-wave amplifier gives only 20 Watts of output power, which feeds into a 4 meter dish antenna. At 8.4 GHz this gives a gain of about 50 dB. EIRP then at 2 MW. (And a free space loss to Saturnus of about 300 dB....)
According to the press kit, the power from the three thermoelectric generators should be at 750 Watts. In addition 82 radioisotope heaters are used, each giving about 1 watt of heat.
The communication with earth is achieved by a 20 W amplifier at 8.4 GHz and a 4 meter parbolic dish antenna.
Re:I know a man who had this in the Eighties...
on
RF-Blocking Wallpaper
·
· Score: 1
As it uses an FSS, it (probably) reflects the waves. If we build a cage of the material, no signal would get out or into the cage in the stopband of the FSS. Other frequencies would be unaffected. The waves on the inside would bounce around until they were absorbed in other materials (building, furniture, people etc.) Some power is also lost at each reflection as the metal in the FSS in not perfectly conducting.
Read the article. The wallpaper uses an FSS, or frequency selective surface. To compare it a simple wire mesh is about equivalent to say that the heat insulation on the wings of the space shuttle is made of the same material as the tile from which you build a fireplace in your home. One is very much more advanced than the other...
The FSS, or frequency selective surface, which is used in the panels described in the article works as a frequency selective filter to an electromagnetic wave. The one by the british firm is used as a stop band filter, which lets everything except WiFi-frequencies pass. It is also possible to make FSS which works as pass-band filters, usually for radar applications. (Stealth planes incorporates FSS in order to have a reflecting surface for the enemys radar, but which is still transparent for the planes own radar.)
So it is very different from ordinary aluminium foil. Foil wallpaper and window treatments have been available for quite a while, both for security applications and for people concerned about electromagnetic radiation. But these blocks all frequencies.
Because it would cost money to build those roads, vs. that it will cost money to exchange all radios to ones with "steering wheel" so that they can move over?
Just a thought...
B(Beware of analogies - they seldom give any insight in how to solve a problem...)
For the physisists out there: There is no magic involved. According to the specification from the Radiation Shield Technologies homepage: "CIVILIANS
DEMRON(TM) is effective as a radiation shield, comparable to lead in terms of g/cm2 and tantalum
according to the mass attenuation coefficient, against gamma, x-ray and beta emissions."
Which gives that the weight for equal protection as a certain thickness of lead will be the same!
They assume that if somewhone is shouting at the same time that somebody is whispering, the shouting will always be louder. But if you are far away from the shouter, who you whant to listen to, a whispering conversation close to you may easily drown the shouter.
And in the case of listening, everybody has roughly the same sensitivity. But in the case of radio transmission, it is a very large difference between an astronomical radio telescope with a 70 m parabolic dish and an FM radio for $5. How is the smart radio going to make sure that the silent frequency it has found is not a just barely discernable signal from mars? With regulation, this is not a problem. Whithout...
The blood clumping is very very theoretical: it only looked at two perfect spherical bloodcells in infinite space of water, and did see an increase in the attractive force betwen them.
The amount of simplification is staggering, and to go from there to an actual medical condition like blood-clotting is just pure speculation. A lot of verification has to be done.
> Your antenna would be infinitely large...
Your resonant wire antenna that is. You can always build a coil antenna, or a non-resonant antenna. Otherwise it would have been hard to get the AM-reciever and antenna into the car stereo...
One would think that we would learn from history, but we dont.
Civilian deaths and disregard of the Geneva convention is what has plased the US in trouble a lot of times! (politically, that is)
This device is intended to minimize the civilian deaths, without getting more dead american soldiers (which gets you into trouble in the US)
You have to remeber that they are talking about the US. It is new there. And it is a problem, as they are paying for incoming calls. And they seem to not have a general, working do-not-call registry(?). Strange, but true.
Can somebody point me to a defintion of this?
Because it seems to be a, by some law, necessity to any "good" film or book, but at the same time lacking from some of the books and films that I really have loved. (Star Wars 4, LotR,... )
Is it a term you all learn in art class in US High Schools or something???
IANAL, but please observe that how the law works is different in the US and in most places in Europe.
AFIK, in the US the rulings of the courts makes up the law, in large parts of Europe (except GB?)the law is what, and only what, is printed in the original text. Most eropean lawyers do not spend their time going through old cases, as can be seen in american movies. Because the old cases does not give how the law should be intrepreted.
Slashdot Mirror
OK, sorry about my short answer, but to really explain how modern RF transmission works is more complicated than a short slashdot post.
I think I can guess your resoning in the parent, and I think you make a mistake. If we take your example with the green photons, A(t) is the amplitude of the signal, i.e. the number of incoming photons per second. But if all the photons are exactly the same kind of green, then F(t) is fixed and can not transmit any information. Because if we change F(t), then we will change the colour of the photon. In the case with a single frequency transmitter we can only change the amplitude. (Which in turn will widen the spectrum of the transmitted signal. From Shannon we get that we must occupy a non-zero bandwidth in order to be able to transmit any information at all.)
In RF we can either change the frequency of the signal, or the amplitude. High-capacity modulation schemes changes both at the same time, as in 64-QAM etc.
If this does not solve your problem, please define, in physics terms if you prefer, what A(t) and F(t) is to be interpreted as in your equation.
"Now, a phased array of parabolic dishes is obviously no different from a phased array, except you're specifying the unit antenna technology."
What I suggested was not a phased array of parabolic dishes, but one parabolic dish, on a servo-controlled gimbal. This has the same properties of being able to follow a certain transmitter in spatial space, without using any phased-array technology.
Phased arrays is in engineering language a specific technology where the signals from two or more separate antennas are combined to synthesize another, more directive, antenna. By varying the phase and amplitudes in the combination we can steer the main direction of the phased array electronically. By using more advanced combination mathematics we can sythesize multiple main beams, but then we need more elements in the array. Very nice technology, having many applications, but still not anything fundamentally different from placing a highly directive antenna on a gimbal.
(All this applies in the reverse to transmission also.)
And there is still no difference. Two parabolic dish antennas on the same mast can differentiate between two physically separated sources on the same frequency. No fundamental difference, as I said.
The benefit from the phased arrays are mainly that they are more compact than a set of dish antennas, and that they are electronically steerable, that is, you can choose the direction electronically instead of mechanically rotating an antenna.
Please educate me how phased arrays are fundamentally different from other directional antennas, such as parabolic dishes??? Which have coexisted with the FCC for quite some time...
My short answer: in no way. And the introduction of phased arrays does give benefits, but in no way reduce the need for spectrum planning.
"Is there something I'm missing?"
Actually, yes. Like nearly 100 years of development within radio transmission technology. Ordinary QAM modulation is more or less what you describe: to send independent information in the phase and the amplitude regime.
And there are problems with UWB and collisions. And the addition of UWB or CDMA only adds the complexity of assigning codes to transmitters, and does not remove the frequency planning part. If you do not suggest putting a stop to a lot of scientific applications. (and military. and radar. and instrument navigation. etc.)
"I think the key point not being well expressed in the article is that the spectrum above about 3 GHz is not as precious and should be opened to more comercial use."
And how do you make that judgement? Some applications work better at higher frequencies, like point-to-point radio links (f.ex. sattelites) and radar. There is also a lot of future communication systems studied at higher frequencies (17GHz and 60GHz, for example).
I do not see how this part of the spectrum is less valuable, especially as it also supports more bandwidth. (One could argue that the lower frequencies are less valuable as they travel far and thus make spectrum reuse schemes much more less efficient.)
Price of computing power with the same performance as a ten year old PC: almost free... In comparison with the modern PC with the "supercomputer power".
Shows that the simpler solution still is the cheaper one...
Are you seriously saying that the early US rockets did not rely a lot on the design of the German V2 rocket??? From having seen both, I must say that they are very similar! The same trust vectoring scheme, for example.
(And Von Braun was supervising the design of the Redstone rockets, at least according to Wikipedia?)
There is a difference between banning something because it is sure to make the plane crash, and banning something because it might make a plane crash. You assume that mobile phones are banned because of the first, but it might be the latter.
Ask yourself: If it were the case that mobile phone use would crash a plane every 10.000 landing, would you allow it to be used? Or every 100.000 landing? Especially in the US with the system of suing people for negligence?
(AFAIK, one reason for not being allowed to use anything during takeoff and landing is because mobile phones, electronic games and laptops are too good at playing projectiles if the plane has to make an emergency stop...)
I doubt that it is original 48 kHz master DAT tapes - The studios I have been into which do productions for CD has switched the button on the DAT deck to 44.1 kHz a long time ago, and never moved it since... Which raises the question of resampling...
The travelling-wave amplifier gives only 20 Watts of output power, which feeds into a 4 meter dish antenna. At 8.4 GHz this gives a gain of about 50 dB. EIRP then at 2 MW. (And a free space loss to Saturnus of about 300 dB....)
According to the press kit, the power from the three thermoelectric generators should be at 750 Watts. In addition 82 radioisotope heaters are used, each giving about 1 watt of heat.
The communication with earth is achieved by a 20 W amplifier at 8.4 GHz and a 4 meter parbolic dish antenna.
As it uses an FSS, it (probably) reflects the waves. If we build a cage of the material, no signal would get out or into the cage in the stopband of the FSS. Other frequencies would be unaffected. The waves on the inside would bounce around until they were absorbed in other materials (building, furniture, people etc.) Some power is also lost at each reflection as the metal in the FSS in not perfectly conducting.
Read the article. The wallpaper uses an FSS, or frequency selective surface. To compare it a simple wire mesh is about equivalent to say that the heat insulation on the wings of the space shuttle is made of the same material as the tile from which you build a fireplace in your home.
One is very much more advanced than the other...
And that got moderated informative...
The FSS, or frequency selective surface, which is used in the panels described in the article works as a frequency selective filter to an electromagnetic wave. The one by the british firm is used as a stop band filter, which lets everything except WiFi-frequencies pass. It is also possible to make FSS which works as pass-band filters, usually for radar applications. (Stealth planes incorporates FSS in order to have a reflecting surface for the enemys radar, but which is still transparent for the planes own radar.)
So it is very different from ordinary aluminium foil. Foil wallpaper and window treatments have been available for quite a while, both for security applications and for people concerned about electromagnetic radiation. But these blocks all frequencies.
Because it would cost money to build those roads, vs. that it will cost money to exchange all radios to ones with "steering wheel" so that they can move over?
Just a thought...
B(Beware of analogies - they seldom give any insight in how to solve a problem...)
"Moore posts his defence to the alligations the websites propose on his own website."
Could you supply a link? Couldn't find it...
For the physisists out there: There is no magic involved. According to the specification from the Radiation Shield Technologies homepage:
"CIVILIANS DEMRON(TM) is effective as a radiation shield, comparable to lead in terms of g/cm2 and tantalum according to the mass attenuation coefficient, against gamma, x-ray and beta emissions."
Which gives that the weight for equal protection as a certain thickness of lead will be the same!
They do the same mistakes as usual:
They assume that if somewhone is shouting at the same time that somebody is whispering, the shouting will always be louder. But if you are far away from the shouter, who you whant to listen to, a whispering conversation close to you may easily drown the shouter.
And in the case of listening, everybody has roughly the same sensitivity. But in the case of radio transmission, it is a very large difference between an astronomical radio telescope with a 70 m parabolic dish and an FM radio for $5. How is the smart radio going to make sure that the silent frequency it has found is not a just barely discernable signal from mars? With regulation, this is not a problem. Whithout...
The blood clumping is very very theoretical: it only looked at two perfect spherical bloodcells in infinite space of water, and did see an increase in the attractive force betwen them.
The amount of simplification is staggering, and to go from there to an actual medical condition like blood-clotting is just pure speculation. A lot of verification has to be done.
> Your antenna would be infinitely large... Your resonant wire antenna that is. You can always build a coil antenna, or a non-resonant antenna. Otherwise it would have been hard to get the AM-reciever and antenna into the car stereo...
One would think that we would learn from history, but we dont.
Civilian deaths and disregard of the Geneva convention is what has plased the US in trouble a lot of times! (politically, that is)
This device is intended to minimize the civilian deaths, without getting more dead american soldiers (which gets you into trouble in the US)
You have to remeber that they are talking about the US. It is new there. And it is a problem, as they are paying for incoming calls. And they seem to not have a general, working do-not-call registry(?).
Strange, but true.
(Have Karma, flame away...)
Can somebody point me to a defintion of this?
Because it seems to be a, by some law, necessity to any "good" film or book, but at the same time lacking from some of the books and films that I really have loved. (Star Wars 4, LotR,... )
Is it a term you all learn in art class in US High Schools or something???
IANAL, but please observe that how the law works is different in the US and in most places in Europe.
AFIK, in the US the rulings of the courts makes up the law, in large parts of Europe (except GB?)the law is what, and only what, is printed in the original text. Most eropean lawyers do not spend their time going through old cases, as can be seen in american movies. Because the old cases does not give how the law should be intrepreted.